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HEART
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7
NOITCES
Aortic valve, left coronary leaflet Fig. 57.17 A dissection opening the
ventricles, viewed from the front. (With
Aortic valve, permission from Waschke J, Paulsen F
Left atrium
non-adjacent leaflet (eds), Sobotta Atlas of Human
Anatomy, 15th ed, Elsevier, Urban &
Ascending aorta
Fischer. Copyright 2013.)
Aortic leaflet
Mitral valve
Aortic sinus Mural leaflet
Right auricle
Right coronary artery
Interventricular septum, Pericardium
membranous part
Superolateral papillary muscle
Tricuspid valve,
inferior leaflet
Tricuspid valve,
Inferoseptal papillary muscle
septal leaflet
Pericardium
Anterior papillary muscle
Inferior papillary muscle
Interventricular septum, muscular part
Right coronary artery Subpulmonary infundibulum
Pulmonary trunk Supraventricular crest
Medial papillary muscle
Aorta
Septomarginal trabeculation
Superior vena cava
Septoparietal trabeculations
Venous
component
Anterior
pM ao pd ile lar ra yt o mr ub sa cn ld
e
V
e
Fossa ovalis stib
ule
Inferior papillary muscle
Inferior vena cava Tricuspid valve
Thebesian valve
Eustachian valve
Coronary sinus Sub-Thebesian recess
Fig. 57.18 A ‘window dissection’ of a cadaveric heart, prepared by removing the anterosuperior wall of the right atrium and ventricle, to expose their
internal features. The Eustachian valve separates the inferior vena cava from the sub-Thebesian recess. The Thebesian valve guards the entry into the
coronary sinus. The smooth circumferential area of atrial wall that surrounds the orifice of the tricuspid valve is the vestibule. Note the location of the
supraventricular crest and septomarginal trabeculation. The body of the septomarginal trabeculation continues as an important muscular strand, the
moderator band, to the anterior papillary muscle and the parietal wall of the right ventricle. (Specimen courtesy of M Loukas MD, PhD.)
anterolateral right ventricular wall. The posterolateral aspect of the crest caused by a myriad of endocardial, lined, irregular muscular ridges and
provides a principal attachment for the anterosuperior leaflet of the protrusions collectively known as trabeculae carneae. These protrusions
tricuspid valve. The septal limb of the crest may be continuous with, or and intervening grooves impart great variation in wall thickness; the
embraced by, the septal limbs of the septomarginal trabeculation. The protrusions vary in extent from mere ridges to trabeculations, fixed at
inlet and outlet regions extend apically into and from the prominent both ends but otherwise free. Other conspicuous protrusions are the
coarsely trabeculated component of the ventricle. The inlet component papillary muscles, which are inserted at one end on to the ventricular
itself is also trabeculated, whereas the outlet component (infundibu- wall and are continuous at the other end with collagenous cords, the
lum) has predominantly smooth walls. The trabeculated appearance is chordae tendineae (tendinous cords), inserted on the free edge of the | 1,392 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Heart
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atrioventricular valves. One protrusion in the right ventricle, the septo- leaflets. The connective tissues around the orifice of the atrioventricular
marginal trabeculation or septal band, is particularly prominent, rein- valves separate the atrial and ventricular myocardial masses completely,
forcing the septal surface where, at the base, it divides into limbs that except at the point of penetration of the atrioventricular bundle; they
embrace the supraventricular crest. Towards the apex, it supports the vary in density and disposition around the valvular circumference.
anterior papillary muscle of the tricuspid valve and, from this point, Extending from the right fibrous trigone component of the central
crosses to the parietal wall of the ventricle as the moderator band (the fibrous body is a pair of curved, tapered, subendocardial tendons, or
name reflects an earlier idea that septomarginal trabeculation prevented ‘prongs’ (fila coronaria), which partly encircle the circumference. The
overdistension of the ventricle). The role of the moderator band as part latter is completed by more tenuous, deformable fibroblastic sulcal
of the conduction system of the heart involves the right atrioventricular areolar tissue. Although the extent of fibrous tissue varies with sex and
bundle, as conduction cardiomyocytes move towards the apex of the age, the tissue within the atrioventricular junction around the tricuspid
ventricle before entering the anterior papillary muscle. The moderator orifice is always less robust than similar elements found at the attach-
band may be short/thick, long/thick, short/thin, long/thin: it is occa- ments of the mitral valve. The topographical ‘attachment’ of the free
sionally absent. A further series of prominent trabeculations, the septo- valvular leaflets in the tricuspid valve does not wholly correspond to
parietal trabeculations, extend from its anterior surface and run on to the internal level of attachment of the fibrous core of the valve to the
the parietal ventricular wall. The smooth-walled outflow tract, or junctional atrioventricular connective tissue. The line of attachment of
infundibulum, ascends to the left, superior to the septoparietal trabecu- the leaflet is best appreciated in the heart when examined grossly, this
lations and inferior to the arch of the supraventricular crest to the feature being more readily discerned clinically.
pulmonary orifice (Spicer and Anderson 2013).
Tricuspid valve leaflets
Tricuspid valve
When they are closed, it is usually possible to distinguish the three
The atrioventricular valvular complex, in both ventricles, consists of the leaflets in the tricuspid valve on the basis of the zones of apposition
orifice and its associated anulus, the leaflets, the supporting chordae between them: hence the name. The leaflets are located anterosuperi-
tendineae of various types and the papillary muscles. Harmonious orly, septally and inferiorly, corresponding to the marginal sectors of
interplay of all of these, together with the myocardial mass, depends the atrioventricular orifice named in conjunction. The inferior leaflet is
on the conduction tissues and mechanical cohesion provided by the often described as being posterior, but when assessed in the attitudi-
cardiac skeleton. All parts change substantially in position, shape, angu- nally correct anatomical position, the leaflet is positioned inferiorly
lation and dimensions during the cardiac cycle (see Fig. 57.20). (Anderson and Loukas 2009). Each leaflet is a reduplication of endo-
cardium enclosing a collagenous core, continuous marginally and on
Tricuspid valvular orifice its ventricular aspect with diverging fascicles of chordae tendineae (see
The tricuspid valve orifice is best seen from the atrial aspect. It measures, below) and basally confluent with the anular connective tissue. In
on average, 11.4 cm in circumference in males and 10.8 cm in females. passing from the free margin to the inserted margin, all leaflets of the
There is a clear line of transition from the atrial wall or septum to the atrioventricular valves display rough, clear and basal zones. The rough
lines of attachment of the valvular leaflets. Its margins are not precisely zone is relatively thick, opaque and uneven on its ventricular aspect
in a single plane. It is almost vertical but at 45° to the sagittal plane where most chordae tendineae are attached; its atrial aspect makes
and slightly inclined to the vertical, such that it ‘faces’ (on its ventricular contact with the comparable surface of the adjacent leaflets during full
aspect) anterolaterally to the left and somewhat inferiorly (Fig. 57.19). valve closure. The clear zone is smooth and translucent, receives few
Roughly triangular, its margins are described as anterosuperior, inferior chordae tendineae and has a thinner, fibrous core. The basal zone,
and septal, corresponding to the lines of attachment of the valvular extending 2–3 mm from the circumferential attachment of the leaflets,
is thicker from increased connective tissue, vascularized and innervated.
It contains the insertions of the atrial myocardium. The anterosuperior
leaflet is the largest component of the tricuspid valve, attached chiefly
to the atrioventricular junction on the posterolateral aspect of the
supraventricular crest, and extending along its septal limb to the mem-
1 1
branous septum ending at the anteroseptal commissure. One or more
notches often indent its free margin. The attachment of the septal leaflet
passes from the inferoseptal commissure on the inferior ventricular wall
across the muscular septum, then angling across the membranous
2 2
septum to the anteroseptal commissure. The septal leaflet defines one
of the borders of the triangle of Koch, thereby aiding location of the
A P atrioventricular node at the apex of this triangle, and ensuring avoid-
P
3 3 ance during tricuspid valve surgery (see Figs 57.13, 57.17). The inferior
leaflet is wholly mural in attachment and guards the diaphragmatic
surface of the atrioventricular junction, its limits being the inferoseptal
A and anteroinferior commissures. The zone of apposition between the
4 M 4 inferior and the anterosuperior leaflets is supported by the septal papil-
lary muscle of the conus.
T Opening of the tricuspid valve
5 5 Despite its name, the tricuspid valve acts more like a bicuspid valve
T because its smallest septal leaflet is fixed between the atrial and ven-
M tricular septa. The remainder of the tricuspid anulus is muscular. During
diastole, the anulus dilates with right ventricular relaxation and the
6 6 large anterior and posterior leaflets move away from the plane of the
anulus into the right ventricle. During systole, the anulus constricts as
the right ventricle contracts and the two major leaflets move like sails
about a relatively immobile septal leaflet and the septum itself
7 7 (Fig. 57.20).
Chordae tendineae (tendinous cords)
The chordae tendineae are fibrous collagenous structures that support
Fig. 57.19 The relation of the sternocostal surface and valves of the heart
the leaflets of the atrioventricular valves. Sometimes, false chordae
to the thoracic cage. The right heart is blue, the arrow denoting the inflow
connect the papillary muscles to each other or to the ventricular wall
and outflow channels of the right ventricle; the left heart is treated
or septum, or pass directly between points on the wall or septum, or
similarly in red. The positions, planes and relative sizes of the cardiac
valves are shown. The position of the letters A, P, T and M indicate the both. Their numbers and dimensions vary in the right ventricle; approx-
aortic, pulmonary, tricuspid and mitral auscultation areas of clinical imately 40% of these false cords contain conduction cardiomyocytes.
practice, respectively. Note that, for the purpose of illustration, the orifices The true chordae usually arise from small projections on the tips or
of the aortic, mitral and tricuspid valves are shown with some separation margins of the apical third of papillary muscles, although they some-
between them, whereas, in reality, the leaflets of the three valves are in times arise from the papillary muscle bases or directly from the ven-
fibrous continuity (see Fig. 57.24). tricular walls and septum. They attach to various parts of the ventricular | 1,393 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
HEART
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7
NOITCES
aspects or the free margins of the leaflets. True chordae are classified ventricular aspect) of the zones of apposition between leaflets and to
into first-, second- and third-order types, according to the distance of the ends of adjacent leaflets. Rough-zone chordae arise from a single
the attachment from the margins of the leaflets; the scheme has little stem that usually splits into three components that attach to the free
functional or morphological merit. Fan-shaped chordae have a short margin, the ventricular aspect of the rough zone and to some intermedi-
stem from which branches radiate to attach to the margins (or the ate point on the leaflet, respectively. Free-edge chordae are single,
thread-like and often long, passing from either the apex or the base of
120 a papillary muscle into a marginal attachment, usually near the mid-
point of a leaflet or one of its scallops. Deep chordae pass beyond the
100
margins and, branching to various extents, reach the more peripheral
Aorta
Pressure 80 rough zone or even the clear zone. Basal chordae are round or ribbon-
(mmHg) like, long and slender, or short and muscular; they arise from the
60
in left side smooth or trabeculated ventricular wall and attach to the basal compo-
of heart 40 nent of a leaflet.
Left atrium
20
Left venticle Papillary muscles
Pressure 0 The two major papillary muscles in the right ventricle are located in
(mmHg) 20 Pulmonary artery anterior and inferior positions. A third, smaller muscle lies medially,
in right side 0 Right atrium together with several smaller, variable muscles attached to the ventricu-
of heart Right ventricle lar septum. The anterior papillary muscle is the largest, its base arising
Atrium Ventricle from the right anterolateral ventricular wall inferior to the anteroinfe-
Mechanical Left Ejection Stipple marks isometric rior commissure of the inferior leaflet, also blending with the right end
activity Right Ejection contraction and relaxation of the septomarginal trabecula. The inferior, papillary muscle, often
bifid or trifid, arises from the myocardium inferior to the inferoseptal
Sequence of commissure. The septal (medial) papillary muscle of the conus, the
valve motion muscle of Lancisi, is almost always present and is the most superior and
largest of the small septal papillary muscles. It arises from the posterior
Closure of 1 5 Closure of septal limb of the septomarginal trabeculation and locates the right
mitral valve aortic valve
bundle branch within the right ventricle. All the major papillary
6 Closure of muscles supply chordae to adjacent components of the leaflets they
Closure of 2 pulmonary support (see Figs 57.17, 57.18). A feature of the right ventricle is that
tricuspid valve valve the septal leaflet is tethered by individual chordae tendineae directly to
the ventricular septum; such septal insertions are never seen in the left
7 Opening of ventricle. When closed, the three leaflets fit snugly together, the pattern
tricuspid
of the zones of apposition confirming the trifoliate arrangement of the
valve
Opening of 3 tricuspid valve.
pulmonary valve
8 Opening of Pulmonary valve
mitral valve
Opening of 4 The pulmonary valve, guarding the outflow from the right ventricle,
aortic valve surmounts the infundibulum and is situated at some distance from the
other three cardiac valves (Figs 57.21, 57.23). Its general plane faces
superiorly to the left and slightly posteriorly. It has three semilunar
Phonocardiogram
First heart Second heart leaflets, attached by convex edges partly to the infundibular wall of the
sound sound right ventricle and partly to the origin of the pulmonary trunk. The line
R
Electrocardiogram P T of attachments is curved, rising at the periphery of each leaflet near their
Q S zones of apposition (the commissures) and reaching the sinutubular
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 ridge of the pulmonary trunk (Fig. 57.24). Removal of the leaflets
Time (seconds) reveals that the fibrous semilunar attachments enclose three crescents
Fig. 57.20 A summary of some of the principal events that occur in of infundibular musculature within the pulmonary sinuses, whereas
the cardiac cycle and that are mentioned at various points throughout three roughly triangular segments of arterial wall are incorporated
this chapter. Systole begins at the onset of the first heart sound (see within the ventricular outflow tract beneath the apex of each commis-
phonocardiogram) and ends at the onset of the second heart sound, sural attachment. Thus there is no proper circular ‘anulus’ supporting
when diastole begins, and this cycle repeats itself. the leaflets of the valve, and the fibrous semilunar attachment is an
Pulmonary trunk Fig. 57.21 The base of the ventricles, after
removal of the atria and the pericardium,
Non-adjacent Left coronary leaflet exposing the coronary arteries and cardiac veins.
leaflet Contrast the planes and positions of the aortic
Pulmonary valve Right adjacent Right coronary leaflet Aortic valve and pulmonary valves, and with Figure 57.23.
leaflet
(With permission from Waschke J, Paulsen F
Left adjacent
(eds), Sobotta Atlas of Human Anatomy, 15th ed,
leaflet Non-adjacent leaflet
Elsevier, Urban & Fischer. Copyright 2013.)
Anterior interventricular branch
Right coronary artery
Left coronary artery
Circumflex branch Right fibrous trigone
Left fibrous trigone Right fibrous ring
Great cardiac vein
Atrioventricular bundle
Left fibrous ring
Valve of coronary sinus
Right marginal branch
Left marginal branch
Middle cardiac vein
Opening of coronary sinus
Right coronary artery,
Inferior interventricular vein
inferior interventricular branch | 1,394 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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RETPAHC
essential requisite for snug closure of the nodules and lunules of the of the anatomical base of the heart and is approximately quadrangular,
leaflets during ventricular diastole (see below). receiving the terminations of (usually) two pulmonary veins from each
It is difficult to name the leaflets and corresponding sinuses of the lung, forming the anterior wall of the oblique pericardial sinus (see Fig.
pulmonary valve and trunk precisely according to the coordinates of 57.3). This surface ends at the shallow vertical interatrial groove that
the body because the valvular orifice is obliquely positioned. Termino- descends to the cardiac crux.
logia Anatomica (2011) refers to anterior, posterior and septal leaflets on The left atrial appendage is characteristically longer, narrower and
the basis of their fetal position but this changes with development, more hooked than the right, and is a finger-like extension with more
becoming anterior, right and left, respectively, in the adult. Each leaflet deeply indented margins. It is constricted at its atrial junction and all
is an endocardial fold with a variably developed intervening substantial its contained pectinate muscles are much smaller than their right coun-
fibrous core that traverses both the free edge and the semilunar attached terparts. The left atrium lacks a crista terminalis, and the muscle bundles
border. The latter is particularly thickened at its deepest central part in the appendage are arranged in a whorl-like fashion rather than being
(nadir) of the base of each leaflet, and therefore never forms a simple in an array. The tip of the appendage has a variable position lying over
complete fibrous ring. The free margin of each leaflet contains a central the pulmonary trunk and anterior interventricular artery, pointing pos-
localized collagenous thickening, the nodule of Arantius. Perforations teriorly towards the aorta (Fig. 57.22). Its narrow morphology renders
within the leaflets close to the free margin and near the commissures the left atrial appendage a potential site for deposition of thrombi.
are frequently present and are of no functional significance. Each semi- The four pulmonary veins open into the superior posterolateral
lunar leaflet is contained within one of the three sinuses of the pulmo- surfaces of the left atrium, two on each side (see Figs 57.3, 57.4B). This
nary trunk. typical arrangement is present in 20–60% of the population. A common
variation includes the presence of a short or long left common venous
Opening of the pulmonary valve trunk and multiple pulmonary veins on the right (Fig. 57.25). The right
During diastole, all three leaflets of the pulmonary valve are tightly pulmonary veins travel posterior to their respective venae cavae. Their
apposed. The pulmonary valve is difficult to visualize at echocardio- orifices are smooth and oval, the left pair frequently opening via a
graphy and usually only the posterior leaflet is visible when the valve common channel. Interpulmonary ridges are usually found between
is closed; atrial systole may cause a slight posterior movement of the ipsilateral orifices; the most prominent is located between the openings
valve leaflets. The pulmonary valve opens passively during ventricular of the left atrial appendage and left superior pulmonary vein. The ridges
systole and then closes rapidly at the end of systole (see Fig. 57.20). are infoldings of the left atrial wall and contain adipose tissue, atrial
arteries and nerve bundles. At the site of the pericardial reflection, the
atrial musculature extends into the pulmonary veins, forming myocar-
Left atrium
dial sleeves that are thickest in the inferior wall of the superior pulmo-
nary veins and the superior walls of the inferior pulmonary veins. They
General, external and internal features
lie external to the venous tunica media and internal to the epicardium/
Although smaller in volume than the right, the left atrium has thicker adventitia and are often the site of focal electrical activity that initiates
walls (3 mm on average). It possesses a venous component that receives atrial fibrillation. Atrial myocardial bridges and crossing strands are
the right and left superior and inferior pulmonary veins, a vestibule and often present, connecting the left superior and inferior pulmonary
an appendage. Its cavity and walls are formed largely by the proximal veins.
parts of the pulmonary veins that are incorporated into the atrium Several epicardial fat pads on the pulmonary venous component
during development. Its extensive body is a remnant of the initial atrial house the superior left, posterolateral, left inferior and posteromedial
component of the primary heart tube. The left atrium is roughly cuboi- ganglionated cardiac intrinsic nerve plexuses (typically four). Minimal
dal, extending posterior to the right atrium and separated from it by cardiac veins (venae cordis minimae) return blood directly from the
the obliquely positioned septum. The right atrium is therefore antero- myocardium to the left atrial cavity. The left atrial aspect of the septum
lateral to the right part of the left atrium. The left part is concealed has a characteristically rough appearance, bounded by a crescentic,
anteriorly by the initial segments of the pulmonary trunk and aorta: superiorly concave ridge that marks the site of the foramen ovale. The
part of the transverse pericardial sinus lies between it and these arterial smooth circumferential area of atrial wall that surrounds the orifice of
trunks. Anteroinferiorly, and to the left, it adjoins the base of the left the mitral valve is the vestibule (see Fig. 57.25A, Fig. 57.26). The mus-
ventricle at the orifice of the mitral valve. Its posterior aspect forms most culature between the ostium of the inferior pulmonary vein and the
Ligamentum arteriosum Fig. 57.22 The anterior or sternocostal surface of the
Aortic arch
heart. (With permission from Waschke J, Paulsen F
(eds), Sobotta Atlas of Human Anatomy, 15th ed,
Serous pericardium, parietal layer
Superior vena cava Elsevier, Urban & Fischer. Copyright 2013.)
Serous pericardium, Left pulmonary artery
parietal layer
Pulmonary trunk
Right pulmonary artery
Ascending aorta
Left coronary artery
Transverse
Left atrium, left appendage
pericardial sinus
Great cardiac vein
Right coronary artery
Left coronary artery,
circumflex branch
Right appendage
Infundibulum (conus
Right atrium arteriosus)
Left coronary artery,
anterior interventricular branch
Right ventricular veins
Atrial branch
Anterior interventricular
vein
Right marginal branch
Apex of heart
Notch of cardiac apex | 1,395 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
HEART
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NOITCES
Arch of aorta
Right pulmonary artery
Pulmonary trunk
Ascending aorta
Tendon of infundibulum
(conus ligament) Ostia of coronary arteries
Fibrous attachment of
pulmonary valve leaflets
Fibrous attachment of aortic valve:
Left coronary leaflet
Left fibrous trigone
Right coronary leaflet
Non-adjacent leaflet
Subaortic curtain
and leaflet extension
Line of aortic leaflet,
Tendon of Todaro
mitral valve
Membranous part of septum
MITRAL VALVE ANULUS
Atrioventricular node
Fila coronaria Line of septal leaflet, tricuspid valve
Sulcal connective tissue TRICUSPID VALVE ANULUS
Fila coronaria
Sulcal connective
tissue
Mitral and aortic ‘anuli’
Right fibrous trigone
Tricuspid and pulmonary ‘anuli’ (central fibrous body)
Tendon of the infundibulum
Fig. 57.23 Principal elements of the fibrous skeleton of the heart. For clarity, the view is from the right posterosuperior aspect. Perspective causes the
pulmonary anulus to appear smaller than the aortic anulus, whereas, in fact, the reverse is the case. Consult the text for an extended discussion.
(Copyright of The Royal College of Surgeons of England. Reproduced with permission.)
anulus of the mitral valve is the left atrial or mitral isthmus, and is an The effect of obesity on the heart is apparent as early as the second year
area where the vestibule of the left atrium directly opposes the wall of of life. Obese children aged 2 years have a greater left ventricular mass
the great cardiac vein, coronary sinus and circumflex coronary artery. compared with normal weight controls (de Jonge et al 2011).
Internal features
Left ventricle
The left ventricle has an inlet region guarded by the mitral valve (ostium
venosum), an outlet region guarded by the aortic valve (ostium arterio-
General and external features
sum) and an apical trabecular component. The left atrioventricular
The left ventricle is constructed in accordance with its role as a powerful orifice admits atrial blood during diastole, the flow being directed
pump for the high-pressured systemic arterial circulation. Variously towards the cardiac apex (Fig. 57.28). After closure of the mitral leaflets
described as half-ellipsoid or cone-shaped, it is longer and narrower and throughout the ejection phase of systole, blood is expelled from
than the right ventricle, extending from its base in the plane of the the apex through the aortic orifice. In contrast to the orifices within the
atrioventricular groove to the cardiac apex. Its long axis descends ante- right ventricle, those of the left ventricle are in close contact with
riorly and to the left. In transverse section, at right angles to the axis, fibrous continuity between the leaflets of the aortic and mitral valves
its cavity is oval or nearly circular, with walls three times thicker (the ‘subaortic curtain’) (Fig. 57.29); the inlet and outlet turn sharply
(8–12 mm) than those of the right ventricle (Fig. 57.27). It forms part round this fibrous curtain. The anterolateral wall is the muscular ven-
of the sternocostal, left and inferior (diaphragmatic) cardiac surfaces. tricular septum, the convexity of which completes the circular outline
Except where obscured by the aorta and pulmonary trunk, the base of of the left ventricle (see Fig. 57.27). Towards the aortic orifice, the
the ventricular cone is superficially separated from the left atrium by septum becomes the thin and collagenous interventricular component
part of the atrioventricular groove with the coronary sinus within in of the membranous septum, an oval or round area below and conflu-
its posterior aspect (see Fig. 57.4B,D). The anterior and posterior ent with the fibrous triangle separating the right and the non-coronary
(inferior) interventricular grooves indicate the lines of mural attach- leaflets of the aortic valve. Between the inferior limits of the free
ment of the ventricular septum and the limits of the ventricular territo- margins of the leaflets of the mitral valve and the ventricular apex, the
ries. The sternocostal surface of the ventricle curves bluntly into its left muscular walls exhibit deeper, finer and more intricate trabeculae
surface at the obtuse margin. carneae than those of the right ventricle, characteristically more devel-
The shape of the left ventricle changes from elliptical in the neonatal oped nearer the apex, and becoming smoother as the superior septal
period to the round adult shape later in infancy (Azancot et al 1983). surface is reached. | 1,396 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Heart
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RETPAHC
A
Commissural ring
(sinutubular junction)
LAA
Aortic wall
within ventricle
(interleaflet triangle) LUPV
e
V rine gn t ari ncu dl o jua nr cte tir oia nl
O
LLPV
estibul
MV
V
Ventricle within sinus
Basal ring
A
B
LAA
Sinutubular Haemodynamic ventriculoarterial
junction junction (semilunar)
Commissure LUPV
os
LLPV
Artery as part
Arterial of ventricle ule
wall estib MV
V
Ventricle
Ventricle as part
of aorta
B GCV
Anatomical ventriculoarterial
junction (circular) Fig. 57.25 Sagittal sections showing the left side of the left atrium in a
cadaveric heart. A, The oesophagus (O) passing behind the posterior left
atrial wall and a broad left-lateral ridge (double-headed arrow). The left
upper (LUPV) and left lower (LLPV) pulmonary veins enter the left atrium
C Pulmonary trunk Sinutubular junction
Non-adjacent leaflet via a short common stem. Other abbreviations: LAA, left atrial appendage;
Right coronary Left coronary Ventriculoarterial MV, mitral valve. B, The section passes through the os of the left atrial
leaflet leaflet junction appendage and the infolding of the ridge. The triangle indicates the carina
or interpulmonary ridge between the upper and lower pulmonary veins.
The great cardiac vein (GCV) runs underneath the left atrial wall. (With
permission from Ho SY, McCarthy KP, Faletra FF. 2011. Anatomy of the
left atrium for interventional echocardiography. Eur J Echocardiogr
12:11–15.)
Hypertrophy of heart muscle
Available with the Gray’s Anatomy e-book
Mitral valve
The general comments already made for the tricuspid valve also apply
to the mitral valve. Thus it has an orifice with a supporting anulus,
leaflets and a variety of chordae tendineae and papillary muscles.
Muscular septum Mitral valve Left fibrous trigone
Mitral valvular orifice
Right fibrous trigone
Central fibrous body
Membranous septum The mitral orifice is a well-defined transitional zone between the atrial
wall and the leaflet bases, being smaller than the tricuspid orifice (mean
Fig. 57.24 A, The structure of the aortic root is best conceptualized in
circumference is 9.0 cm in males and 7.2 cm in females). The approxi-
terms of a three-pronged coronet; there are at least three rings within this
mately circular orifice is almost vertical and at 45° to the sagittal plane
coronet but none supports the entirety of the attachments of the valvular
in diastole, but with a slight anterior tilt. Its ventricular aspect faces
leaflets (compare with C). B, The leaflets have been resected at their
anterolaterally to the left and a little inferiorly towards the left ventricu-
attachment to the aortic wall. Note the relationship of the leaflet insertions
lar apex. It is almost co-planar with the tricuspid orifice but postero-
and the ventriculoarterial junction. C, The root of the aorta has been cut
open and distended, in order to show the insertion of the semilunar superior to it, whereas it is posteroinferior and slightly to the left of the
leaflets. Note the zone of fibrous continuity between the leaflets of the aortic orifice. The mitral, tricuspid and aortic orifices are intimately
aortic and mitral valves and their relationship to the fibrous trigones, and connected at their central fibrous body. When the mitral valve leaflets
the semilunar attachment of the leaflets (compare with B). (Redrawn with close, they form a single zone of coaptation, termed the commissure.
permission, courtesy of Professor RH Anderson, Institute of Child Health, The anulus of the valve is not a simple fibrous ring but is made up of
University College, London.) fibrocollagenous elements of varying consistency, from which the
fibrous leaflet cores take origin; the variable consistency is essential to
allow the major changes in anular shape and dimensions during the
cardiac cycle that are needed for optimal valvular efficiency. The area of | 1,397 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Hypertrophic cardiomyopathy is characterized by myocardial wall
thickening, particularly a disproportionate thickening of the interven-
tricular septum in comparison with the posterior wall. Echocardiogra-
phy accurately assesses the degree of thickening and its effect on systolic
function, such as dynamic left ventricular outflow obstruction, systolic
anterior motion of the aortic mitral valve leaflet and mid-systolic
closure of the aortic valve. There may also be a degree of diastolic dys-
function. Serial short-axis gradient echo MRI allows accurate measure-
ment of wall thickness and is particularly useful in assessing apically
confined hypertrophy. A number of histological changes are observed,
including cardiomyocytic disarray with replacement fibrosis and col-
lagenous component expansion. Treatment is usually medical, except
for refractory cases and those in whom the left ventricular outflow tract
obstruction has a gradient of greater than 50 mmHg. Ventricular septal
myotomy and myectomy are performed in such cases. Catheter alcohol
septal ablation has been introduced as a non-surgical alternative. A
number of patients may also require implantation of cardiac defibrilla-
tors to prevent sudden cardiac death.
An athlete’s heart may physiologically hypertrophy but in a
uniform fashion; the left ventricle cavity is usually less than 55 mm in
size, and thickness decreases on deconditioning. In contrast, hyper-
trophic cardiomyopathy reveals asymmetric patterns of left ventricular
hypertrophy, often with sharp segmental transitions, left atrial enlarge-
ment and bizarre electrocardiographic patterns. Furthermore, there is
an autosomal dominant inheritance pattern of abnormalities in genes
coding for myocardial proteins associated with hypertrophic cardio-
myopathy. Individuals with mutations of the β-MHC (major histo-
compatibility complex) gene usually develop the classic form of
hypertrophy, whereas those with cardiac troponin T gene mutations
generally have only mild or clinically undetectable hypertrophy. Rare
forms of hypertrophy include localized left ventricular apical hypertro-
phy as a result of cardiac troponin I mutations, and isolated mid-
cavity hypertrophy caused by cardiac actin and MLC (myosin light
chain) gene mutations. | 1,398 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Aorta
Pulmonary trunk
Superior vena cava
Anterior interventricular
artery
Right atrium
Left atrial appendage Fossa
ovalis
Right upper
Venous mponent pulmonary vein
ule
Body co
Right lower
b
Circumflex coronary artery esti pulmonary vein
V
Mitral valve Left atrium
Fig. 57.26 The posterior wall of the left atrium close to the posterior interatrial groove in a cadaveric heart. The smooth-walled venous component of the
left atrium is the most extensive component. The septal aspect of the left atrium shows the crescentic line of the free edge of the flap valve against the
rim of the fossa ovalis. The orifices of the right superior and inferior pulmonary veins are adjacent to the plane of the septal aspect of the left atrium.
(Specimen courtesy of M Loukas MD, PhD.)
Anterior interventricular vein Serous pericardium, visceral layer (epicardium)
Myocardium
Left coronary artery,
Endocardium
anterior interventricular branch
Right ventricle
Anterior interventricular sulcus
Septomarginal trabecula
(moderator band)
Superoposterior Right coronary artery,
papillary muscle right marginal branch
Left coronary artery, Myocardium
left marginal branch
Superolateral papillary
muscle
Trabeculae
Left ventricle carneae
Interventricular septum,
muscular part
Inferoseptal papillary
muscles Tricuspid valve, septal leaflet
Chordae tendineae
Inferior interventricular sulcus
Middle cardiac vein Right coronary artery, inferior interventricular branch
Fig. 57.27 Left and right ventricles: cross-section perpendicular to the axis of the heart, superior aspect. (With permission from Waschke J, Paulsen F
(eds), Sobotta Atlas of Human Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.)
the anulus increases linearly with body surface area in children and commissure. These anteromedial (inferoseptal) and posterolateral
young adults (Poutanen et al 2006). The anulus is strongest at the (superoposterior) extremities may be regarded as two independent
internal aspects of the left and right fibrous trigones. Extending from commissures, each positionally named as indicated in brackets.
these structures, the anterior and posterior coronary prongs (tapering, Although simple, the official names for these leaflets – anterior and
fibrous, subendocardial tendons) partly encircle the orifice at the atrio- posterior, respectively – are somewhat misleading because of the obliq-
ventricular junction (see Fig. 57.23). Between the prong tips, the atrial uity of the valve.
and ventricular myocardial masses are separated by a more tenuous When the valve is laid open, the anterior leaflet (aortic, septal,
sheet of deformable fibroelastic connective tissue. Spanning anteriorly ‘greater’ or anteromedial) is seen to guard one-third of the circumfer-
between the trigones, the fibrous core of the central part of the aortic ence of the orifice and to be semicircular or triangular, with few or no
leaflet of the mitral valve is a continuation of the fibrous subaortic marginal indentations. Its fibrous core (lamina fibrosa) is continuous
curtain that descends from the adjacent halves of the left and adjacent on the outflow aspect, beyond the margins of the fibrous subaortic
(non-coronary) valve leaflets (see Fig. 57.29). curtain, with the right and left fibrous trigones (see Figs 57.17, 57.21,
57.24C). Between the trigones, it is continuous with the fibrous curtain
Mitral valve leaflets itself and, beyond the trigones, with the roots of the anular fibrous
The mitral valvular leaflets have long been described as paired struc- prongs (see Fig. 57.23). The leaflet has a deep crescentic rough zone
tures. (The name ‘bicuspid valve’ is explicit but erroneous because the that receives various chordae tendineae. The ridge limiting the outer
leaflets are not cuspid, or ‘peaked’, in form). Small accessory leaflets are margin of the rough zone indicates the maximal extent of surface
almost always found between the two major leaflets and so the mitral contact with the mural leaflet in full closure. A clear zone is seen
valve should be described as a continuous veil that is attached around between the rough zone and the valvular anulus; it is devoid of attach-
the entire circumference of the mitral orifice. Its free edge bears several ments of chordae, although its fibrous core carries extensions from
indentations, of which two are sufficiently deep and regular to be chordae attached in the rough zone. The anterior leaflet has no basal
nominated as the ends of a solitary and oblique zone of apposition or zone and continues into the valvular curtain. Hinging on its anular | 1,399 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Superior vena cava
Right upper
pulmonary vein
Aorta
comV pe on no eu ns
t
pulmR oig nh at
r
ylo vw ee inr
Fossa
Pulmonary trunk ovalis
Body
Left atrium
Septal perforator
A arn tete ryrior interventricular Vestibule
Circumflex
coronary artery
Superolateral Mitral valve
papillary muscle
Inferoseptal
papillary muscle
Fig. 57.28 A dissection of the left ventricle in a cadaveric heart, exposing the papillary muscles of the ventricle. Notice the thick wall of the left ventricle
and the chordae tendineae of the mitral valve attaching to the papillary muscles. (Specimen courtesy of M Loukas MD, PhD.)
Left coronary leaflet Left coronary artery
Aortic bulb Left coronary artery,
anterior interventricular branch
Non-adjacent leaflet
Interventricular septum, membranous part
Aortic sinus
Myocardium
Pulmonary trunk Chordae tendineae
Posterolateral
papillary muscle
Left coronary leaflet
Right coronary artery
Nodule of left coronary
leaflet
Left atrioventricular orifice
Right coronary leaflet
Mitral valve, aortic leaflet
Non-adjacent leaflet
Inferoseptal papillary muscle
Fig. 57.29 The aortic orifice opened from the front to show the leaflets of the aortic valves, their nodules, lunules, commissures and the triple-scalloped
line of their anular attachment. Also shown are the continuity of the subaortic curtain with the mitral aortic leaflet (i.e. ‘aortic baffle’) and the coronary
ostia, and the spatial relationship of the aortic orifice to the pulmonary orifice and to the left ventricle. (With permission from Waschke J, Paulsen F (eds),
Sobotta Atlas of Human Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.) | 1,400 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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NOITCES
attachment, and continuous with the subaortic curtain, it is critically the atrial cavity, and the atrial aspects of the rough zones come into
placed between the inlet and the outlet of the ventricle. During passive maximal contact. Precise papillary contraction, and increasing tension
ventricular filling and atrial systole, its smooth atrial surface is impor- in the chordae, continue to prevent valvular eversion and maintain
tant in directing a smooth flow of blood towards the body and apex of valvular competence. The orifices and the leaflets of both atrioventricu-
the ventricle. After the onset of ventricular systole and closure of the lar valves undergo considerable changes in position, form and area
mitral valve, the ventricular aspect of its clear zone merges into the during a cardiac cycle. Both valves move anteriorly and to the left during
smooth surface of the subaortic curtain, which, with the remaining systole, and reverse their motion in diastole. The mitral valve reduces
fibrous walls of the subvalvular aortic vestibule, forms the smooth its orificial (anular) area by as much as 40% in systole; its shape changes
boundaries of the ventricular outlet. from circular to crescentic at the height of systole, the anular attachment
The posterior leaflet (mural, ventricular, ‘smaller’ or posterolateral) of its aortic leaflet being the concavity of the crescent. The attachment
usually has two or more minor indentations. Lack of definition of the of its mural leaflet, although remaining convex, contracts towards the
major intervalvular commissures has led to disagreement and confu- anterior cardiac wall. The smooth left ventricular outflow tract (aortic
sion concerning the territorial extent of this leaflet and the possible vestibule) terminates at the aortic valve leaflets. Although stronger in
existence of accessory scallops. Examination of the valve in the closed construction, the aortic valve resembles the pulmonary valve (see Figs
position reveals that the posterior leaflet may conveniently be regarded 57.21, 57.24, 57.29) in possessing three semilunar leaflets, supported
as comprising all the valvular tissue posterior to the anterolateral within the three aortic sinuses of Valsalva. Although the aortic valve,
(inferoseptal) and posteromedial (superoposterior) ends of the major like the pulmonary valve, is often described as possessing an anulus in
zone of apposition with the aortic leaflet. Thus defined, it has a wider continuity with the fibrous skeleton, there is no complete collagenous
attachment to the anulus than does the anterior leaflet, guarding two- ring that supports the attachments of the leaflets. As with the pulmo-
thirds of the circumferential attachments. Further indentations usually nary valve, the anatomy of the aortic valve is dominated by the fibrous
divide the mural leaflet into a relatively large middle scallop and semilunar leaflet attachment (see Fig. 57.24C).
smaller lateral and septal commissural scallops. Each scallop has a
crescentic opaque rough zone, receiving on its ventricular aspect the Mitral chordae tendineae
attachments of the chordae that define the area of valvular apposition Mitral chordae tendineae resemble those supporting the tricuspid valve.
in full closure. From the rough zone to within 2–3 mm of its anular False chordae are also irregularly distributed as in the right ventricle.
attachment, there is a membranous clear zone devoid of chordae. They are single or multiple, thin, fibrous or fibromuscular structures
The basal 2–3 mm is thick and vascular, and receives basal chordae. that traverse the cavity of the left ventricle and have no connection with
The ratio of rough to clear zone in the anterior leaflet is 0.6 and in the the valvular leaflets (Fig. 57.30). They occur commonly in human left
middle scallop of the posterior leaflet is 1.4. Much more of the mural ventricles and often cross the subaortic outflow. Histologically, false
leaflet is in apposition with the aortic leaflet during closure of the chordae sometimes contain extensions from the ventricular conducting
mitral valve. tissues; these left ventricular bands are often identified on echocardiog-
raphy. It has been suggested that false chordae produce premature
Opening of the mitral valve ventricular contractions and be the possible cause of functional heart
At the onset of diastole, opening is passive but rapid, the leaflets parting murmurs or innocent murmurs in children and young adults.
and projecting into the ventricle as left atrial pressure exceeds left ven- True mitral valve chordae may be divided into four types: inter-
tricular diastolic pressure. Passive ventricular filling proceeds as atrial leaflet (commissural), rough zone (including the special strut chordae),
blood pours to the apex, directed by the pendant aortic valvular leaflet. ‘cleft’ and basal chordae. Most true chordae divide into branches from
The leaflets begin to float passively together, hinging on their anular a single stem soon after their origin from the apical third of a papillary
attachments and partially occluding the ventricular inlet. Atrial systole muscle, or proceed as single chordae that divide into several branches
now occurs, jetting blood apically and causing re-opening of the leaf- near their attachment. Basal chordae, in contrast, are solitary structures
lets. As maximal filling is achieved, the leaflets again float rapidly passing from the ventricular wall to the mural leaflet. There is such
together. Closure is followed by ventricular systole, which starts in the marked variation between the arrangement of the chordae that any
papillary muscles and continues rapidly as a general contraction of the detailed classification loses much of its clinical significance. Suffice it
walls and septum. Coordinated contraction of the papillary muscles to say that, in the majority of hearts, the chordae support the entire free
increases the tension in the chordae and promotes joining of the cor- edges of the valvular leaflets, together with varying degrees of their
responding points on opposing leaflets, preventing their eversion. With ventricular aspects and bases, and there is some evidence to suggest that
general mural and septal excitation and contraction, left ventricular those valves with unsupported free edges become prone to prolapse in
pressure increases rapidly (see Fig. 57.20). The leaflets ‘balloon’ towards later life.
Fig. 57.30 The aorta has been
transected at the level of the
Aorta Right coronary orifice
sinutubular junction in this
cadaveric heart in order to
Left atrium reveal the closed leaflets of the
aortic valve. Note how the
supporting sinuses may be
Interleaflet triangle described as left coronary, right
Pulmonary trunk
coronary and non-adjacent,
according to the origin of the
Membranous septum coronary arteries. However, this
Aortic-mitral
Circumflex continuity terminology could be
coronary artery ambiguous if the coronary
arteries arise in variable
locations, whereas the
Anterior interventricular
terminology of right, left and
artery
Superolateral non-facing aortic sinus,
Left bundle papillary muscle respectively, is not ambiguous.
branch Note the inter-leaflet triangles,
membranous septum, and
fibrous continuity between the
aorta and mitral valve.
Inferoseptal
papillary muscle (Specimen courtesy of M
Loukas MD, PhD.)
Left ventricle
Fine trabeculations | 1,401 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Papillary muscles except at its midpoint, where there is an aggregation of fibrous tissue,
The two muscles supporting the leaflets of the mitral valve vary in length the valvular nodule of the semilunar leaflet. The fibrous core that flanks
and breadth, and may be bifid. The anterolateral (superolateral) muscle each nodule is tenuous, forming the lunules of translucent and occa-
arises from the sternocostal mural myocardium, and the posteromedial sionally fenestrated valvular tissue; fenestrations are of no functional
(inferoseptal) from the diaphragmatic region (see Fig. 57.27). Chordae significance. The aortic surface of each leaflet is rougher than its ven-
tendineae arise mostly from the tip and apical third of each muscle but tricular aspect.
sometimes take origin near their base. The chordae from each papillary Confusingly, three sets of names are used to describe the aortic
muscle diverge and are attached to corresponding areas of closure on leaflets. Posterior, right and left refer to their fetal positions before
both valvular leaflets. full cardiac rotation has occurred (Ch. 52). Corresponding terms based
on their approximate positions in maturity are anterior, left and right
posterior. Widespread clinical terminology, which links both leaflets
Aortic root
and sinuses to the origins of the coronary arteries, has replaced anterior,
left and right leaflets with right and left coronary and non-adjacent
The aortic root, the anatomical bridge between the left ventricle and the (and, usually, non-coronary) leaflets, respectively; these clinical terms
ascending aorta, consists of the aortic valvular leaflets (supported by are preferable in the normal heart because they are simple and
the aortic sinuses of Valsalva) and the inter-leaflet triangles interposed unambiguous.
between their basal attachments (see Fig. 57.24). As such, it possesses
significant length, but because of the semilunar attachment of the leaf- Aortic sinuses (of Valsalva)
lets, it has no discrete proximal border. It is limited distally by the The aortic sinuses are more prominent than those in the pulmonary
sinutubular junction (see Fig. 57.30). The essential feature is the semi- trunk. The upper limit of each sinus reaches considerably beyond the
lunar attachments of the valve leaflets; their hinge lines cross the ana- level of the free border of the leaflet and forms a well-defined circum-
tomical ventriculoarterial junction, marking a transition from the ferential sinutubular ridge on the aortic inner surface, just above the
myocardium of the left ventricle to the fibroelastic tissue of the valve aortic valvular leaflets (see Fig. 57.24C). Coronary arteries usually open
sinuses (Fig. 57.31). The muscular portion of the aortic root is roughly near this ridge within the upper part of the sinus but are markedly vari-
two-thirds of its widest circumference. Descriptions of the aortic root able in their origin. The walls of the sinuses are largely collagenous near
over the years have been bedevilled by accounts of a valve anulus. the attachment of the leaflets but the amount of lamellated elastic tissue
Although echocardiographers used to describe this proximal border in increases with distance from the zone of attachment. At the midlevel
terms of an ‘anulus’, examination of cross-sections of the left ventricular of each sinus, its wall is about half the thickness of the supravalvular
outflow tract has never found any circular anatomical boundary or a aortic wall and less than one-quarter of the thickness of the sinutubular
distinct boundary of any kind (Loukas et al 2014a). There are at least ridge. At this level, the mean luminal diameter at the commencement
two rings within the root; neither serves to support the valve leaflets, of the aortic root is much larger than that of the ascending aorta; these
which are attached in semilunar fashion from the sinutubular junction details are functionally significant in the mechanism of valvular motion.
to a basal ventricular attachment. Two leaflets are supported by muscle, A linear relationship between the diameter of the aortic sinus and the
and the third has an exclusively fibrous attachment. The root acts as a square root of body surface area has been described in children (Kaiser
bridging structure not only anatomically, separating the myocardial and et al 2008).
arterial components of the left ventricular pathway, but also function-
ally because its proximal and distal components can withstand consid-
Opening of the aortic valve
erable changes in ventricular and arterial pressures.
During diastole, the closed aortic valve supports an aortic column of
blood at high but slowly diminishing pressure (see Fig. 57.20). Each
Aortic valve leaflets
sinus and its leaflet form a hemispherical chamber. The three nodules
The aortic valve leaflets are attached in part to the aortic wall and in
are apposed and the margins and lunular parts of adjacent leaflets are
part to the supporting ventricular structures. The situation is more
tightly apposed on their ventricular aspects. From the aortic aspect, the
complicated than in the pulmonary valve because parts of the leaflets
closed valve is triradiate, three pairs of closely compressed lunules
also take origin from the fibrous subaortic curtain, and are continuous
radiating from their nodules to their peripheral commissural attach-
with the aortic leaflet of the mitral valve (see Fig. 57.29). This area of
ments at the sinutubular junction (see Fig. 57.21). As ventricular systolic
continuity is thickened at its two ends to form the right and left fibrous
pressure increases, it exceeds aortic pressure and the valve is passively
trigones (see Fig. 57.21). As with the pulmonary valve, the semilunar
opened.
attachments incorporate segments of ventricular tissue within the bases
The fibrous wall of the sinuses nearest the aortic vestibule is almost
of two of the aortic sinuses. The sinuses and leaflets are conveniently
inextensible but, more superiorly, the wall is fibroelastic. Under left
named as right, left and non-coronary, according to the origins of the
ventricular ejection pressure, the radius here increases 16% in systole,
coronary arteries (see Fig. 57.24C). However, the so-called non-coronary
as the commissures move apart to form a fully open triangular orifice.
leaflet is better termed the non-adjacent leaflet because it rarely gives
The free margins of the leaflets then become almost straight lines
rise to a coronary artery.
between peripheral attachments. However, they do not flatten against
The semilunar attachments incorporate three triangular areas (trigo-
the sinus walls, even at maximal systolic pressure, which is probably an
nes) of aortic wall within the apex of the left ventricular outflow tract.
important factor in their subsequent closure. During ejection, most
They are interposed between the bulbous aortic sinuses and separate
blood enters the ascending aorta but some enters the sinuses, forming
the cavity of the left ventricle from the pericardial space. Removal of the
vortices that help to maintain the triangular ‘mid position’ of the leaflet
trigones in an otherwise intact heart is instructive in demonstrating the
during ventricular systole and also probably initiate their approxima-
relationships of the aortic valve, which, justifiably, may be considered
tion at the end of systole. Tight and full closure ensues with the rapid
as the keystone of the heart. The first triangle, between the non-coronary
decrease in ventricular pressure in diastole. Commissures narrow,
and left coronary leaflets, has a base continuous inferiorly with the
nodules aggregate and the valve reassumes its triradiate form. Experi-
fibrous aortic–mitral curtain. The second triangle, between right and
ments indicate that 4% of ejected blood regurgitates through a valve
non-coronary leaflets, has the membranous components of the inter-
with normal sinuses, whereas 23% regurgitates through a valve without
ventricular septum as its base and thus ‘faces’ the right ventricle, whereas
them. The normal structure of the aortic sinuses also promotes non-
its apex ‘points’ towards the transverse pericardial space behind the
turbulent flow into the coronary arteries.
origin of the right coronary artery. The third triangle, between the two
coronary leaflets, has its base on the muscular interventricular septum
Echocardiography
and its apex ‘points’ to the plane of space found between the aortic wall
and the free-standing sleeve of right ventricular infundibular muscula-
ture that supports the leaflets of the pulmonary valve. Although the Echocardiography allows a detailed assessment of the functional
basal attachments of each aortic valvular leaflet are thickened and col- anatomy of the heart. The gross anatomy of the heart can be evaluated
lagenous at their ventricular origins, the leaflets lack a continuous col- by two-dimensional echocardiography in the parasternal, apical,
lagenous circular skeletal support; valvular function depends primarily suprasternal and subcostal positions (Fig. 57.32). The standardized
upon the semilunar attachments of the leaflets. planes used are long-axis, short-axis and four-chamber. The long-axis
The leaflets are endocardial folds with a central fibrous core. With view is obtained by placing the ultrasound transducer in the left apico-
the valve half-open, each equals slightly more than a quarter of a sphere, sternal position and provides detailed images of the left ventricle, aorta,
an approximate hemisphere being completed by the corresponding left atrium, and mitral and aortic valves (Fig. 57.32C). Angling the
sinus. Each leaflet has a thick basal border, deeply concave on its aortic beam towards the right also allows assessment of the right atrium, right
aspect, and a horizontal free margin that is only slightly thickened, ventricle and tricuspid valves. Rotating the transducer by 90° in the | 1,402 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Sinus wall
Ventriculo-
arterial
junction Leaflet
Transitional
zone
Hinge
Ventricular
myocardium
Fig. 57.31 A histological section through one of the coronary aortic
sinuses to demonstrate the way in which ventricular muscle supports the
transition from the fibroelastic wall of the sinus to the tissues of the
leaflet. The transitional area is anchored to the ventricular muscle. The
hinge of the leaflet is well below the level of the ventriculoarterial junction.
Importantly, there is no ring-like structure in the form of an ‘anulus’
supporting the hinge of the leaflet within the ventricle. The muscular
tissue of the ventricle is stained pink; fibrous tissue, which would show
up as a characteristic light colour with this stain, is absent. Haematoxylin
and eosin stain. (Courtesy of Diane E Spicer.) | 1,403 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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NOITCES
RV RV
PV
R LV
TV
AV
RV NA
LV L
RA MV
LA
LA
RA
LA
A B C
RV
RV
RV
AV
RA LV PV
RA AV
LV
LA
LA MV
LA
D E F
Fig. 57.32 Cardiac anatomy shown by transthoracic echocardiography and CT. A, Four-chamber view. B, Short-axis view at aortic valve level. Note
three aortic leaflets – right, left and non-adjacent – and the central position of the aorta. C, Parasternal long-axis view. D–F, Corresponding images by
CT. Note the different orientation compared with transthoracic echocardiography (looked at from below, foot to head). Abbreviations: A, anterior; AV,
aortic valve; F, foot; H, head; L, left; LA, left atrium; LV, left ventricle; MV; mitral valve; NC, non-adjacent; P, posterior; PV, pulmonary valve; R, right; RA,
right atrium; RV, right ventricle; TV, tricuspid valve. (Images courtesy of Dr Konstantinos Dimopoulos, Royal Brompton and Chelsea and Westminster
Hospitals, London.)
clockwise direction produces the short-axis view, which allows assess- connective tissue matrix itself is interconnected laterally to form
ment of the left ventricle, papillary muscles, chordae tendineae and bundles, strands or sheets of macroscopic proportions showing a
mitral valves (Fig. 57.32B). The four-chamber view demonstrates the complex geometric pattern. Surrounding and attaching to larger myo-
ventricles, atria, and mitral and tricuspid valves (Fig. 57.32A). Rotation cardial bundles are stronger perimysial condensations. The overall
of the transducer allows two-chamber views of the heart and more pattern is described in terms of struts and weaves. Despite its impor-
detailed assessment of the aorta and aortic valves. Cardiac MRI and CT tance, the myocardial matrix cannot be grossly dissected.
provide similar information on cardiac structure and function (see Figs Running at the ventricular base is a complex framework of dense
57.2, 57.35A,B), together with complementary information on great collagen with membranous, tendinous and fibroareolar extensions,
vessels (Fig. 57.32D–F) and other extracardiac intrathoracic structures. intimately related to atrioventricular valves and the aortic orifice. The
whole is sufficiently distinct to be termed the fibrous skeleton of the
heart, but although it is often stated that all four valves are contained
CONNECTIVE TISSUE AND FIBROUS SKELETON OF
within this skeleton, this is not the case. The leaflets of the pulmonary
THE HEART valve are supported on a free-standing sleeve of right ventricular
infundibulum that can easily be removed from the heart without dis-
From epicardium to endocardium and from the orifices of the great turbing either the fibrous skeleton or the left ventricle. Another point
veins to the roots of the arterial trunks, the intercellular spaces between of confusion is the idea that the ‘skeleton’ provides the support for the
contractile and conduction elements are permeated by connective cardiac valves. In reality, it is the overall structure of the atrioventricular
tissue; the amount, arrangement and texture vary greatly with location. junctions that supports the mitral and tricuspid valves, whereas the
Over much of the heart, a fine layer of areolar tissue is found beneath arterial valves are hinged within the valvular sinuses. The fibrous skel-
the mesothelium of the serous (visceral) epicardium that accumulates eton is strongest at the junction of the aortic, mitral and tricuspid valves,
subepicardial fat, concentrated along the acute margin, the atrioven- the so-called central fibrous body (see below) (see Figs 57.21, 57.23).
tricular and interventricular grooves, and their side channels. The coro- Two pairs of curved, tapering, collagenous prongs, fila coronaria, extend
nary vessels and their main branches are embedded in this fat; the from the central fibrous body. They are stronger on the left, where they
amount increases with age. The endocardium also lies on a fine areolar pass partially around the mitral and tricuspid orifices. These orifices are
tissue rich in elastic fibres. Fibrocellular components of these subepi- almost co-planar and incline to face the cardiac apex. In contrast, the
cardial and subendocardial layers blend on their mural aspects with the aortic valve faces superiorly, lying anterosuperior and to the right of the
endomysial and perimysial connective tissue on the myocardium. Each mitral orifice. Two of the leaflets of the aortic valve are in fibrous con-
cardiac myocyte is invested by a delicate endomysium composed of fine tinuity with the aortic leaflet of the mitral valve; this subaortic curtain
reticular, collagen and elastin fibres embedded in ground substance. is also an integral part of the fibrous skeleton (see Figs 57.21, 57.24C).
This matrix is lacking only at desmosomal and gap junctional contacts The two ends of the curtain are strengthened as the right and left fibrous
of intercalated discs. Similar arrangements apply to ventricular conduc- trigones, which are the strongest parts of the skeleton. The right trigone,
tion myocytes and their extensive working myocardial contacts. The together with the membranous septum, constitutes the central fibrous | 1,404 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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body, which is penetrated by the atrioventricular bundle of His (see
below). The membranous septum is crossed on its right aspect by the
attachment of the tricuspid valve, dividing the septum into atrioven-
tricular and interventricular components.
The aortic root is central within the fibrous skeleton and is often
described in terms of an ‘anulus’ integrated within the fibrous skeleton
(Anderson et al 2013b). However, as with the pulmonary valve, the
structure of the aortic root corresponds to the triple fibrous semilunar
attachments of its leaflets. Within this complex circumferential zone
are three crucially important triangular areas that separate, on the ven-
tricular aspect, the aortic bulbous sinuses that house the valvular leaf-
lets. As a whole, three triangles, known as the subaortic spans, can be
conceptualized in terms of a three-pointed coronet; their triangular
apices correspond to the tips of the valvular commissures and their
walls, significantly thinner than those of the sinuses, consist variously
of collagen or admixed muscle strands and fibroelastic tissue. They
form the subvalvular extensions of the aortic vestibule. The first span is
the interval between the non-coronary and left coronary sinuses that is
filled with the deformable subaortic curtain. The second span between
the non-coronary and right coronary sinuses is continuous with the
anterior surface of the membranous septum. The third span, between
the two coronary aortic sinuses, is filled with loose fibroelastic tissue
and separates the extension of the subaortic root from the wall of the
free-standing subpulmonary infundibulum. Previously, this was
Fig. 57.33 A reconstruction of a porcine heart made following diffusion
thought to be the location of the tendon of the infundibulum (conal tensor MRI of an autopsied heart. The tracks are created from the first
(conus) ligament) (Loukas et al 2007); research using mouse hearts eigenvectors and represent the alignment of the aggregated myocytes.
has shown that the ligament is found at the level of the sinutubular This technique enables the identification of reproducible tracks, or
junctions at the site of initial fusion of the distal outflow cushions. The pathways, through the myocardium that connect remote end and
line of proximal fusion is the longitudinal raphe sometimes seen in epicardial regions by means of simultaneous changes in helical and
the muscular subpulmonary infundibulum. intrusion angles. (With permission from Anderson R, Smerup M, Sanchez-
Similar fibrous triangles are found separating the sinuses of the Quintana D, Loukas M, Lunkenheimer P. 2009. The three-dimensional
pulmonary trunk but these are significantly less robust. Use of the terms arrangement of the myocytes in the ventricular walls. Clin Anat 22:64–76.)
mitral and tricuspid ‘anuli’ implies that the atrioventricular valves are
supported by discrete circular fibrous rings, when, in reality, they are
D-shaped structures integrally attached to the fibrous cardiac skeleton.
estimated at 8 per 1000 live births but they are found in up to 2% of
It is therefore inaccurate to consider these valvular orifices as circular.
stillbirths. Only a small proportion of the anomalies are directly attrib-
Rather, the straight edge of the ‘D’-shaped mitral valve represents a
utable to genetic or environmental factors and the majority are the
fibrous continuity between the anterior leaflet and the aortic root, and
result of multifactorial events.
the remainder supports the mural leaflet. The straight edge of the tri-
cuspid valve represents the attachment of the septal leaflet, marking Abnormalities of cardiac position
the inferior border of the triangle of Koch, and the remainder supports
the anterosuperior and inferior leaflets. The valvular attachments of the
Available with the Gray’s Anatomy e-book
atrioventricular valves are not simple, rigid collagenous structures but
dynamic, deformable lines that vary greatly at different peripheral
points and change considerably with each phase of the cardiac cycle Acyanotic cardiac defects
and with increasing age. The tricuspid attachments are even less robust
than those of the mitral valve. At several sites, only fibroareolar tissue Available with the Gray’s Anatomy e-book
separates the atrial and ventricular muscular masses.
The fibrous skeleton ensures electrophysiological discontinuity
Cyanotic cardiac defects
between the atrial and ventricular myocardial masses (except at the site
of penetration of the conduction tissue). It also provides direct attach-
ment for the myocardium and for fibrous tissue throughout the Available with the Gray’s Anatomy e-book
heart as a support matrix for a three-dimensional meshwork of
cardiomyocytes.
CONDUCTION TISSUES
Arrangement of cardiomyocytes The microstructure of cardiac
muscle is described in detail in Chapter 6. Ventricular myocytes form a The cells of cardiac muscle differ from those of skeletal muscle in having
three-dimensional mesh in a supporting fibrous matrix. One popula- the inherent ability to contract and relax spontaneously. This myogenic
tion is aligned so that the long axis of the aggregated cells is tangential rhythm is shown by small pieces of cardiac tissue, and even isolated
to the epicardial and endocardial borders, albeit with marked variation myocytes. Ventricular cells contract and relax at a lower frequency than
in the angulation relative to the ventricular equator. Correlation with atrial cells, but in the intact heart, both are synchronized to a more
measurements taken using force probes shows that these myocytes rapid rhythm, generated by pacemaker tissue in the sinus and atrioven-
produce the major unloading of the blood during ventricular systole. A tricular nodes and conveyed by a system of specialist conduction fibres
second population is aligned at angles of up to 40° from the epicar- in the atrioventricular conduction axis and the ventricular conducting
dium towards the endocardium and produces auxotonic forces during pathways (Purkinje cells). For an account of excitation–contraction
the cardiac cycle. The three-dimensional arrangement of the mesh as coupling in cardiac muscle, see page 138.
demonstrated in MRI of the porcine heart also mediates the realign- The anatomical arrangement of these tissues is described in the
ment of cardiomyocytes that must take place during ventricular con- context of the heart. Here, consideration is restricted to the cells that
traction and accounts for the extent of systolic mural thickening make up the impulse-generating and conduction system. All are modi-
(Fig. 57.33). fied cardiac cells. Three types within a continuum of morphology may
The finding that the number of cardiomyocytes in the left ventricle be distinguished from normal working cells, namely: nodal cells, tran-
increases between the first and the twentieth year of life suggests that sitional cells and Purkinje cardiomyocytes.
children may be able to regenerate myocardium (Mollova et al 2013).
Overview of the conduction system
CONGENITAL CARDIAC MALFORMATIONS
Of all the cells in the heart, those of the sinu-atrial node generate the
Congenital malformations of the heart are common and amount to most rapid rhythm, and therefore function as the cardiac pacemaker.
about one-quarter of all developmental anomalies. Their incidence is The impulse, believed to be generated in the nodal cells, is transmitted | 1,405 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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The most severe abnormality of position is an extrathoracic heart Most congenital heart abnormalities can be detected during antena-
(ectopia cordis), where the heart usually projects to the surface through tal ultrasound screening (Fig. 57.34). Neonates with severe congenital
the lower thoracic and upper abdominal wall, remaining covered, in heart disease may present with tachypnoea, difficulty in feeding, cyano-
most instances, by the fibrous pericardium, and usually accompanied sis and/or cardiovascular collapse, and there may be audible murmurs
by herniation of the abdominal contents. A mirror image, i.e. reversal on auscultation. The vast majority of abnormalities may be detected by
in cardiac shape and position, occurs predominantly in the right postnatal echocardiography; in a very few cases, cardiac catheterization
hemithorax (dextroposition). The apex of the heart may be directed to and direct measurements of pressure, oxygen saturations and angiogra-
the right instead of the left (dextrocardia). This arrangement may phy may be required.
be part of ‘situs inversus totalis’, where the heart, great vessels and
abdominal organs all occupy mirror-imaged positions. The heart may Acyanotic cardiac defects are the result of either left-to-right cardiac
also be right-sided in Kartagener’s syndrome (a subgroup of ciliary shunting through heart defects (intra- or extracardiac) or of obstruction.
dyskinesias). Left-to-right shunting leads to an increased workload and stress on the
More usually, an abnormal location of the heart occurs in cases of heart and the lungs as a consequence of increased pulmonary blood
isomerism, in which both sides of the thorax, including the main flow and increased pulmonary venous return. Depending on the loca-
bronchi and the atrial appendages, retain features of either morphologi- tion of the shunt and the magnitude of left-to-right shunting, patients
cal right- or left-sidedness. Isomerism is also commonly associated with are at risk of developing pulmonary arterial hypertension unless
the anomalous arrangement of the abdominal organs: right isomerism timely heart surgery is undertaken. Examples of defects leading to left-
with absence of the spleen (asplenia) and left isomerism with multiple to-right shunting are simple septal defects such as atrial or ventricular
spleens (polysplenia). Intracardiac anatomy in cases of isomerism is septal defects or patent ductus arteriosus, or more complex atrioven-
almost universally abnormal, and there is a range of heart defects tricular septal defects, and/or a combination of any of these defects with
(usually more simple in left and more complex in right isomerism). abnormal atrioventricular or ventriculoarterial connections (e.g. a
These intrathoracic abnormal arrangements, with or without abdom- double-outlet right ventricle, where more than 50% of both the aorta
inal abnormalities, often first manifest themselves incidentally follow- and the pulmonary artery originate from the right ventricle) (Ch. 52).
ing chest radiography. Reversal of normal anatomy has obvious clinical Obstructive lesions may involve the atrioventricular or arterial valves
implications, a typical example being a patient with mirror-image (mitral, aortic or pulmonary valve stenosis), or narrow vessels (e.g.
arrangements and appendicitis, who presents with an acute left lower coarctation of the aorta or interrupted aortic arch). Depending on the
quadrant pain. level and severity of the obstruction, patients may have a range of
RV
LV MV
VSD RA LA LV RV LV RV TV
RA
A B C
VSD
RV
LV
RV RV Ao Ao
PA
RA LV
D E F
Fig. 57.34 A, Tricuspid atresia at 21 weeks’ gestation. A four-chamber view showing a large left ventricle and a hypoplastic right ventricle. The mitral
valve is seen; no tricuspid valve is identified. There is an associated ventricular septal defect. B, An atrioventricular septal defect at 20 weeks’ gestation.
A common atrioventricular valve (arrow) is associated with a defect in the atrioventricular septum. C, Hypoplastic left heart syndrome at 32 weeks’
gestation. This four-chamber view shows a large right atrium, right ventricle and tricuspid valve. There is a hypoplastic left ventricle; no mitral valve is
identified. D, Hypoplastic left heart syndrome at 32 weeks’ gestation. This four-chamber view shows colour flow from right atrium to right ventricle
across the tricuspid valve; no mitral valve is identified and there is no flow in the left side of the heart. E, Tetralogy of Fallot at 33 weeks’ gestation. The
aorta arises astride a ventricular septal defect. F, Transposition of the great arteries at 21 weeks’ gestation. The aorta and pulmonary artery arise in
parallel orientation. The aorta arises from the right ventricle and the pulmonary artery from the left ventricle. Abbreviations: Ao, aorta; LA, left atrium; LV,
left ventricle; MV, mitral valve; PA, pulmonary artery; RA, right atrium; RV, right ventricle; TV, tricuspid valve; VSD, ventricular septal defect. (Courtesy of
Gurleen Sharland, Evelina London Children’s Hospital.) | 1,406 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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A B
Fig. 57.35 A, Cardiac magnetic resonance angiography in a patient with a normal heart. Note the criss-cross relationship of the great arteries; the aorta
arises from the left ventricle and runs to the right and posteriorly to the pulmonary trunk (at its origin) and towards the head. The pulmonary artery arises
from the right and anterior right ventricle, crosses over and then runs to the left of the aorta and towards the back (where it bifurcates into the right and
left pulmonary arteries at the underside of the aortic arch). B, A cardiac magnetic resonance angiogram from a patient with transposition of the great
arteries. Note the parallel or side-by-side relationship of the great vessels and loss of their normal criss-cross relationship. The aorta runs anteriorly and
comes off the right ventricle. The hypertrophied right ventricle supports the systemic circulation, and the ventricular septum bows from right to left.
Abbreviations: Ao, aorta; LV, left ventricle; PT, pulmonary trunk; RV, right ventricle. (Courtesy of Dr Philip Kilner, Royal Brompton Hospital, London.)
clinical presentations from an asymptomatic heart murmur (common) position of the great arteries (Fig. 57.35; p. 924) and tricuspid and
to cardiovascular collapse (uncommon). Treatment in all cases is pulmonary atresia (often in the setting of hypoplastic right ventricle
directed towards normalizing heart workload, systemic and pulmonary and functionally univentricular physiology). Neonates with severe cyan-
blood flow, and cardiac output, and may be surgical and/or catheter- otic congenital heart defects may be dependent on the patency of the
based. ductus arteriosus; early diagnosis, treatment with intravenous prosta-
glandin infusion and timely transfer to a tertiary centre for more defini-
Cyanotic cardiac defects may be attributable to a right-to-left intra- or tive therapy is key to survival and good long-term outcomes.
extracardiac shunt or to a severe reduction in pulmonary blood flow. Major advances in the diagnosis and management of infants with
They may be caused by simple lesions such as severe pulmonary steno- congenital cardiac malformations in recent years have resulted in an
sis with an atrial septal defect and right-to-left shunting; moderate increased number of adolescents and adults with palliated or repaired,
lesions, including Fallot’s tetralogy, in which there is a ventricular septal but not cured, congenital heart disease. This is an area that poses mul-
defect, right ventricular outflow obstruction, right ventricular hypertro- tiple challenges to both cardiovascular and other medical disciplines.
phy and an overriding aorta; or more complex lesions, including trans- | 1,407 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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over preferentially conducting pathways to right and left atria, and to parts of the right atrium (see Figs 57.13A, 57.37). In hearts over 65 years
the atrioventricular node. At the atrioventricular node, the impulse is of age, a layer of connective or fatty tissue between the subendocardium
delayed by 40 ms, allowing the atria to eject their contents fully before and the body of the node may sometimes render it visible to the naked
commencement of ventricular contraction, and also placing an upper eye. Extending on the right from the crest of the right appendage, the
limit on the frequency of signals that can be transmitted to the ventri- node typically courses posteroinferiorly into the upper part of the ter-
cles. The transitional cells interpose between the atrial cardiomyocytes minal groove; in about 1 in 10 hearts it extends in horseshoe fashion
and the nodal cells. There is no transition in humans between the across the crest of the appendage. Nodal tissue does not occupy the full
node and the penetrating bundle, and the cells are virtually identical. thickness of the right atrial wall from epicardium to endocardium but
Here, they become continuous with the more distinctively appearing sits as a wedge of specialized subepicardial tissue within the terminal
Purkinje cells. Conduction of the impulse is rapid in the bundle and groove. Its location is consistently marked by a large central artery,
its branches (2–3 m/sec, as opposed to 0.6 m/sec in normal myocar- which originates from either the proximal part of the right coronary or
dium). The cardiac impulse therefore arrives at the apex of the heart circumflex arteries in equal proportion. Nodal cells are grouped circum-
before spreading through the ventricular walls, producing a properly ferentially around the sinu-atrial nodal artery, packed within a dense
coordinated ventricular ejection. The human heart beats ceaselessly at matrix of connective tissue as interlacing strands of myocytes. They are
70 cycles every minute for many decades, maintaining perfusion of smaller, paler and more empty-looking than working atrial myocardial
pulmonary and systemic tissues. The rate and stroke volume fluctuate fibres, being 5–10 µm in their greatest diameter, with a large central
in response to prevailing physiological demands. The principal events nucleus. Their pale appearance is attributable to the sparsity of
in a cardiac cycle are summarized in Figure 57.20, including the elec- organelles; myofibrils are few and irregularly arranged, and there is no
trical events recorded in the electrocardiogram; the mechanical proper sarcotubular system with little glycogen.
sequences of diastole, atrial systole, volumetric contraction, ejection The sinu-atrial node is described as having a head, body and tail,
and isovolumetric relaxation in ventricular systole; the acoustic phe- from which 5–8 short digitations of nodal tissue radiate towards the
nomena recorded in the phonocardiogram; the pressure profiles of superior vena cava, subepicardium and crista terminalis, penetrating the
right and left hearts and arterial trunks; and the sequences of valvular working atrial myocardium (Figs 57.38–57.39). At the nodal periphery,
events. nodal cells intermingle with slender, fusiform, transitional ‘linking’
Cardiac efficiency depends on precise timing of the operation in cells that are part of a heterogeneous cellular group intermediate in
interdependent structures. Passive diastolic filling of the atria and ven- appearance between nodal cells and normal working atrial myocytes.
tricles is followed by atrial systole, stimulated by discharge from the (For further reading on the use of molecular markers to map the extent
sinu-atrial node, which completes ventricular filling. Excitation and of nodal tissue, see Monfredi et al (2010).) There are no autonomic
contraction of the atria must be synchronous and finish before ventricu- ganglion cells within the node, although many border it anteriorly and
lar contraction; this is effected by a delay in the conduction of excitation posteriorly. Nerve fibres are present but do not appear to contact the
from atria to ventricles. Thereafter, ventricular contraction proceeds in nodal myocytes.
a precise manner. The atrioventricular valves are closed by ventricular
Paranodal area
systole, which must occur prior to closure; ventricular activation must
therefore precede valvular closure, which spreads from the ventricular A paranodal area within the terminal crest, between the cells of the
apices towards the outflow tracts and orifices. sinu-atrial node and the working atrial cardiomyocytes, and possessing
Cardiac contraction originates unequivocally in specialized cardio- properties of both nodal and atrial tissues, has been identified (Molenaar
myocytes, but neural influences are important in adapting the intrinsic et al 2011). Its precise function remains to be determined, but computer
cardiac rhythm to functional demands from the entire body. All cardio- simulations suggest that it is an integral part of normal atrial activation
myocytes are excitable. They display autonomous rhythmic depolariza- and may play a role in pacemaking.
tion and repolarization of their cell membranes, conduction of waves
Internodal atrial myocardium
of excitation via gap junctions to adjacent cardiomyocytes, and
excitation–contraction coupling to their actomyosin complexes. These Specialized pathways have been alleged to connect the sinus and atrio-
properties are developed to different degrees in different sites and in ventricular nodes, but there is no evidence that tracts insulated from
different types of cardiomyocyte (Ch. 6). The rate of depolarization and the working myocardium, as occurs in the ventricular conduction path-
repolarization is slowest in the ventricular myocardium, intermediate ways, exist within the atrial walls. The impulse generated by the sinu-
in the atrial muscle, and fastest in the myocytes of the sinu-atrial node. atrial node is conducted more rapidly via the long axis of the atrial
The latter override those generating slower rhythms and, in the normal muscle bundles than it is transversely. The main pathways for conduc-
heart, are the locus for the rhythmic initiation of cardiac cycles. Con- tion towards the atrioventricular node are the terminal crest and the
versely, conduction velocity is slow in nodal myocytes, intermediate in margins of the oval fossa. Conduction to the left atrium is preferentially
general ‘working’ cardiac myocytes, and fastest in the myocytes of the through Bachmann’s bundle; additional pathways occur through the
ventricular conduction system. margins of the oval fossa and through the muscular connections
The nodes and networks of the so-called specialized myocardial cells between the walls of the coronary sinus and left atrium. During devel-
constitute the cardiac conduction system (Figs 57.36–57.37). The com- opment, the walls of the systemic venous sinus are exclusively com-
ponents of this system are the sinus and atrioventricular nodes, the posed of primary myocardium. Although pathways within these walls
atrioventricular bundle with its left and right bundle branches, and the may be identified in prenatal stages, primary myocardium is slowly
subendocardial plexus of ventricular conduction cells (Purkinje cells). conducting, which means that these pathways do not represent areas of
The main pacemaker rhythm of the heart (sinus rhythm) is generated preferentially rapid conduction.
within the system but is influenced by nerves. It is transmitted specifi-
Atrioventricular node
cally from atria to ventricles via the atrioventricular node and bundle.
The spread of excitation is very rapid but not instantaneous. Different The atrioventricular node is an oblique, half-oval atrial structure, located
parts of the ventricles are excited at slightly different times, with impor- within the atrial component of the muscular atrioventricular septum
tant functional consequences. Failure of the conduction system will not and separated from the ventricular musculature by the insulating tissues
block cardiac contraction but the system will become poorly coordi- of the atrioventricular groove (see Fig. 57.37). Its anatomical landmarks
nated. The rhythm will be slower because it originates from a spontane- are the boundaries of the triangle of Koch, i.e. the attachment of the
ous (myogenic) activity in the working cardiac myocytes or in a septal leaflet of the tricuspid valve inferiorly, the ostium of the coronary
subsidiary pacemaker in a more distal part of the diseased or disrupted sinus basally and the tendon of Todaro superiorly (see Fig. 57.13). The
conduction system. There are no specialized internodal and interatrial atrial aspect of the node is convex and overlain by atrial myocardium.
conduction pathways; the excitation emanating from the sinu-atrial Its left margin is concave and abuts on to the superior aspect of the
node spreads to the atrial musculature and to the atrioventricular node central fibrous body. The basal end projects into the atrial muscle and
through ordinary atrial working myocardium. The geometric arrange- the anteroinferior end enters the central fibrous body to become the
ment of fibres along well-organized atrial muscle bundles, e.g. the ter- penetrating atrioventricular bundle.
minal crest, the rims of the fossa ovalis and Bachmann’s bundle, ensures The node consists of two zones, compact and transitional, pervaded
that conduction is marginally more rapid than elsewhere within the by an irregular collagenous reticulum that enmeshes the myocytes (Fig.
atrium. 57.40). The compact zone consists of frequently stratified, interlocking
nodal cells. Cells from the right and left atrial walls and the atrial
Sinu-atrial node
septum feed directly into the compact zone. The transitional zone
In the majority of hearts, the sinu-atrial node is a crescent-shaped struc- envelops the compact portion of the node and consists of elongated
ture, between 8 and 25 mm long, located at the embryonic junction ‘transitional cells’, intermediate in morphology and function between
between the venous part (sinus venosus) and the atrium proper derived compact nodal cells and working atrial cardiomyocytes. | 1,408 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Sinu-atrial node artery Terminal crest
Endocardium
A
F
Width Terminal crest
A B C G
D E F
Detail of panel B
5 mm
Fig. 57.38 Measurements of the width and height of the sinu-atrial node and the distances of nodal tissue to epicardium (a) and endocardium (b),
measured in cadaveric tissue. (Top) A gross cadaveric specimen together with an example of a histological section and a diagram to indicate where
measurements were made on each histological section. (Bottom) Histological sections (Masson trichrome stain) taken through levels A–F as indicated on
the gross specimen. (G) The red dotted line delineates the nodal boundaries. Note the irregular contour of the node and the extensions towards the
neighbouring myocardium (arrows). Abbreviations: SVC, superior vena cava. (With permission from Sánchez-Quintana D, Cabrera JA, Farré J, Climent V,
Anderson RH, Ho SY. 2005. Sinu-atrial node revisited in the era of electroanatomical mapping and catheter ablation. 2005 91:189–94.)
muidracipE
Terminal groove SVC
Height
b
a
Histological sections
Head
Body Body
Body Tail Tail
f
f
f
f
f
A B C
Fig. 57.39 Histological sections of the nodal body. A, Fibro-fatty tissue (f) between the caudal aspect of the nodal body and the subendocardium.
B–C, Fragmentation of the nodal tail into clusters. Masson trichrome stain. (With permission from Sánchez-Quintana D, Cabrera JA, Farré J, Climent V,
Anderson RH, Ho SY. 2005. Sinu-atrial node revisited in the era of electroanatomical mapping and catheter ablation. 2005 91:189–94.) | 1,409 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Atrial Transitional Compact Atrial Penetrating Fig. 57.40 Histological sections showing the
overlay cells cells AV node myocardium AV bundle features of (A) the atrioventricular (AV) node and
(B) the penetrating atrioventricular bundle.
Trichrome method, fibrous tissue stained green.
(With permission from Anderson RH, Boyett MR,
Dobrzynski H, Moorman AF. 2013. The anatomy
of the conduction system: implications for the
clinical cardiologist. J Cardiovasc Transl Res.
6:187–196.)
A B
Atrial Insulating Ventricular Insulating Ventricular
septum tissues septum tissues myocardium | 1,410 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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A
Aorta
Right pulmonary artery Right appendage
Pulmonary valve
Superior vena cava
Sinu-atrial node
Aortic mound
Fossa ovalis Membranous part of
interventricular septum
Tendon of Todaro Radiation of left branch
Valve of inferior vena cava Right bundle branch
Coronary sinus
Septal leaflet of tricuspid valve
Inferior vena cava
Atrioventricular node
Septomarginal trabecula
(moderator band)
Papillary muscles
B
Aorta
Left appendage
Left pulmonary artery
Cut chordae tendineae
of mitral valve
Right pulmonary veins
Superoposterior papillary muscle
Aortic valve
Radiation of left branch
Inferior vena cava
Fig. 57.36 The conduction tissue of the heart. A, Right aspect. B, Left aspect. The elements of the conduction system are shown in purple. Conduction
tissue accompanies fine trabeculae carneae and false chordae. In reality, the radiation of the left bundle branch is directly related to the leaflets of the
aortic valve.
Extensions of nodal cardiomyocytes run in the direction of the coro-
Atrioventricular bundle
nary sinus along the tricuspid anulus (the putative ‘slow pathway’); in
the anterior portion of the triangle of Koch near the compact portion of The atrioventricular bundle (of His) is the direct continuation of the
the atrioventricular node (the putative ‘fast pathway’); and in the direc- atrioventricular node. It becomes oval, quadrangular or triangular in
tion of the mitral anulus (the left atrial extension) (Mani and Pavri transverse sectional profile as it enters the central fibrous body. It
2014). In both sinus and atrioventricular nodes, the intercellular con- traverses the fibrous body and branches on the crest of the muscular
tacts between nodal cells, and between nodal and transitional cells, are interventricular septum; the branching tract is sandwiched between the
much less specialized than the intercalated discs between normal cardiac muscular and the membranous components of the septum.
cells (p. 137). A sparsity of gap junctions is consistent with the absence The right branch of the bundle (crus dextrum) is a narrow, discrete,
from these areas of connexin-43 (a major protein component of mam- rounded group of fascicles that courses at first within the myocardium
malian gap junctions), and probably accounts for the observed difficulty and then subendocardially towards the ventricular apex, entering the
in exciting these cells from adjacent cells. The atrioventricular delay may septomarginal trabecula to reach the anterior papillary muscle. Its
owe much to this relative non-excitability, which appears to disturb the branches to the ventricular walls are few in its septal course. At the
spread of potential, delaying propagation; the narrow diameter of the origin of the anterior papillary muscle, it divides profusely into fine
transitional cells may also contribute to conduction delay. subendocardial fascicles that diverge, first embracing the papillary
The arterial supply to the atrioventricular node is from a character- muscle, then recurving subendocardially for distribution to the remain-
istic vessel that originates from the dominant coronary artery at the ing ventricular walls.
cardiac crux. Autonomic ganglia are present between the node and the The left branch (crus sinistrum) arises as numerous fine, intermin-
coronary sinus. gling fascicles that leave the left margin of the branching bundle through | 1,411 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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oblique inverted crown within the atrioventricular groove. They also
R
form a variable and often insignificant anastomosis (in the non-
pathological state) via marginal and interventricular (descending)
loops that intersect at the cardiac apex. The main arteries and major
P Q S T
branches are usually subepicardial, but those in the atrioventricular and
interventricular grooves are often deeply sited, and occasionally hidden
by overlapping myocardium or embedded in it (myocardial bridging).
The term ‘dominant’ is used to refer to the coronary artery giving off
the posterior interventricular (posterior descending or inferior interven-
Fibro-fatty atrioventricular
groove (separation of atrial tricular) branch, which supplies the posterior (inferior) part of the
SVC and ventricular myocardium) ventricular septum and often part of the posterolateral (inferolateral)
wall of the left ventricle. The right artery is the dominant artery in 60%
LA
of hearts. Anastomoses between right and left coronary arteries are
Sinu-atrial node
(pacemaker) abundant in the fetus but are much reduced by the end of the first year
RA of life. Anastomoses providing collateral circulation may become prom-
Atrioventricular inent in conditions of chronic hypoxia and in coronary artery disease.
node (delay)
An additional collateral circulation is provided by small branches from
Atrioventricular mediastinal, pericardial and bronchial vessels.
bundle and branches
(insulated) Coronary arterial original calibre, based on arterial casts or angio-
gram measurements, ranges between 1.5 and 5.5 mm. The calibre of
the left origin exceeds the right in 60% of hearts, the right being larger
in 17%, and both vessels being of approximately equal calibre in 23%.
The external diameter of the left coronary artery increases from 2.1 mm
at the age of 1 year to 3.3 mm at the age of 15 years (Pesonen et al 1991)
Purkinje fibres and the diameters of the coronary arteries may increase up to the 30th
(activation) year. A significant association has been found between the diameters of
the right and left coronary arteries at birth and at 1 and 6 months of
Fig. 57.37 The basic structure of the conduction system and its
age and birth weight, height and body surface area (Karagol et al 2012).
relationship with the electrocardiogram. Note the foramen ovale allowing
for communication between the right atrium (RA) and the left atrium (LA).
Right coronary artery
Other abbreviations: SCV, superior vena cava. (Redrawn by courtesy of
Professor RH Anderson, Institute of Child Health, University College, The right coronary artery arises from the anterior (‘right coronary’)
London.) aortic sinus; its ostium is usually below the sinutubular junction. The
artery is usually single but as many as four right ostia have been
observed, reflecting the independent origins of the conal, sinu-atrial
node and ventricular arteries (Figs 57.42–57.43). The right coronary
most of its course along the crest of the muscular ventricular septum artery passes at first anteriorly and slightly to the right between the right
(see Fig. 57.36). These fascicles form a flattened sheet down the smooth atrial appendage and pulmonary trunk, where the sinus usually bulges.
left ventricular septal surface that diverges apically and subendocar- On reaching the atrioventricular groove, it descends almost vertically to
dially across the left aspect of the ventricular septum, trifurcating into the right (acute) cardiac border, curving around it into the posterior
anterior, septal and posterior divisions. Fine branches leave the sheets, (inferior) part of the groove, where the latter approaches its junction
forming subendocardial networks, which first surround the papillary with both interatrial and interventricular grooves, the appropriately
muscles and then curve back subendocardially to be distributed to all termed cardiac crux. The artery ends a little to the left of the crux, often
parts of the ventricle. The principal branches of the bundle are insulated by anastomosing with the circumflex branch of the left coronary artery.
from the surrounding myocardium by sheaths of connective tissue. The right coronary artery may end near the right cardiac border, between
Functional contacts between ventricular conduction and working this and the crux, or more often it reaches the left border, replacing the
myocytes become numerous only in the subendocardial terminal rami- more distal part of the circumflex artery. Its branches supply the right
fications. Hence, papillary muscles contract first, followed by a wave of and variable parts of the left chambers and atrioventricular septum.
excitation and ensuing contraction that travels from the apex of the Usually, the first branch is the right conal artery (conus artery, artery of
ventricle to the arterial outflow tract. Because the Purkinje network is the conus, arteria coni arteriosi; Loukas et al 2014b). (This vessel arises
subendocardial, muscular excitation proceeds from endocardium to independently from the anterior aortic sinus in approximately one-
epicardium. third of hearts and is therefore sometimes termed the ‘third coronary
In the developing heart, the bundle responsible for atrioventricular artery’; a similarly named vessel arises from the left coronary circulation
conduction is a much more extensive structure. Immunohistochemical and so this title is inappropriate.) The right conal artery ramifies antero-
analysis has revealed that the precursor of the system is a ring of cells inferiorly over the pulmonary conus and over the superior aspect of the
that surrounds the inlet and outlet components of the developing ven- right ventricle, sometimes anastomosing with a similar branch from the
tricular loop (Ch. 52). left interventricular (anterior descending) artery to form the anulus of
Vieussens, a tenuous anastomosis around the right ventricular outflow
Cardiac pacing
tract (Figs 57.44–57.45) (Loukas et al 2009).
The first segment of the right coronary artery (between its origin and
Available with the Gray’s Anatomy e-book the right cardiac margin) gives off anterior atrial and ventricular
branches that diverge widely, approaching a right angle in the case of
Cardiac conduction studies the ventricular arteries, an arrangement that is in marked contrast to
the more acute origins of the left coronary ventricular branches. The
Available with the Gray’s Anatomy e-book anterior ventricular branches, usually two or three, ramify towards the
cardiac apex, which they rarely reach (unless the right marginal artery
Congenital conduction abnormalities is included within this group of branches, as it is by some authors). The
right marginal artery is greater in calibre than the other anterior ven-
tricular arteries and long enough to reach the apex in most hearts. When
Available with the Gray’s Anatomy e-book
it is very large, there may be only one other remaining anterior ven-
tricular branch, or even no other branches. Up to three small posterior
(inferior) ventricular branches, most often two, arise from the second
VASCULAR SUPPLY AND LYMPHATIC DRAINAGE
segment of the right coronary artery between the right border and crux
to supply the right ventricular diaphragmatic aspect. Their size is
Coronary arteries
inversely proportional to that of the right marginal artery, which usually
extends to the cardiac diaphragmatic surface. On approaching the crux,
The right coronary artery arises from the anterior (‘right coronary’) sinus the right coronary artery normally produces up to three posterior (infe-
and the left coronary artery from the left posterior (‘left coronary’) sinus rior) interventricular branches (occasionally none). The posterior (infe-
of the ascending aorta (see Figs 57.21–57.22; Fig. 57.41); ostia levels rior) interventricular artery itself, lying within the interventricular
vary. The two arteries, as indicated by their generic name, form an groove, may therefore be flanked, either to the right or to the left, or on | 1,412 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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This ring is in continuity with the atrioventricular bundle, itself part
of an interventricular ring of specialized cardiomyocytes. The segment
of the interventricular ring that encircles the developing left ventricular
outflow tract subsequently breaks down. The segment that persists
within the ventricles extends along the septum beyond the branching
atrioventricular bundle and forms a dead-end tract. The dorsal compo-
nent of the interventricular ring is part of the definitive atrioventricular
node, continuous with the atrioventricular bundle. The rightward com-
ponent of the atrioventricular ring system, emerging inferiorly from the
atrioventricular node, is part of the slow nodal pathway. The cardio-
myocytes that formed the ring initially possessed a primary phenotype,
i.e. they would have conducted slowly.
Wolff–Parkinson–White syndrome is caused by abnormal small
strands of otherwise unremarkable ventricular myocardium that run
through the fibroareolar tissue of the atrioventricular groove, connect-
ing the atrial and ventricular myocardial masses at some point around
the atrioventricular junctions.
Temporary pacing wires are usually inserted by cannulation of either
the internal jugular or subclavian veins; the latter approach carries a
slightly greater risk of a pneumothorax because of the proximity of the
pleural cavity. Other potential risks are brachial plexus injury if the entry
Conal artery Right coronary artery
site is too posterior, and thoracic duct injury if the left subclavian vein
Fig. 57.43 The right coronary sinus, revealing a coronary orifice for the
is cannulated. The most common location for permanent pacemaker
right coronary artery and a coronary orifice for the conal artery. (With
devices is subcutaneously on the anterior chest wall. Access to the
permission from Loukas M, Sharma A, Blaak C, Sorenson E, Mian A.
chambers and endocardium of the right heart is gained via the cephalic
2013. The clinical anatomy of the coronary arteries. J Cardiovasc Transl
vein within the deltopectoral groove.
Res. 6:197–207.)
Intracardiac electrocardiography and electrophysiology are used to
assess cardiac conduction and rhythm abnormalities. A catheter is
inserted via the femoral, subclavian or internal jugular veins using a
guidewire technique. Fluoroscopy, echocardiography and, more
recently, cardiac magnetic resonance are used to guide accurate place- Aorta
ment of the catheters to the appropriate position. The sites of study are
Right
the high right atrium (for assessing the atrioventricular bundle and right coronary
bundle branch) and the coronary sinus (for evaluating atrioventricular artery
junctional arrhythmias and accessory pathways). The multipolar elec- Conal artery
trodes provide detailed electro-anatomical mapping of the sequence of
excitation from the atria, atrioventricular junction and ventricles. The
*
origin of supraventricular arrhythmias, ventricular tachycardias, acces-
sory conduction pathways and re-entrant pathways can be identified Anterior
and used to guide radiofrequency ablation. interventricular
artery
In the past, there was an anatomical basis for the majority of presenting
congenital conduction abnormalities: they were the product of either Ventricular
accessory pathways or conduction tissue dysgenesis at any point from branches
the atrioventricular node to the atrioventricular bundle. Today, conduc-
tion abnormalities are increasingly likely to relate to long-standing
haemodynamic problems and/or the effects of previous surgery for
**
patients with congenital heart defects. This reflects the fact that, although
surgery for most of these defects has been available for the past four
decades, surgery itself has not been curative; more often than not,
patients develop conduction abnormalities and arrhythmia from surgi- ***
cal scars that cause haemodynamic problems such as chamber dilation
and/or hypertrophy. Occasionally, conduction abnormalities are caused
by tumours such as multifocal Purkinje cell tumours, or benign con-
genital polycystic tumours of the atrioventricular node.
Congenital abnormalities of the coronary arteries are found rarely
in children. The two most common abnormalities are coronary arterio-
venous fistula and anomalous left coronary artery arising from the
Fig. 57.44 A variation of the anulus of Vieussens (*). This corrosion cast
pulmonary artery (Uysal et al 2014). Other congenital abnormalities
specimen shows the right conal artery, a branch of the right coronary
include ectopic origin of left circumflex artery from right coronary
artery, anastomosing with a proximal ventricular branch of the anterior
artery, single coronary artery arising from right sinus of Valsalva, and interventricular artery. A second anastomosis (**) occurs between the
ectopic right coronary artery arising from the left sinus of Valsalva ventricular branches of the right coronary and anterior interventricular
(Clemente et al 2010). arteries. Close to the apex, a third anastomosis (***) appears between the
distal part of the anterior interventricular artery and branches of the acute
marginal artery. (With permission from Loukas M, Bilinsky S, Bilinsky E,
Matusz P, Anderson RH. 2009. The clinical anatomy of the coronary
collateral circulation. Clin Anat. 22:146–160.) | 1,413 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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A B
Arch of aorta
Pulmonary trunk
Left coronary artery (main stem)
Superior vena cava
Anterior interventricular
(descending) artery
Sinu-atrial nodal
artery Circumflex artery
Left atrial auricle
Right coronary artery Left atrial rami
Outlines of: Left conal artery
Anterior aortic sinus Circumflex artery Sinu-atrial artery
Right posterior aortic sinus Left (obtuse)
Left posterior aortic sinus marginal artery C
Right conal artery Diagonal artery
Right anterior
ventricular arteries
Atrioventricular
Interventricular
nodal artery
anterior septal branches
Inferior interventricular
(descending) arteries
Right (acute)
marginal artery
D E
Ascending aorta
Right posterior
Pulmonary trunk Superior vena cava atrial arteries
Left pulmonary veins
Stem of posterior Right pulmonary veins
atrial arteries
Circumflex artery Region of
crux of heart
Inferior vena cava
Right coronary artery
Anterior interventricular
(descending) artery (termination) Inferior interventricular
(descending) arteries
Fig. 57.41 Anterior views of the coronary arterial system, with the principal variations. The right coronary arterial tree is shown in purple, the left in red.
In both cases, posterior distribution is shown in a paler shade. A, The most common arrangement. B, A common variation in the origin of the sinu-atrial
nodal artery. C, An example of left ‘dominance’ by the left coronary artery, also showing an uncommon origin of the sinu-atrial nodal artery.
Posteroinferior views of the coronary arterial system. The right coronary arterial tree is shown in purple, the left in red. D, An example of the more normal
distribution in right ‘dominance’. E, A less common form of left ‘dominance’. In these ‘posterior’ views, the diaphragmatic (inferior) surface of the
ventricular part of the heart has been artificially displaced and foreshortening ignored, to clarify the details of the so-called posterior (inferior) distribution
of the coronary arteries. | 1,414 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Aorta Fig. 57.42 A dissection of a cadaveric
heart in which both coronary arteries
have been exposed to reveal their
branches to the right and left ventricles,
respectively. Notice how the great
cardiac vein is intertwined around the
Left atrium
anterior interventricular artery.
Left coronary (Specimen courtesy of M Loukas MD,
Arterial branch artery PhD.)
Right coronary Sinu-atrial nodal
artery artery
Acute marginal Circumflex
artery coronary artery
Coronary sinus
Diagonal arteries
Ventricular branches
Anterior
Infundibular branch interventricular
artery
Great cardiac vein
Conal artery Anterior lateral branches – occasionally double, and very rarely triple – mainly
interventricular artery supply the right atrium. The posterior branch is usually single and sup-
plies both atria.
The artery of the sinu-atrial node is an atrial branch, distributed
largely to right atrial myocardium. Its origin is variable: most commonly,
it arises from the anterior atrial branch of the right coronary artery, less
*
often from its right lateral part, and least often from its posterior atriov-
entricular part. This ‘nodal’ artery thus usually passes posteriorly in the
groove between the right atrial appendage and aorta. It may originate
from the circumflex branch of the left coronary artery. Whatever its
** origin, it usually branches around the base of the superior vena cava,
typically as an arterial loop from which small branches supply the right
atrium. A large branch, the ramus cristae terminalis, traverses the sinu-
atrial node; it would seem more appropriate to name this branch the
‘nodal artery’, on the grounds that the vessel that currently bears this
name actually supplies the atria and serves as the ‘main atrial branch’.
Septal perforating branches of the right coronary artery are relatively
*** short, and leave the posterior (inferior) interventricular branch to
supply the posterior interventricular septum. They are numerous but
do not usually reach the septal apex. The largest posterior septal perfo-
rating artery, usually the first, commonly arises from the inverted loop
Right coronary Ventricular
artery branches said to characterize the right coronary artery at the crux; it almost always
supplies the atrioventricular node. Small, recurrent atrioventricular
Fig. 57.45 A coronary angiogram demonstrating three collateral arterial
branches originate from the ventricular branches of the right coronary
anastomoses. At the area of the subpulmonary infundibulum, the right
artery as they cross the atrioventricular groove, and supply adjacent
conal artery, a branch of the right coronary artery, anastomoses with the
atrial myocardium.
left conal artery, a branch of the anterior interventricular artery, to form
the anulus (arterial circle or vascular ring) of Vieussens (*). Ventricular
Left coronary artery
branches of the right coronary artery anastomose with the proximal (**)
and distal portions (***) of the anterior interventricular artery, forming two The left coronary artery is usually larger in calibre than the right. It
collateral pathways. As a result, there is contrast medium in the anterior supplies a greater volume of myocardium, including almost all of the
interventricular artery. (With permission from Loukas M, Bilinsky S, left ventricle and atrium, and most of the interventricular septum (see
Bilinsky E, Matusz P, Anderson RH. 2009. The clinical anatomy of the Fig. 57.42; Figs 57.49–57.51). In hearts with ‘right dominance’, the
coronary collateral circulation. Clin Anat. 22:146–160.) right coronary artery supplies a variable posterior region of the left
ventricle (see Fig. 57.41A–C).
The left coronary artery arises from the left posterior (left coronary)
aortic sinus; the ostium sometimes lies inferior to the margin of the
both sides, by these parallel branches. When these flanking vessels exist, leaflets and may be double, leading into major initial branches, usually
branches of the posterior (inferior) interventricular artery are small and the circumflex and anterior interventricular (descending) arteries. Its
sparse. The posterior (inferior) interventricular artery is occasionally initial portion, between its ostium and its first branches, varies in length
replaced by a left coronary branch. Although the atrial branches of the from a few millimetres to a few centimetres. The artery lies between the
right coronary artery are sometimes described as part of anterior, lateral pulmonary trunk and the left atrial appendage, emerging into the atrio-
(right or marginal) and posterior groups, they are usually small single ventricular groove, where it turns left. This part is loosely embedded in
vessels, 1 mm in diameter (Figs 57.46–57.48). The right anterior and subepicardial fat and usually has no branches, but may give off a small | 1,415 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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A PA
Fig. 57.47 Normal ECG-gated multidetector row CT anatomy of the right
coronary artery and its branches. This lateral oblique volume-rendered
image shows the caudal course of the proximal right coronary artery (long
Fig. 57.46 Normal ECG-gated CT anatomy of the right coronary artery
arrow), which gives off an acute marginal branch (short arrows) to the
and its branches. This oblique volume-rendered image of the superior
right ventricle. (With permission from Kim SY, Seo JB, Do KH, et al. 2006.
aspect of the heart shows the right coronary artery (arrow) arising from
Coronary artery anomalies: classification and ECG-gated multi-detector
the right sinus of Valsalva and coursing in the right atrioventricular groove
row CT findings with angiographic correlation. Radiographics. 26:317–33.)
towards the posterior interventricular septum. Abbreviations: A, aorta; PA,
pulmonary artery. The conal artery and the sinu-atrial nodal artery were
too small to be seen in this case. (With permission from Kim SY, Seo JB,
Do KH, et al 2006. Coronary artery anomalies: classification and
ECG-gated multi-detector row CT findings with angiographic correlation.
Radiographics. 26:317–33.)
PA
A
Fig. 57.49 Normal ECG-gated multidetector row CT anatomy of the left
coronary artery and its branches. This oblique volume-rendered image of
Fig. 57.48 Normal ECG-gated multidetector row CT anatomy of the right the top of the heart shows the left coronary artery (long white arrow)
coronary artery and its branches. This posterior oblique volume-rendered arising from the left sinus of Valsalva and trifurcating into the left anterior
image shows that the distal right coronary artery divides into the posterior interventricular artery (thick black arrow), the left circumflex artery (thin
(inferior) interventricular artery (long black arrow) and posterior left black arrow), and the ramus intermedius (short white arrow), which takes
ventricular branches (short black arrows). The posterior (inferior) a course similar to that of the usual first diagonal branch. The left anterior
interventricular artery courses in the posterior (inferior) interventricular interventricular artery then gives rise to diagonal branches (short black
groove, parallel to the middle cardiac vein (white arrow). (With permission arrows) to the anterior free wall of the left ventricle. Abbreviations: A,
from Kim SY, Seo JB, Do KH, et al. 2006. Coronary artery anomalies: aorta; PA, pulmonary artery. (With permission from Kim SY, Seo JB, Do
classification and ECG-gated multi-detector row CT findings with KH, et al. 2006. Coronary artery anomalies: classification and ECG-gated
angiographic correlation. Radiographics. 26:317–33.) multi-detector row CT findings with angiographic correlation.
Radiographics. 26:317–33.) | 1,416 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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A
PA
Fig. 57.50 An anterior oblique volume-rendered image showing the left
anterior ventricular artery (thin black arrows) coursing along the anterior
interventricular groove, and the left circumflex artery (thick black arrow)
coursing in the left atrioventricular groove. Obtuse marginal branches
(short white arrow) and diagonal branches (short black arrows) are also Fig. 57.51 A posterior oblique volume-rendered image showing the left
shown. Abbreviations: A, aorta; PA, pulmonary artery. (With permission anterior ventricular artery (long white arrows) coursing along the anterior
from Kim SY, Seo JB, Do KH, et al. 2006. Coronary artery anomalies: interventricular groove, and the left circumflex artery (thick black arrow)
classification and ECG-gated multi-detector row CT findings with coursing in the left atrioventricular groove. Obtuse marginal branches
angiographic correlation. Radiographics. 26:317–33.) (short white arrows) and a diagonal branch (short black arrow) are also
shown. (With permission from Kim SY, Seo JB, Do KH, et al 2006.
Coronary artery anomalies: classification and ECG-gated multi-detector
row CT findings with angiographic correlation. Radiographics. 26:317–33.) | 1,417 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Fig. 57.52 A dissection of a cadaveric
heart revealing the course of the left
Aorta
coronary artery and its branches. (With
Superior
vena cava permission from Loukas M, Sharma A,
Blaak C, Sorenson E, Mian A. 2013. The
clinical anatomy of the coronary arteries.
J Cardiovasc Transl Res. 6:197–207.)
Conal artery
Left atrium
Circumflex
Right atrium artery
Diagonal artery
Right coronary
artery
Anterior
interventricular
artery
Acute marginal
artery
atrial ramus and, rarely, the sinu-atrial nodal artery. Reaching the atrio- posterior branches of the circumflex artery also supply the left ventricle.
ventricular groove, the left coronary artery divides into its main branches: Anterior ventricular branches (from one to five, commonly two or
namely, the circumflex and anterior interventricular arteries. three) course parallel to the diagonal artery when it is present, and
The anterior interventricular artery is commonly described as the replace it when it is absent. Posterior ventricular branches are smaller
continuation of the left coronary artery. It descends obliquely forwards and fewer because the left ventricle is partly supplied by the posterior
and to the left in the interventricular groove (Fig. 57.52), sometimes (inferior) interventricular artery. When this artery is small or absent, it
deeply embedded in or crossed by bridges of myocardial tissue (myo- is accompanied or replaced by often doubled or tripled interventricular
cardial bridges), and by the great cardiac vein and its tributaries. continuations of the circumflex artery.
Almost invariably, the anterior interventricular artery reaches the The artery to the sinu-atrial node is often derived from the anterior
apex, where it terminates in one-third of hearts. More frequently, it circumflex segment (less often from the circum-marginal segment). It
turns round the apex into the posterior interventricular groove and passes over and supplies the left atrium, encircles the superior vena cava
passes one-third to one-half of the way along its length, meeting the (like a right coronary nodal branch) and sends a large branch through
terminal twigs of the posterior (inferior) interventricular branches of the node; despite its name, it is predominantly atrial in distribution.
the right coronary artery (see above). The artery to the atrioventricular node, sometimes the terminal branch
The anterior interventricular artery gives off right and left anterior of the circumflex artery (20%), arises near the crux. When this occurs,
ventricular and anterior septal branches, and a variable number of cor- the circumflex artery usually gives off the posterior interventricular
responding posterior branches. Anterior right ventricular branches are artery, an example of so-called ‘left dominance’.
small and rarely number more than one or two; the right ventricle is
Coronary arterial distribution
supplied almost entirely by the right coronary artery. Up to nine large
left anterior ventricular arteries branch at acute angles from the anterior Details of coronary arterial distribution require integration into a
interventricular artery, crossing the anterior aspect of the left ventricle concept of total cardiac supply. Most commonly, the right coronary
diagonally, with the largest reaching the rounded (obtuse) left cardiac artery supplies all of the right ventricle (except a small region to the
border. One often dominates, sometimes arising separately from the right of the anterior interventricular groove); a variable part of the dia-
left coronary trunk, which then ends by trifurcation. This left diagonal phragmatic aspect of the left ventricle; the posteroinferior third of the
artery, reported to exist in at least 33–50% of hearts, may be doubled interventricular septum; the right atrium and part of the left atrium; and
(20%). A small left conal artery frequently leaves the anterior interven- the conduction system as far as the proximal parts of the right and left
tricular artery near its origin, and anastomoses on the conus with its crura. Left coronary distribution is reciprocal and includes most of the
counterpart from the right coronary artery and with the vasa vasorum left ventricle; a narrow strip of right ventricle; the anterior two-thirds of
of the pulmonary artery and aorta. The anterior septal perforating the interventricular septum; and most of the left atrium. As noted previ-
branches leave the anterior interventricular artery almost perpendicu- ously (see Fig. 57.41), variations in the coronary arterial system mainly
larly, and pass posteroinferiorly within the septum, usually supplying affect the diaphragmatic aspect of the ventricles and reflect the relative
its ventral two-thirds. The first septal perforator artery usually supplies ‘dominance’ of coronary arterial supply. The term is misleading because
the atrioventricular bundle at the point of its division. Small posterior the left artery almost always supplies a greater volume of tissue than
septal branches from the same source supply the posterior third of the the right. In ‘right dominance’, the posterior (inferior) interventricular
septum for a variable distance from the cardiac apex (Loukas et al artery is derived from the right coronary artery; in ‘left dominance’, it
2009). is derived from the left coronary artery. In the so-called ‘balanced’
The circumflex artery, comparable to the anterior interventricular pattern, branches of both arteries run in or near the posterior (inferior)
artery in calibre, curves left in the atrioventricular groove, and continues interventricular groove.
round the left cardiac border into the posterior part of the groove, ter- Less is known about variations in atrial supply because the small
minating left of the crux in most hearts, although sometimes continu- vessels involved are not easily preserved in the corrosion casts that are
ing as the posterior (inferior) interventricular artery. Proximally, the left used for analysis. In more than 50% of individuals, the right atrium is
atrial appendage usually overlaps it. A large ventricular branch, the left supplied only by the right coronary artery, and in the remainder the
marginal artery, normally arises perpendicularly from the circumflex supply is dual. More than 62% of left atria are supplied mainly by the
artery and ramifies over the rounded ‘obtuse’ margin, supplying much left coronary artery, 27% by the right coronary artery (in each group a
of the adjacent left ventricle, typically to its apex. Smaller anterior and small accessory supply from the other coronary artery exists), and 11% | 1,418 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Aorta
Pulmonary
vein
Pulmonary Left auricle
trunk
Conal artery Circumflex
artery
Right coronary Diagonal artery
artery
Myocardial
bridge
Anterior
interventricular
artery
Fig. 57.53 A dissection of a cadaveric heart in which a large part of the anterior interventricular artery is covered by a myocardial bridge.
Myocardial bridges are reported to have a frequency varying from
0.5 to 40% when identified clinically and from 15 to 85% when found
at autopsy (Fig. 57.53). The wide variation in frequency indicates that
many bridges may be asymptomatic during life. The major clinical
conditions produced by a myocardial bridge are cardiac ischaemia,
atherosclerosis and sudden cardiac death. The incidence of atheroscle-
rosis is increased when the right coronary artery is bridged. Although a
relationship between myocardial bridges and sudden cardiac death has
not been established, autopsy series have shown histological evidence
of otherwise unexplained ischaemia in individuals with myocardial
bridges; many died during exercise and had no other risk factors for
coronary arterial disease. | 1,419 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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are supplied almost equally by both arteries. Arterial supply to the sinu- develop later in life. Congenital fistulae are more common and account
atrial and atrioventricular nodes also varies: the sinu-atrial node is for 50% of paediatric coronary vascular aberrations; they are believed
supplied more often by the right coronary artery; fewer than 10% of to be derived from Thebesian vessels. Acquired coronary artery fistulae
sinu-atrial nodes receive a bilateral supply. The atrioventricular node is are most commonly iatrogenic in aetiology but may also occur after
usually supplied by the right coronary artery. traumatic injury; these most commonly are of the coronary cameral
type, from the right coronary artery into the right side of the heart.
Coronary anastomoses
The cardiac collateral circulation represents a native system for coronary Cardiac veins
arterial bypass. The first few centimetres of the arterial main stems are
devoid of anastomotic branches, but further distally, collateral channels
The cardiac venous system is divided into two major parts. The greater
are abundant, exhibit variable calibres and occupy numerous locations,
system consists of large vessels that lie within the subepicardial myo-
allowing for bidirectional flow between most native arteries. Approxi-
cardium and drain most of the outer myocardium. These veins extend
mately 30 different sites of collateral extramural vessels have been
over the myocardial surface and do not adhere to topographical borders,
described, the most frequent being at the apex; the anterior aspect of
although the larger collecting vessels lie within the interventricular
the right ventricle; the posterior aspect of the left ventricle; the crux;
grooves before draining into the coronary sinus. The intercommunicat-
the interatrial and interventricular grooves; and between the sinu-atrial
ing parts of this system are the coronary sinus and its tributaries, the
nodal and other atrial vessels (see Figs 57.44, 57.45). Anastomoses
anterior cardiac venous system, and the ventricular septal and atrial
between branches of the coronary arteries, both subepicardial and myo-
veins. The coronary sinus and its tributaries return blood to the right
cardial, and between these arteries and extracardiac vessels, are of prime
atrium from the entire heart (including its septa), except for the anterior
medical importance. Clinical studies suggest that anastomoses cannot
region of the right ventricle and small, variable parts of both atria and
rapidly provide collateral routes sufficient to circumvent sudden coro-
the left ventricle. The anterior cardiac veins drain an anterior region of
nary obstruction (see Figs 57.44, 57.45, 57.54). Nevertheless, it has long
the right ventricle, expanding to include a region around the right
been established that anastomoses do occur, particularly between fine
cardiac border when the right marginal vein joins this group.
subepicardial branches, and they may increase during individual life by
The smaller system functions primarily to return venous blood from
mechanisms of angiogenesis and arteriogenesis. The anulus of Vieus-
the inner myocardial walls into the right atrium and ventricle and, to
sens is a collateral vessel that crosses the subpulmonary infundibulum,
a lesser extent, into the left atrium and sometimes the left ventricle. It
providing an anastomosis between the conal branch of the right coro-
contains the smallest cardiac veins (Thebesian veins) that drain the
nary artery and the anterior interventricular artery. The artery to the
subendocardial myocardium either directly, via connecting intramural
sinu-atrial node commonly provides a communication between the
arteries and veins, or indirectly, via subendocardial sinusoidal spaces.
proximal parts of the coronary arteries. The apical collateral artery joins
the interventricular arteries. The frequent enlargement of the first septal
Variation in cardiac veins Attempts to categorize variations in
branch of the anterior inter ventricular artery, Kugel’s anastomotic artery
cardiac venous circulation into ‘types’ have not produced any accepted
(arteria anastomotica auricularis magna), has been described as running
pattern. The coronary sinus may receive all the cardiac veins other than
between the proximal parts of the coronary arteries along the antero-
the Thebesian veins, including the anterior cardiac veins, which may be
superior margin of the oval fossa to anastomose with the distal part of
reduced by diversion into the small cardiac vein and then to the coro-
the right coronary artery.
nary sinus.
Extracardiac anastomoses
Coronary sinus
Extracardiac anastomoses connect various coronary branches with other
Most cardiac veins drain into the wide coronary sinus, 2 or 3 cm long,
thoracic vessels, most commonly involving the bronchial and internal
lying in the posterior atrioventricular groove between the left atrium
thoracic arteries (Fig. 57.54). To a much lesser degree, anastomoses
and ventricle (see Fig. 57.4B; Fig. 57.59). The sinus opens into the right
between coronary arteries and pericardiacophrenic branches of the
atrium between the opening of the inferior vena cava and the right
internal thoracic, anterior mediastinal, intercostal and oesophageal
atrioventricular orifice. The opening may be guarded by an endocardial
arteries also exist. The posterior pericardium also receives a direct
fold (semilunar valve of the coronary sinus, Thebesian valve; see Fig.
supply from the bronchial arteries; extracardiac coronary anastomoses
57.13A); the fold may be absent or may cover the ostium of the sinus
involving bronchial arteries are typically found at the pericardial reflec-
completely. The tributaries of the coronary sinus are the great, small
tions, such as the points of entry of the venae cavae. The most common
and middle cardiac veins, the posterior vein of the left ventricle and the
anastomoses are with the circumflex branch of the left coronary artery
oblique vein (of Marshall) of the left atrium; all except the oblique vein
via the posterior pericardial reflections and reflect the close proximity
have orificial valves. Isolated absence of the coronary sinus has been
of the bronchial arteries within the pulmonary hila. In pathological
reported, with coronary venous drainage into the pulmonary trunk
conditions, notably those resulting in pericardial adhesions, it is
(Ogawa et al 2013).
also possible for extracardiac anastomoses to develop through trans-
pericardial vascularization.
Extracardiac communications also exist with coronary atrial
branches, especially the sinu-atrial nodal artery. The effectiveness of any
of these connections as collateral routes in coronary occlusion is not
Aorta
well quantified. Coronary arteriovenous anastomoses and numerous
connections between the coronary circulation and cardiac cavities, pro- Pulmonary trunk
ducing so-called ‘myocardial sinusoids’ and ‘arterioluminal vessels’, Superior vena
cava
have been reported, but their importance in coronary disease remains
uncertain. Left pulmonary veins
Coronary angiography Right pulmonary
Oblique vein of
veins
left atrium
Available with the Gray’s Anatomy e-book
Great cardiac vein
Coronary revascularization Right atrium
Left marginal vein
Available with the Gray’s Anatomy e-book
Inferior vein of
Coronary sinus
left ventricle
Coronary artery fistula Inferior vena
A coronary artery fistula is an abnormal connection that directly links cava
one or more coronary arteries to a heart chamber or to major thoracic
vessels without an interposed capillary bed. Small cardiac vein
Middle
Coronary artery fistulae are rare (Fig. 57.58); those that arise from cardiac vein
Right marginal vein
a coronary artery and then terminate in a chamber of the heart are
known as coronary cameral fistulae, while those terminating into a vein
are coronary arteriovenous fistulae. Fistulae may be congenital or may Fig. 57.59 The principal veins of the heart. | 1,420 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Table 57.1 Patterns of cardiac collateral arteries Anterior interventricular artery
Grade Description
0 Total absence of any collateral arteries
1 Poorly developed collateral arteries with no prominent distal channel visualized by
angiography
2 Presence of moderate collateral arteries providing faint but delayed opacification of
a prominent distal channel
3 Good collateral arteries giving clear opacification of a prominent distal channel
4 Excellent collateralization giving full and brisk opacification of prominent distal
vessels
Clinical imaging (catheter angiography and colour Doppler ultra-
sound) has led to the development of a grading system to describe the
overall pattern of cardiac collateral arteries (Table 57.1).
Coronary angiography may be performed by introducing a catheter
through the femoral, radial or brachial arteries. The femoral artery is
punctured with a needle 3 cm below the inguinal ligament while the
leg is held adducted and slightly externally rotated. The exact position
is guided by palpation of the femoral arterial pulse, and the needle is
inserted at an angle of 45°. After arterial puncture, a fine guidewire is
inserted through the needle and fed into the artery. The catheter is then Circumflex coronary artery Lower lobe of left lung
inserted over the guidewire and manipulated via the iliac artery into the
Fig. 57.54 A left coronary angiogram in left lateral projection, showing a
aorta, up the aortic arch and into the ascending aorta. The brachial or
large, tortuous vessel (arrow) arising from the proximal circumflex branch
radial artery may be used for percutaneous access to the circulation.
of the left coronary artery and anastomosing with the bronchial artery,
Once the catheter is located in the ascending aorta, a variety of
which goes on to supply the lower lobe of the left lung. (With permission
guidewires may be used to enter the coronary vessels for selective arte-
from Stefas L, Assayag P, Aubry P, et al, Coronary to bronchial artery
riography and interventions. Angiography is performed with standard anastomosis with bronchial steal syndrome demonstrated by thallium-201
high-osmolality contrast medium with cineangiography. In selected myocardial tomoscintigraphy. Eur Heart J, 1990, 11, 275–279.)
patients, new-generation, low-osmolality contrast medium may also be
used. All the coronary arteries are catheterized and evaluated in a variety
of views to obtain a full evaluation of their anatomy and to determine
Cn
the location and degree of any stenoses (Figs 57.55–57.56). The ostium
of the left coronary artery arises from the left aortic sinus and is best
viewed in the direct frontal and left anterior oblique projections. The
SA
right anterior oblique view is useful in demonstrating the diagonal
branches and anterior interventricular (descending) coronary artery.
The right coronary artery originates from the right sinus of Valsalva and
is usually visualized in the right anterior oblique view. Pressure and
Rv
oxygen saturations can be measured via the catheter; changes in pres-
sure across valves allow the degree of stenosis to be measured. Coronary
blood flow and relative flow reserve can also be calculated. Significant Rm
stenosis may be treated initially by balloon angioplasty followed by
stent insertion. The balloon exerts pressure against the plaque in the
arterial wall, fracturing and splitting the plaque. The splinting effect of
the plaque and elastic recoil are reduced, resulting in an increase in the
PIA
arterial lumen. Stent insertion reduces the re-stenosis rate.
Fig. 57.55 A right coronary angiogram showing several branches of the
right coronary artery. Abbreviations: Cn, conal artery; PIA, posterior
(inferior) interventricular artery; Rm, right marginal artery; Rv, right
ventricular branches; SA, artery to the sinu-atrial node. (Courtesy of
M Loukas MD, PhD.)
LCA
Sp
AIA Latr
LCx
ObM
PIA
Fig. 57.56 A left coronary angiogram showing several branches of the left
coronary artery (LCA). Other abbreviations: AIA, anterior interventricular
artery; Latr, left atrial branch; LCx, left circumflex artery; ObM, obtuse
marginal; PIA, posterior (inferior) interventricular artery; Sp, septal
perforator. (Courtesy of M Loukas MD, PhD.) | 1,421 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Fig. 57.57 A, A left coronary angiogram showing
a stent placement within the anterior
interventricular artery. B, After stent placement
(and once the contrast medium has filled the
coronary arterial tree), the anterior interventricular
artery shows no evidence of stenosis.
Abbreviations: AIA, anterior interventricular artery;
Stent Dg, diagonal branch; LCx, left circumflex artery.
(Courtesy of M Loukas MD, PhD.)
AIA LCx
Dg
A B
Atherosclerosis causing more than 60% stenosis of the terminal diam-
eter of the coronary arteries is likely to cause significant reduction in
myocardial perfusion. Patients with high-grade lesions, left main stem
coronary artery or triple-vessel disease with impaired left ventricular
function are usually considered for coronary artery bypass grafting. The
common grafts that are used are the internal thoracic (mammary) and
radial arteries. The left internal thoracic artery and radial artery grafts
have a greater patency rate than saphenous vein grafts. Approximately
15% of saphenous vein grafts occlude in 1 year and, from then on, at
an annual rate of 1–2% in the first 6 years and 4% thereafter; between
40% and 50% of saphenous vein grafts have occluded by 10 years,
whereas only about 10% of left internal thoracic or radial artery grafts
have occluded over this time. The common surgical approach is via a
midline sternotomy. If the internal thoracic artery is used as a donor
graft, it is divided distally (maintaining its proximal origin from the
subclavian artery) and anastomosed to the coronary artery distal to the A
stenosis. If radial artery grafts are used, they must be anastomosed both
proximal and distal to the coronary artery, to bridge the site of the
stenosis. In selected cases, minimally invasive direct coronary artery
bypass grafting is performed, but the approach is dependent on the
vessel being grafted. The anterior approach is via mini-thoracotomy
over the fourth intercostal space underneath the nipple for grafting the
mid-left anterior interventricular (descending) and diagonal branches.
The anterolateral approach is via an incision in the third intercostal
space from the mid-clavicular to anterior axillary lines and is used for
grafting early marginal branches of the circumflex system. The lateral
approach allows grafting of the circumflex vessels via a lateral thora-
cotomy measuring only 10 cm in size through the fifth or sixth inter-
costal spaces. Extrathoracic approaches that are occasionally used
include the subxiphoid approach for the distal right coronary artery and
posterior interventricular (descending) artery. Port access surgery allows
for full revascularization with cardiopulmonary bypass but obviates the
need for midline sternotomy. However, the vast majority of patients are B
treated with stent placement (Fig. 57.57).
Fig. 57.58 A coronary artery fistula in a 54-year-old woman with
palpitations. A, A CT image showing a tortuous left circumflex artery
(white arrows) that is dilated in comparison with the anterior
interventricular artery (black arrow). B, A volume-rendered CT image
shows the markedly tortuous left circumflex artery (arrows). (With
permission from Shriki JE, Shinbane JS, Rashid MA, Hindoyan A, Withey
JG, DeFrance A, Cunningham M, Oliveira GR, Warren BH, Wilcox A.
2012. Identifying, characterizing, and classifying congenital anomalies of
the coronary arteries. Radiographics 32:453–468.) | 1,422 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Great cardiac vein The great cardiac vein begins at the cardiac apex, veritable venous plexus. Not only are adjacent veins often connected,
and ascends in the anterior interventricular groove to the atrioventricu- but connections also exist between tributaries of the coronary sinus and
lar groove, which it follows, passing to the left and posteriorly to enter those of the anterior cardiac veins. Abundant anastomoses occur at the
the coronary sinus at its origin (see Fig. 57.59). It receives tributaries apex and its anterior and posterior aspects. Like the coronary arteries,
from the left atrium and both ventricles, including the large left mar- cardiac veins connect with extracardiac vessels, particularly the vasa
ginal vein that ascends the left aspect (obtuse border) of the heart. It vasorum of the large vessels that are continuous with the heart.
usually courses superior to the arterial branches. The valve of Vieussens
normally guards the orifice of the great cardiac vein at its junction with Lymphatic drainage of the heart
the oblique vein; smaller diminutive valves may occur.
Cardiac lymphatic vessels form subendocardial, myocardial and sub-
Small cardiac vein The small cardiac vein lies in the posterior atrio-
epicardial plexuses. Efferents from the subepicardial plexuses form the
ventricular groove between the right atrium and ventricle, receiving
left and right cardiac collecting trunks; two or three left-sided trunks
blood from their posterior parts and opening into the atrial end of the
ascend the anterior interventricular groove, receiving vessels from both
coronary sinus (see Fig. 57.59). The right marginal vein passes right,
ventricles. On reaching the atrioventricular groove, they are joined by a
along the inferior cardiac margin (acute border), and sometimes joins
large vessel from the diaphragmatic surface of the left ventricle, which
the small cardiac vein in the atrioventricular groove, typically opening
first ascends in the posterior interventricular groove and then turns left
directly into the right atrium.
along the atrioventricular groove. The vessel formed by this union
ascends between the pulmonary artery and the left atrium, and usually
Middle cardiac vein The middle cardiac vein begins at the cardiac
ends in an inferior tracheobronchial node. The right trunk receives
apex and runs posteriorly in the inferior interventricular groove to end
afferents from the right atrium and the right border and diaphragmatic
in the coronary sinus near its atrial end (see Fig. 57.59). The vein is also
surface of the right ventricle. It ascends in the atrioventricular groove,
described as meeting the great cardiac vein at the apex, so forming,
near the right coronary artery, and then anterior to the ascending aorta,
together with the coronary sinus, a full venous circle.
and ends in a brachiocephalic node, usually on the left (Fig. 57.60).
(For further reading, see Loukas et al (2011).)
Inferior vein of the left ventricle The inferior vein of the left
ventricle (previously named as the posterior vein of the left ventricle)
lies on the diaphragmatic surface of the left ventricle, a little to the left INNERVATION
of the middle cardiac vein, and usually opens into the middle of the
coronary sinus, sometimes into the great cardiac vein (see Fig. 57.59).
Initiation of the cardiac cycle is myogenic, originating in the sinu-atrial
Rarely, the inferior vein of the left ventricle is absent, in which case the
node. It is harmonized in rate, force and output by autonomic nerves
left marginal vein drains most of the left ventricular wall.
that operate on the nodal tissues and their prolongations, on coronary
vessels and on the working atrial and ventricular musculature. All the
Oblique vein of the left atrium The diminutive oblique vein of
cardiac branches of the vagus (parasympathetic) and all the sympathetic
the left atrium descends obliquely on the posterior aspect of the left
branches (other than the cardiac branch of the superior cervical sym-
atrium to join the coronary sinus (see Fig. 57.59). It is continuous above
pathetic ganglion) contain both afferent and efferent fibres; the cardiac
with the ligament of the left vena cava; both structures are remnants of
branch of the superior cervical sympathetic ganglion is entirely efferent.
the left common cardinal vein.
Sympathetic fibres accelerate the heart and dilate the coronary arteries
Left marginal vein when stimulated, whereas vagal fibres slow the heart and cause coro-
The left (obtuse) marginal vein courses over the left oblique marginal nary arterial constriction.
surface of the heart, draining much of the left ventricular myocardium. Preganglionic cardiac sympathetic axons arise from neurones in the
It runs superficial to the marginal branch of the left coronary artery and intermediolateral column of the upper four or five thoracic spinal seg-
usually drains into the great cardiac vein, although may sometimes ments. Some synapse in the corresponding upper thoracic sympathetic
drain directly into the coronary sinus. ganglia, while others ascend to synapse in the cervical ganglia; postgan-
glionic fibres from these ganglia form the sympathetic cardiac nerves.
Anterior cardiac veins Preganglionic cardiac parasympathetic axons arise from neurones either
The anterior cardiac veins drain the anterior part of the right ventricle. in the dorsal vagal nucleus or near the nucleus ambiguus, and run in
Usually two or three, sometimes even five, they ascend in subepicardial vagal cardiac branches to synapse in the cardiac plexuses and atrial
tissue to cross the right part of the atrioventricular groove, passing deep walls. In humans (like most mammals), intrinsic cardiac neurones are
or superficial to the right coronary artery. They end in the right atrium, limited to the atria and interatrial septum, and are most numerous in
near the atrioventricular groove, separately or in variable combinations. the subepicardial connective tissue near the sinus and atrioventricular
A subendocardial collecting channel, into which all may open, has been nodes. The intrinsic ganglia are thought not to be simple nicotinic
described. relays, but may act as sites for the integration of extrinsic nervous inputs
and form complex circuits for the local neuronal control of the heart,
Right marginal vein
and perhaps even local reflexes.
The right marginal vein courses along the inferior (acute) cardiac
margin, draining adjacent parts of the right ventricle, and usually opens Cardiac plexus
separately into the right atrium, although it may join the anterior
cardiac veins or, less often, the coronary sinus. It is often grouped with
Nearing the heart, the autonomic nerves form a mixed cardiac plexus,
the small cardiac veins but it is larger in calibre, comparable to the
usually described in terms of a superficial component inferior to the
anterior cardiac veins or even wider.
aortic arch, lying between it and the pulmonary trunk, and a deep part
Small cardiac veins between the aortic arch and tracheal bifurcation. The cardiac plexus is
The existence of small cardiac (venae cordis minimae; Thebesian) veins, also described by regional names for its coronary, pulmonary, atrial and
opening into all cardiac cavities, has been confirmed but they are dif- aortic extensions (Fig. 57.61). Ganglion cells are largely confined to the
ficult to demonstrate. Their numbers and size are highly variable: vessels atrial tissues, with a preponderance adjacent to the sinu-atrial node, but
up to 2 mm in diameter open into the right atrium and ones as small some may also be found within the heart along the branches of the
as 0.5 mm in diameter open into the right ventricle, all with valveless plexuses. Their axons are considered to be largely, if not exclusively,
orifices. Numerous small cardiac veins have been identified in the right postganglionic parasympathetic. Cholinergic and adrenergic fibres,
atrium and ventricle but they are rarely found in the left side. Four types arising in or passing through the cardiac plexus, are distributed most
of Thebesian veins have been described: venoluminal veins drain profusely to the sinus and atrioventricular nodes; the supply to the atrial
directly into the cardiac chambers; venosinusoidal veins drain into and ventricular myocardium is much less dense. Adrenergic fibres
subendocardial sinusoids (which, in turn, drain into the cardiac cham- supply the coronary arteries and cardiac veins. Rich plexuses of nerves
bers); arterioluminal veins connect small arteries and arterioles directly containing cholinesterase, adrenergic transmitters and other peptides,
with the cardiac chambers; and arteriosinusoidal veins connect thin e.g. neuropeptide Y, are found in the subendocardial regions of all
arteries or arterioles with subendocardial sinusoidal spaces. chambers and within the valvular leaflets.
Cardiac venous anastomoses Superficial (ventral) part of the cardiac plexus The superficial
Widespread anastomoses occur at all levels of the cardiac venous circu- (ventral) part of the cardiac plexus lies inferior to the aortic arch and
lation, on a scale exceeding that of the arteries and amounting to a anterior to the right pulmonary artery. It is formed by the cardiac branch | 1,423 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Right internal jugular vein Paratracheal lymph nodes Fig. 57.60 The cardiac
lymphatic system. (With
permission from Loukas,
M, Shah, S, Bhusnurmath
S, et al; A general outline
Left internal jugular vein
Right lymphatic duct of the cardiac lymphatic
system. In: The Cardiac
Lymphatic System,
Thoracic duct
Karunamuni, G (ed).
Springer. 2013.)
Right subclavian vein Left brachiocephalic vein
Right brachiocephalic vein
Posterior mediastinal
lymph nodes Posterior mediastinal
lymph nodes
Tracheobronchial
lymph nodes
Anterior mediastinal Anterior mediastinal
lymph nodes lymph nodes
Thoracic duct
Right sympathetic trunk Left sympathetic trunk Fig. 57.61 The cardiac plexus: its
source from the cervical parts of
the vagus nerves and sympathetic
Left vagus nerve trunks and its extensions, the
Right vagus nerve pulmonary, atrial and coronary
plexuses. Note the numerous
junctions between sympathetic and
Left recurrent laryngeal nerve
Right recurrent parasympathetic (vagal) branches
laryngeal nerve that form the plexus.
Left common carotid artery
Trachea
Oesophagus Left subclavian artery
Right recurrent laryngeal nerve Third thoracic sympathetic ganglion
Thoracic cardiac branch
of vagus nerve
Thoracic (sympathetic)
Brachiocephalic trunk cardiac branches
Thoracic cardiac branch
Thoracic (sympathetic) of vagus nerve
cardiac branches
Arch of aorta
Deep cardiac plexus
Superficial cardiac plexus
Left recurrent laryngeal nerve
Ligamentum arteriosum
Left pulmonary artery
Superior vena cava | 1,424 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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of the left superior cervical sympathetic ganglion and the lower of the onwards to form part of the right coronary plexus. Fibres passing pos-
two cervical cardiac branches of the left vagus. A small cardiac ganglion terior to the pulmonary artery supply a few filaments to the right atrium
is usually present in this plexus immediately below the aortic arch, to and then continue into the left coronary plexus. The left half of the deep
the right of the ligamentum arteriosum. This part of the cardiac plexus part of the cardiac plexus is connected to the superficial part; it supplies
connects with the deep part, the right coronary plexus and the left filaments to the left atrium and left anterior pulmonary plexus, and
anterior pulmonary plexus. forms much of the left coronary plexus.
Deep (dorsal) part of the cardiac plexus The deep (dorsal) part Left coronary plexus The left coronary plexus is larger than the
of the cardiac plexus lies anterior to the tracheal bifurcation, superior right and is formed mainly by the prolongation of the left half of the
to the point of division of the pulmonary trunk and posterior to the deep part of the cardiac plexus and a few fibres from the right half. It
aortic arch. It is formed by the cardiac branches of the cervical and accompanies the left coronary artery to supply the left atrium and
upper thoracic sympathetic ganglia, the vagus and recurrent laryngeal ventricle.
nerves. The only cardiac nerves that do not join it are those that join
the superficial part of the plexus. The deep plexus consists of right and Right coronary plexus The right coronary plexus is formed from
left halves; the right typically surrounds the brachiocephalic trunk, and both superficial and deep parts of the cardiac plexus. It accompanies
the left surrounds the aortic arch. The more dorsal (deep) aspect is the right coronary artery to supply the right atrium and ventricle.
larger than its more ventral (superficial) aspect on both sides. Branches
from the right half of the deep part of the cardiac plexus pass both Atrial plexuses The atrial plexuses are derivatives of the right and
anterior and posterior to the right pulmonary artery. Fibres passing left continuations of the cardiac plexus along the coronary arteries.
anterior to the pulmonary artery are more numerous; they supply a few Their fibres are distributed to the corresponding atria, overlapping those
filaments to the right anterior pulmonary plexus before continuing from the coronary plexuses.
Bonus e-book images and table
Fig. 57.5 Acute cardiac tamponade due to F, Transposition of the great arteries at 21 ventricular artery coursing along the anterior
ruptured aortic dissection. weeks’ gestation. interventricular groove, and the left
circumflex artery coursing in the left
Fig. 57.6 A, The subxiphoid approach in Fig. 57.35 A, Cardiac magnetic resonance atrioventricular groove.
pericardiocentesis. B, A mid-sagittal section angiography in a patient with a normal
of a cadaver. C, A cross-section of the heart. B, A cardiac magnetic resonance Fig. 57.51 A posterior oblique volume-
lower part of the thorax to show the angiogram from a patient with transposition rendered image showing the left anterior
relationships of the pericardial cavity with of the great arteries. ventricular artery coursing along the anterior
adjacent structures. D, Bedside cardiac interventricular groove, and the left
ultrasound performed in a 62-year-old male, Fig. 57.38 Measurements of the width and circumflex artery coursing in the left
demonstrating a large pericardial effusion height of the sinu-atrial node and the atrioventricular groove.
consistent with cardiac tamponade. distances of nodal tissue to epicardium and
endocardium, measured in cadaveric tissue. Fig. 57.53 A dissection of a cadaveric
Fig. 57.7 The typical appearance of a heart in which a large part of the anterior
pericardial cyst. Fig. 57.39 Histological sections of the nodal interventricular artery is covered by a
body. myocardial bridge.
Fig. 57.8 Congenital absence of the
pericardium. Fig. 57.40 Histological sections showing the Fig. 57.54 A left coronary angiogram in left
features of (A) the atrioventricular (AV) node lateral projection, showing a large, tortuous
Fig. 57.11 The fundamental differences and (B) the penetrating atrioventricular vessel arising from the proximal circumflex
between describing the heart according to bundle. branch of the left coronary artery and
the conventional (A) or the attitudinally anastomosing with the bronchial artery,
correct (B) orientation. Fig. 57.43 The right coronary sinus, which goes on to supply the lower lobe of
revealing a coronary orifice for the right the left lung.
Fig. 57.15 An inferior view of a cadaveric coronary artery and a coronary orifice for
heart, demonstrating an exaggerated the conal artery. Fig. 57.55 A right coronary angiogram
Eustachian valve occupying a significant showing several branches of the right
portion of the lumen of the inferior vena Fig. 57.44 A variation of the anulus of coronary artery.
cava. Vieussens.
Fig. 57.56 A left coronary angiogram
Fig.57.16 Chiari’s network. Fig. 57.46 Normal ECG-gated CT anatomy showing several branches of the left
of the right coronary artery and its branches. coronary artery.
Fig. 57.31 A histological section through
one of the coronary aortic sinuses to Fig. 57.47 Normal ECG-gated multidetector Fig. 57.57 A, A left coronary angiogram
demonstrate the way in which ventricular row CT anatomy of the right coronary artery showing a stent placement within the
muscle supports the transition from the and its branches. anterior interventricular artery. B, After stent
fibroelastic wall of the sinus to the tissues of placement (and once the contrast medium
the leaflet. Fig. 57.48 Normal ECG-gated multidetector has filled the coronary arterial tree), the
row CT anatomy of the right coronary artery anterior interventricular artery shows no
Fig. 57.34 A, Tricuspid atresia at 21 weeks’ and its branches. evidence of stenosis.
gestation. B, An atrioventricular septal
defect at 20 weeks’ gestation. C, Fig. 57.49 Normal ECG-gated multidetector Fig. 57.58 A coronary artery fistula in a
Hypoplastic left heart syndrome at 32 row CT anatomy of the left coronary artery 54-year-old woman with palpitations.
weeks’ gestation. D, Hypoplastic left heart and its branches.
syndrome at 32 weeks’ gestation. E, Table 57.1 Patterns of cardiac collateral
Tetralogy of Fallot at 33 weeks’ gestation. Fig. 57.50 An anterior oblique volume- arteries.
rendered image showing the left anterior | 1,425 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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REFERENCES
Anderson R, Smerup M, Sanchez-Quintana D et al 2009a The three- Loukas M, Patel S, Cesmebasi A et al 2014b The clinical anatomy of the
dimensional arrangement of the myocytes in the ventricular walls. Clin conal artery. Clin Anat. doi: 10.1002/ca.22469 (ePub ahead of print).
Anat 22:64–76. Loukas M, Tubbs RS, Bright JL et al 2007 The anatomy of the tendon of the
Anderson RH, Boyett MR, Dobrzynski H et al 2013a The anatomy of the infundibulum revisited. Folia Morphol (Warsz) 66:33–8.
conduction system: implications for the clinical cardiologist. J Cardio- Mani BC, Pavri BB 2014 Dual atrioventricular nodal pathways physiology:
vasc Transl Res 6:187–96. a review of relevant anatomy, electrophysiology, and electrocardio-
Anderson RH, Loukas M 2009 The importance of attitudinally appropriate graphic manifestations. Indian Pacing Electrophysiol J 14:12–25.
description of cardiac anatomy. Clin Anat 22:47–51. Molenaar P, Anderson R, Sharma V et al 2011 Computer three-dimensional
Anderson RH, Spicer DE, Hlavacek AM et al 2013b Wilcox’s Surgical anatomical reconstruction of the human sinus node and a novel para-
Anatomy of the Heart, 4th ed. Cambridge: Cambridge University nodal area. Anat Rec (Hoboken) 294:970–9.
Press. Mollova M, Bersell K, Walsh S et al 2013 Cardiomyocyte proliferation
Azancot A, Caudell TP, Allen HD et al 1983 Analysis of ventricular shape by contributes to heart growth in young humans. Proc Nat Acad Sci U S A
echocardiography in normal fetuses, newborns, and infants. Circulation 110:1446–51.
68:1201–11. Monfredi O, Dobrzynski H, Mondal T et al 2010 The anatomy and physiol-
Clemente A, Del Borrello M, Greco P et al 2010 Anomalous origin of the ogy of the sinoatrial node – a contemporary review. Pacing Clin Elec-
coronary arteries in children: diagnostic role of three-dimensional coro- trophysiol 33:1392–406.
nary MR angiography. Clin Imaging 34:337–43. Nidorf SM, Picard MH, Triulzi MO et al 1992 New perspectives in the assess-
de Jonge LL, van Osch-Gevers L, Willemsen SP et al 2011 Growth, obesity, ment of cardiac chamber dimensions during development and adult-
and cardiac structures in early childhood: the Generation R study. hood. J Am Coll Cardiol 19:983–8.
Hypertension 57:934–40. Ogawa K, Hishitani T, Hoshino K 2013 Absence of the coronary sinus with
Ho SY, McCarthy KP, Faletra FF 2011 Anatomy of the left atrium for inter- coronary venous drainage into the main pulmonary artery. Cardiol
ventional echocardiography. Eur J Echocardiogr 12:11–15. Young 23:759–62.
Hutchison SJ 2009 Pericardial Diseases: Clinical Diagnostic Imaging Atlas. Ozdemir O, Hizli S, Abaci A et al 2010 Echocardiographic measurement of
Philadelphia: Saunders; pp. 8–15. epicardial adipose tissue in obese children. Pediatr Cardiol 31:
Kaiser T, Kellenberger CJ, Albisetti M et al 2008 Normal values for aortic 853–60.
diameters in children and adolescents – assessment in vivo by contrast- Pesonen E, Hirvonen J, Karkola K et al 1991 Dimensions of the coronary
enhanced CMR-angiography. J Cardiovasc Magn Reson 10:56. arteries in children. Ann Med 23:85–8.
Karagol BS, Orun UA, Zenciroglu A et al 2012 The diameter of coronary Poutanen T, Tikanoja T, Sairanen H et al 2006 Normal mitral and aortic
arteries in healthy newborns at birth, 1 and 6 months of ages. J Matern valve areas assessed by three- and two-dimensional echocardiography
Fetal Neonatal Med 25:2729–34. in 168 children and young adults. Pediatr Cardiol 27:217–25.
Kortelainen ML 1997 Adiposity, cardiac size and precursors of coronary Sánchez-Quintana D, Pizarro G, López-Mínguez JR et al 2013 Standardized
atherosclerosis in 5 to 15-year-old children: a retrospective study of 210 review of atrial anatomy for cardiac electrophysiologists. J Cardiovasc
violent deaths. Int J Obes Relat Metab Disord 21:691–7. Transl Res 6:124–44.
Loukas M, Abel N, Tubbs RS et al 2011 The cardiac lymphatic system. Clin Spicer DE, Anderson RH 2013 Methodological review of ventricular
Anat 24:684–91. anatomy – the basis for understanding congenital cardiac malforma-
Loukas M, Bilinsky E, Bilinsky S et al 2014a The anatomy of the aortic root. tions. J Cardiovasc Transl Res 6:145–54.
Clin Anat 27:748–56. Uysal F, Bostan OM, Semizel E et al 2014 Congenital anomalies of coronary
Loukas M, Groat C, Khangura R et al 2009 The normal and abnormal arteries in children: the evaluation of 22 patients. Pediat Cardiol
anatomy of the coronary arteries. Clin Anat 22:114–28. 35:778–84. | 1,426 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
CHAPTER
58
Great vessels
pulmonary trunk atretic, small or even normal in size, making diagnosis
MAJOR BLOOD VESSELS
challenging. A diminished pulmonary flow is supplied through a patent
ductus arteriosus (Smith and McKay 2004), and a concomitant ven-
The major blood vessels are the pulmonary trunk, the thoracic aorta tricular septal defect may permit outflow from the right ventricle. Surgi-
and its branches, and the superior and inferior venae cavae and their cal repair is necessary to allow adequate oxygenation throughout the
tributaries. body.
In truncus arteriosus, a single arterial trunk exits the heart and sub-
sequently divides into the pulmonary trunk and the aorta. Early neo-
ARTERIES
natal life is possible because there is usually a coexisting ventricular
septal defect; expedited surgical repair is necessary to avoid congestive
Pulmonary trunk
heart failure, failure to thrive and death.
Right and left pulmonary arteries
The pulmonary trunk, or pulmonary artery, conveys deoxygenated
blood from the right ventricle to the lungs. About 5 cm in length and The pulmonary arteries are described on page 959.
3 cm in diameter, it is the most anterior of the cardiac vessels and arises
from the pulmonary anulus surrounding the subpulmonary infundibu- Thoracic aorta
lum at the base of the right ventricle, superior and to the left of the
supraventricular crest. It slopes posterosuperiorly, at first anterior to the
Ascending aorta
ascending aorta and then to its left; at the level of the fifth thoracic
vertebra, inferior to the aortic arch at the left of the midline, it divides The ascending aorta is typically 5 cm long. It originates at the base of
into right and left pulmonary arteries, of almost equal size. The bifurca- the left ventricle, level with the inferior border of the third left costal
tion of the pulmonary trunk lies anteroinferior and to the left of the cartilage, and ascends obliquely, curving anteriorly and to the right, and
tracheal bifurcation and its associated inferior tracheobronchial lymph passing from posterior to the left half of the sternum to the level of the
nodes and deep cardiac plexus. In the fetus, at the level of the bifurca- superior border of the second left costal cartilage. In children, the diam-
tion, the pulmonary artery is connected to the aortic arch by the ductus eter of the thoracic aorta correlates most closely with body surface area
arteriosus. (Kervancioglu et al 2006, Kaiser et al 2008).
Relations The pulmonary artery is entirely within the pericardium, Relations The ascending aorta lies within the fibrous pericardium,
enclosed with the ascending aorta in a common tube of visceral peri- enclosed in a tube of serous pericardium together with the pulmonary
cardium. The fibrous pericardium gradually disappears within the trunk (see Figs 57.3, 57.4A–C). The infundibulum, initial segment of
adventitia of the pulmonary arteries. Anteriorly, it is separated from the the pulmonary trunk and right appendage are anterior to its lower
sternal end of the left second intercostal space by the pleura, left lung part. Superiorly, it is separated from the sternum by the pericardium,
and pericardium. Posterior relations are the ascending aorta and left right pleura, anterior margin of the right lung, loose areolar tissue and
coronary artery initially, then the left atrium. The ascending aorta ulti- the thymus or its remnants. The left atrium, right pulmonary artery and
mately lies on its right. The appendage and coronary artery lie on each principal bronchus are posterior. The superior vena cava and right
side of its origin. The superficial cardiac plexus lies between the pulmo- atrium, the former partly posterior, are to the right. The left atrium and,
nary bifurcation and the aortic arch. The tracheal bifurcation, lymph more superiorly, the pulmonary trunk are to the left. At least two aort-
nodes and nerves are superior, bilateral and to the right. icopulmonary bodies lie between the ascending aorta and the pulmo-
nary trunk. The inferior aorticopulmonary body is near the heart and
Variations and congenital conditions The pulmonary trunk is anterior to the aorta, and the middle aorticopulmonary body is near
a relatively constant structure and there are minimal variations in the right side of the ascending aorta.
healthy individuals. Congenital anomalies include pulmonary atresia The aortopulmonary window is a space between the pulmonary
and truncus arteriosus. artery and aortic arch, bordered by the ascending aorta anteriorly, the
The coronary arteries usually originate from within the aortic sinuses, descending aorta posteriorly, the mediastinal pleura laterally and the
but occasionally may arise from ectopic locations. Most commonly, an left principal bronchus medially (Deutsch and Savides 2005) (Fig.
ectopic left coronary artery arises from the pulmonary trunk or one of 58.3). It contains lymph nodes, fatty tissue, the ligamentum arteriosum
its branches (Bland–White–Garland syndrome). This potentially fatal and the left recurrent laryngeal nerve.
condition requires urgent surgical correction because the myocardium
Aortic arch
is supplied with pulmonary blood instead of systemic blood (Loukas
et al 2009). Infantile symptoms include pallor, fatigue, irritability, weak The aortic arch continues from the ascending aorta (see Figs 57.3,
cry, cough, dyspnoea, and signs of ischaemia and cardiac failure pre- 57.4A–C). Its origin, slightly to the right, is level with the superior
cipitated by feeding, bowel movements or crying. The electrocardio- border of the right second sternocostal joint. The arch first ascends
gram may reveal deep narrow Q waves, left ventricular hypertrophy and diagonally and posteriorly to the left over the anterior surface of the
left axis deviation. Radiologically, cardiomegaly is present with left trachea, then posteriorly across its left side, finally descending to the
ventricular and left atrial enlargement. Colour flow imaging can identify left of the fourth thoracic vertebral body, continuing as the descending
the anomalous origin of the left coronary artery. The pulmonary trunk thoracic aorta. It terminates level with the sternal end of the left second
may also give rise to the right coronary artery, the left interventricular costal cartilage and so lies wholly within the superior mediastinum. It
(anterior descending) coronary artery, or even both coronary arteries. curves around the hilum of the left lung, and extends superiorly to the
Typically, there is a large development of collateral vessels in the heart midlevel of the manubrium of the sternum.
(Figs 58.1–58.2). The shadow of the arch is easily identified in frontal chest radio-
Pulmonary atresia is caused by a complete obstruction of pulmonary graphs; its left profile is sometimes called the aortic ‘knuckle’ or ‘knob’
outflow and may be due to an absence or defect of the pulmonary (see Fig. 56.16). There may also be an ‘aortic nipple’ (the shadow of
valvular leaflets. It is associated with a blind-ending pulmonary trunk the adjacent left superior intercostal vein crossing posteroanteriorly to
1024 that causes right ventricular hypoplasia. Reduced flow may render the its left). The aortic arch is best visualized in left anterior oblique views | 1,427 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Great vessels
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Pulmonary valve Left coronary artery orifice Anterior interventricular artery
Tricuspid valve
Fig. 58.1 A case of a left anterior interventricular artery arising from the
pulmonary trunk. (Courtesy of Professor Loukas. With permission from
Loukas M, Groat C, Khangura R, Owens DG, Anderson R. The normal
and abnormal anatomy of the coronary arteries. Clinical Anatomy. 2009;
22: 114–128.) | 1,428 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
GREAT vEssEls
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7
NOITCEs
A
A PA
PA
A B
A
PPAA
A
PA
*
C D
A
PA
Fig. 58.2 Bland–White–Garland syndrome in a 29-year-old woman. A, A
preoperative anterior oblique volume-rendered (VR) image shows a dilated
right coronary artery (arrow) and the anterior interventricular artery with
multiple collateral vessels at the right ventricular wall (arrowheads).
B–C, Preoperative VR images (cardiac chambers removed with manual
editing) clearly demonstrate the anomalous origin of the left coronary artery
(long arrow) from the pulmonary trunk, along with multiple collateral
vessels within the interventricular septum (short arrows in B) and the
dilated right coronary artery (short arrow in C). D–E, Postoperative VR
images, obtained after ligation of the original os of the left coronary artery
from the pulmonary trunk and creation of an anastomosis between the left
internal thoracic artery (short white arrows) and the left coronary artery
* (long white arrow), demonstrate a decrease in the size of the right coronary
artery (black arrow) and markedly diminished collateral vessels in the
interventricular septum and right ventricular wall (*). Abbreviations: A, aorta;
PA, pulmonary artery. (With permission from Kim SY, Seo JB, Do KH, et al
2006 Coronary artery anomalies: classification and ECG-gated multi
E detector row CT findings with angiographic correlation. Radiographics
26:317–33; discussion 333–4.) | 1,429 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Major blood vessels
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AP window Pneumomediastinum and aortic nipple
Available with the Gray’s Anatomy e-book
Variations of the arch The summit of the arch is usually about
2.5 cm inferior to the sternal notch but may diverge from this. In the
infant, it is closer to the superior border of the sternum; the same is
often the case in senescence as a result of vascular ectasia/unfolding.
In a right-sided aortic arch, the aorta curves over the right pulmonary
hilum and descends to the right of the vertebral column; this is usually
associated with transposition of the thoraco-abdominal viscera. Less
often, after arching over the right hilum, the aorta may pass posterior
to the oesophagus to gain its position (this is not accompanied by
visceral transposition). The presence of a right-sided arch is of relevance
to the paediatric surgeon who is planning repair of oesophageal atresia
in neonates.
The aorta may divide into ascending and descending trunks, the
former dividing into three branches to supply the head and upper
limbs. It may divide near its origin, producing a double aortic arch; the
two branches soon reunite and the oesophagus and trachea usually pass
through the interval between them. If the aorta, ductus arteriosus or
descending aorta entraps the oesophagus and/or trachea, this is referred
A to as a vascular ring.
AP window Branches and variations Three branches arise from the convex
aspect of the arch: the brachiocephalic trunk, left common carotid and
left subclavian arteries (see Figs 57.3–57.4). They may branch from the
beginning of the arch or the superior part of the ascending aorta. The
distance between these origins varies, the most frequent being approxi-
mation of the left common carotid artery to the brachiocephalic trunk.
Other branches may arise from the aortic arch, including the inferior
thyroid, thyroidea ima, thymic, left coronary and bronchial arteries
(Bergman et al 1988).
Coarctation of the aorta The aortic lumen is occasionally partly
or completely obliterated, either above (preductal or infantile type),
opposite or just beyond (postductal or adult type), the entry of the
ductus arteriosus. In the preductal type, the length of coarctation is
variable, aortic arch hypoplasia is common, and the left subclavian and
even the brachiocephalic trunk may be involved. Severe forms of infan-
tile coarctation and its extreme form (aortic interruption) may be patent
B ductus arteriosus-dependent, as there is no time for effective collateral
circulation to develop. Prostaglandin infusion prior to transfer, and
surgery at a tertiary centre often provide a very good mid- to long-term
Fig. 58.3 The aortopulmonary (AP) window. A, A posteroanterior (PA)
outlook for such infants.
chest radiograph. B, A coronal computed tomography (CT) scan
The postductal type of coarctation has been attributed to abnormal
reconstruction.
extension of the ductal tissue into the aortic wall, stenosing both
vessels as the duct contracts after birth. This form may permit years of
on angiography and with equivalent computed tomography (CT) normal life, allowing the development of an extensive collateral circu-
reconstruction planes; the pulmonary trunk and its left branch may be lation to the aorta distal to the stenosis (Figs 58.6–58.7). High vascu-
discerned nestling inferiorly in its concavity. The diameter of the arch larity of the thoracic wall is important and clinically characteristic;
initially matches that of the ascending aorta but is significantly reduced many arteries arising indirectly from the aorta proximal to the coarcta-
distal to the origin of the great vascular branches. The aortic isthmus, a tion segment anastomose with vessels connected with it distal to the
small stricture at the border with the descending thoracic aorta, may block, and all of these vessels become greatly enlarged. Thus, in the
be followed by a dilation; in the fetus, the isthmus lies between the anterior thoracic wall, the thoraco-acromial, lateral thoracic and sub-
origin of the left subclavian artery and the opening of the ductus scapular arteries (from the axillary artery), the suprascapular artery
arteriosus. (from the subclavian artery) and the first and second posterior inter-
costal arteries (from the costocervical trunk) anastomose with other
Relations The left mediastinal pleura is anterior and to the left of the posterior intercostal arteries, and the internal thoracic artery and its
arch. Deep to the pleura, the arch is crossed, in anteroposterior order, terminal branches anastomose with the lower posterior intercostal and
by the left phrenic nerve, left lower cervical cardiac branch of the vagus inferior epigastric arteries.
nerve, left superior cervical cardiac branch of the sympathetic trunk and Posterior intercostal arteries are always involved, and enlargement
the left vagus nerve (see Figs 57.3, 57.61). As the left vagus nerve crosses of their dorsal branches may eventually groove (‘notch’) the inferior
the arch, its recurrent laryngeal branch hooks below the vessel, to the margins of the ribs. The radiographic shadow of the enlarged left sub-
left and behind the ligamentum arteriosum, then ascends on the right clavian artery is also increased. Enlargement of the scapular vessels and
of the arch. The left superior intercostal vein ascends obliquely anteri- anastomoses may lead to widespread interscapular pulsation (easily
orly on the arch, superficial to the left vagus nerve, deep to the left appreciated with the palm of the hand, and sometimes heard on
phrenic nerve. The left lung and pleura separate all these from the auscultation).
thoracic wall. Posterior and to the right are the trachea and the deep
cardiac plexus, the left recurrent laryngeal nerve, oesophagus, thoracic Aortic aneurysm formation Degeneration of the aortic tunica
duct and vertebral column. Superiorly, the brachiocephalic trunk, left media and intimal dissection play a major role in the pathogenesis of
common carotid and subclavian arteries arise from its convexity, and aneurysms affecting the ascending aorta and arch. Smooth muscle cells
are crossed anteriorly near their origins by the left brachiocephalic vein. are lost and elastic fibres degenerate, producing cystic spaces in the
The pulmonary bifurcation, left principal bronchus, ligamentum arte- media, which then fill with mucoid material. The loss of these structural
riosum, superficial cardiac plexus and the left recurrent laryngeal nerve cells leads to weakening of the wall with progressive dilation. Ageing
are all inferior. The concavity of the aortic arch, best viewed from the and hypertension are major predisposing factors to cystic medial degen-
left, is the upper curved limit through which structures gain access to, eration and there is a strong link with cigarette smoking. Thoracic aortic
or leave, the hilum of the left lung. aneurysms are categorized by their location. A particular pattern of | 1,430 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Pneumomediastinum is an encompassing term that describes the pres- Aortic arch Superior intercostal vein/aortic nipple
ence of air in the mediastinum. It may arise from a wide range of
pathological conditions or physiological states, e.g. penetrating trauma,
ruptured major airways or oesophagus, hyperventilation or distressed
ventilation such as acute asthma, periparturition or diabetic ketoacido-
sis. The ‘aortic nipple’ is the radiographic term used to describe a lateral
nipple-like projection from the aortic knuckle seen in a small number
of individuals that corresponds to the end-on appearance of the left
superior intercostal vein coursing anteriorly. It may be mistaken radio-
logically for lymphadenopathy or an intrapulmonary nodule/neoplasm.
Despite their relative independence, the aortic nipple is defined by new
contours in cases of pneumomediastinum, taking on an ‘inverted aortic
nipple’ appearance (Fig. 58.4). In this position, the inverted aortic
nipple may facilitate radiographic discrimination of pneumomediasti-
num from similar conditions. An aortic nipple has been shown to
precede pathological conditions such as venous obstruction in the supe-
rior and inferior vena cavae or left brachiocephalic vein, and has been
identified in conditions where venous flow through the left superior
intercostal vein is increased (e.g. portal hypertension and certain con-
genital venous anomalies).
There are several variants of this arrangement, of which the most
common are as follows: a right-sided aortic arch and upper portion of
the descending aorta pass anterior to the oesophagus and trachea, and
the ductus arteriosus passes posterior to the oesophagus into an aortic
diverticulum; a right-sided aortic arch and the upper portion of the
descending aorta pass anteriorly, and the ductus arteriosus is inserted
Pneumomediastinum Pleura
into the left subclavian artery, which arises as a fourth branch from the
aortic arch; a left-sided descending aorta is attached to a left-sided Fig. 58.4 A PA chest radiograph, anteroposterior view, showing the
ductus arteriosus anterior to the oesophagus, and a right-sided arch classic ‘aortic nipple’ in a patient with pneumomediastinum. A label is
added on the left to delineate the nipple-like appearance of the left
passes posteriorly; the right superior portion of the descending aorta
superior intercostal vein more clearly. (Courtesy of Professor Loukas. With
wraps around the oesophagus and the ductus arteriosus is right-sided;
permission from Walters A, Cassidy L, Muhleman M, Peterson A, Blaak C,
or the right upper portion of the aorta wraps around the oesophagus
Loukas M. Pneumomediastinum and the aortic nipple: the clinical
and the ductus arteriosus is left-sided (Bergman et al 1988).
relevance of the left superior intercostal vein. Clinical Anatomy 2013;
The right common carotid and subclavian arteries may arise sepa-
27:757–63.)
rately, in which case the latter often branches from the left end of the
arch distal to the left subclavian artery, and usually passes posterior to
the oesophagus as an aberrant right subclavian artery. When this artery
arises from a dilated portion of the descending aorta, the diverticulum Right common carotid artery Trachea RtRSA Oesophagus
of Kommerell, it is known as the lusoria artery (Fig. 58.5). It may
become aneurysmal and cause fatal haemorrhage during endoscopy. It
may form a vascular ring around the oesophagus and trachea, present-
ing in the neonate as a feeding disorder with failure to thrive.
The left vertebral artery may arise between the left common carotid
and the subclavian arteries.
A rare avian form has been reported in which the right common
carotid and subclavian arteries arise from the aortic arch, and the left
common carotid and subclavian arteries arise from the descending
aorta (Bergman et al 1988). Another rare avian form with two brachio-
cephalic trunks, the right trunk originating both common carotid arter-
ies, and the left trunk originating both subclavian arteries, has been
reported. Another rare order of the aortic branches is (in order from
right to left): the right subclavian artery, left subclavian artery, followed
by the right common carotid, and left common carotid arteries close
together – almost forming a common carotid trunk.
The aortic arch may also curve behind the oesophagus and trachea,
instead of in front, with variations in the aortic branches as well.
Another rare avian form reported is with both carotid arteries originat-
ing from the same stem, and a left subclavian artery originating from
the arch, while the right subclavian artery arises from the descending
aorta. One or more of the ductus arteriosi may remain patent.
Very rarely, external and internal carotid arteries arise separately, the Left common Right and left Left subclavian
common carotid artery being absent on one or both sides, or both carotid artery vertebral arteries artery
carotid arteries and one or both vertebral arteries may be separate Fig. 58.5 A dissection showing a left aortic arch that gives rise to a
branches. When a ‘right aorta’ occurs, the arrangement of its three common vertebral trunk and a retrotracheal right subclavian artery
branches is reversed and the common carotid arteries may have a single (RtRSA), also known as a lusoria artery. (Courtesy of Professor Loukas
trunk. Other arteries may branch from it: most commonly, one or both with permission from Loukas M, Louis RG Jr, Gaspard J, Fudalej M,
bronchial arteries and the thyroidea ima artery. Tubbs RS, Merbs W. A retrotracheal right subclavian artery in association
Associations also exist between thoracic aortic aneurysm and other with a vertebral artery and thyroidea ima. Folia Morphol (Warsz). 2006
connective tissue diseases such as homocysteinuria and Ehlers–Danlos Aug;65(3):236–41.)
syndrome. A genetic relation is seen in familial thoracic aortic aneurysm
syndrome (Baliga et al 2007). Rarely, aneurysms may occur as a result
of Takayasu’s arteritis, or infections within the aortic wall. | 1,431 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Fig. 58.6 A cardiac magnetic resonance (MR) angiograph showing
three-dimensional reconstruction of a native aortic coarctation (arrow) in
an adult with extensive collateral flow. Note the marked dilation of the left
subclavian artery, supplying most of the collateral vessels, and mild aortic
arch hypoplasia. (Courtesy of Dr Raad Mohiaddin, Royal Brompton
Hospital, London.)
Fig. 58.7 The collateral circulation at MR angiography and phase-contrast
velocity-encoded cine MRI. The MR angiogram shows the intercostal
(short arrows) and internal thoracic (medium arrow) arteries, obtained in
a patient with a haemodynamically significant aortic coarctation (long
arrow). Note that the arteries appear enlarged. (With permission from Hom
JJ, Ordovas K, Reddy GP. Velocity-encoded cine MR imaging in aortic
coarctation: functional assessment of hemodynamic events.
Radiographics 2008 Mar–Apr;28(2):407–16.) | 1,432 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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aortic root involvement is seen in those with Marfan’s syndrome, diaphragm. The vertebral column and hemiazygos veins are posterior.
known as anulo-aortic ectasia (Baliga et al 2007). Descending aortic Posterior to the right are the azygos vein and thoracic duct, and inferi-
aneurysms are generally caused by atherosclerosis (90%); the remainder orly, the right pleura and lung; the pleura and lung are to the left. The
result from mycotic disease or trauma. oesophagus with its plexus of nerves is located laterally and to the right
Some aortic aneurysms are incidental findings on chest films or CT in the upper thorax, anteriorly in the lower thorax and descends to a
studies. Symptomatic cases present with breathlessness, unbearable left anterolateral position when it reaches the diaphragm. To a limited
chest and back pain, hoarse voice, cough and haemoptysis. Early diasto- degree, the descending aorta and oesophagus are mutually spiralized.
lic murmurs caused by aortic regurgitation may be audible. Repair is Occasionally, the aorta enters the diaphragm to the left and behind the
carried out in patients with symptoms or fusiform dilation measuring oesophagus (Berdjas and Turina 2011).
more than 5 cm in diameter.
Aneurysms may also occur in an aberrant right subclavian artery and Surface anatomy The descending thoracic aorta may be projected
may or may not involve the diverticulum of Kommerell, leading to as a 2.5 cm broad band from the sternal end of the second left costal
dysphagia and even tracheal compression. Inadvertent rupture may cartilage to a median position 2 cm above the transpyloric plane at the
occur during endoscopy because of its retro-oesophageal position. first lumbar vertebra.
Aortic dissection Branches
The thoracic aorta provides visceral branches to the pericardium,
Available with the Gray’s Anatomy e-book lungs, bronchi and oesophagus, and parietal branches to the thoracic
wall.
Aortopulmonary paraganglia Pericardial branches A few small vessels are distributed to the
posterior aspect of the pericardium.
Aortopulmonary paraganglia (aortic bodies) belong to the branchio-
meric category of paraganglia. They are chemoreceptors and respond to Bronchial arteries Bronchial arteries vary in number, size and
changes in arterial gas concentrations such as lowered pO, increased origin. There is usually only one right bronchial artery; it arises from
2
pCO and increased hydrogen ion concentration. These microscopic either the third posterior intercostal or the upper left bronchial artery,
2
structures occur in several locations within the thorax: coronary para- and runs posteriorly on the right principal bronchus. Its branches
ganglia lie between the ascending aorta and pulmonary trunk, either supply these structures, the pulmonary areolar tissue and the broncho-
anteriorly or posteriorly, adjacent to the aortic root; pulmonary para- pulmonary lymph nodes, pericardium and oesophagus. The left bron-
ganglia lie in the groove between the ductus arteriosus and the pulmo- chial arteries, usually two, arise from the thoracic aorta – the upper near
nary artery; and subclavian–supra-aortic paraganglia lie between either the fifth thoracic vertebra, the lower below the left principal bronchus
the right subclavian and right common carotid arteries or the left sub- – and run posterior to the left main bronchus; their branches are dis-
clavian and left common carotid arteries, or caudal to the left subclavian tributed as on the right.
artery, adjacent to the aortic arch.
Oesophageal branches Two or three bronchial arteries supply the
Brachiocephalic trunk (artery) thoracic portion of the oesophagus. In addition, two or three oesopha-
geal arteries that arise either anteriorly or from the right side of the aorta
supply the distal oesophagus (Norton et al 2008).
The brachiocephalic (innominate) artery (trunk), the largest branch of
the aortic arch, is 4–5 cm in length (see Fig. 57.4A,B). It arises from the
Mediastinal branches Numerous small vessels supply lymph
convexity of the arch posterior to the centre of the manubrium of the
nodes and areolar tissue in the posterior mediastinum.
sternum, and ascends posterolaterally to the right, at first anterior to
the trachea, then on its right. The brachiocephalic and left common
Phrenic branches Superior phrenic arteries arise from the lower
carotid arteries often share a common origin (Osborn 1998). It divides
thoracic aorta and are distributed posteriorly to the superior diaphrag-
into the right common carotid and subclavian arteries level with the
matic surface, anastomosing with the musculophrenic and pericardi-
upper border of the right sternoclavicular joint.
acophrenic arteries.
Relations Sternohyoid and sternothyroid, thymic remnants, left
Posterior intercostal arteries The posterior intercostal arteries
brachiocephalic and right inferior thyroid veins, crossing its root,
and their branches are described on page 943.
and sometimes the right cardiac branches of the vagus nerve, all sepa-
rate the brachiocephalic trunk from the manubrium. Posterior are the
Subcostal arteries Subcostal arteries are the last paired branches of
trachea (superiorly) and the right pleura (inferiorly). The right vagus
the thoracic aorta, in series with the posterior intercostal arteries and
nerve is posterolateral before passing lateral to the trachea. On its right
inferior to the twelfth ribs. Each runs laterally anterior to the twelfth
side are the right brachiocephalic vein and the upper part of the supe-
thoracic vertebral body and posterior to the splanchnic nerves, sympa-
rior vena cava and pleura, and on its left side are thymic remains, the
thetic trunk, pleura and diaphragm. The right subcostal artery is also
origin of the left common carotid artery, the inferior thyroid veins and
posterior to the thoracic duct and azygos vein, while the left is posterior
the trachea.
to the accessory hemiazygos vein. Each artery enters the abdomen at
the lower border of the twelfth rib, accompanied by the twelfth thoracic
Branches The brachiocephalic trunk usually has only terminal
(subcostal) nerve, lying posterior to the lateral arcuate ligament and
branches, the right common carotid and subclavian arteries. Occasion-
kidney, and anterior to quadratus lumborum. The right artery courses
ally, a thymic or bronchial branch, or a thyroidea ima artery arise from
posterior to the ascending colon, and the left courses posterior to the
it. The thyroidea ima artery is a small and inconstant artery that may
descending colon. Piercing the aponeurosis of transversus abdominis,
arise from the aorta, right common carotid, subclavian or internal
each subcostal artery proceeds between this and internal oblique, and
thoracic arteries; it ascends on the trachea to the thyroid isthmus, where
anastomoses with the superior epigastric, lower posterior intercostal
it terminates.
and lumbar arteries. Each has a dorsal branch, distributed like those of
the posterior intercostal arteries.
Descending thoracic aorta
Aberrant artery A small artery sometimes leaves the descending
The descending aorta is the segment of the thoracic aorta that is con- thoracic aorta on its right near the right bronchial artery origin. It
fined to the posterior mediastinum (see Figs 56.1–56.2, 56.6–56.7B, ascends to the right behind the trachea and oesophagus, and may anas-
56.13–56.14A, 56.19D,E). It begins level with the lower border of the tomose with the right superior intercostal artery. It is a vestige of the
fourth thoracic vertebra, continuous with the aortic arch, and ends right dorsal aorta and, occasionally, it is enlarged as the first part of a
anterior to the lower border of the twelfth thoracic vertebra in the aortic right subclavian artery.
hiatus. At its origin, it is left of the vertebral column; as it descends, it
reaches and terminates in the midline. Aortic rupture in trauma Rupture of the ascending aorta is usually
associated with a high immediate mortality (Baliga et al 2007). Blunt
Relations Anterior to the descending thoracic aorta, from superior to aortic rupture commonly occurs in road traffic accidents and has a 20%
inferior, are the left pulmonary hilum, the pericardium separating it survival rate. There is usually a transverse tear involving the tunica
from the left atrium, oesophagus and the vertebral portion of the intima and tunica media of the aortic wall; systemic circulatory pressure | 1,433 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Aortic dissection occurs as a result of degeneration of the tunica media Aortic dissections are classified as types I, II, IIIa and IIIb (De Bakey
of the aortic wall and is associated with senescence, persistent hyperten- classification), or types A and B (Stanford classification). Dissections
sion or collagen vascular diseases such as Marfan’s syndrome. Many that are proximal to the left subclavian artery, with or without distal
patients with aortic dissection have a pre-existing aneurysm. Other extension, are classified as type I, II or A. Type I may involve the entire
associations include aortic coarctation, Turner’s syndrome, cocaine aorta, whereas type II involves the ascending aorta only. Dissections
abuse (<1%) and trauma during surgical procedures. There is a higher that are distal to the left subclavian artery are classified as type IIIa
prevalence in men than women; after the age of 75, however, there is (involve the distal aorta up to the diaphragm), IIIb (extend below the
no sex difference (Baliga et al 2007). In a classic aortic dissection, an diaphragm) or B. These cases present acutely with severe retrosternal,
intimal tear may occur, producing a split into the tunica media that neck or interscapular chest pain. Depending on the extent of the dis-
creates a false lumen (Fig. 58.8). If another tear occurs, connection can section, they may be associated with neurological signs, diarrhoea or
be made once again with the true lumen (the double-barrel aorta). leg weakness. Extension into the pericardium causes cardiac tamponade
Additional aetiopathologies include penetrating atherosclerotic ulcera- and circulatory collapse. Diagnosis is established by echocardiography
tion, where an atherosclerotic plaque ruptures into the aortic tunica and on contrast-enhanced CT or magnetic resonance imaging (MRI).
media, and aortic intramural haematoma, where the vasa vasorum Medical management is possible for descending aortic dissections,
haemorrhage into the wall of the aorta (Baliga et al 2007). while surgical repair is essential for ascending aortic or aortic arch
dissection.
A B
C D E
Fig. 58.8 A Stanford type A aortic dissection. A–B, Axial images taken through the thorax. A, Dissection flap involvement of the aortic root and
descending aorta. B, The dissection flap in the aortic arch. C–E, A type A aortic dissection in a different patient. C–D, Sagittal reformatted images
through the thorax and upper abdomen obtained at different levels from 64-slice multi-detector CT demonstrating intimal flap involvement of the
ascending thoracic aorta. Note the extension of the dissection flap into aortic branch vessels (arrow). E, A sagittal maximum-intensity projection image
showing dissection flap involvement of both the ascending and descending aorta. (With permission from McMahon MA, Squirrell CA. Multidetector CT of
Aortic Dissection: A Pictorial Review. Radiographics. 2010 Mar;30(2):445–60.) | 1,434 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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may cause the formation of a false aneurysm. Rupture of the isthmus VEINS
region of the descending aorta is more common probably because it
marks the junction between the mobile and fixed portions of the aorta. Brachiocephalic veins
Other sites include the ascending aorta proximal to the origin of the
brachiocephalic trunk, the aortic arch and the abdominal aorta. Rupture
The right and left brachiocephalic veins join to form the superior
is likely to be the result of a number of factors, including torsion, shear
vena cava.
and stretching forces, possibly compounded by hydrostatic pressure.
Right brachiocephalic vein
Aortic atherosclerosis or calcification Echocardiography, par-
The right brachiocephalic vein is about 2.5 cm long. It arises posterior
ticularly trans-oesophageal, allows very detailed assessment of proximal
to the sternal end of the right clavicle and descends almost vertically to
aortic atherosclerosis implicated in systemic embolic events and strokes.
join the left brachiocephalic vein, forming the superior vena cava pos-
The extent of turbulent flow may be documented. MRI may also allow
terior to the inferior border of the first right costal cartilage, near the
an accurate assessment of the composition and size of atherosclerotic
right sternal border. It is anterolateral to the brachiocephalic trunk and
plaques and flow dynamics, permitting assessment of the risk of plaque
right vagus nerve; the right pleura, phrenic nerve and internal thoracic
rupture and thrombus formation.
artery are initially posterosuperior, becoming lateral inferiorly (see Fig.
29.14). Its tributaries are the right vertebral, internal thoracic and infe-
Subclavian arteries rior thyroid veins, and sometimes the first right posterior intercostal
veins.
Right subclavian artery
Left brachiocephalic vein
The right subclavian artery arises from the brachiocephalic trunk, origi-
nating posterior to the upper border of the right sternoclavicular joint The left brachiocephalic vein is about 6 cm long, over twice the length
(see Fig. 51.2). It ascends superomedial to the clavicle and posterior to of the right. It arises posterior to the sternal end of the left clavicle,
scalenus anterior, then descends laterally to the outer border of the first anterior to the cervical pleura, and descends obliquely to the right,
rib, where it becomes the axillary artery. posterior to the superior half of the manubrium sterni, reaching the
sternal end of the first right costal cartilage where it joins the right
Left subclavian artery brachiocephalic vein to form the superior vena cava (see Fig. 29.14). It
is separated from the left sternoclavicular joint and manubrium by
In the majority of individuals, the left subclavian artery originates inde-
sternohyoid and sternothyroid, the thymus or its remnants, and areolar
pendently from the aortic arch after the origins of the brachiocephalic
tissue; terminally, it is overlapped by the right pleura. It crosses anterior
and left common carotid arteries (see Fig. 57.4). It rises into the neck
to the left internal thoracic, subclavian, brachiocephalic and common
lateral to the medial border of scalenus anterior, crosses posterior to
carotid arteries, left phrenic and vagus nerves, and the trachea. The
this muscle and then descends towards the outer border of the first rib,
aortic arch is inferior to it. Its tributaries are the left vertebral, internal
where it becomes the left axillary artery. A common origin occasionally
thoracic, inferior thyroid and superior intercostal veins, and sometimes
exists between the left subclavian and vertebral arteries. Rarely, there are
the first left posterior intercostal, thymic and pericardial veins.
bilateral brachiocephalic trunks, which subsequently divide on both
In children, the length and diameter of the left brachiocephalic vein
sides into common carotid and subclavian arteries.
are closely related to height; the diameter reaches adult dimensions at
Relations In the thorax, the left subclavian artery is related anteri- the age of 10 years (Figs 58.9–58.10) (Sanjeev and Karpawich 2006).
orly to the left common carotid artery and left brachiocephalic vein,
Superior vena cava
from which it is separated by the left vagus, cardiac and phrenic
nerves. More superficially, the anterior pulmonary margin, pleura,
sternothyroid and sternohyoid lie between the vessel and the upper The superior vena cava returns blood to the heart from the tissues above
left area of the manubrium of the sternum. On the left side of the the diaphragm. It is approximately 7 cm in length, and is formed by the
oesophagus, the thoracic duct and longus colli are posterior. The left junction of the brachiocephalic veins posterior to the lower border of
subclavian artery is in contact posterolaterally with the left lung and the first right costal cartilage. It descends vertically, posterior to the first
pleura. The trachea, left recurrent laryngeal nerve, oesophagus and and second intercostal spaces, and drains into the upper right atrium
thoracic duct are medial. Laterally, the artery grooves the mediastinal posterior to the third right costal cartilage. Its inferior half is within the
surface of the left lung and pleura, which also encroach on its anterior fibrous pericardium, which it pierces level with the second costal carti-
and posterior aspects. lage. Covered anterolaterally by serous pericardium (from which a ret-
rocaval recess projects), it is slightly convex to the right (see Figs 57.3,
57.4A,B, 57.12, 29.14). The superior vena cava is valveless. In children,
Common carotid arteries
the length and diameter of the superior vena cava are also closely related
to height; the diameter reaches adult dimensions at the age of 10 years
The right and left common carotid arteries differ in their length and (see Figs 58.9–58.10) (Sanjeev and Karpawich 2006).
origin. The right is exclusively cervical and arises from the brachio-
cephalic trunk posterior to the right sternoclavicular joint. The left Relations The anterior margins of the right lung and pleura are ante-
originates directly from the aortic arch immediately posterolateral to rior and the pericardium intervenes below; these structures separate the
the brachiocephalic trunk and therefore has both thoracic and cervical superior vena cava from the right internal thoracic artery, first and
parts. second intercostal spaces, and second and third costal cartilages. The
trachea and right vagus nerve are posteromedial, the right lung and
Right common carotid artery
pleura are posterolateral, and the right pulmonary hilum is posterior.
The right common carotid artery and its relations are described in The right phrenic nerve and pleura are immediate right lateral relations
Chapter 29. and the brachiocephalic trunk and ascending aorta lie to the left, the
aorta overlapping the superior vena cava (see Fig. 55.7).
Left common carotid artery
The left common carotid artery (see Figs 57.4, 29.7) ascends until level Tributaries Tributaries of the superior vena cava are the azygos vein
with the left sternoclavicular joint, where it enters the neck. Its thoracic and small veins from the pericardium and other mediastinal structures
portion is 20–25 mm long and it lies first anterior to the trachea, then (see Fig. 56.7A).
inclines to the left. The further course of the artery is described in
Chapter 29. Superior vena cava obstruction Superior vena cava obstruction
is characterized by headaches, facial and neck venous congestion, and
Relations Sternohyoid and sternothyroid, the anterior parts of the left oedema, reflecting impaired venous drainage of the head, neck and
pleura and lung, the left brachiocephalic vein and the thymic remnants arms, and of the collateral circulation, resulting in chest wall telangiecta-
are anterior and separate the left common carotid artery from the sia. Several of the symptoms may subside with recumbency, or may be
manubrium. The trachea, left subclavian artery, left border of the aggravated by standing up. The obstruction may be either partial or
oesophagus, left recurrent laryngeal nerve and thoracic duct are poste- complete, and may occur suddenly or gradually. It is usually caused by
rior. To the right are the brachiocephalic trunk (inferior) and the mediastinally invasive right upper lobe primary bronchogenic carci-
trachea, inferior thyroid veins and thymic remains (superior). To the noma or by metastatic involvement of the right paratracheal lymph
left are the left vagus and phrenic nerves, left pleura and lung. nodes. | 1,435 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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A
B
C
D
Fig. 58.9 Sites of measurement of the left brachiocephalic (innominate)
vein and superior vena cava at angiography. Key: A, distal
brachiocephalic vein; B, mid-brachiocephalic vein; C, brachiocephalic–
superior vena cava junction; D, mid-superior vena cava. (Redrawn with
permission from Sanjeev S, Karpawich PP. Superior vena cava and
innominate vein dimensions in growing children: an aid for interventional
devices and transvenous leads. Pediatr Cardiol. 2006
Jul–Aug;27(4):414–9.)
18
16
14
12
10
Fig. 58.10 Diameters of the distal brachiocephalic (innominate) vein
(dis-INN), mid-brachiocephalic vein (mid-INN), brachiocephalic–superior
vena cava junction (INN-SVC) and mid-superior vena cava (mid-SVC) in
children of varying ages. (Redrawn with permission from Sanjeev S,
Karpawich PP. Superior vena cava and innominate vein dimensions in
growing children: an aid for interventional devices and transvenous leads.
Pediatr Cardiol. 2006 Jul–Aug;27(4):414–9.)
)mm(
sretemaiD
<2 yr
3–4 yr
5–8 yr
8
8–9 yr
6
10–12 yr
4
2
0
Dis-INN Mid-INN INN-SVC Mid-SVC | 1,436 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Haemorrhagic intrathoracic goitre, mediastinitis (either benign, malig- and central area of the central tendon of the diaphragm at the level of
nant or fibrous), mediastinal haematoma, constrictive pericarditis, the eighth and ninth thoracic vertebrae, and drains into the inferopos-
mediastinal cyst, thrombosis of the superior vena cava and sarcoidosis terior part of the right atrium (see Fig. 55.1, 57.4B). The thoracic part
are less common aetiologies. Radiographic findings might include wid- is very short, and is partly inside and partly outside the pericardial sac.
ening of the upper mediastinum on the frontal film or obliteration of The extrapericardial part is separated from the right pleura and lung by
the retrosternal space on the lateral film. Other correlative findings may the right phrenic nerve, and the intrapericardial part is covered, except
include pulmonary or mediastinal masses, lymphadenopathy, enlarged posteriorly, by inflected serous pericardium. The abdominal course of
or obliterated azygos venous system, pleural effusion or rib notching. the inferior vena cava is described in Chapter 62.
This is usually considered to be an oncological emergency and symp-
toms are often completely and promptly relieved by insertion of a Collateral venous channels In obstruction of the upper inferior
vascular stent via the common femoral vein or by radiotherapy to the vena cava, the azygos and hemiazygos veins and vertebral venous plex-
affected region after a tissue diagnosis is established. uses are the main collateral channels that maintain venous circulation.
They connect the superior and inferior venae cavae and communicate
Variations of the brachiocephalic veins and superior with the common iliac vein by the ascending lumbar veins and with
vena cava many tributaries of the inferior vena cava.
Available with the Gray’s Anatomy e-book Variations Broadly speaking, the inferior vena cava may be congeni-
tally interrupted, duplicated, left-sided or even absent.
Inferior vena cava
The inferior vena cava returns blood to the heart from infradiaphrag-
matic tissues. It passes through the diaphragm between the right leaf
Bonus e-book images
Fig. 58.1 A case of a left anterior trunk and a retrotracheal right subclavian Fig. 58.9 Sites of measurement of the left
interventricular artery arising from the artery, also known as a lusoria artery. brachiocephalic (innominate) vein and
pulmonary trunk. superior vena cava at angiography.
Fig. 58.6 A cardiac magnetic resonance
Fig. 58.2 Bland–White–Garland syndrome in angiograph showing three-dimensional Fig. 58.10 Diameters of the distal
a 29-year-old woman. reconstruction of a native aortic coarctation brachiocephalic (innominate) vein mid-
in an adult with extensive collateral flow. brachiocephalic vein, brachiocephalic–
Fig. 58.4 A PA chest radiograph, superior vena cava junction and
anteroposterior view, showing the classic Fig. 58.7 The collateral circulation at MR mid-superior vena cava in children of
‘aortic nipple’ in a patient with angiography and phase-contrast velocity- varying ages.
pneumomediastinum. encoded cine MR imaging.
Fig. 58.5 A dissection showing a left aortic Fig. 58.8 A Stanford type A aortic
arch that gives rise to a common vertebral dissection. | 1,437 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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The brachiocephalic veins may enter the right atrium separately, the Embryologically, if the right subcardinal vein fails to anastomose
right vein descending like a normal superior vena cava. During embryo- with the hepatic sinusoids, the hepatic segment of the inferior vena cava
logical development, if the cardinal vein does not become obliterated, fails to develop. When this occurs, the hemiazygos or azygos veins,
it will persist as a left-sided superior vena cava. A left superior vena cava which both originate from the cranial supracardinal veins, return blood
may have a slender connection with the right and then cross the left to the heart. Azygos continuation of the inferior vena cava, character-
side of the aortic arch to pass anterior to the left pulmonary hilum ized by a prominent azygos vein, is an entity of which the paediatric
before turning to enter the right atrium. It replaces the oblique vein of surgeon should be aware when undertaking repair of oesophageal
the left atrium and coronary sinus, and receives all the tributaries of atresia and tracheo-oesophageal atresia in neonates. The azygos vein,
the coronary sinus. The left brachiocephalic vein sometimes projects which is commonly ligated and divided during this procedure, should
above the manubrium (more frequently in childhood), and crosses the be spared because ligation of this vessel in neonates with azygos con-
suprasternal fossa in front of the trachea. A left-sided superior vena cava tinuation of the inferior vena cava leads to intraoperative circulatory
may cause difficulties when placing a cardiac catheter, pacing or defibril- collapse and death. Double inferior vena cava (right side usually domi-
lating electrodes because the angle between the left superior vena cava nant) is a result of the persistence of all or any segments of the subcar-
and the left subclavian vein is much more acute than that between the dinal veins. One of the most common variations is a left-sided inferior
subclavian and a normal left brachiocephalic vein. Its calibre may also vena cava, which is formed if the right supracardinal vein regresses and
be smaller than that of the right. Even if insertion of a catheter into a the left supracardinal vein persists. There may also be a duplication of
left superior vena cava is possible, the angle at which the catheter enters the inferior vena cava, which typically occurs below the renal veins, and
the right atrium causes difficulty when attempting to place it into the is the result of persistence of the left lumbar and thoracic supracardinal
right ventricle and pulmonary trunk; this generally leaves the catheter veins and left suprasubcardinal anastomosis as well as malformation of
tip against the coronary sinus, making it difficult to obtain blood right subcardinal–hepatic anastomosis. Abnormalities associated with
samples. In the majority of persistent left superior venae cavae, blood duplication of the inferior vena cava include: congenital heart disease,
drains into the right atrium via the coronary sinus. When this does not congenital absence of the right kidney, cloacal extrophy, renal ectopia
happen, the coronary sinus is absent, and the persistent left superior with abdominal aneurysm, right retrocaval ureter, left retrocaval ureter
vena cava drains directly into the atrium. Cyanosis reflects a persistent and congenital absence of the iliac anastomosis, abnormal left arm
right-to-left shunt and affected individuals have a higher risk for para- drainage and transcaval ureter.
doxical embolism. Radiographically, there is a paramediastinal bulge In situs inversus with dextrocardia, the inferior vena cava passes
before the aortic arch. Electrocardiograms show a left P-wave axis. Diag- inferiorly along the left side instead of the right (as opposed to situs
nosis can be confirmed by cardiac catheterization and angiography. inversus with levocardia, in which the inferior vena cava remains on
Persistent left superior vena cava may be associated with extracardiac the right side). In situs ambiguus, otherwise known as heterotaxy, the
conditions such as VACTERL association (vertebral defects, anal atresia, major organs are arranged ambiguously within the body. Prominent
cardiac malformations, tracheo-oesophageal fistula with oesophageal azygos veins with interrupted inferior vena cava are associated with
atresia, radial and renal dysplasia, and limb anomalies); trisomy 21; heterotaxy (Punn and Olson 2010). Situs ambiguus with polysplenia is
22q11; CHARGE association (coloboma, heart defects, choanal atresia, associated with an absence of portions of the inferior vena cava on the
mental retardation, genital and ear anomalies); and 45 XO karyotype right side (with continuation through the azygos or hemiazygos vein),
(Turner’s syndrome). transposition of the inferior vena cava to the left side, or duplication of
If the superior vena cava is duplicated, the right superior vena cava the inferior vena cava with one on the right and one on the left. Situs
may drain into the right atrium and the left superior vena cava into the inversus with asplenia is similar to that of polysplenia, in that the infe-
left atrium. Although double superior vena cava is largely asympto- rior vena cava may be absent with azygos continuation or with the
matic, it is usually (along with a sole left-sided superior vena cava) inferior vena cava to the left of the midline. In situs inversus totalis,
associated with congenital cardiac anomalies, such as pulmonary steno- transposition of the inferior vena cava consists of a right-sided inferior
sis, coarctation of the aorta, tetralogy of Fallot and atrial septal defects. vena cava. The inferior vena cava may have an abnormally high inser-
tion into the right atrium. Congenital agenesis of the inferior vena cava
may occur and may be completely asymptomatic because venous drain-
age of the lower limbs occurs through anastomosed channels of the
azygos and hemiazygos veins. That said, this condition may be associ-
ated with a higher risk for deep vein thrombosis. | 1,438 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
GREAT vEssEls
1028.e2
7
NOITCEs
REFERENCES
Baliga RR, Neinaber CA, Isselbacher EM et al 2007 Aortic Dissection and Norton JA, Barie PS, Bollinger RR et al 2008 Surgery: Basic Science and
Related Syndromes. Ann Arbor, MI: Springer. Clinical Evidence (2nd ed). New York: Springer.
Berdjas D, Turina MI 2011 Operative Anatomy of the Heart. Berlin: Springer. Osborn AG 1998 Diagnostic Cerebral Angiography. Philadelphia: Lippin-
Bergman RA, Thompson SA, Afifi AK et al 1988 Compendium of Human cott, Williams & Wilkins.
Anatomic Variation. Baltimore: Urban & Schwarzenberg. Punn R, Olson I 2010 Anomalies associated with a prominent azygos vein
Deutsch J, Savides TJ 2005 Normal Thoracic Anatomy in Digital Human on echocardiography in the pediatric population. J Am Soc Echocardi-
Anatomy and Endoscopic Ultrasonography. Hamilton, ON: BC Decker. ogr 23:282–5.
Kaiser T, Kellenberger CJ, Albisetti M et al 2008 Normal values for aortic Sanjeev S, Karpawich PP 2006 Superior vena cava and innominate vein
diameters in children and adolescents–assessment in vivo by contrast- dimensions in growing children: an aid for interventional devices and
enhanced CMR-angiography. J Cardiovasc Magn Reson 10:56. transvenous leads. Pediatr Cardiol 27:414–19.
Kervancioglu P, Kervancioglu M, Tuncer CM 2006 Echocardiographic study Smith A, McKay R 2004 A Practical Atlas of Congenital Heart Disease.
of aortic root diameter in healthy children. Saudi Med J 27:27–30. London: Springer.
Loukas M, Groat C, Khangura R et al 2009 The normal and abnormal
anatomy of the coronary arteries. Clin Anat 22:114–28. | 1,439 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
COMMENTARY
Technical aspects and applications of
7.1
diagnostic radiology
Jonathan D Spratt
Magnetic resonance imaging tions for the treatment of reperfusion injury and research into the
physiology of solid tumours and angiogenesis. There is every reason to
believe that continued efforts to push the envelope of high-field-
Magnetic resonance imaging (MRI) produces images by first magnet-
strength applications will open new vistas in what appears to be a
izing a patient in the bore of a powerful magnet and then broadcasting
never-ending array of potential clinical applications.
short pulses of radiofrequency (RF) energy at 46.3 MHz that resonate
T1 weighted images best accentuate fat and other soft tissues,
mobile protons (hydrogen nuclei) in the fat, protein and water of the
whereas fluid is low-signal; these images are nicknamed the ‘anatomy
patient’s soft tissues and bone marrow. The protons produce RF echoes
weighting’ amongst radiologists who publish or teach anatomy. T2
when their resonant energy is released; their density and location can
weighted images reveal fluid as high signal as well as fat. Fat suppression
be exactly correlated into an image matrix by complex mathematical
sequences using T2 ‘fat sat’ (T2FS) or short tau inversion recovery (STIR)
algorithms.
are very sensitive in highlighting the soft tissue or bone marrow oedema
The spinning proton of the hydrogen nucleus acts like a tiny bar
that almost invariably accompanies pathological states such as inflam-
magnet, aligning either with or against the magnetic field, and produc-
mation or tumours. Contrast-enhanced images with gadolinium, when
ing a small net magnetic vector. RF energy from various types of coil,
used with T1 fat saturation (T1FS) sequences, also exquisitely highlight
either built into the scanner or attached to specific body parts, generates
hypervascularity, particularly that associated with tumours and inflam-
a second magnetic field perpendicular to the static magnetic field that
mation, especially in pathologies where the blood–brain barrier is com-
rotates or ‘flips’ the protons away from the static magnetic field. When
promised. Metallic artefact reduction sequences (MARS) are superior in
the RF pulse is switched off, the protons flip back (relax) to their origi-
imaging periprosthetic soft tissues after joint replacement or other
nal position of equilibrium, emitting the RF energy they had acquired
orthopaedic metalwork implantation.
into the antenna around the patient. This information is then ampli-
fied, digitized and spatially encoded by the array processor.
MR tractography
MRI systems are graded according to the strength of the magnetic
field they produce. Routine high-field systems are those capable of
producing a magnetic field strength of 3–7 T (Tesla), using a supercon- MRT is a three-dimensional modelling technique used to represent
ducting electromagnet immersed in liquid helium. Open magnets for neural tracts visually using data collected by DTI or, more recently, by
claustrophobic patients and limb scanners use permanent magnets of HARDI, with results presented in two- and three-dimensional images
0.2–0.75 T. For comparison, Earth’s magnetic field varies from 30 to (Nucifora et al 2007).
60 µT. MRI does not present any recognized biological hazard. Patients In addition to the long tracts that connect the brain to the rest of
who have any form of pacemaker or implanted electro-inductive device, the body, there are complicated neural networks formed by short con-
ferromagnetic intracranial aneurysm clips, certain types of cardiac valve nections among different cortical and subcortical regions, their exist-
replacement or intraocular metallic foreign bodies must never be exam- ence revealed by histochemistry and postmortem biological techniques.
ined because there is a high risk of death or blindness. Many extracra- Central nervous system tracts are not identifiable by direct examination,
nial vascular clips and orthopaedic prostheses are now ‘MRI-friendly’ CT or conventional MRI scans, explaining the paucity of their descrip-
but may cause local artefacts; newer sequences exist to reduce artefact. tion in neuroanatomy atlases and the poor understanding of their
Loose metal items, ‘MR-unfriendly’ anaesthetic equipment and credit functions.
cards must be excluded from the examination room. Pillows contain- The MRI sequences used look at the symmetry of water diffusion in
ing metallic coiled springs have been known nearly to suffocate the brain. Bundles of fibre tracts make the water diffuse asymmetrically
patients, and heavy floor buffing equipment has been found wedged in a ‘tensor’, the major axis parallel to the direction of the fibres. There
in the magnet bore because domestic staff had been suboptimally is a direct relationship between the number of fibres and the degree of
informed. anisotropy. DTI assumes that the direction of least restriction corre-
New methods of analysing normal and pathological brain anatomy sponds to the direction of white matter tracts. Diffusion MRI was intro-
are now at the forefront of research. These are MR spectroscopy (MRS); duced in 1985. In the more recent evolution of the technique into
functional MRI (fMRI); diffusion tensor imaging (DTI); high angular diffusion tensor MRI (DTI), the relative mobility of the water molecules
resolution diffusion imaging (HARDI) for MR tractography (MRT, see from the origin is modelled as an ellipsoid rather than a sphere. This
below); and molecular MRI (mMRI), which has taken on a new direc- allows full characterization of molecular diffusion in the three dimen-
tion since the description of the human genome. sions of space and the formation of tractograms. Barriers cause uneven
MRS assesses function within the living brain. It capitalizes on the anisotropic diffusion. In white matter, the principal barrier is the myelin
fact that protons residing in differing chemical environments possess sheath, whereas bundles of axons provide a barrier to perpendicular
slightly different resonant properties (chemical shift). For a given diffusion and a path for parallel diffusion along the orientation of the
volume of brain, the distribution of these proton resonances can be fibres. Anisotropic diffusion is expected to be increased overall in areas
displayed as a spectrum. Discernible peaks can be seen for certain neu- of high mature axonal order. Conditions where barriers offered by the
rotransmitters: N-acetylaspartate varies in multiple sclerosis, stroke and myelin sheaths or the axons are disrupted, e.g. in trauma, tumours and
schizophrenia while choline and lactate levels have been used to evalu- inflammation, reduce anisotropy and yield DTI data used to seed
ate certain brain tumours. various tractographic assessments of the brain (p. 391). Data sets may
fMRI depends on the fact that haemoglobin is diamagnetic when be rotated continuously into various planes in order to appreciate the
oxygenated but paramagnetic when deoxygenated. These different structure better; colour may be assigned based on the dominant direc-
signals can be weighted to the smaller vessels, and hence closer to the tion of the fibres. A leading clinical application of MRT is in the
active neurones, by using larger magnetic fields. mMRI uses biomarkers presurgical mapping of eloquent regions. Intraoperative electrical stim-
that interact chemically with their surroundings and alter the image ulation (IES) provides a clinical gold standard for the existence of
according to molecular changes occurring within the area of interest, functional motor pathways that can be used to determine the accuracy
potentially enabling early detection and treatment of disease and basic and sensitivity of fibre-tracking algorithms.
pharmaceutical development and quantitative testing. Intersecting tracts or partial volume averaging of adjacent pathways
High-field-strength magnets give significant improvement in spatial with different fibre orientations are the reasons why DTI does not accu-
resolution and contrast. MR images of the microvasculature of the live rately describe the microstructure in complex white matter voxels that
human brain that allow close comparison with the detail seen in his- contain more than one fibre population, e.g. in the centrum semiovale,
tological slides have been acquired at 8 T. This has significant implica- where major white matter tracts such as the pyramidal tract, the e67 | 1,440 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Technical aspecTs and applicaTions of diagnosTic radiology
e68
7
noiTces
superior longitudinal fasciculus and the corpus callosum intersect. This radiation dose to the target organ. For example, 99mtechnetium or
has hindered preoperative mapping of the pyramidal tract in brain 123iodine may be used to detect thyroid disease, but certain thyroid
tumour patients. HARDI permits more accurate delineation of pathways diseases or thyroid cancer may be treated solely or in part with 131iodine.
within complex regions of white matter. The q-ball reconstruction of The difference in the agent used depends on the type and energy levels
HARDI data provides an orientation distribution function (ODF) that of the radiation particle that the radioisotope emits.
can be used to determine the orientations of multiple fibre populations Radionuclides used in nuclear medicine are often chemically bound
contributing to a voxel’s diffusion MR signal, mapping fibre trajectories to a complex called a tracer. The way the body handles a tracer may
through regions of complex tissue architecture in a clinically feasible differ in disease or pathological processes. For example, the tracer used
timeframe. in bone imaging is methylene-diphosphonate (MDP) bound to 99mtech-
netium. MDP attaches to hydroxyapatite in bone; altered bone physiol-
ogy, such as occurs in a fracture, metastatic bone disease or arthritic
Ultrasound
change, produces an increase in biochemical bone activity and an accu-
mulation of MDP that is seen as a focal ‘hot spot’ of the radiopharma-
Uniquely, ultrasound images do not depend on the use of electromag- ceutical on a bone scan.
netic wave forms. The properties of high-frequency sound waves (lon- 99mTechnetium is the major workhorse radioisotope of nuclear medi-
gitudinal waves) and their interaction with biological tissues are cine. It can be eluted from a molybdenum/technetium generator stored
responsible for the production of ‘echograms’ (Desser and Jeffrey 2001). within a nuclear medicine department, allowing for easy access. It has a
A sound wave of appropriate frequency (diagnostic range 3.5–20 MHz) short half-life (6 hours), which allows for ease of medical imaging
is produced by piezo-electric principles. Image production is deter- and disposal. Its pharmacological properties allow it to be easily bound
mined by attenuation and reflection as the beam passes through tissues. to various tracers and it emits gamma rays that are of suitable energy
Attenuation is caused by the loss of energy due to absorption, reflection for medical imaging. In addition to 99mtechnetium, the most com-
and refraction in soft tissues, resulting in a reduction in signal intensity. mon intravenous radionuclides used in nuclear medicine are 123iodine
Reflection of sound waves within the range of the receiver produces the and 131iodine, 201thallium, 67gallium, 18fluorodeoxyglucose (FDG) and
image, and the echotexture is dependent on tiny differences in acoustic 111indium-labelled leukocytes. The most common gaseous/aerosol radio-
impedance between different tissues. Blood flow and velocity can be nuclides used are 133xenon, 81mkrypton, 99mtechnetium (Technegas) and
measured (using the Doppler principle) in duplex mode. 99mtechnetium diethylene triamine pentaacetic acid (DTPA).
Techniques such as harmonic imaging and the use of ultrasound The images obtained from nuclear medicine imaging can be single
contrast agents (stabilized microbubbles) have enabled non-invasive or multiple. Image sets may be represented by time sequence imaging
determination of myocardial perfusion. These contrast agents also (e.g. cine), such as dynamic imaging or cardiac gated sequences, or by
clearly improve the detection of metastases in the liver and spleen. spatial sequence imaging, where the gamma camera is moved relative
Ultrasound is the most common medical imaging technique for pro- to the patient, e.g. in SPECT imaging. Spatial sequence imaging allows
ducing elastograms, in which stiffness or strain images of soft tissue are the images to be presented as a slice-stack much in the way that CT or
used to detect or classify tumours. Cancer is 5–28 times stiffer than the MRI images are displayed. It may also be fused with concomitant CT
background of normal soft tissue; when a mechanical compression or or MRI to provide combined physiological and anatomical imaging.
vibration is applied, a tumour deforms less than the surrounding tissue. A PET scan is a specialized type of nuclear medicine imaging that
Elastography may be used, for example, to measure the stiffness of the measures important body functions, such as blood flow, oxygen use or
liver in vivo or in the detection of breast or thyroid tumours. A correla- glucose metabolism. It involves short-lived radioactive tracer isotopes
tion between liver elasticity and the cirrhosis score has been shown (Yeh that emit positrons (positively charged subatomic particles with the
et al 2002, Foucher et al 2006). same mass and magnitude of charge as electrons). The radioisotopes
Interpretation of anatomy and pathology from static ultrasound are chemically incorporated into biologically active molecules: most
images is more difficult than that from other imaging modalities: commonly, the sugar FDG (2-deoxy-2-[fluorine-18]fluoro-D-glucose).
compare the real-time nature ultrasound in Video 14.1 with the static An hour after injection, FDG becomes concentrated into the tissues of
images in Fig 14.4. The technique is highly operator-dependent and interest; images are obtained as the isotope undergoes positron emis-
provides unique information on tissue structure and form not obtained sion decay. A positron travels only a few millimetres before reacting
from other imaging techniques. with an electron by annihilation, producing a pair of gamma photons
that move in opposite directions. The PET scan detectors process only
those photon pairs that are detected simultaneously (coincident detec-
Nuclear medicine
tion) to create an image of tissue activity with respect to that particular
isotope. These images may subsequently be fused with CT or MR
Historically, the field of nuclear medicine began in 1946 when images. The short half-life of the isotopes limits PET imaging; close
radio active iodine was administered as an ‘atomic cocktail’ to treat access to a cyclotron for generation of the isotopes plays an important
thyroid cancer. Since that time, nuclear medicine has advanced to the role in the feasible location of a PET scanner. Typical isotopes used in
point where it was recognized in the early 1970s as a diagnostic sub- medical imaging and their half-lives are: 11carbon (about 20 min),
specialty. 13nitrogen (about 10 min), 13oxygen (about 2 min) and 18fluorine
Unlike diagnostic radiology, where an image is created by passing (about 110 min).
energy through the body from an external source, nuclear medicine
creates an image by measuring the radiation emitted from tracers taken
Angiography/interventional radiology
internally. Overall, the radiation dosages are comparable with CT and
vary depending on the examination. Nuclear medicine also differs from
most other imaging modalities in that the tests demonstrate the physio- Angiographic imaging was first described in 1927, when Egas Moniz, a
logical function of a specific area of the body. In some instances, this physician and neurologist, introduced contrast X-ray cerebral angiogra-
physiological information may be fused with the more anatomical phy. (Moniz was awarded the Nobel Prize for his work in 1949.) In
imaging of CT or MRI, combining the strengths of anatomy and func- 1953, the field was revolutionized by the Seldinger technique, in which
tion for diagnosis. no sharp needles remained inside the vascular lumen during imaging.
Nuclear medicine uses pharmaceuticals that have been labelled with Although angiography initially involved X-ray and fluoroscopic imaging
a radionuclide (radiopharmaceuticals) and which are administered to of blood vessels and organs of the body after injecting radiopaque
patients by intravenous injection, ingestion or inhalation (the method contrast agents into the blood stream, it has evolved to encompass so
of administration depends on the type of examination and the organ much more. Many of the procedures currently performed by angiogra-
or organ process to be imaged). Emitted radiation is detected and phy may be diagnostic; following the advent of minimally invasive
imaged with specialized equipment such as gamma cameras, positron procedures performed with image guidance, the name of the discipline
emission tomography (PET) or single photon emission computed changed to interventional radiology (or vascular and interventional
tomography (SPECT). Radiation may be measured from parts of the radiology).
body by the use of probes, or samples may be taken from patients and Angiograms are typically performed by gaining access to the blood
measured in counters. vessels, through either the femoral artery, femoral vein or jugular vein,
Radiopharmaceuticals may be used to image a disease process or to depending on the area of interest to be imaged (e.g. cerebral, coronary
treat diseases. Those used for imaging emit a gamma ray (γ) and those or pulmonary angiograms). Following vascular access, catheters are
used for treatment emit a beta (β) particle. Gamma rays are of higher directed to the specific location to be imaged by the use of guidewires,
energy in order to pass through the body and be detected by a detection and contrast agents are injected through these catheters to visualize the
camera, whereas β particles travel only short distances and emit their vessels or the organ with X-ray imaging. Imaging of the arterial and | 1,441 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Technical aspects and applications of diagnostic radiology
e69
1.7
yraTneMMoc
venous circulation of the arms and legs may demonstrate peripheral attenuation coefficient of all the tissues in the path of the X-ray beam
vascular disease. form the image. CT obtains a series of different angular X-ray projec-
Treatment and/or interventions can often be performed through tions that are processed by a computer to give a section of specified
similar catheter-based examinations. Such procedures might involve thickness. The CT image comprises a regular matrix of picture elements
angioplasties, where a balloon mechanism is placed across an area of (pixels). All of the tissues contained within the pixel attenuate the X-ray
narrowing (stenosis) in a vessel or lumen. With controlled inflation of projections and result in a mean attenuation value for the pixel. This
the balloon, the area of narrowing can be widened. value is compared with the attenuation value of water and is displayed
Imaging in diagnostic or interventional procedures may produce still on a scale (the Hounsfield scale). Water is said to have an attenuation
or motion (cine) images. The technique often used, digital subtraction of 0 Hounsfield units (HU); air typically has an HU number of −1000;
angiography (DSA), involves taking images at 2–30 frames per second fat is approximately −100 HU; soft tissues are in the range +20 to
to allow imaging of the flow of blood through vessels. A preliminary +70 HU; and bone is usually greater than +400 HU.
image of the area is taken before the contrast is injected; this ‘mask’ Modern multislice helical CT scanners can obtain images in sub-
image is then electronically subtracted from all subsequent images, second times, and imaging of the whole body from the top of the head
leaving only the vessels filled with contrast. For optimal subtraction, to the thighs can take as little as a single breath-hold of only a few
the patient must remain motionless. seconds. The fast scan times allow dynamic imaging of arteries and
Angiograms of the heart may be performed to visualize the size and veins at different times after the injection of intravenous contrast agents.
contractility of the chambers and the anatomy of the coronary vessels. The continuous acquisition of data from a helical CT scanner allows
The thorax may also be studied to evaluate the pulmonary arteries and reconstruction of an image in any plane (multiplane reconstruction,
veins for vascular malformations, blood clots and possible origins of MPR), commonly sagittal and coronal, as may be seen in many of the
haemoptysis. In the investigation of atherosclerotic disease, vascular images throughout this forty-first edition of Gray’s Anatomy. This
malformations or tumoral vascularization, the neck is often imaged in orthogonal imaging greatly improves the understanding of the three-
order to visualize the vessels that supply the brain in their entirety, from dimensional aspects of radiological anatomy and now forms part of the
the points at which they arise from the aortic arch to their termination standard practice of assessing disease.
as cerebral vessels. Renal artery imaging may elucidate the cause of No specific preparation is required for most CT examinations of the
hypertension in selected patients, and imaging of the mesenteric vessels brain, spine or musculoskeletal system. Studies of the chest, abdomen
may identify the origin of gastrointestinal bleeding or mesenteric and pelvis, and those of the brain with complex histories, usually
angina. require intravenous contrast medium that contains iodine because this
In addition to angiograms and venograms, the field of interventional defines vascular relationships and differentiates normal and pathologi-
radiology also includes such procedures as coil embolization of aneu- cal soft tissues more effectively. Opacification of the bowel in CT studies
rysms and vascular malformations; balloon angioplasty and stent place- of the abdomen and pelvis may be accomplished by oral ingestion of
ment; chemoembolization directly into tumours; drainage catheter a water-soluble contrast medium from 24 hours prior to the examina-
insertion; embolization (e.g. uterine artery for treatment of fibroids); tion, in order to outline the colon, combined with further oral intake
thrombolysis to dissolve blood clots; tissue biopsy (percutaneous or 0–60 minutes prior to the scan, in order to outline the stomach and
transvascular); radiofrequency ablation and cryoablation of tumours; small bowel. This procedure is much less frequently performed with the
line insertions for specialized vascular access; inferior vena cava filter latest generation of scanners, which exquisitely differentiate various
placements; vertebroplasty; nephrostomy placement; gastrostomy tube enhancing layers within the bowel wall. Occasionally, direct insertion
placement for feeding; dialysis access; transjugular intrahepatic porto- of rectal contrast to show the distal large bowel may be required.
systemic shunt (TIPS) placement; biliary interventions; and, most Generally, all studies are performed with the patient supine and
recently, endovenous laser ablation of varicose veins. images are obtained in the transverse or axial plane. Modern CT scan-
ners allow up to 25° of gantry angulation, which is particularly valuable
in spinal imaging. Occasionally, direct coronal images are obtained in
Computed tomography
the investigation of cranial and maxillofacial abnormalities; in these
cases, the patient lies prone with the neck extended and the gantry
The limitation of all plain radiographic techniques is the two- appropriately angled, but this technique has largely been superseded
dimensional representation of three-dimensional structures; the linear by the orthogonal imaging described above.
REFERENCES
Desser TS, Jeffrey RB 2001 Tissue harmonic imaging techniques: physical Nucifora PG, Verma R, Lee SK et al 2007 Diffusion-tensor MR imaging and
principles and clinical applications. Semin Ultrasound CT MR 22: tractography: exploring brain microstructure and connectivity. Radiol-
1–10. ogy 245:367–84.
Foucher J, Chanteloup E, Vergniol J et al 2006 Diagnosis of cirrhosis by Yeh WC, Li PC, Jeng YM et al 2002 Elastic modulus measurements of human
transient elastography (FibroScan): a prospective study. Gut 55:403–8. liver and correlation with pathology. Ultrasound Med Biol 28:467–74. | 1,442 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
COMMENTARY
7.2
Endobronchial ultrasound
Natalie M Cummings
History tively, compared to 69% and 88% for EBUSTBNA alone. A more recent
study of 44 patients, where the same operator performed EBUSTBNA
and then EUSFNA by inserting the EBUS bronchoscope into the
It is more than 35 years since the first description of blind transbron
oesophagus, found that the sensitivity, specificity and accuracy of
chial needle aspiration (TBNA) biopsies of paratracheal masses was
mediastinal lymph node staging using combined EBUS/EUSFNA were
published (Wang et al 1978). Prior to this, surgery had been the only
all 100%, compared to 79%, 100% and 84%, respectively, for EBUS
way to obtain tissue from mediastinal masses or lymph nodes. TBNA
alone (Lee et al 2014). The ASTER trial randomized 241 patients to
is less invasive than surgery but the blind nature of the technique dict
either combined EBUS/EUSFNA or conventional surgical staging
ates that sampling only bulky masses or nodal tissue results in an
(Annema et al 2010). Where endoscopic staging showed no evidence of
acceptable yield. In the early 1990s, the first report of the new technique
locally advanced disease, the patient underwent surgical staging (n = 65).
of ‘endobronchial sonography’ appeared (Hürter and Hanrath 1992).
Sensitivity was significantly greater for combined surgical/endoscopic
A small ultrasound catheter was passed through the working channel
staging (94% versus 79%, P = 0.02) with similar NPVs (93% versus 86%,
of a bronchoscope, giving a 360° (radial) ultrasound image. Biopsies
P = 0.18) and complication rates. A headtohead study of EBUSTBNA
could be taken by inserting standard biopsy forceps through a sheath
versus the surgical approach of videoassisted mediastinoscopy (VAM)
left in place to mark the correct position once the ultrasound catheter
in 153 patients was published in 2011 (Yasufuku et al 2011). No signifi
was removed. In 2003, the first report of a prototype bronchoscope,
cant differences were found between the two procedures in determining
incorporating a curved linear array electronic transducer at the end of
the true pathological Nstage, although the authors admitted that the
the bronchoscope, was published (Krasnik et al 2003). When the trans
EBUSTBNA yield may have been improved by the fact that the proce
ducer was closely applied to the bronchial wall, ultrasound scanning of
dures were all carried out under general anaesthetic by thoracic sur
mediastinal structures (to a depth of 5 cm) was possible and a 22gauge
geons who were extremely familiar with mediastinal anatomy. At
needle inserted through the biopsy channel and into the mass in ques
present, the European Society of Thoracic Surgeons continue to recom
tion was visible in real time. This meant that smaller lesions could be
mend that patients with mediastinal lymphadenopathy on PET/CT and
biopsied more accurately, with reduced potential for the wrong area
negative endoscopic staging proceed to VAM because of the higher NPV
to be sampled inadvertently. This new biopsy technique was termed
(de Leyn et al 2014). However, mediastinoscopy can be avoided if endo
endobronchial ultrasound (EBUS)TBNA or fine needle aspiration
scopic staging is positive.
(EBUSFNA).
Technique Other uses
Although the initial procedures took place under general anaesthetic, Although most commonly used in lung cancer investigation, EBUS is
most EBUS procedures today take place under conscious sedation and increasingly employed to diagnose other causes of mediastinal lymph
local anaesthetic. Using computed tomography (CT), with or without adenopathy and paramediastinal masses. Von Bartheld et al (2013)
positron emission tomography (PET) scanning, the areas that require carried out a randomized controlled trial demonstrating that EBUS or
sampling are identified. These lymph nodes or masses are then found EUSFNA was superior to combined endobronchial and transbronchial
during bronchoscopy using the ultrasound scanning probe. The infla biopsy (conventionally, the method of choice to obtain a tissue diag
tion of a small waterfilled balloon around the scanning probe can nosis in sarcoidosis) in the detection rate of noncaseating granulomas.
improve contact with the bronchial wall, and thus image quality, Sensitivity for the diagnosis of Mycobacterium tuberculosis has been
although in most cases it is not needed. A needle is inserted through reported at 85–94% (Sun et al 2013, Navani et al 2011), whilst for
the working channel of the bronchoscope and suction applied, via a lymphoma it may be as high as 89% and even higher for relapsed rather
syringe, at the proximal end of the needle. Under direct vision, the than de novo disease (Moonim et al 2013). Controversy remains about
needle is passed several times through the lesion in order to obtain a whether the cytological sample obtained at EBUS can give sufficient
cytological specimen. Suction is removed and the needle withdrawn information about lymphoma subtype compared to the larger samples
from the bronchoscope. The specimen is either smeared on to slides obtained by core or surgical biopsies that have been traditionally
and airdried, or placed into pots containing liquid preservative for favoured. At present, the British Thoracic Society feels that there is insuf
laboratory processing (Medford et al 2010). The power Doppler facility ficient evidence to justify the use of EBUSTBNA in lymphoma diagno
enables safer identification of vessels to avoid puncture of these sis (du Rand et al 2011) but this may change in the future as endoscopists
structures. and cytopathologists become more skilled. Using EBUS, the diagnosis
of metastatic extrathoracic malignancy (Ozgül et al 2013), chondrosar
Diagnosis and staging of lung cancer coma (Wang et al 2014), malignant pleural mesothelioma (Lococo et al
2014), vertebral body tumour (Ojha et al 2014), pulmonary artery
aneurysm (Lerner and Riker 2014), parathyroid adenoma (Buderi et al
The main use of EBUS in today’s clinical practice is in the diagnosis and
2014) and various other benign pathologies have all been reported in
staging of lung cancer. Surgical sampling of the mediastinum, whilst
the literature.
remaining the gold standard, has a number of limitations, including
invasiveness and cost. In 2009, a new lymph node map was published
Complications
by the International Association for the Study of Lung Cancer (Rusch
et al 2009). Using this as a guide, EBUS can access lymph node stations
2R, 2L, 3P, 4R, 4L, 7, 10R, 10L, 11R and 11L. When combined with A recent review of 190 studies published between 1995 and 2012,
endoscopic ultrasound (EUS), where an endoscope fitted with a linear comprising 16,181 patients, found a serious adverse event rate of 0.05%
ultrasound transducer is inserted into the oesophagus, additional sta for EBUS, increasing to 0.14% with the addition of figures for EUS (von
tions 8 and 9 can be sampled, as well as the left suprarenal gland, the Bartheld et al 2014). Abscess formation, sepsis, pneumothorax and
left lobe of the liver and the coeliac axis nodes, if necessary. Stations 5 other respiratory complications accounted for the EBUS adverse events,
and 6 can only be accessed via a surgical approach. whereas EUS had higher rates of infectious complications (including
Wallace et al (2008) showed, in 42 patients with malignant media mediastinitis), oesophageal perforation and haemorrhage. The results
stinal lymphadenopathy, that the sensitivity and negative predictive of the AQuIRE registry, published in 2013, reported a 1.44% complica
e70 value (NPV) of combined EBUS/EUSFNA were 93% and 97%, respec tion rate in 1,317 patients undergoing EBUS, including pneumothorax, | 1,443 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Endobronchial ultrasound
e71
2.7
YRATNEMMOC
bleeding, sustained hypoxia and respiratory failure (Eapen et al 2013); to yield greater amounts of tumour RNA when compared to the other
it is unclear how many of these cases also feature in the figures of the methods (although this only reached significance when compared to
aforementioned metaanalysis. Single case reports of needle breakage bronchoscopy). Certain genetic changes (particularly in the EGFR and
(Ozgül et al 2014) and pneumomediastinum/pneumopericardium ALK genes) may determine the chemotherapy agent of choice; a further
(Ortiz et al 2014) have also been published. However, the procedure is study has demonstrated that 52 of 55 samples obtained by EBUSTBNA
generally accepted to be safe. in patients with NSCLC contained sufficient material for fluorescent in
situ hybridization (FISH) analysis for ALK rearrangement or amplifica
The future
tion (Neat et al 2013). Yarmus et al (2013) found that four needle
passes (in conjunction with rapid onsite cytopathology evaluation)
In this era of increasingly personalized medicine, it is important for any yielded adequate amounts of tissue for EGFR and KRAS mutation analy
sampling technique to provide sufficient tissue for molecular analysis. sis on tumour DNA as well as ALK rearrangement testing by FISH
In a recent study of 106 patients with nonsmall cell lung cancer (Yarmus et al 2013).
(NSCLC), 101 samples taken at either standard bronchoscopy, EBUS The applications of EBUS continue to expand and with increased
TBNA or CTguided core biopsy were sufficient to yield RNA for further experience of both the operators and the cytopathologists examining
molecular testing (SchmidBindert et al 2013). EBUSTBNA was found the samples, the technique goes from strength to strength.
REFERENCES
Annema JT, van Meerbeeck JP, Rintoul RC et al 2010 Mediastinoscopy vs Ortiz R, Hayes M, Arias S et al 2014 Pneumomediastinum and pneumoperi
endosonography for mediastinal nodal staging of lung cancer: a rand cardium after endobronchial ultrasoundguided transbronchial needle
omized trial. JAMA 304:2245–52. aspiration. Ann Am Thorac Soc 11:680–1.
Buderi SI, Saleh HZ, Theologou T et al 2014 Endobronchial ultrasound Ozgül MA, Cetinkaya E, Tutar N et al 2013 Endobronchial ultrasound
guided biopsy to diagnose large posterior mediastinal parathyroid guided transbronchial needle aspiration for the diagnosis of intratho
adenoma prior to videoassisted thoracoscopic resection. BMJ Case Rep racic lymphadenopathy in patients with extrathoracic malignancy: a
May 13:2014. study in a tuberculosisendemic country. J Cancer Res Ther 9:416–21.
De Leyn P, Dooms C, Kuzdzal J et al 2014 Revised ESTS guidelines for preop Ozgül MA, Cetinkaya E, Tutar N et al 2014 An unusual complication of
erative mediastinal lymph node staging for nonsmallcell lung cancer. endobronchial ultrasoundguided transbronchial needle aspiration
Eur J Cardiothorac Surg 45:787–98. (EBUSTBNA): the needle breakage. Ann Thorac Cardiovasc Surg 20
Du Rand IA, Barber PV, Goldring J et al 2011 British Thoracic Society guide Supplement:567–9.
line for advanced diagnostic and therapeutic flexible bronchoscopy in Rusch VW, Asamura H, Watanabe H et al 2009 The IASLC lung cancer
adults. Thorax 66 Suppl 3:iii1–21. staging project: a proposal for a new international lymph node map in
Eapen GA, Shah AM, Lei X et al 2013 Complications, consequences, and the forthcoming seventh edition of the TNM classification for lung
practice patterns of endobronchial ultrasoundguided transbronchial cancer. J Thorac Oncol 4:568–77.
needle aspiration: results of the AQuIRE registry. Chest 143:1044–53. SchmidBindert G, Wang Y, Jiang H et al 2013 EBUSTBNA provides highest
Hürter T, Hanrath P 1992 Endobronchial sonography: feasibility and pre RNA yield for multiple biomarker testing from routinely obtained small
liminary results. Thorax 47:565–7. biopsies in nonsmall cell lung cancer patients – a comparative study
of three different minimal invasive sampling methods. PLoS One
Krasnik M, Vilmann P, Larsen SS et al 2003 Preliminary experience with a
8:e77948.
new method of endoscopic transbronchial real time ultrasound guided
biopsy for diagnosis of mediastinal and hilar lesions. Thorax 58: Sun J, Teng J, Yang H et al 2013 Endobronchial ultrasoundguided trans
1083–6. bronchial needle aspiration in diagnosing intrathoracic tuberculosis.
Ann Thorac Surg 96:2021–7.
Lee KJ, Suh GY, Chung MP et al 2014 Combined endobronchial and trans
esophageal approach of an ultrasound bronchoscope for mediastinal von Bartheld MB, Dekkers OM, Szlubowski A et al 2013 Endosonography
staging of lung cancer. PLoS One 9:e91893. vs conventional bronchoscopy for the diagnosis of sarcoidosis: the
GRANULOMA randomized clinical trial. JAMA 309:2457–64.
Lerner AD, Riker DR 2014 Use of endobronchial ultrasonography in the
diagnosis of a pulmonary artery aneurysm. Ann Thorac Surg 97: von Bartheld MB, van Breda A, Annema JT 2014 Complication rate of
e139–41. endosonography (endobronchial and endoscopic ultrasound): a sys
tematic review. Respiration 87:343–51.
Lococo F, Rossi G, Agostini L et al 2014 ‘Dry’ pleural mesothelioma success
fully diagnosed on endobronchial ultrasound (EBUS)guided trans Wallace MB, Pascual JM, Raimondo M et al 2008 Minimally invasive endo
bronchial needle aspiration (TBNA). Intern Med 53:467–9. scopic staging of suspected lung cancer. JAMA 299:540–6.
Medford AR, Bennett JA, Free CM et al 2010 Endobronchial ultrasound Wang KP, Terry P, Marsh B 1978 Bronchoscopic needle aspiration biopsy of
guided transbronchial needle aspiration (EBUSTBNA): applications in paratracheal tumors. Am Rev Respir Dis 118:17–21.
chest disease. Respirology 15:71–9. Wang R, Folch E, Paul M et al 2014 The use of CPEBUSTBNA in the diag
Moonim MT, Breen R, Fields PA et al 2013 Diagnosis and subtyping of de nosis of chondrosarcoma in a patient with Maffucci syndrome. J Bron
novo and relapsed mediastinal lymphomas by endobronchial ultra chology Interv Pulmonol 21:177–80.
sound needle aspiration. Am J Respir Crit Care Med 188:1216–23. Yarmus L, Akulian J, Gilbert C et al 2013 Optimizing endobronchial ultra
Navani N, Molyneaux PL, Breen RA et al 2011 Utility of endobronchial sound for molecular analysis. How many passes are needed? Ann Am
ultrasoundguided transbronchial needle aspiration in patients with Thorac Soc 10:636–43.
tuberculous intrathoracic lymphadenopathy: a multicentre study. Yasufuku K, Pierre A, Darling G et al 2011 A prospective controlled trial of
Thorax 66:889–93. endobronchial ultrasoundguided transbronchial needle aspiration
Neat MJ, Foot NJ, Hicks A et al 2013 ALK rearrangements in EBUSderived compared with mediastinoscopy for mediastinal lymph node staging of
transbronchial needle aspiration cytology in lung cancer. Cytopathology lung cancer. J Thorac Cardiovasc Surg 142:1393–400.e1.
24:356–64.
Ojha S, Ie S, Boyd M et al 2014 Vertebral body tumor biopsy: an expanded
role of endobronchial ultrasoundguided transbronchial needle aspira
tion. J Bronchology Interv Pulmonol 21:85–7. | 1,444 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Abdomen and pelvis: overview and CHAPTER
59
surface anatomy
GENERAL STRUCTURE AND FUNCTION OF THE MUSCULOSKELETAL FRAMEWORK OF THE
ABDOMINOPELVIC CAVITY ABDOMEN AND PELVIS
Although often considered separately, the abdomen and pelvis form the The walls of the abdominopelvic cavity consist of five lumbar vertebrae
largest continuous visceral cavity of the body. Together, they provide and their intervening intervertebral discs (lying in the posterior midline);
multiple vital functions, including: housing and protection of the diges- the muscles of the anterior abdominal wall lying anteriorly (rectus
tive and urinary tracts and of the internal reproductive organs; a conduit abdominis) and anterolaterally (transversus abdominis, internal
for neurovascular communication between the thorax and lower limb; oblique and external oblique); the muscles of the posterior abdominal
support and attachment for the external genitalia; access to and from wall (psoas, quadratus lumborum and the diaphragm); the bony ‘basin’
the internal reproductive organs and urinary tract; assistance with formed by the walls of the false and true pelvis; the muscles of the pelvic
physio logical functions such as respiration, defecation and micturition; floor and perineum lying inferiorly; and the diaphragm lying superiorly
support for the vertebral column in weight-bearing, maintenance of (Fig. 59.1). In addition, the upper abdominal cavity gains protection
posture and movement; and, in women, the ability to support human from the lower six ribs and their cartilages, even though these structures
gestation. are technically part of the thoracic wall.
Fig . 59 .1 The bony and muscular structures making up
the abdominopelvic ‘cavity’ . The anterolateral abdominal
muscles have been removed for clarity .
Right cupola
(of diaphragm) Medial arcuate
ligament
Lateral arcuate
ligament
Right crus Tip of eleventh rib
Quadratus lumborum Tip of twelfth rib
Psoas minor
Iliac crest
Psoas major
Piriformis
Iliacus
Ischium
Obturator internus
Levator ani
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The muscles of the abdominal wall play an important role in move- tion. Parasympathetic stimulation leads to opposing effects. Visceral
ment of the trunk (flexion, extension and rotation). The anterolateral afferents also pass through these autonomic plexuses.
muscles, in particular, provide assistance with rotation of the thorax in
relation to the pelvis (or vice versa if the thorax is fixed). Sympathetic innervation
The abdominal cavity is somewhat kidney-shaped in horizontal
cross-section due to the posterior indentation of the vertebral column. The cell bodies of neurones of the sympathetic supply of the abdomen
Consequently, there are two distinct paravertebral gutters on either and pelvis lie in the intermediolateral grey matter of the first to the
side of the spine. The lordosis of the lumbar spine combined with the twelfth thoracic and the first two lumbar spinal segments. Myelinated
backward angulation of the sacrum gives each paravertebral gutter a axons from these neurones travel in the ventral ramus of the spinal
parabola shape in sagittal section. In standing, the pelvic brim lies at nerve of the same segmental level, leaving it via a white ramus com-
an angle of about 55° to the horizontal such that the anterior supe- municans to enter a thoracic or lumbar paravertebral sympathetic gan-
rior iliac spines and pubic tubercles are in approximately the same glion. Visceral branches may exit at the same level or ascend or descend
coronal plane. The mean angle between the upper border of the first several levels in the sympathetic chain before exiting; they leave the
sacral vertebra and the horizontal plane is about 40–45° (Woon et al ganglia without synapsing and pass medially, giving rise to the paired
2013). greater, lesser and least splanchnic nerves, and the lumbar and sacral
splanchnic nerves. Axons destined to supply somatic structures synapse
Thoracoabdominal interface
in the sympathetic ganglion of the same level, and postganglionic,
unmyelinated axons leave the ganglion as one or more grey rami com-
The diaphragm constitutes the interface between the thoracic and municantes to enter the spinal nerve of the same segmental level.
abdominal cavities (Ch. 55). Three principal pathways exist between
Greater splanchnic nerve
the two cavities across the diaphragm: the caval opening in the central
tendon transmits the inferior vena cava and right phrenic nerve; the On each side, the greater splanchnic nerve is derived from the medial,
oesophageal hiatus, encircled by the right crus of the diaphragm, trans- visceral branches of the fifth to ninth thoracic sympathetic ganglia. It
mits the oesophagus, vagal trunks and vessels; and the aortic hiatus, gives off branches to the descending aorta and enters the abdomen
posterior to the median arcuate ligament of the diaphragm, transmits through the fibres of the ipsilateral crus of the diaphragm, on which it
the aorta, thoracic duct and, usually, the azygos vein. The hemiazygos descends anteroinferiorly. The main trunk of the nerve enters the supe-
vein usually enters the thorax through the left crus of the diaphragm. rior aspect of the coeliac ganglion, where most of the preganglionic
Other lymphatics from the abdomen drain to the thorax alongside the fibres synapse (but not those destined for the suprarenal medulla).
inferior vena cava and via small vessels passing through and around
lesser splanchnic nerve
the diaphragm. Thoracic splanchnic nerves reach the abdomen through
the diaphragmatic crura and behind the medial arcuate ligaments, On each side, the lesser splanchnic nerve is derived from the medial,
and the left phrenic nerve pierces the muscle of the left hemidiaphragm. visceral branches of the tenth and eleventh thoracic ganglia (or ninth
The subcostal vessels pass into the abdomen beneath the lateral arcuate and tenth). It enters the abdomen running through the lowermost fibres
ligaments of the diaphragm. Anteriorly, the superior epigastric vessels of the ipsilateral crus of the diaphragm or under the medial arcuate
pass between the costal and xiphoid attachments of the diaphragm. ligament, and then lies on the crus as it runs anteroinferiorly. The trunk
Neurovascular structures also cross between the thorax and abdomen of the nerve joins the aorticorenal ganglion and may give branches to
within the subcutaneous tissues. the lateral aspect of the coeliac ganglion. It occasionally joins the greater
and least splanchnic nerves as a single splanchnic nerve.
Pelvis–lower limb interface
least splanchnic nerve
On each side, the least splanchnic nerve is derived from the medial,
The pelvis forms an integral part of the bony structure of both the
visceral branches of the eleventh and/or twelfth thoracic ganglia. It
abdominopelvic cavity and the lower limb. It transmits the weight of
enters the abdomen medial to the sympathetic chain under the medial
the upright body, as well as providing a stable platform for movement
arcuate ligament of the diaphragm and runs inferiorly to join the renal
of the hip joint and bipedal locomotion. Its bony surfaces provide
plexus. The trunk of the nerve enters the aorticorenal ganglion and may
attachment sites for the muscles of the buttock and thigh (Ch. 80), the
give branches to the lateral aspect of the coeliac ganglion. It is some-
pelvic floor and perineal membrane, the abdominal wall and lower
times part of the lesser splanchnic nerve, when it forms a twig that
back. The pelvis also transmits the neurovascular structures that supply
enters the renal plexus just below the aorticorenal ganglion.
the lower limb. There are four principal pathways between the pelvis
The thoracic splanchnic nerves are subject to considerable individual
and lower limb: the interval beneath the inguinal ligament anterior to
variation in their origin and distribution (Loukas et al 2010). For
the superior pubic ramus and ilium, which transmits the femoral neu-
example, the greater splanchnic nerve may receive a contribution from
rovascular structures and lymphatics; the greater and lesser sciatic
the fourth or tenth thoracic sympathetic ganglia or originate only from
foramina, which transmit the gluteal vessels and nerves, sciatic nerve,
the sixth to ninth ganglia.
and internal pudendal vessels and pudendal nerve; and the obturator
foramen, which transmits the obturator nerve, vessels and lymphatics. lumbar sympathetic system
Autonomic nerves travel with the arterial supply to the lower limb and
The lumbar part of each sympathetic trunk usually contains four inter-
with the branches of the sacral plexus. Neurovascular structures also
connected ganglia lying on the anterolateral aspects of the lumbar
cross between the lower limb and pelvis within the subcutaneous
vertebrae along the medial margin of psoas major (see Figs 59.2, 62.14)
tissues.
(Murata et al 2003). Superiorly, it is continuous with the thoracic sym-
pathetic trunk posterior to the medial arcuate ligament. Inferiorly, it
passes posterior to the common iliac vessels and is continuous with the GENERAL ARRANGEMENT OF ABDOMINOPELVIC
sacral sympathetic trunk. On the right side, it lies posterior to the infe-
AUTONOMIC NERVES
rior vena cava; on the left, it is posterior to the lateral aortic lymph
nodes. It is anterior to most of the lumbar vessels but may pass behind
What follows is a brief overview of the autonomic nervous system in some lumbar veins.
the abdominopelvic region; descriptions of the neurovascular supply to On each side, the first, second and, sometimes, the third lumbar
individual organs are given in the relevant chapters. The autonomic ventral spinal rami are connected to the lumbar sympathetic trunk by
supply to the abdominal and pelvic viscera is via the abdominopelvic white rami communicantes. All lumbar ventral rami are joined near
part of the sympathetic chain and the greater, lesser and least splanchnic their origins by long, slender, grey rami communicantes from the four
nerves (sympathetic), and the vagus and pelvic splanchnic nerves (para- lumbar sympathetic ganglia. Their arrangement is irregular: one gan-
sympathetic). Numerous interconnections occur between plexuses and glion may give rami to two or three lumbar ventral rami, one lumbar
ganglia, particularly in the major plexuses around the abdominal aorta; ventral ramus may receive rami from two ganglia, or grey rami may
hence, the descriptions tend to be simplifications based on the ‘main’ leave the sympathetic trunk between ganglia (Murata et al 2003).
supply to each organ (Fig. 59.2). The details of the terminations of
these fibres are given in the description of the microstructure of the gut Somatic and vascular branches
wall. Sympathetic nerve branches accompany the lumbar arteries round the
As a general rule, sympathetic neurones from the abdominopelvic sides of the vertebral bodies, medial to the fibrous arches to which psoas
autonomic plexuses inhibit visceral smooth muscle motility and glan- major is attached, to provide sympathetic innervation to the lumbar
dular secretions, induce sphincter contraction and cause vasoconstric- somatomes. Branches from the lumbar ganglia innervate the abdominal | 1,450 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Fig . 59 .2 The overall arrangement of the autonomic
plexuses of the abdominal and pelvic viscera .
Anterior and
posterior
vagal trunks
Superior
mesenteric Coelic plexus and ganglia
plexus and ganglia
T12 sympathetic
ganglion Left aorticorenal plexus
and ganglion
Right renal ganglion
and plexus
Intermesenteric
L1–4 sympathetic plexuses
ganglia
Inferior mesenteric
plexus and ganglia
Right lumbar
Superior hypogastric
sympathetic chain
plexus
Hypogastric nerve
Inferior hypogastric
plexus
aorta and common, external and internal iliac arteries, forming delicate Damage to these nerves, e.g. during aortoiliac surgery, can result in
nerve plexuses that extend along the vessels. Other postganglionic sym- sexual dysfunction.
pathetic nerves to vessels and skin travel with somatic nerves. Thus, the
femoral nerve carries vasoconstrictor sympathetic nerves to the femoral Pelvic sympathetic system
artery and its branches in the thigh, as well as sympathetic fibres in its The sacral region of the sympathetic trunk usually consists of four or
cutaneous branches. Postganglionic fibres travelling with the obturator five ganglia located medial or anterior to the anterior sacral foramina
nerve supply the obturator artery and the skin of the medial thigh. beneath the presacral fascia (Oh et al 2004). Occasionally, one or two
Sympathetic denervation of vessels in the lower limb can be effected by coccygeal ganglia are present. The sacral sympathetic trunk is continu-
removing or ablating the upper three lumbar ganglia and intervening ous above with the lumbar sympathetic trunk, and preganglionic fibres
parts of the sympathetic trunk; this procedure may be useful in treating descend from the lower lumbar spinal cord segments via this route. The
some varieties of vascular insufficiency of the lower limb. first sacral sympathetic ganglion is the largest. More caudal ganglia
become progressively smaller (Blaszczyk 1981). The sacral sympathetic
Lumbar splanchnic nerves chain is often asymmetric, with absent or fused ganglia, and cross-
Four lumbar splanchnic nerves pass as medial branches from the communications between each side are frequent. Each ganglion sends
ganglia to join the coeliac, inferior mesenteric and superior hypogastric at least one grey ramus communicans to its adjacent spinal nerve
plexuses. The first lumbar splanchnic nerve, from the first ganglion, but up to 11 such branches from a single ganglion have been reported
gives branches to the coeliac, renal and inferior mesenteric plexuses. (Potts 1925).
The second nerve joins the inferior part of the intermesenteric or infe- The pelvic sympathetic chain converges caudally to form a
rior mesenteric plexus. The third nerve arises from the third or fourth solitary retroperitoneal structure, the ganglion impar (or ganglion of
ganglion and joins the superior hypogastric plexus. The fourth lumbar Walther), which lies at a variable level between the sacrococcygeal
splanchnic nerve from the lowest ganglion passes anterior to the joint and the tip of the coccyx; it is occasionally paired, unilateral
common iliac vessels to join the lower part of the superior hypogastric or absent (Oh et al 2004). It conveys sympathetic efferents to and
plexus, or the hypogastric nerves. It is important to note that lumbar nociceptive afferents from the perineum and terminal urogenital
splanchnic sympathetic nerves contribute to the superior and inferior regions. Ganglion impar blockade may be used to treat intractable
hypogastric plexuses and, therefore, contribute to the innervation of the perineal pain of sympathetic origin in patients with pelvic cancers
bladder neck, ductus deferens and prostate, among other structures. (Toshniwal 2007). | 1,451 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Somatic and vascular branches gastric branch, and run beneath the peritoneum, deep to the posterior
Grey rami communicantes containing postganglionic sympathetic wall of the upper part of the lesser sac, to reach the coeliac plexus. Their
nerves pass from the pelvic sympathetic ganglia to the sacral and coc- synaptic relays with postganglionic neurones are situated in the mye-
cygeal spinal nerves. There are no white rami communicantes at this nteric (Auerbach’s) and submucosal (Meissner’s) plexuses in the wall
level. The postganglionic fibres are distributed via the sacral and coc- of the gut (see below).
cygeal plexuses (Woon and Stringer 2014). Thus, sympathetic fibres in
Pelvic splanchnic nerves
the tibial nerve are conveyed to the popliteal artery and its branches in
the leg and foot, whilst those in the pudendal and superior and inferior Pelvic splanchnic nerves to the pelvic viscera travel in the anterior rami
gluteal nerves accompany these arteries to the perineum and buttocks. of the second, third and fourth sacral spinal nerves. They leave the
Small branches also travel with the median and lateral sacral arteries. nerves as they exit the anterior sacral foramina and pass in the presacral
tissue as a fine network of branches that are distributed to three prin-
Sacral splanchnic nerves cipal destinations. Most pass anterolaterally into the network of nerves
Sacral splanchnic nerves pass directly from the ganglia to the inferior that form the inferior hypogastric plexus; from here, they pass to the
hypogastric plexus and, from there, to pelvic viscera; they usually arise pelvic viscera. Some join directly with the hypogastric nerves and ascend
from the first two sacral sympathetic ganglia. out of the pelvis, as far as the superior hypogastric plexus; from here,
they are distributed with branches of the inferior mesenteric artery
Parasympathetic innervation (p. 1153). A few run superolaterally in the presacral tissue, over the
pelvic brim anterior to the left iliac vessels, and pass directly into the
tissue of the retroperitoneum and the mesentery of the sigmoid and
The parasympathetic neurones innervating the abdomen and pelvis lie
descending colon.
either in the dorsal motor nucleus of the vagus nerve or in the interme-
The pelvic splanchnic nerves are motor to the smooth muscle of the
diolateral grey matter of the second, third and fourth sacral spinal
hindgut and bladder wall, supply vasodilator fibres to the erectile tissue
segments. The vagus nerves supply parasympathetic innervation to the
of the penis and clitoris, and are secretomotor to the hindgut.
abdominal viscera as far as the distal transverse colon, i.e. they supply
the foregut and midgut. The hindgut is supplied by parasympathetic
Abdominopelvic autonomic plexuses
fibres travelling via the pelvic splanchnic nerves (see below); the overlap
and ganglia
between these two supplies is variable. The vagal trunks are derived
from the oesophageal plexus and enter the abdomen via the oesopha-
geal hiatus, closely related to the anterior and posterior walls of the The abdominopelvic autonomic plexuses are somewhat variable and
abdominal oesophagus (see Fig. 56.6). The anterior vagal trunk is often fuse or are closely interrelated. The following descriptions recog-
mostly derived from the left vagus and the posterior from the right nize their main features (Figs 59.3–59.4).
vagus. The nerves supply the intra-abdominal oesophagus and stomach
Coeliac plexus
directly. The anterior trunk gives off a hepatic branch, which innervates
the liver parenchyma and vasculature, the biliary tree including the The coeliac plexus is located at the level of the twelfth thoracic and first
gallbladder, and the structures in the free edge of the lesser omentum. lumbar vertebrae, and is the largest major autonomic plexus. It is a
The posterior trunk supplies branches to the coeliac plexus; these fibres dense network that unites the coeliac ganglia, and surrounds the coeliac
frequently constitute the largest portion of the fibres contributing to the artery and the root of the superior mesenteric artery. It is posterior to
plexus. They arise directly from the posterior vagal trunk and from its the stomach and lesser sac, and anterior to the crura of the diaphragm
Sympathetic Parasympathetic
Greater splanchnic nerve (T5–9) Posterior vagal trunk
T12
Lesser splanchnic nerve (T10,11)
Coeliac plexus
T12g
L1
Superior mesenteric plexus
L1g
Intermesenteric plexus
L2
First lumbar sympathetic nerve
L2g Inferior mesenteric plexus
Second lumbar sympathetic nerve
Lumbar splanchnic nerves L3 Superior hypogastric plexus
L3g
Third lumbar sympathetic nerve
L4 Retroperitoneal parasympathetic fibres
Fourth lumbar sympathetic nerve
L4g
Inferior hypogastric nerve
Inferior hypogastric plexus
S1g
Sacral splanchnic nerves
Pelvic splanchnic nerves
S2g
Key
S2
T12g – 12th thoracic sympathetic ganglion S1g – 1st sacral sympathetic ganglion S3g Nervous structures
L1g – 1st lumbar sympathetic ganglion S2g – 2nd sacral sympathetic ganglion S3 Sympathetic fibres
Parasympathetic fibres
L2g – 2nd lumbar sympathetic ganglion S3g – 3rd sacral sympathetic ganglion S4g S4 Ganglion
L3g – 3rd lumbar sympathetic ganglion S4g – 4th sacral sympathetic ganglion Plexus tissue
L4g – 4th lumbar sympathetic ganglion Nerve fibres
Fig . 59 .3 The autonomic plexuses innervating the abdominal and pelvic viscera: schematic diagram . | 1,452 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Fig . 59 .4 The autonomic
Branches of posterior vagal trunk
plexuses of the abdominal
Greater splanchnic nerve
and pelvic viscera .
Lesser splanchnic nerve
Coeliac plexus and ganglia
Middle colic artery Superior mesenteric plexus and ganglion
Left renal vein
First and second lumbar nerves
Intermesenteric plexus
Right colic artery
Inferior mesenteric plexus and ganglion
Left ureter
Third and fourth lumbar nerves
Sigmoid branches of inferior mesenteric artery
Lumbar sympathetic chain Retroperitoneal parasympathetic fibres
External iliac artery
Internal iliac artery
Inferior hypogastric plexus
Inferior hypogastric plexus
Sacral sympathetic chain
Sacral parasympathetic roots
Communication with Fig . 59 .5 Distribution of
phrenic plexus the upper abdominal
autonomic plexuses .
Right coeliac ganglion
Right aorticorenal ganglion Coeliac plexus
Right suprarenal gland
Left greater
splanchnic nerve
Left lesser
splanchnic nerve
Right kidney
Superior
mesenteric
plexus
Left renal plexus
Intermesenteric plexus
Aorta
and the beginning of the abdominal aorta, and lies medial to the supra- Anaesthesia or ablation of these nerves (coeliac plexus block) is some-
renal glands. The plexus and ganglia receive the greater and lesser times undertaken to treat intractable pain from pancreatic disorders.
splanchnic nerves and branches from the vagal trunks. The plexus is in
continuity with small branches along adjacent arteries and is connected Coeliac and aorticorenal ganglia
to the phrenic, splenic, hepatic, superior mesenteric, suprarenal, renal The coeliac ganglia are irregular neural masses, measuring approxi-
and gonadal plexuses (Fig. 59.5). Visceral afferents in the coeliac plexus mately 2 cm across, located between the origin of the coeliac trunk and
convey pain and other sensations from upper abdominal viscera. superior mesenteric artery, medial to the suprarenal glands and anterior | 1,453 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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to the crura of the diaphragm (Zhang et al 2006). They vary in number, internal iliac vessels and the attachments of levator ani and obturator
size, shape and precise location; there are often two, one on each side. internus lie laterally, and the superior vesical and obliterated umbilical
The right ganglion is frequently posterior to the inferior vena cava, and arteries superiorly. In males, the inferior hypogastric plexus lies postero-
the left ganglion often lies posterior to the origin of the splenic artery. laterally on either side of the seminal vesicles, prostate and the base of
The ipsilateral greater splanchnic nerve joins the upper part of each the urinary bladder. In men, the point where the vas (ductus) deferens
ganglion and the lesser splanchnic nerve joins the lower part. The lower- crosses the ureter provides an approximate guide to the upper limit of
most part of each ganglion forms a distinct subdivision, usually termed the plexus (Mauroy et al 2003). The upper border of the plexus lies
the aorticorenal ganglion, which receives the ipsilateral lesser splanch- beneath the peritoneum of the rectovesical pouch and is in contact
nic nerve and gives origin to the majority of the renal plexus (which, with the lateral aspect of the base of the bladder. The anterior border
most commonly, lies anterior to the origin of the renal artery). reaches the posterior aspect of the prostate; at its inferior limit, the
cavernous (deep, cavernosal) nerve passes forwards to reach the postero-
Phrenic plexus lateral aspect of the prostate (see Fig. 75.11). In females, each plexus
The phrenic plexus is a periarterial extension of the coeliac plexus lies lateral to the uterine cervix, vaginal fornix and the posterior part of
around the right inferior phrenic artery, adjacent to the right crus of the the urinary bladder, often extending into the broad ligaments of the
diaphragm (Rusu 2006). It contains one or two phrenic ganglia and a uterus. The upper limit of the plexus corresponds approximately to the
definable nerve trunk that connects the coeliac plexus and phrenic level where the uterine artery crosses the ureter in the base of the broad
nerve. The plexus supplies branches to the suprarenal glands and ligament (Azaïs et al 2013).
diaphragm. The inferior hypogastric plexus is formed mainly from pelvic
splanchnic (parasympathetic) and sacral splanchnic (sympathetic)
Superior mesenteric plexus and ganglion
branches; a smaller contribution is derived from sympathetic fibres
The superior mesenteric plexus lies in the pre-aortic connective tissue (from the lower lumbar ganglia), which descend into the plexus from
posterior to the pancreas, around the origin of the superior mesenteric the superior hypogastric plexus via the hypogastric nerves. It gives origin
artery. It is an inferior continuation of the coeliac plexus, and includes to a complex network of small pelvic branches, which supply the pelvic
branches from the posterior vagal trunk and coeliac plexus. Its branches viscera either directly or indirectly via periarterial plexuses. The branches
accompany the superior mesenteric artery and its divisions. The supe- of the inferior hypogastric plexus supply the vas deferens, seminal vesi-
rior mesenteric ganglion lies superiorly in the plexus, usually above the cles, prostate, accessory glands and penis in males; the ovary, Fallopian
origin of the superior mesenteric artery. tubes, uterus, uterine cervix and vagina in females; and the urinary
bladder and distal ureter in both sexes. The plexus plays a key role in
Intermesenteric plexus
continence and sexual function.
Like other parts of the abdominal aortic autonomic plexus, the interme-
senteric plexus is not a discrete structure but is part of a continuous Hypogastric nerves The hypogastric nerves are usually paired nerve
periarterial nerve plexus connected to the gonadal, inferior mesenteric, bundles but may consist instead of multiple filaments. They contain
iliac and superior hypogastric plexuses. It lies on the lateral and anterior sympathetic fibres (mostly descending from the superior hypogastric
aspects of the aorta, between the origins of the superior and inferior plexus) and parasympathetic fibres (ascending from the inferior
mesenteric arteries, and consists of numerous fine, interconnected nerve hypogastric plexus). The nerves run between the superior and inferior
fibres and a few ganglia continuous superiorly with the superior hypogastric plexuses on each side behind the presacral fascia medial to
mesenteric plexus and inferiorly with the superior hypogastric plexus. the internal iliac vessels and lateral to the anterior sacral foramina.
It is not well characterized but receives parasympathetic and sympa-
thetic branches from the coeliac plexus and additional sympathetic Other autonomic plexuses and ganglia
rami from the first and second lumbar splanchnic nerves. Additional plexuses are described for abdominopelvic viscera, such as
the hepatic and gonadal plexuses. Each tends to lie around the main
Inferior mesenteric plexus
arterial supply to the organ. They receive both sympathetic and para-
The inferior mesenteric plexus lies around the origin of the inferior sympathetic fibres from one or more of the major autonomic plexuses
mesenteric artery and is distributed along its branches. It is formed and have one or more ganglia. Thus, autonomic ganglia supplying the
predominantly from the aortic plexus, supplemented by sympathetic testis are found around the origin of the testicular arteries from the
fibres from the first and second lumbar splanchnic nerves and ascend- abdominal aorta and have connections with the renal, lumbar and
ing pelvic parasympathetic fibres from the inferior hypogastric plexus intermesenteric autonomic plexuses (Motoc et al 2010).
(via the hypogastric nerves and superior hypogastric plexus). Disrup-
tion of the inferior mesenteric plexus alone rarely causes clinically
Para-aortic bodies
significant disturbances of autonomic function.
Superior hypogastric plexus The para-aortic bodies (also known as paraganglia or, collectively, as
The superior hypogastric plexus lies anterior to the aortic bifurcation, the organ of Zuckerkandl) are collections of neural crest-derived chro-
the left common iliac vein, median sacral vessels, fifth lumbar vertebral maffin tissue found in close relation to the aortic autonomic plexuses.
body and sacral promontory, and between the common iliac arteries. They are relatively large in the fetus, reach a maximum size at around
It is occasionally referred to as the presacral nerve, but is seldom a single 3 years of age, and have usually regressed by adulthood. They are most
nerve and is prelumbar rather than presacral. It lies within extraperito- commonly found as a pair of bodies lying anterolateral to the aorta in
neal connective tissue in the midline, extending a little to the left. The the region of the inferior mesenteric and superior hypogastric plexuses,
breadth of the plexus and its constituent nerves varies; appearances but multiple smaller collections may be present. Occasionally, they are
range from a reticular-like arrangement to a band-like structure or one found as high as the coeliac plexus or as low as the inferior hypogastric
or two distinct nerve trunks (Paraskevas et al 2008). The medial attach- plexus in the pelvis, or may be closely applied to the sympathetic
ment of the sigmoid mesocolon and upper limit of the mesorectum lie ganglia of the lumbar chain. Scattered cells that persist into adulthood
anterior to the lower part of the plexus, separated from it by a thin layer may, rarely, be the sites of paraganglioma (extra-adrenal phaeochromo-
of loose connective tissue. The plexus is formed by branches from three cytoma) (Subramanian and Maker 2006).
main sources: the aortic plexus (sympathetic and parasympathetic),
lumbar splanchnic nerves (sympathetic) and pelvic splanchnic nerves
GENERAL ARRANGEMENT OF ABDOMINOPELVIC
(parasympathetic), which ascend from the inferior hypogastric plexus
via the right and left hypogastric nerves. Visceral afferents also pass VASCULAR SUPPLY
through the plexus. The hypogastric nerves lie in loose connective tissue
just posterolateral to the upper mesorectum and pass over the pelvic The major vessels that occupy the abdomen and pelvis not only supply
brim medial to the internal iliac vessels. The superior hypogastric plexus the viscera, retroperitoneal structures and much of the bony and soft
conveys branches to the inferior mesenteric plexus and to the ureteric, tissue walls of both cavities, but also course through the cavities en route
gonadal and common iliac nerve plexuses; additional small branches to supply the lower limbs. The arteries and systemic veins of the
turn abruptly forwards into the upper mesorectum to travel with the abdomen and pelvis lie predominantly posteriorly in the abdomen and
superior rectal artery. posterolaterally in the pelvis. From the caval and aortic openings in the
diaphragm, they follow the general parabolic shape of the lumbar
Inferior hypogastric plexus spine. The pelvic divisions follow the contours of the brim and side
The inferior hypogastric plexus lies in the thin extraperitoneal connec- wall of the true pelvis (Figs 59.6–59.7). The individual parts of the
tive tissue on the pelvic side wall anterolateral to the mesorectum. The aortoiliac and iliocaval systems are described in the relevant chapters. | 1,454 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Fig . 59 .6 The overall arrangement of the aortoiliac arterial
tree of the abdomen and pelvis .
Left inferior
phrenic artery
Coeliac trunk
Right suprarenal Left renal artery
artery
Superior
Abdominal aorta mesenteric artery
Left gonadal artery
Right second, third and fourth
lumbar arteries
Inferior
mesenteric artery
Right common
iliac artery
Right iliolumbar Left internal
artery iliac artery
Right external
iliac artery
Arterial supply to the gastrointestinal tract (Ch. 69). Anastomoses between the territories of the superior and infe-
rior mesenteric arteries are less numerous; the most consistent is the
marginal artery of the colon (Ch. 66).
The arterial supply to the gastrointestinal tract is derived from the ante-
rior midline visceral branches of the aorta. There are usually three
Portal venous system
anterior branches: the coeliac trunk and the superior and inferior
mesenteric arteries. Major variants in the origin of the arteries are
uncommon (Ch. 62). Accessory or replaced branches to the abdominal The (hepatic) portal system, like all portal venous systems, connects two
viscera are more common. The inferior mesenteric artery almost always capillary beds: that of the abdominal and pelvic parts of the gut from
arises separately but replaced, accessory or anastomotic vessels may the abdominal part of the oesophagus to the lower anal canal, together
arise from the proximal superior mesenteric artery or its branches. with all derived organs other than the liver (i.e. the pancreas, gallblad-
Occasionally, these may contribute to the arterial supply of the inferior der and spleen), and the hepatic sinusoidal ‘capillary’ bed. The intra-
mesenteric artery (Horton and Fishman 2002). hepatic portal vein ramifies and ends in the hepatic sinusoids; from
The coeliac trunk and its branches supply the part of the foregut that here, blood drains to central veins that converge to form the hepatic
extends from the distal oesophagus to the mid part of the descending veins which drain into the inferior vena cava (Ch. 67). In adults, the
duodenum, together with associated viscera (liver, biliary tree, spleen, portal vein has no valves. In fetal and early postnatal life, valves are
dorsal pancreas, greater and lesser omenta). The superior mesenteric demonstrable in tributaries of the portal vein but they usually atrophy
artery supplies the midgut, which extends from the mid descending with further maturation.
duodenum to the distal third of the transverse colon (including
Portal vein
jejunum, ileum, caecum, appendix, ascending and transverse colon).
The inferior mesenteric artery supplies the part of the hindgut that The portal vein is formed behind the neck of the pancreas at the level
extends from the distal transverse colon to the upper anal canal. Even of the L1/2 intervertebral disc (in the transpyloric plane) from the
in the absence of accessory arteries, numerous anastomoses exist convergence of the superior mesenteric and splenic veins (Fig. 59.8). It
between these vascular territories. For example, anastomoses around the is approximately 8 cm long in the adult and ascends obliquely to the
head of the pancreas and the duodenum are formed between the ante- right behind the first part of the duodenum, the common bile duct and
rior and posterior superior pancreaticoduodenal arteries and the ante- gastroduodenal artery; at this point, it is directly anterior to the inferior
rior and posterior inferior pancreaticoduodenal arteries, and between vena cava. It enters the right border of the lesser omentum and ascends
the posterior superior pancreaticoduodenal artery and jejunal arteries anterior to the epiploic foramen to reach the right end of the porta | 1,455 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Fig . 59 .7 The overall arrangement of the iliocaval venous
system of the abdomen and pelvis .
Inferior
vena cava
Hemiazygos vein
Left suprarenal vein
Right subcostal
Left renal vein
vein
Left gonadal vein
Right first
lumbar vein
Left lumbar veins
Right ascending
lumbar vein
Right
gonadal vein
Right iliolumbar
Left internal
vein
iliac vein
Right common
iliac vein Left external iliac vein
hepatis, where it divides into right and left main branches, which the hindgut traverses the pelvic floor; in these sites, the gut tube is sur-
accompany the corresponding branches of the hepatic artery into the rounded by a connective tissue adventitia. Neural elements invade the
liver. In the lesser omentum, the portal vein lies posterior to both the gut from neural crest tissue (Ch. 17). The smooth muscle of the mus-
common bile duct and the hepatic artery. It is surrounded by the hepatic cularis externa layers of the alimentary canal is supplemented with
nerve plexus and accompanied by lymphatics and some lymph nodes. striated muscle at the beginning (from the branchial arches) and end
of the gut tube.
Tributaries of the portal vein The mature gut wall has four main layers: mucosa, submucosa,
The main extrahepatic tributaries of the portal vein are the left gastric muscularis externa and serosa (Fig. 59.9). The mucosa (mucous mem-
(coronary) vein and the posterior superior pancreaticoduodenal vein brane) is the innermost layer and is subdivided into a lining epithelium,
(Ch. 67). Within the liver, the left branch receives the obliterated an underlying lamina propria (a layer of loose connective tissue, where
umbilical vein via the ligamentum teres, which connects to its vertical many of the glands are also found) and a thin layer of smooth muscle,
portion. the muscularis mucosae. The submucosa is a strong and highly vascular-
ized layer of connective tissue. The muscularis externa consists of inner
circular and outer longitudinal layers of smooth muscle; an incomplete
GENERAL MICROSTRUCTURE OF THE GUT WALL
oblique muscle layer is present only in the stomach. The external
surface is bounded by a serosa or adventitia, depending on its position
The gut wall displays a common structural plan that is modified region- within the body.
ally to take account of local functional differences. The general micro-
structure is best appreciated by reference to the development of the gut
Mucosa
(Ch. 60). Much of the alimentary canal originates as a tube of endo-
derm enclosed in splanchnopleuric mesoderm. Its external surface faces
the embryonic coelom, and the endodermal lining forms the epithe- Epithelium
lium of the canal and also the secretory and ductal cells of various The epithelium is the site of secretion and absorption, and provides a
glands that secrete into the lumen, including the pancreas and liver. The defence against various threats, including microorganisms. Its protec-
splanchnopleuric mesoderm forms the connective tissue, muscle layers, tive function against mechanical, thermal and chemical injury is par-
blood vessels and lymphatics of the wall, and its external surface ticularly evident in the oesophagus and anal canal, where it is thick,
becomes the visceral mesothelium or serosa. There is no serosa sur- stratified and covered in mucus, which serves as a protective lubricant.
rounding the cervical and thoracic portions of the gut, or below where At other sites, the epithelium lining the gut wall is single-layered, and | 1,456 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Fig . 59 .8 The overall arrangement of the portal
venous system draining the abdominal viscera .
Inferior
vena cava Short gastric veins
Portal vein
Splenic vein
Pancreatico-
Left gastroepiploic vein
duodenal veins
Superior
mesenteric vein
Inferior mesenteric vein
Middle colic vein
Left colic vein
Marginal colic veins
Ileocolic vein
Sigmoid veins
Superior rectal vein
either cuboidal (in glands) or columnar. It contains cells modified for mucosae are found inside the villi or between the tubular glands of the
absorption, as well as various types of secretory cell. stomach and large intestine. By its contraction, the muscularis mucosae
The barrier function and selectivity of absorption depend on tight can alter the surface configuration of the mucosa locally, allowing it to
junctions over the entire epithelium. The surface area of the lumen adapt to the shapes and mechanical forces imposed by the contents of
available for secretion or absorption is increased by the presence of the lumen, and in the intestinal villi, promoting vascular exchange and
mucosal folds, crypts, villi and glands (see Fig. 59.9). Microvilli on the lymphatic drainage.
surfaces of individual absorptive cells amplify the area of apical plasma
membrane in contact with the contents of the gut. Some glands lie in Submucosa
the lamina propria and some in the submucosa; others (the liver and
pancreas) are totally external to the wall of the gut. All of these glands
The submucosa contains large bundles of collagen and is the strongest
drain into the lumen of the gut through individual ducts. The epithe-
layer of the gut wall. However, it is also pliable and deformable, and
lium also contains scattered neuroendocrine (enteroendocrine) cells.
can therefore adjust to changes in the length and diameter of the gut.
Lamina propria Its contained arterial network is relatively dense and supplies both the
mucosa and the muscle coat. The submucosa extends into the rugae of
The lamina propria consists of compact connective tissue, often rich in
the gastric wall, the plicae circulares of the small intestine (but not the
elastin fibres, which supports the surface epithelium and contains nutri-
villi), and the folds that project into the lumen of the colon and rectum.
ent vessels and lymphatics. Lymphoid follicles are present in many
regions of the gut, most notably in Peyer’s patches. Cells within the
Muscularis externa
lamina propria are the source of growth factors that regulate cell turn-
over, differentiation and repair in the overlying epithelium.
The muscularis externa usually consists of distinct inner circular and
Muscularis mucosae outer longitudinal layers that create waves of peristalsis responsible for
The muscularis mucosae is particularly well developed in the oesopha- the movement of ingested material through the lumen of the gut. In
gus and in the large intestine, especially in the terminal part of the the stomach, where movements are more complex, there is an incom-
rectum. In addition, single muscle cells originating from the muscularis plete oblique layer of muscle, internal to the other two layers. The | 1,457 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Layers of the gut wall
A. Mucosa
B. Submucosa
C. Muscularis externa
D. Serosa
Epithelium
A
Lamina propria
Muscularis
mucosae
B Submucosa
Inner Colon
circular
layer
Ileum
C
Jejunum
Outer
longitudinal Duodenum
layer
Stomach
Secretions
Oesophagus of liver and
D Serosa pancreas
Fig . 59 .9 The general arrangement of the alimentary canal to show the layers of the gut wall at the levels indicated .
circular muscle layer is invariably thicker than the longitudinal muscle, stomach, or partitions them, as occurs at the pyloric sphincter. The
except in the colon, where the longitudinal muscle is condensed into muscle maintains a constant volume, so that shortening of a segment
three cords (taenia coli). of the gut wall is accompanied by an increase in thickness of the
The muscularis externa is composed almost exclusively of smooth muscle layer.
muscle, except in the upper oesophagus, where smooth muscle blends Intestinal smooth muscle exhibits variable and changing degrees of
with striated muscle. Although the upper oesophageal musculature contraction on which rhythmic (or phasic) contractions are superim-
resembles that of the pharynx, it is entirely under involuntary control. posed. Slow waves of rhythmic electrical activity, driven by changes in
For most of its length, the smooth muscle of the gut wall consists of membrane potentials in pacemaker cells (interstitial cells), spread
ill-defined bundles of cells, typically visceral in type, and somewhat throughout the thickness of the circular and longitudinal smooth
larger than vascular smooth muscle cells. They are approximately muscle coats. After spreading circumferentially, slow waves can move
500 µm long, regardless of body size, and are electrically and mechani- in either oral or anal directions, causing segmental contraction. The
cally coupled. Their fasciculi lack a perimysium but have sharp distances of propagation and the patterns of this spontaneous activity
boundaries. vary between areas of the intestine. Neural regulation of slow and
The arrangement of the musculature allows a segment of gut to phasic contractions involves excitatory and inhibitory transmitters that
undergo extensive changes in diameter (to virtual occlusion of the are released from the myenteric plexus. This motor control is closely
lumen) and length, although elongation is limited by the presence of coordinated with mucosal absorption and secretion, and is mediated
mesenteries. The coordinated activity of the two muscle layers pro- via intrinsic nerves in the submucous plexus. The peristaltic reflex
duces a characteristic motor behaviour that is mainly propulsive and occurs during passage of luminal contents down the intestine. It
directed aborally (peristalsis), combined with a non-propulsive motor involves ascending contraction and descending relaxation; the sensory
activity that either mixes the luminal contents, as occurs in the limb is mediated by sensory neurones that respond to either mucosal | 1,458 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
General microstructure of the gut wall
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stimulation (intrinsic primary afferents) or muscle stretch (extrinsic The latter is not essential for function, as evidenced by intestinal activity
afferents). after transplantation of the extrinsically denervated gut. In contrast,
neuropathies affecting the enteric nervous system, such as Hirsch-
Interstitial cells
sprung’s disease, are potentially life-threatening. For a detailed descrip-
Interstitial cells of Cajal (ICCs) are found throughout the entire length tion of the enteric nervous system, see Furness et al (2014).
of the gastrointestinal tract, where they lie in close contact with nerve
terminals; they have numerous gap junctions with each other and with Extrinsic innervation
smooth muscle cells. Distinct networks are found in the myenteric
Extrinsic innervation of the gut is from sympathetic, parasympathetic
plexus between the circular and longitudinal muscle. Looser arrange-
and visceral sensory nerves. The cell bodies of preganglionic parasym-
ments exist within the individual muscle layers and the submucosa of
pathetic efferent axons are found in the vagal dorsal motor nucleus in
the gut, and isolated or small groups of ICCs are also found in the
the medulla oblongata and in the sacral segments of the spinal cord.
subserosal region. ICCs originate from mesenchymal cells and resemble
Their main target in the gut is the enteric neurones of the myenteric
smooth muscle cells but have fewer contractile elements and their
plexus. Vagal efferents play a major role in oesophageal propulsion,
intermediate filaments contain vimentin rather than desmin. They are
gastric acid secretion and emptying, gallbladder contraction and pan-
involved in the generation of pacemaker signals, the propagation of
creatic exocrine secretion. Pelvic efferents innervate the distal colon and
electrical slow wave activity, neuromuscular transmission, and mech-
rectum. Sympathetic efferent neurones have their cell bodies in the
anosensation (p. 1135) (Sanders et al 2014). Defective ICC function has
intermediolateral grey matter (lamina VII) of the thoracolumbar seg-
been implicated in a wide range of gastrointestinal motility disorders
ments of the spinal cord; those destined for the smooth muscle of the
(Al-Shboul 2013), and in the development of gastrointestinal stromal
gut mostly pass through the sympathetic chain without synapsing and
tumours (Roggin and Posner 2012).
relay in prevertebral ganglia (coeliac, mesenteric and pelvic), whereas
Cells with a similar morphology have been found in association
those mediating vasoconstriction synapse in the sympathetic chain or
with smooth muscle at many other sites, such as the urethra, ductus
prevertebral ganglia. Postganglionic sympathetic fibres are distributed
deferens, prostate, bladder, corpus cavernosum, ureter, uterine tube, and
with the branches of the coeliac trunk and mesenteric arteries to three
uterus. They may act as electrical pacemakers in the urethra and ureter
principal targets: the myenteric and submucosal ganglia (causing inhi-
but their role at other sites is less certain (Drumm et al 2014).
bition), blood vessels (inducing vasoconstriction) and sphincter muscle
(inducing contraction).
Serosa and adventitia
Visceral sensory endings are distributed throughout the layers of the
gut wall. They respond to various stimuli, including excessive muscular
A layer of connective tissue, of variable thickness, lies external to the contraction or distension, ischaemia and inflammation; their cell
muscularis externa. In many places, it contains adipose tissue. Where bodies are located in the nodose ganglion of the vagus nerve (vagal
the gut is covered by visceral peritoneum, the external layer is a serosa, afferents) and in thoracic and lumbosacral dorsal root ganglia (visceral
consisting of mesothelium overlying a thin layer of connective tissue. afferents, which run with sympathetic efferents). Their central projec-
In extraperitoneal regions, the surfaces of the gut in contact with the tions reach the brainstem and spinal cord, respectively. Vagal afferents
peritoneum are covered by serosa, while other parts are covered by con- are more numerous in the foregut than the midgut and are concerned
nective tissue that blends with the surrounding fasciae and is referred with physiological responses such as satiety, whereas pain and discom-
to as an adventitia. fort are mediated by spinal pathways.
Vascular plexuses Intrinsic innervation
The intrinsic innervation of the gut is derived from enteric neurones
Vascular plexuses are present at various levels of the wall, especially in distributed throughout its wall in thousands of small ganglia, each
the submucosa and mucosa; they connect with vessels that supply the consisting of neuronal cell bodies supported by enteric glial cells; it is
surrounding tissues or those entering through the mesentery, and estimated that there are between 200 and 600 million neurones in the
accompany the ducts of outlying glands. human enteric nervous system. Enteric neurones are derived from
neural crest cells. The enteric nervous system innervates the gut from
Innervation
oesophagus to anus, together with the pancreas and biliary tree.
The majority of enteric neurones in the wall of the gut are found in
The gut wall is densely innervated by both the enteric nervous system two ganglionated plexuses (Fig. 59.10). The most extensive of these is
(intrinsic control) and the autonomic nervous system (extrinsic control). the myenteric (Auerbach’s) plexus, which consists of a network of nerve
Myenteric plexus
Circular muscle
Longitudinal muscle Deep muscular plexus
Inner SMP
Outer SMP
Submucosal artery
Mucosa
Muscularis mucosae
Fig . 59 .10 The organization of the enteric nervous system in the human small intestine . There are two ganglionated plexuses: the myenteric plexus
between the longitudinal and circular layers of the external musculature, and the submucosal plexus (SMP), which has outer and inner components .
Nerve fibre bundles connect the ganglia and form plexuses innervating the longitudinal muscle, circular muscle, muscularis mucosae, intrinsic arteries
and the mucosa . Axons of extrinsic origin also run in these nerve fibre bundles . There are also innervations of gastroenteropancreatic (GEP) endocrine
cells and gut-associated lymphoid tissue (GALT), which are not shown here . (Redrawn with permission from Furness JB . The enteric nervous system and
neurogastroenterology . Nat Rev Gastroenterol Hepatol 2012;9:286–294 . Reprinted with permission from Nature Publishing Group .) | 1,459 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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fibres and small ganglia lying between the circular and longitudinal mesenteric and splenic veins behind the neck of the pancreas); the
layers of the muscularis externa. It runs in continuity from the oesopha- hilum of the left kidney (the hilum of the right kidney is slightly lower);
gus to the anus. The submucosal (Meissner’s) plexus has outer and the origin of the renal arteries; the level of the duodenojejunal flexure
inner components, and is present throughout the intestine but absent (Mirjalili 2012b); and the termination of the spinal cord. The pylorus
or minimal in the oesophagus and stomach. may be found in the transpyloric plane but is not a constant feature.
Interconnecting, non-ganglionated nerve plexuses lie at various The subcostal plane is defined by a line that joins the lowest point
levels in the wall of the gut, including the lamina propria (mucosal of the costal margin on each side (usually, the tenth costal cartilage); it
plexus), at the interface between the submucosa and muscularis externa, is most commonly at the level of the second lumbar vertebra (range
between the circular and longitudinal muscles (the non-ganglionated T12/L1 disc to upper L3) (Mirjalili et al 2012a).
part of the myenteric plexus), and within the serosa. The supracristal plane joins the highest point of the iliac crest on
Individual enteric neurones function in one of several ways: as affer- each side. It serves as a useful landmark when performing a lumbar
ent (sensory) nerves responding to mechanical and chemical stimuli; puncture or spinal injection, and usually lies at the level of the L4 body
as efferent (motor) nerves innervating epithelial cells (influencing or L4/5 disc and its spinous process (see Fig. 78.16). The bifurcation of
absorption, secretion and/or the release of hormones), smooth muscle the abdominal aorta lies approximately in this plane (Mirjalili et al
(excitatory or inhibitory), arterioles (vasoconstriction or vasodilation) 2012a).
and lymphoid tissue; or as interneurones that relay and integrate The transtubercular plane joins the tubercles of the iliac crests and
signals. Collectively, they are involved in a hierarchy of enteric reflexes is traditionally reported to lie at the level of the body of L5, near its
that include local reflexes within the gut wall; reflexes mediated through upper border. It is an approximate landmark for the origin of the infe-
prevertebral sympathetic ganglia; and reflexes mediated through the rior vena cava from the confluence of the common iliac veins.
central nervous system (the gut–brain axis). The functions of enteric The plane of the pubic crest is in line with the upper border of the
neurones may be further modulated by local environmental factors, e.g. pubic symphysis. In supine individuals, this plane frequently intersects
enteric glia, gut microbiota and feeding state, and by general factors in the tip of the coccyx and the femoral head (Mirjalili et al 2012a), but
the host, e.g. the immune system, stress and disease (Brierley and there are variations relating to the degree of lumbar lordosis, sacral
Linden 2014). Pathological states become manifest by abnormal secre- inclination and pelvic tilt.
tion, impaired absorption, disordered gastrointestinal motility and
Abdominal regions
pain.
The abdomen can be divided into nine regions using the subcostal,
transtubercular and two paramedian planes (Fig. 59.11A). These regions
SURFACE ANATOMY OF THE ABDOMEN are used in clinical practice for descriptive localization of a patient’s
AND PELVIS pain or tenderness, or the position of a mass, and can be used to refer-
ence the position of abdominal viscera. From superior to inferior, the
ABDOMINAL PLANES AND REGIONS nine regions are: the epigastrium, flanked by the right and left hypo-
chondrium; the umbilical, or central, flanked by the right and left
lumbar; and the suprapubic or hypogastrium, flanked by the right and
For descriptive purposes, the abdomen can be divided into regions
left iliac fossae. In practice, these regions are often loosely defined
using a combination of horizontal and vertical planes that are based
without strict reference to their boundaries. An alternative system of
on skeletal landmarks. Published descriptions of surface anatomy
description involves dividing the abdomen into quadrants using the
largely apply to adults, in whom attempts have been made to validate
median plane and a horizontal line passing through the umbilicus.
or update standard descriptions using cross-sectional imaging. The
extent to which many of these surface projections can be extrapolated
to children is uncertain; some differences are inevitable, particularly in ANTERIOR ABDOMINAL WALL
infants, given their different visceral and body proportions (Stringer
2011). In this chapter, descriptions of the surface projections of abdomi-
Skeletal landmarks
nal structures refer to the most commonly encountered arrangement
The superior boundary of the anterior abdominal wall is formed by
seen in adults. However, it is important to note that there is consider-
several clear landmarks (Fig. 59.11B). The xiphoid process is palpable
able individual variation in surface anatomy, compounded further by
at the inferior sternum, in the midline. From here, the costal margins
potential variations related to age, sex, posture, respiration, body mass
can be felt passing inferolaterally from the seventh costal cartilage at the
and ethnicity (Mirjalili and Stringer 2012).
xiphisternal joint to the tip of the twelfth rib (the latter is often difficult
Vertical lines and planes to feel in the obese or if it is short). The lower border of the ninth costal
The midline (or median plane) passes through the xiphoid process and cartilage can usually be defined as a distinct ‘step’ along the costal
the pubic symphysis. There are two paramedian lines, left and right, margin. The lowest part of the costal margin lies in the mid-axillary line
that extend from the mid-clavicular point to the mid-inguinal point, a and is formed by the inferior margin of the tenth costal cartilage.
point midway between the anterior superior iliac spine and the pubic The inferior boundary of the anterior abdominal wall is formed,
symphysis (Fig. 59.11A); this line crosses the costal margin just lateral from lateral to medial, by the iliac crest, which descends to the anterior
to the tip of the ninth costal cartilage. In the upper abdomen, it approxi- superior iliac spine; the inguinal ligament, which runs obliquely down-
mates to the lateral border of rectus abdominis. wards to the pubic tubercle; and the pubic crest, which extends from
the pubic tubercle laterally to the pubic symphysis in the midline. The
Horizontal lines and planes
pubic tubercle is palpable on the anterosuperior surface of the pubic
Several horizontal reference planes have been defined but, with modern bone approximately 2 cm lateral to the midline. The prominent tendon
cross-sectional imaging, their clinical utility for positioning abdominal of adductor longus (best felt with the hip flexed, abducted and exter-
viscera has become limited. Nevertheless, they help to conceptualize nally rotated) attaches to the pubis directly below the pubic tubercle,
the relative positions of abdominal viscera with respect to vertebral and can therefore be used to verify its position.
levels and bony surface landmarks. The posterolateral boundary of the anterior abdominal wall is the
The xiphisternal joint most often lies in the same horizontal (axial) mid-axillary line.
plane as the T9 vertebra (Mirjalili et al 2012b).
Soft tissue landmarks
The transpyloric plane lies midway between the suprasternal notch
of the manubrium and the upper border of the pubic symphysis. This umbilicus
corresponds to a plane that is approximately midway between the The umbilicus is an obvious but inconstant landmark. In the supine
xiphisternal joint and the umbilicus, or slightly below (Mirjalili et al adult, it usually lies around the L4 level (range L2/3 disc to upper S1)
2012a). Posteriorly, the plane intersects the lower half of the body of (Mirjalili et al 2012b). The umbilicus may lie at a lower level in the
the first lumbar vertebra, the L1/2 intervertebral disc, or the upper half erect position, and in children, the obese and in individuals with a
of the body of the second lumbar vertebra in most individuals (range pendulous abdomen.
lower T12 to lower L2); it sits higher in males (lower L1–L1/2) than
females (lower L2) (Mirjalili et al 2012a). Anteriorly, it intersects the rectus abdominis
costal margin at the ninth costal cartilage, where the linea semilunaris In a thin, muscular individual, the tendinous intersections of rectus
crosses, and where a distinct ‘step’ may be palpable in the rib margin. abdominis may be visible, especially when the muscle is tensed by
The following structures lie approximately within the transpyloric plane lifting the head against resistance or by sitting up; the intersections are
(Mirjalili et al 2012a, 2012b): the origin of the superior mesenteric usually situated at the level of the umbilicus, the level of the xiphoid
artery; the origin of the portal vein (from the confluence of the superior process and midway between these two points (Fig. 59.11B). | 1,460 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Surface anatomy of the abdomen and pelvis
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A B
10 10
1 2 3
1 2 3 4 D1
5
D2 D4
6
11
D3
7
4 5 6
8
9
10
12
7 8 9
C
T11
T12
1
L1
L2
L3
2 L4
L5
Fig . 59 .11 A, Nine regions of the anterior abdominal wall . Key: 1, right hypochondrium; 2, epigastrium; 3, left hypochondrium; 4, right lumbar; 5,
umbilical/central; 6, left lumbar; 7, right iliac fossa; 8, suprapubic/hypogastrium; 9, left iliac fossa; 10, paramedian line; 11, subcostal plane; 12,
transtubercular plane . B, The surface projection of the abdominal viscera . Key: 1, diaphragm position: right dome level with fifth intercostal space and
left dome with sixth rib; 2, liver: mapped between three points: right fifth rib/intercostal space mid-clavicular line, left fifth intercostal space/sixth rib
mid-clavicular line and right tenth costal cartilage mid-axillary line; 3, zone of gastro-oesophageal junction position (white): mainly located posterior to left
seventh costal cartilage, at approximately T11; 4, transpyloric plane; 5, zone of gallbladder fundus position (white); 6, duodenum: four parts marked
D1–D4; 7, linea semilunaris; 8, position of small intestine mesentery; 9, linea alba; 10, tendinous intersection of rectus abdominis . C, The surface position
of the spleen and kidneys . Key: 1, spleen; sits deep to ribs 10–12 with long axis aligned with rib 11; 2, supracristal plane . (C, Derived with permission
from Mirjalili SA, McFadden SL, Buckenham T, Stringer MD . 2012b A reappraisal of adult abdominal surface anatomy . Clin Anat 25:844–50 .)
linea alba Inferior epigastric artery
The linea alba is usually only visible in thin, muscular individuals. It is The inferior epigastric artery lies along the medial border of the deep
wider and more obvious above the umbilicus, and is almost linear and inguinal ring immediately above the inguinal ligament. Up to the level
less visible below this level (Ch. 61) (Fig. 59.11B; see Fig. 61.2). of the umbilicus, it follows a course that lies approximately 40% of the
distance between the midline and a sagittal plane running through the
linea semilunaris anterior superior iliac spine (Epstein et al 2004). The surface anatomy
The linea semilunaris lies along the lateral margin of the rectus sheath of the artery is particularly important in laparoscopic surgery because
and is visible as a shallow, curved groove in muscular individuals, par- trocar insertion may injure the vessel, causing a rectus sheath hae-
ticularly when the abdominal muscles are tensed, e.g. by sitting up from matoma or intra-abdominal bleeding. The artery can be avoided if a
the lying position (Fig. 59.11B). It passes from the ninth costal cartilage trocar is inserted at least two-thirds of the distance along a horizontal
to the pubic tubercle. line between the midline and a sagittal plane passing through the ante-
rior superior iliac spine.
mid-inguinal point
Superficial reflexes
The mid-inguinal point lies at the midpoint of a line between the pubic
symphysis and the anterior superior iliac spine. In adults, it is the Cremasteric reflex
approximate surface marking of the femoral artery (just below the liga- Stroking the skin of the medial side of the thigh evokes a reflex con-
ment) and the deep inguinal ring (just above the ligament) (Hale et al traction of cremaster, which elevates the ipsilateral testis. The reflex is
2010). mediated by the genitofemoral nerve (L1 and L2 nerve roots), although | 1,461 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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the afferent arc of the reflex may be via sensory fibres in the ilioinguinal line to the left fifth intercostal space/sixth rib in the mid-clavicular line,
nerve. The reflex is usually absent if there is torsion of the testicle. and can be mapped with the contour of the diaphragm (Mirjalili et al
2012c). This border curves slightly downwards at its centre and crosses
Superficial abdominal reflex the midline behind the xiphisternal joint. The right border of the liver
Gently stroking each of the four quadrants of the anterior abdominal is curved to the right and joins the upper and lower right limits. The
wall normally elicits a visible contraction of ipsilateral abdominal upper border of the liver may be defined by dullness to percussion when
muscles. The reflex can be used to help localize lesions in the spinal compared with the resonance of the lungs above.
cord but is now of minor clinical significance because of the availability
of neuroimaging and the difficulties of eliciting the reflex in multipa- Gallbladder
rous women, the elderly and the obese (Gosavi and Lo 2014). The fundus of the gallbladder is commonly identified with the tip of
the ninth costal cartilage (in the transpyloric plane), near the junction
of the linea semilunaris with the costal margin (see Fig. 59.11B). Recent
INTRA-ABDOMINAL VISCERA
data have shown that the fundus lies in the transpyloric plane in
approximately one-third of supine individuals and below the plane in
The surface markings of the intra-abdominal viscera are variable and most others (Mirjalili et al 2012b).
depend on age, sex, body habitus, nutritional state, phase of ventilation
and body position. The availability of cross-sectional and ultrasound Spleen
medical imaging of the abdominal viscera has led to a decline in the use The spleen is traditionally described as sitting on the left posterolateral
of surface anatomy, except for descriptive purposes. The following abdominal wall deep to ribs 9–11. Recent data show that the spleen sits
descriptions are, at best, regarded as the most common or approximate deep to ribs 10–12 in 50% of subjects and deep to ribs 9–11 in 25% of
markings in a healthy supine adult (Fig. 59.11B,C). The spinous proc- supine individuals; its long axis corresponds most closely to the elev-
esses of the lumbar vertebrae can be used to locate vertebral levels, with enth rib or tenth rib, respectively, and passes anterior to the mid-axillary
the lower part of the spinous process marking the level of the interverte- line in most subjects (Mirjalili et al 2012b) (see Fig. 59.11C). The spleen
bral disc below the correspondingly numbered vertebra. extends from a point about 5 cm to the left of the posterior midline at
the level of the eleventh thoracic spine and extends about 3 cm anterior
Diaphragm
to the mid-axillary line. Its normal size approximates roughly to that
In the supine position at end-tidal inspiration, the dome of the dia-
of the individual’s clenched fist.
phragm is most frequently located level with the fifth intercostal space
in the mid-clavicular line on the right and the sixth rib in the mid-
clavicular line on the left, and ranges from the fourth intercostal space RETROPERITONEAL VISCERA
to below the costal margin (Mirjalili et al 2012c) (see Fig. 59.11B) (see
Ch. 55 for further discussion of the diaphragm). These levels are
The surface projections of the retroperitoneal viscera are reasonably
approximate, not only because of individual variation but also because
reliable but have limited clinical utility since most interventions and
diaphragmatic excursion in the erect position during quiet breathing is
procedures are guided by medical imaging.
about 2 cm and increases to about 7 cm during deep breathing (Bous-
suges et al 2009). The dome of the diaphragm can reach as high as the Pancreas
fourth rib on maximal expiration.
The surface projection of the head of the pancreas lies within the duo-
Stomach denal curve on the right side of the second lumbar vertebra; the neck
lies in the transpyloric plane, level with the L1/2 intervertebral disc; and
The gastro-oesophageal junction lies to the left of the midline, posterior
the body passes obliquely up and to the left towards the spleen, lying
to the left seventh costal cartilage, at the level of the eleventh thoracic
slightly above the transpyloric plane, near the tail.
vertebra (range upper T10 to L1/2), with the level being lower in females
and higher in the obese (Mirjalili et al 2012b) (see Fig. 59.11B). The
Kidney
stomach lies in a curve within the left hypochondrium and epigastrium,
The right kidney usually lies, on average, 2 cm lower than the left,
although, when distended, it may lie as far down as the umbilical or
although, in 10% of cases, the left kidney sits lower than the right
suprapubic regions. The epigastrium is the usual place to auscultate for
(Mirjalili et al 2012b). The vertebral limits of the left kidney are T12–
a ‘succussion splash’ caused by gastric outlet obstruction or stasis, and
L3 or L4, while those for the right kidney are L1–L4 (overall range
is also the region where a thickened pylorus is palpable in infantile
upper T11 to lower L5) (see Fig. 59.11C). The upper poles of both
hypertrophic pyloric stenosis.
kidneys lie anterior to rib 12, and they lie anterior to the rib 11 in 30%
Duodenum (left) and 10% (right) of subjects. In supine adults at end-tidal inspira-
The first part of the duodenum sometimes ascends above the transpy- tion, the centre of the renal hilum usually lies at L1/2 or L2 on the left
loric plane; the second part usually lies just to the right of the midline, and at a slightly lower vertebral level on the right. It is important to
alongside the second and third lumbar vertebrae; the third part usually note that both kidneys move vertically by a mean of about 2 cm during
crosses the midline at the level of the third lumbar vertebra; and the deep respiration and both can descend by several centimetres when
fourth part ascends to the left of the second lumbar vertebra, reaching moving from lying to standing (Schwartz et al 1994, Reiff et al 1999).
the transpyloric plane in the region of the lower border of the first The length of the normal adult kidney, measured along its long axis,
lumbar vertebra (see Fig. 59.11B). The duodenojejunal flexure com- is approximately 11.5 cm in men and 11.0 cm in women (Hale et al
monly sits at L1 (range lower T11 to upper L3) (Mirjalili et al 2012b). 2010); the left kidney is a few millimetres longer than the right (Cheong
et al 2007, Glodny et al 2009, Mirjalili et al 2012b). There is a small
Small intestine and its mesentery reduction in renal length beyond 50 years of age (Glodny et al 2009).
The small intestine mesentery runs obliquely in a line from a point just Each kidney is approximately 5–6 cm wide. Both its longitudinal and
to the left of the lower border of the first lumbar vertebra (in the transverse axes are slightly oblique, such that the upper pole of each
transpyloric plane) towards the right iliac fossa. kidney is nearer the midline and the hilum is more anterior than the
lateral surface. The centre of the hilum is approximately 5–6 cm from
Appendix
the midline.
The appendix is located in the right lower quadrant of the abdomen The lower pole of the normal right kidney may occasionally be felt
but is highly variable in its length and position. Studies analysing in thin individuals by bimanual palpation via the renal angle on full
barium enemas in supine adults have shown the position of appendix inspiration.
base is variably located and rarely precisely at McBurney’s point (a point
two-thirds of the way along a line joining the anterior superior iliac Ureter
spine to the umbilicus) (Ramsden et al 1993, Naraynsingh et al 2002). The ureter descends on either side from approximately the level of the
transpyloric plane, slightly lower on the right, about 5 cm from the
Liver
midline. Each passes downwards just medial to the tips of the transverse
At the end of normal tidal inspiration, the inferior border of the liver processes of the lumbar vertebrae. In the pelvic cavity, each ureter curves
extends along a line that passes from the right tenth costal cartilage in medially to enter the base of the bladder.
the mid-axillary line to the left fifth intercostal space/sixth rib in the
mid-clavicular line (see Fig. 59.11B). It may be palpable in healthy adults Abdominal aorta and branches
on deep inspiration. The superior border of the liver follows a line that The abdominal aorta begins at the level of the body of the twelfth
passes from the right fifth rib or intercostal space in the mid-clavicular thoracic vertebra near the midline. It descends and bifurcates at | 1,462 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Key references
approximately L4 (range lower L3 to lower L5), usually just to the left allows access to the peritoneum at a point where there is relatively little
of the midline and up to 3 cm caudal to the umbilicus (Mirjalili et al extraperitoneal fat. Additional working ports are inserted through the
2012b). The position of the aortic bifurcation is shifted slightly proxi- anterior abdominal wall, avoiding major vessels such as the inferior
mally with a greater degree of lumbar lordosis (Moussallem et al 2012). epigastric artery.
The pulsations of the aorta can be felt in a thin, supine individual by
Surgical incisions
pressing firmly in the midline backwards on to the lower lumbar spine.
An easily palpable aorta in an obese person should raise the suspicion Most surgical incisions are sited according to surgical imperatives rather
of an aneurysm. than anatomical constraints. Access to the peritoneal cavity is gained by
dividing or splitting muscles. Common approaches include the midline
unpaired visceral arteries incision through the relatively avascular linea alba, the transverse
The coeliac trunk arises from the aorta immediately after it enters the suprapubic (Pfannenstiel) incision for pelvic procedures, and, in infants
abdomen at T12; the superior mesenteric artery arises most commonly and children, the upper abdominal transverse incision. In recent years,
at L1, close to the transpyloric plane; and the inferior mesenteric artery progressively more abdominal surgery has been performed using
usually arises at L3 (Mirjalili et al 2012b). laparo scopic procedures (minimally invasive or ‘keyhole’ surgery).
renal arteries Intestinal stomas (ileostomy, colostomy)
The renal arteries most commonly arise from between lower L1 and When possible, intestinal stomas are usually formed through transrec-
upper L2, with the lower border of L1 (approximately, the transpyloric tus incisions. A cruciate incision is made in the anterior rectus sheath
plane) being most common on both sides (Mirjalili et al 2012b). and the muscle fibres are split, avoiding injury to the epigastric vessels.
This incision offers the advantage that fibres of rectus abdominis
Iliac arteries
support the stoma, providing a dynamic, contractile surround that
The surface projection of the common iliac artery corresponds to the tends to reduce the risk of herniation occurring around the stoma.
superior third of a broad line, which is slightly convex laterally, from
the aortic bifurcation (see above) to a point midway between the ante- Suprapubic catheterization
rior superior iliac spine and the pubic symphysis. The external iliac The urinary bladder may be accessed for short- or long-term catheteriza-
artery corresponds to the inferior two-thirds of this line. tion through the anterior abdominal wall. As the bladder fills, the upper
Inferior vena cava part of its dome comes to lie in the preperitoneal ‘space’ in the suprapu-
bic region, where it can be relatively easily accessed by a midline trans-
The inferior vena cava most commonly forms at L5 in the transtuber-
cutaneous puncture through the linea alba.
cular plane (range upper L4 to upper S1) approximately to the right of
the midline (Mirjalili et al 2012b). The inferior vena cava leaves the Endoscopic surgery
abdomen by traversing the diaphragm at the level of the eleventh tho-
Endoscopic surgery is a broad term that encompasses all types of
racic vertebra.
surgery that are performed using flexible or rigid fibreoptic endoscopes
inserted through natural body orifices or small surgical incisions. It
PELVIS overlaps with the field of minimally invasive surgery. The aim is to
minimize or eliminate external incisions and hasten the patient’s
The posterior superior iliac spines lie at the level of the second sacral recovery, whilst providing optimum treatment of the pathology with
segment (McGaugh et al 2007); some individuals have an overlying an acceptably low risk of complications. In the abdomen and pelvis,
sacral dimple. This palpable bony landmark corresponds approximately therefore, it includes therapeutic procedures performed using an endo-
to the termination of the dural sac (Senoglu et al 2013) and the middle scope inserted via the mouth (gastroscope or duodenoscope), anus
of the sacroiliac joint. The second dorsal sacral foramina lies approxi- (proctoscope, sigmoidoscope or colonoscope), urethra (cystoscope or
mately 2–3 cm medial to the posterior superior iliac spine on each side ureteroscope) or vagina, or via small surgical incisions in the anterior
at an angle of 45° (McGrath and Stringer 2011). The latter is potentially or posterior abdominal wall (laparoscope and other endoscopic
useful when localizing the branches of the dorsal sacral rami in the systems).
treatment of refractory sacroiliac pain. A refinement of the technique is natural orifice transluminal endo-
scopic surgery, in which abdominal operations are performed using an
Sciatic nerve
endoscope inserted through a natural orifice (e.g. mouth, anus, urethra)
The sciatic nerve leaves the pelvis approximately one-third of the and then through an incision in the viscus that has been entered (e.g.
way along a line between the posterior superior iliac spine and stomach, bladder, vagina). For example, pelvic and intra-abdominal
the ischial tuberosity and enters the thigh approximately half way contents can be accessed through the vagina via the recto-uterine pouch.
between the greater trochanter and ischial tuberosity (see Fig. 78.16) Hysterectomy, oophorectomy, pelvic organ prolapse repair and incon-
(Currin et al 2014). tinence surgery are commonly performed using transvaginal techniques.
Other surface landmarks for pelvic structures are described in This approach avoids the morbidity of abdominal incision but there
Chapter 78. are risks of sciatic, femoral and common fibular nerve injury from
prolonged surgery in the lithotomy position.
A further development of endoscopic minimally invasive surgery has
COMMON CLINICAL PROCEDURES
been the introduction of robotically assisted surgery, which allows the
surgeon to manipulate precision instruments from a console that is
Pneumoperitoneum for laparoscopy remote from the patient whilst viewing the operative field in three
A pneumoperitoneum is frequently established by accessing the perito- dimensions. The procedure is becoming increasingly common in
neal cavity just below the umbilicus. An incision through the linea alba prostatectomy.
KEY REFERENCES
Furness JB, Callaghan BP, Rivera LR et al 2014 The enteric nervous system Mirjalili SA, Stringer MD 2012 The need for an evidence-based reappraisal
and gastrointestinal innervation: integrated local and central control. of surface anatomy. Clin Anat 25:816–18.
Adv Exp Med Biol 817:39–71. This issue of Clinical Anatomy features several original articles
A comprehensive review of gastrointestinal innervation and the complexities reappraising surface anatomy of the trunk using cross-sectional CT imaging
of the enteric nervous system. in supine adults. These articles provide a more evidence-based approach to
key surface anatomy landmarks in the chest, abdomen and pelvis.
Loukas M, Klaassen Z, Merbs W et al 2010 A review of the thoracic splanch-
nic nerves and celiac ganglia. Clin Anat 23:512–22.
A critical review of the thoracic splanchnic nerves. | 1,463 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Abdomen and pelvis: overview and surface anatomy
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REFERENCES
Al-Shboul OA 2013 The importance of interstitial cells of Cajal in the gas- Mirjalili SA, McFadden SL, Buckenham T et al 2012a Anatomical planes: are
trointestinal tract. Saudi J Gastroenterol 19:3–15. we teaching accurate surface anatomy? Clin Anat 25:819–26.
Azaïs H, Collinet P, Delmas V et al 2013 Uterosacral ligament and hypogas- Mirjalili SA, McFadden SL, Buckenham T et al 2012b A reappraisal of adult
tric nerve anatomical relationship. Application to deep endometriotic abdominal surface anatomy. Clin Anat 25:844–50.
nodules surgery. Gynecol Obstet Fertil 41:179–83. Mirjalili S, Hale S, Buckenham T et al 2012c A reappraisal of adult thoracic
Blaszczyk B 1981 Variation of ganglia of the pelvic segment of the sympa- surface anatomy. Clin Anat 25:827–34.
thetic trunk in human fetuses. Folia Morphol (Warsz) 39:313–26. Motoc A, Rusu MC, Jianu AM 2010 The spermatic ganglion in humans: an
Boussuges A, Gole Y, Blanc P 2009 Diaphragmatic motion studied by anatomical update. Rom J Morphol Embryol 51:719–23.
m-mode ultrasonography: methods, reproducibility, and normal values. Moussallem CD, Abou Hamad I, El-Yahchouchi CA et al 2012 Relationship
Chest 135:391–400. of the lumbar lordosis angle to the abdominal aortic bifurcation and
Brierley SM, Linden DR 2014 Neuroplasticity and dysfunction after gastro- inferior vena cava confluence levels. Clin Anat 25:866–71.
intestinal inflammation. Nat Rev Gastroenterol Hepatol 11:611–27. Murata Y, Takahashi K, Yamagata M et al 2003 Variations in the number and
Cheong B, Muthupillai R, Rubin MF et al 2007 Normal values for renal position of human lumbar sympathetic ganglia and rami communi-
length and volume as measured by magnetic resonance imaging. Clin J cantes. Clin Anat 16:108–13.
Am Soc Nephrol 2:38–45. Naraynsingh V, Ramdass MJ, Singh J et al 2002 McBurney’s point: are we
Currin SS, Mirjalili SA, Meikle G, Stringer MD 2014 Revisiting the surface missing it? Surg Radiol Anat 24:363–5.
anatomy of the sciatic nerve in the gluteal region. Clin Anat doi: Oh CS, Chung IH, Ji HJ et al 2004 Clinical implications of topographic
10.1002/ca.22449. anatomy on the ganglion impar. Anesthesiology 101:249–50.
Drumm BT, Koh SD, Andersson KE 2014 Calcium signalling in Cajal-like Paraskevas G, Tsitsopoulos P, Papaziogas B et al 2008 Variability in superior
interstitial cells of the lower urinary tract. Nat Rev Urol 11:555–64. hypogastric plexus morphology and its clinical applications: a cadaveric
Epstein J, Arora A, Ellis H 2004 Surface anatomy of the inferior epigastric study. Surg Radiol Anat 30:481–8.
artery in relation to laparoscopic injury. Clin Anat 17:400–8. Potts TK 1925 The main peripheral connections of the human sympathetic
Furness JB, Callaghan BP, Rivera LR et al 2014 The enteric nervous system nervous system. J Anat 59:129–35.
and gastrointestinal innervation: integrated local and central control. Ramsden WH, Mannion RA, Simpkins KC et al 1993 Is the appendix where
Adv Exp Med Biol 817:39–71. you think it is – and if not does it matter? Clin Radiol 47:100–3.
A comprehensive review of gastrointestinal innervation and the complexities
Reiff JE, Werner-Wasik M, Valicenti RK et al 1999 Changes in the size and
of the enteric nervous system.
location of kidneys from the supine to standing positions and the
Glodny B, Unterholzner V, Taferner V et al 2009 Normal kidney size and its implications for block placement during total body irradiation. Int J
influencing factors – a 64-slice MDCT study of 1.040 asymptomatic Radiat Oncol Biol Phys 45:447–9.
patients. BMC Urol 9:1–19. Roggin KK, Posner MC 2012 Modern treatment of gastric gastrointestinal
Gosavi TD, Lo YL 2014 Images in clinical medicine. Superficial abdominal stromal tumors. World J Gastroenterol 18:6720–8.
reflex. N Engl J Med 370:e29. Rusu MC 2006 Considerations on the phrenic ganglia. Ann Anat
Hale SJ, Mirjalili SA, Stringer MD 2010 Inconsistencies in surface anatomy: 188:85–92.
the need for an evidence-based reappraisal. Clin Anat 23:922–93. Sanders KM, Ward SM, Koh SD 2014 Interstitial cells: regulators of smooth
Horton KM, Fishman EK 2002 Volume-rendered 3D CT of the mesenteric muscle function. Physiol Rev 94:859–907.
vasculature: normal anatomy, anatomic variants, and pathologic condi- Schwartz LH, Richaud J, Buffat L et al 1994 Kidney mobility during respira-
tions. Radiographics 22:161–72. tion. Radiother Oncol 32:84–6.
Loukas M, Klaassen Z, Merbs W et al 2010 A review of the thoracic splanch- Senoglu N, Senoglu M, Ozkan F et al 2008 The level of termination of the
nic nerves and celiac ganglia. Clin Anat 23:512–22. dural sac by MRI and its clinical relevance in caudal epidural block in
A critical review of the thoracic splanchnic nerves. adults. Surg Radiol Anat 35:579–84.
Mauroy B, Demondion X, Drizenko A et al 2003 The inferior hypogastric Stringer MD 2011 Clinical anatomy of the newborn. In: Puri P (ed) Newborn
plexus (pelvic plexus): its importance in neural preservation techniques. Surgery, 3rd ed. London: Hodder Arnold, pp. 29–38.
Surg Radiol Anat 25:6–15. Subramanian A, Maker VK 2006 Organs of Zuckerkandl: their surgical sig-
McGaugh JM, Brismee JM, Dedrick GS 2007 Comparing the anatomical nificance and a review of a century of literature. Am J Surg 192:
consistency of the posterior superior iliac spine to the iliac crest as refer- 224–34.
ence landmarks for the lumbopelvic spine: a retrospective radiological Toshniwal GR, Dureja GP, Prashanth SM 2007 Trans-sacrococcygeal
study. Clin Anat 20:819–25. approach to ganglion impar block for management of chronic perineal
McGrath MC, Stringer MD 2011 Bony landmarks in the sacral region: the pain: a prospective observational study. Pain Physician 10:661–6.
posterior superior iliac spine and the second dorsal sacral foramina: a Woon JT, Perumal V, Maigne JY et al 2013 CT morphology and morpho-
potential guide for sonography. Surg Radiol Anat 33:279–86. metry of the normal adult coccyx. Eur Spine J 22:863–70.
Mirjalili SA, Stringer MD 2012 The need for an evidence-based reappraisal Woon JT, Stringer MD 2014 Redefining the coccygeal plexus. Clin Anat
of surface anatomy. Clin Anat 25:816–18. 27:254–60.
This issue of Clinical Anatomy features several original articles
Zhang XM, Zhao QH, Zeng NL et al 2006 The celiac ganglia: anatomic study reappraising surface anatomy of the trunk using cross-sectional CT imaging
using MRI in cadavers. Am J Roentgenol 186:1520–3.
in supine adults. These articles provide a more evidence-based approach to
key surface anatomy landmarks in the chest, abdomen and pelvis. | 1,464 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
CHAPTER Development of the peritoneal cavity,
60
gastrointestinal tract and its adnexae
muscularis mucosa, the connective tissue of the submucosa, the mus
POSTPHARYNGEAL FOREGUT
cularis externa and the external connective tissue are all derived from
the splanchnopleuric mesenchyme. The outer peritoneal epithelium is
The primitive gut is divided by head and tailfolding into three main derived from the splanchnopleuric coelomic epithelium.
compartments. The foregut extends from the buccopharyngeal mem Throughout the gut, blood vessels, lymphatics and lymph nodes
brane to its continuation into the central midgut region via the cranial develop from local populations of angiogenic mesenchyme. The nerves,
intestinal portal. The midgut extends between the intestinal portals and, which are distributed within the enteric and autonomic systems, are
in the early embryo, is in wide communication with the yolk sac. The derived from the neural crest. There is a craniocaudal developmental
hindgut extends from the caudal intestinal portal to the cloacal mem gradient along the gut, in that the stomach and small intestine develop
brane. The cranial end of the foregut, the embryonic pharynx, is in advance of the colon.
intimately associated with head and neck development (Ch. 36). The Figure 60.1 shows the fundamental relationship of the intraembry
portion of foregut that passes dorsal to the pericardial cavity gives rise onic coelom to the developing gut. Figure 60.2 shows the gut in a stage
to the respiratory diverticulum and oesophagus within the thorax (Chs 12 embryo in relation to the other developing viscera, especially the
36 and 52). Caudal to the developing diaphragm, the enteric gut is heart and liver. Figure 60.3 shows the overall development of the gut
conventionally subdivided into three embryological portions: fore, from stages 13 to 17. These diagrams should be compared.
mid and hindgut. There are no corresponding fundamental morpho All regions of the gut develop from epithelial–mesenchymal inter
logical and cytological distinctions between the three parts (Fig. 60.1), actions that are dependent on the sequential expression of a range of
and so the foregut produces a portion of the duodenum, as does the basic and specific genes; on the regulation of the developmental clock,
midgut, and the midgut similarly produces large intestine, as does the seen in all areas of development; and on endogenous regulatory mecha
hindgut. The differences between the portions of the gut develop as a nisms and local environmental influences (Lebenthal 1989). Although
result of interactions between the three embryonic tissue layers that give all these factors pertain to the whole range of developing tissues, local
rise to the gut: namely, the endodermal inner epithelium, the thick layer differences in any one of these factors along the length of the develop
of splanchnopleuric mesenchyme, and the outer layer of proliferating ing gut promote the differentiation of, for example, the gastric mucosa
splanchnopleuric coelomic epithelium. and hepatocytes; the rotation of the midgut; and the final disposition
The epithelial layer of the mucosa and connected ducts and glands of the sessile portions of the fully formed gastrointestinal tract. The
are derived from the endodermal epithelium. The lamina propria and hedgehog (Hh) ligands, Shh, Ihh and Dhh are expressed in the develop
ing gut: Shh and Ihh in the endodermal epithelium and Dhh in
endothelial cells. These ligands bind to the Patched receptors (Ptch1
and Ptch2), which activate the transcription factor Gli3. Knockout of
Shh and Ihh has been associated with oesophageal atresia, gut malrota
tion, decreased development of the muscularis propria, enteric neurone
anomalies and imperforate anus (Kolterud et al 2009). The gut is func
tional prior to birth and able to interact with the extrauterine environ
Pharynx ment in preterm infants.
OESOPHAGUS
Pericardial cavity
Foregut The oesophagus can be distinguished from the stomach at stage 13
(embryo length 5 mm). It elongates during successive stages and its
absolute length increases more rapidly than the embryo as a whole.
Pericardioperitoneal canals Cranially, it is invested by splanchnopleuric mesenchyme posterior to
the developing trachea and, more caudally, between the developing
Septum transversum lungs and pericardioperitoneal canals posterior to the pericardium.
Caudal to the pericardium, the terminal, pregastric segment of the
Body wall, oesophagus has a short, thick, dorsal mesooesophagus (from splanch
somatopleuric mesenchyme Midgut nopleuric mesenchyme), while ventrally, it is enclosed in the cranial
and coelomic epithelium
stratum of the septum transversum mesenchyme. Each of the above is
continuous caudally with its respective primitive dorsal and ventral
mesogastria. Thus, the oesophagus has only limited areas related to a
Epithelium of midgut,
splanchnopleuric mesenchyme primary coelomic epithelium. However, it is important to note the
and coelomic epithelium subsequent development of the paraoesophageal right and left pneu
Peritoneal cavity matoenteric recesses (see Fig. 60.7), the relation of the ventral aspect of
the middle third of the oesophagus to the oblique sinus of the pericar
dium, and the relation of its lateral walls in the lower thorax to the
mediastinal pleura. All the foregoing are secondary extensions from the
primary coelom.
Hindgut
The oesophageal mucosa consists of two layers of cells by stage 15
Allantois (week 5), but the proliferation of the mucosa does not occlude the
lumen at any time. The mucosa becomes ciliated at 10 weeks, and strati
Fig. 60.1 Major epithelial populations within the early embryo. The fied squamous epithelium is present at the end of the fifth month;
early gut tube is close to the notochord and neural tube dorsally. The occasionally, patches of ciliated epithelium may be present at birth.
splanchnopleuric layer of the intraembryonic coelomic epithelium is in Circular muscle can be seen at stage 15 but longitudinal muscle has not
contact with the foregut ventrally and laterally, with the midgut laterally, been identified until stage 21. Neuroblasts can be demonstrated in the
1048 and the hindgut ventrally and laterally. early stages; the myenteric plexuses have cholinesterase activity by | 1,465 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Postpharyngeal foregut
1049
06
RETPAHC
A Amniotic cavity B Atrioventricular canal
Median thyroid rudiment Left atrium
Pharynx
Otocyst
Bulbus Amniotic
Pharynx cordis cavity
(right
Median ventricle) Lung bud
thyroid
Left horn
rudiment Left
Lung bud ventricle of sinus
venosus
Optic
Foregut
rudiment Septum Foregut
Liver transversum
Stomodeum, diverticulum Liver
oronasal cavity Yolk duct diverticulum
Hepatic
Pericardial cavity trabeculae Gallbladder
Left vitelline vein
rudiment
Yolk stalk Gallbladder
rudiment Left umbilical artery Upper limb
Postanal gut Upper limb bud
bud Peritoneal cavity
Cloacal membrane Midgut
Midgut Cloacal membrane
Notochord
Cloaca
Hindgut Allantois Hindgut Allantois
Fig. 60.2 A, The digestive tube of a human embryo at stage 12, with 29 paired somites, a crown to rump length of 3.4 mm and an estimated age of
27 days. (Pharyngeal development is followed further in Figure 36.18.) B, Reconstruction of a human embryo at the end of the fourth week. The
alimentary canal and its outgrowths are shown in median section. The brain is shown in outline but the spinal cord has been omitted. The heart is shown
in perspective, and the left horn of the sinus venosus is cut just medial to the entrance of the common cardinal vein (see Fig. 52.8A–B). The somites are
indicated in outline.
9.5 weeks and ganglion cells are differentiated by 13 weeks. It has been ous with the dorsal mesentery (mesenteron) of almost all of the remain
suggested that the oesophagus is capable of peristalsis in the first tri der of the intestine, except its caudal short segment.
mester. Periodic fetal swallowing can be seen on ultrasound from In human embryos of 10 mm (stages 15–16), the characteristic
16 weeks. The volume of amniotic fluid ingested increases during the gastric curvatures are already recognizable. Growth is more active along
third trimester to more than 500 ml/day. Oesophageal atresia is one of the dorsal border of the viscus; its convexity markedly increases and the
the more common obstructive conditions of the alimentary tract; it may rudimentary fundus appears. Because of more rapid growth along
be indicated by polyhydramnios. There is evidence of maturation of the the dorsal border, the pyloric end of the stomach turns ventrally and
lower oesophageal sphincter at 32 weeks, when, with the prevention of the concave lesser curvature becomes apparent (see Figs 60.3, 60.6). The
free gastrooesophageal reflex, stomach size increases (Hitchcock et al stomach is now displaced to the left of the median plane and, appar
1992). ently, becomes physically rotated, which means that its original right
surface becomes dorsal and its left surface becomes ventral. Accordingly,
Oesophagus at birth the right vagus is distributed mainly to the dorsal, and the left vagus
mainly to the ventral, surfaces of the stomach. The dorsal mesogastrium
increases in depth and becomes folded on itself. The ventral mesogas
At birth, the oesophagus extends 8–10 cm from the cricoid cartilage to
trium becomes more coronal than sagittal. The pancreaticoenteric
the gastric cardiac orifice. It starts and ends one to two vertebrae, respec
recess (see Fig. 60.7B(ii)), until this point usually described as a simple
tively, higher than in the adult, extending from between the fourth to
depression on the right side of the dorsal mesogastrium, becomes
the sixth cervical vertebra to the level of the ninth thoracic vertebra (see
dorsal to the stomach and excavates downwards and to the left between
Fig. 14.7). Its average diameter is 5 mm and it possesses the constric
the folded layers. It may now be termed the inferior recess of the bursa
tions seen in the adult. The narrowest constriction is at its junction with
omentalis. Put simply, the stomach has undergone two ‘rotations’. The
the pharynx, where the inferior pharyngeal constrictor muscle functions
first is 90° clockwise, viewed from the cranial end; the second is 90°
to constrict the lumen; this region may be easily traumatized with
clockwise, about an anteroposterior axis. The displacement, morpho
instruments or catheters. In the neonate, the mucosa may contain scat
logical changes and apparent ‘rotation’ of the stomach have been attrib
tered areas of ciliated columnar epithelium but these disappear soon
uted variously to its own and surrounding differential growth changes;
after birth. Peristalsis along the oesophagus and at the lower oesopha
extension of the pancreaticoenteric recess with changes in its mesen
geal sphincter is immature at birth and results in frequent regurgitation
chymal walls; and pressure, particularly that exerted by the rapidly
of food in the newborn period. The pressure at the lower oesophageal
growing liver.
sphincter approaches that of an adult at 3–6 weeks of age.
Mucosa
STOMACH
Mucosal and submucosal development can be seen in the eighth to
At the end of the fourth and beginning of the fifth weeks, the stomach ninth weeks. No villi form in the stomach, unlike in other regions of
can be recognized as a fusiform dilation cranial to the wide opening of the gut; instead, glandular pits can be seen in the body and fundus.
the midgut into the yolk sac (see Figs 60.2 and 60.3). By the fifth week, These develop in the pylorus and cardia by weeks 10 and 11, when
this opening has narrowed into a tubular vitelline intestinal duct, which parietal cells can be demonstrated. Although acid secretion has not
soon loses its connection with the digestive tube. At this time, the been demonstrated in the fetal stomach before 32 weeks’ gestation,
stomach is median in position and separated cranially from the peri preterm infants, from 26 weeks’ gestation onwards, are able to secrete
cardium by the septum transversum (see Fig. 60.5A), which extends acid soon after birth. Intrinsic factor has been detected after 11 weeks.
caudally on to the cranial side of the vitelline intestinal duct and ven This increases from the fourteenth to the twentyfifth week, at which
trally to the somatopleure. Dorsally, the stomach is related to the aorta time the pylorus, which contains more parietal cells than it does in the
and, reflecting the presence of the pleuroperitoneal canals on each side, adult, also contains a relatively larger quantity of intrinsic factor. The
is connected to the body wall by a short dorsal mesentery, the dorsal significance of the early production of intrinsic factor and the late pro
mesogastrium (see Figs 60.5B and 60.6). The latter is directly continu duction of acid by the parietal cells is not known. Chief cells can be | 1,466 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
DEvEloPmEnT of THE PERiTonEAl CAviTy, gAsTRoinTEsTinAl TRACT AnD iTs ADnExAE
1050
8
noiTCEs
Site of palatine tonsil Thymus
A B
Pharyngeal pouches
Tubotympanic recess
Inferior parathyroid
Adenohypophysial pouch
Ultimobranchial body
Lateral thyroid
Pharynx Internal carotid artery Superior parathyroid
Thyroid Lung bud
Pulmonary artery
Groove for sinus venosus Stomach Aortic sac
Oesophagus
Septum transversum Dorsal pancreas Trachea Lung
Umbilical vesicle stalk Gallbladder Pulmonary vein Stomach
Allantois Cut ends of hepatic trabeculae
Junction of yolk sac Gallbladder Dorsal pancreas
and intestine Postanal gut Bile duct
Urachus
Mesonephric duct
Umbilical vesicle stalk
Urorectal cleavage line Cloacal membrane Junction of umbilical vesicle
and intestine
Metanephros and ureter Approximate junction of colon and ileum
Mesonephric duct
C Adenohypophysis Thyroid
D
E
Aortic sac
Oesophagus
Trachea Oesophagus
Left primary bronchus Trachea Left primary bronchus
and branches
Umbilical vesicle stalk Hepatic ducts
Trachea
Primary intestinal loop Gallbladder Stomach Oesophagus
Ventral pancreas
Urogenital Urachus Dorsal pancreas
sinus
Stomach
Caecum
Gallbladder
Metanephros Mesonephric duct Hepatic ducts
Bile duct
Caecum Dorsal pancreas
Ventral pancreas Fundus of stomach
Pyloric atrium
Bladder
Hepatic ducts
Body of stomach
Gallbladder
Mesentery Primary intestinal loop
Dorsal pancreas
Mesonephric duct
Ureter Bile duct Ventral pancreas
Metanephros
Renal pelvis
(cranial and caudal poles)
Vermiform appendix
Urachus
Colon
Bladder
Metanephric kidney
0.2 mm
Collecting tubules
Ureter Mesonephric duct
Fig. 60.3 The shape of the endodermal epithelium of the gut at succeeding stages. The scale is constant, illustrating the enormous growth of the
gut over a 13-day period. A, Stage 13. B, Stage 14. C, Stage 15. D, Stage 16. E, Stage 17. Note the separation of the respiratory diverticulum; the
elongation of the foregut and expansion of the stomach; the formation of the hepatic and pancreatic diverticula; the lengthening of the midgut loop,
which protrudes into the umbilical cord; and the separation of the cloaca into enteric and allantoic portions. (Modified from O’Rahilly and Müller.
Developmental Stages in Human Embryos 1987 Carnegie Institution of Washington. Pub 637.) | 1,467 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Postpharyngeal foregut
1051
06
RETPAHC
identified after weeks 12–13, although they cannot be demonstrated to atresia), or with anomalies of the bile duct. In 40–60% of cases, the
contain pepsinogen until term. Mucous neck cells actively produce atresia is complete and pancreatic tissue fills the lumen. The condition
mucus from week 16. Gastrinproducing cells have been demonstrated can be diagnosed on ultrasound examination, which reveals a typical
in the antrum between 19 and 20 weeks, and gastrin levels have been double bubble appearance, caused by fluid enlarging the stomach and
measured in cord blood and in the plasma at term. Cord serum con the proximal duodenum. Polyhydramnios is invariably present and
tains gastrin levels 2–3 times higher than those in maternal serum. often is the indication for the scan. Duodenal atresia commonly occurs
with other developmental defects, e.g. cardiac and skeletal anomalies,
Muscularis and in Down’s syndrome.
The stomach muscularis externa develops its circular layer at 8–9 weeks,
DORSAL AND VENTRAL MESENTERIES
when neural plexuses are developing in the body and fundus. The
longitudinal muscle develops slightly later. Few studies note a time of OF THE FOREGUT
appearance of the oblique layer. The pyloric musculature is thicker than
the rest of the stomach; in general, the thickness of the total muscula The epithelium of the stomach and duodenum does not rotate relative
ture of the stomach at term is reduced, compared to the adult. to its investing mesenchyme. The rotation includes the coelomic epi
thelial walls of the pericardioperitoneal canals, which are on each side
Serosa of the stomach and duodenum and form its serosa, and the elongating
dorsal mesogastrium or the much shorter dorsal mesoduodenum. A
ventral mesogastrium can be seen when the distance between the
The serosa of the stomach is derived from the splanchnopleuric coe
stomach and liver increases. Whereas the dorsal mesogastrium takes
lomic epithelium. No part of this serosa undergoes absorption. The
origin from the posterior body wall in the midline, its connection to
original left side of the gastric serosa faces the greater sac; the right side
the greater curvature of the stomach, which lengthens as the stomach
faces the lesser sac.
grows, becomes directed to the left as the stomach undergoes its first
Stomach at birth rotation. With the second rotation, a portion of the dorsal mesogas
trium now faces caudally (see Fig. 60.6). The ventral mesogastrium
remains as a double layer of coelomic epithelium, which encloses mes
The stomach exhibits fetal characteristics until just after birth, when the
enchyme and forms the lesser omentum (see Fig. 60.7).
initiation of pulmonary ventilation, the reflexes of coughing and swal
Movement of the stomach is associated with an extensive lengthen
lowing, and crying cause the ingestion of large amounts of air and
ing of the dorsal mesogastrium, which becomes the greater omentum;
liquid. Once postnatal swallowing has started, the stomach distends to
this now, from its posterior origin, droops caudally over the small
four or five times its contracted state, and shifts its position in relation
intestine, then folds back anteriorly and ascends to the greater curvature
to the state of expansion and contraction of the other abdominal
of the stomach. The greater omentum is, therefore, composed of a fold
viscera, and to the position of the body. In the neonate, the anterior
containing, technically, four layers of peritoneum. The dorsal mesoduo
surface of the stomach is generally covered by the left lobe of the liver,
denum, or suspensory ligament of the duodenum, is a much thicker
which extends nearly as far as the spleen (see Fig. 14.6B). Only a small
structure, and it fixes the position of the duodenum when the rest of
portion of the greater curvature of the stomach is visible anteriorly. The
the midgut and its dorsal mesentery elongate and pass into the umbili
capacity of the stomach is 30–35 ml in the fullterm neonate, rising to
cal cord.
75 ml in the second week and 100 ml by the fourth week (adult capac
ity is, on average, 1000 ml). The mucosa and submucosa are relatively
thicker than in the adult; however, the muscularis is only moderately
SPECIAL GLANDS OF THE
developed and peristalsis is not coordinated. At birth, gastric acid secre
POSTPHARYNGEAL FOREGUT
tion is low, which means that gastric pH is high for the first 12 postnatal
hours. It falls rapidly with the onset of gastric acid secretion, usually
Pancreas
after the first feed. Acid secretion usually remains low for the first
10 days postnatally. Gastric emptying and transit times are delayed in
the neonate. The pancreas develops from two evaginations of the foregut that fuse
to form a single organ. A dorsal pancreatic bud can be seen in stage 13
embryos as a thickening of the endodermal tube that proliferates into
DUODENUM the dorsal mesogastrium (see Fig. 60.3; Fig. 60.4). A ventral pancreatic
bud evaginates in close proximity to the liver primordium but cannot
The duodenum develops from the caudal part of the foregut and the be clearly identified until stage 14, when it appears as an evagination
cranial part of the midgut. A ventral mesoduodenum, which is continu of the bile duct itself. At stage 16 (5 weeks), differential growth of the
ous cranially with the ventral mesogastrium, is attached only to the wall of the duodenum results in movement of the ventral pancreatic
foregut portion. Posteriorly, the duodenum has a thick dorsal mesoduo bud and the bile duct to the right side and, ultimately, to a dorsal posi
denum, which is continuous with the dorsal mesogastrium cranially tion. It is not clear whether there is a corresponding shift of mesen
and the dorsal mesentery of the midgut caudally. Anteriorly, the extreme chyme during this rotation. However, the ventral pancreatic bud and
caudal edge of the ventral mesentery of the foregut extends on to the the bile duct rotate from a position within the ventral mesogastrium
short initial segment of the duodenum. The liver arises as a diverticu (ventral mesoduodenum) to one in the dorsal mesogastrium (dorsal
lum from the ventral surface of the duodenum at the foregut–midgut mesoduodenum), which is destined to become fixed on to the posterior
junction, i.e. where the midgut is continuous with the yolk sac wall (the abdominal wall. By stage 17, the ventral and dorsal pancreatic buds
cranial intestinal portal). The ventral pancreatic bud also arises from have fused, although the origin of the ventral bud from the bile duct is
this diverticulum. The dorsal pancreatic bud evaginates posteriorly into still obvious. Threedimensional reconstruction of the ventral and
the dorsal mesoduodenum slightly more cranially than the hepatic dorsal pancreatic buds has confirmed that the dorsal pancreatic bud
diverticulum. The rotation, differential growth, and cavitations related forms the anterior part of the head, the body and the tail of the pan
to the developing stomach and omenta cause corresponding move creas, and the ventral pancreatic bud forms the posterior part of the
ments in the duodenum, which forms a loop directed to the right, with head and the posterior part of the uncinate process. The ventral pan
its original right side now adjacent to the posterior abdominal wall (see creatic bud does not form all of the uncinate process (Collins 2002a).
Fig. 60.6). This shift is compounded by the migration of the bile duct The developing pancreatic ducts usually fuse in such a way that most
and ventral pancreatic duct around the duodenal wall. Their origin of the dorsal duct drains into the proximal part of the ventral duct (see
shifts until it reaches the medial wall of the second part of the fully Figs 60.3–60.4). The proximal portion of the dorsal duct usually per
formed duodenum; the bile duct passes posteriorly to the duodenum sists as an accessory duct. The fusion of the ducts takes place late in
and travels in the free edge of the ventral duodenum and ventral meso development or in the postnatal period; 85% of infants have patent
gastrium. Local adherence and subsequent absorption of part of the accessory ducts, as compared to 40% of adults. Fusion may not occur
duodenal serosa and the parietal peritoneum result in almost the whole in 10% of individuals, in which case separate drainage into the duode
of the duodenum, other than a short initial segment, becoming retro num is maintained: socalled pancreatic divisum (pancreas divisum).
peritoneal (sessile). Failure of the ventral pancreatic diverticulum to migrate will result in
Duodenal atresia is a developmental defect found in 1 in 5000 live an anular pancreas, which may constrict the duodenum locally.
births (Whittle 1999). It may be associated with an anular pancreas, The ventral pancreas does not always extend anterior to the superior
which may compress the duodenum externally (20% of duodenal mesenteric vein but remains related to its right lateral surface. Initially, | 1,468 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
DEvEloPmEnT of THE PERiTonEAl CAviTy, gAsTRoinTEsTinAl TRACT AnD iTs ADnExAE
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A ductules, which terminate as blindending acini or as tubular, acinar
elements.
Oesophagus
The ductal branching pattern and acinar structure of the pancreas
are determined by the pancreatic mesenchyme. This mesenchyme gives
rise to connective tissue between the ducts, which, in the fetus, appears
to be important in stimulating pancreatic proliferation and maintaining
the relative proportions of acinar, α and β cells during development. It
also provides cell lines for smooth muscle within the pancreas. Ang
iogenic mesenchyme invades the developing gland to produce blood
and lymphatic vessels.
Stomach
The process of islet differentiation is divided into two phases (Collins
2002a). Phase I, characterized by proliferation of polyhormonal cells,
Hepatic ducts
occurs from weeks 9–15. Phase II, characterized by differentiation of
monohormonal cells, is seen from week 16 onwards. The β cells, pro
ducing insulin and amylin, differentiate first, followed by α cells, which
Gallbladder Duodenum produce glucagon. The δ cells, which produce somatostatin, are seen
after 30 weeks. The dorsal bud gives rise mostly to α cells, and the
ventral bud to most of the pancreatic polypeptideproducing cells. The
Ventral pancreatic outgrowth
Dorsal pancreatic β cells develop from the duct epithelium throughout development and
outgrowth into the neonatal period. Later, in weeks 10–15, some of the primitive
ducts differentiate into acinar cells, in which zymogen granules or
acinar cell markers can be detected at 12–16 weeks.
The pancreas in the neonate has all of the normal subdivisions of
the adult. The head is proportionately large in the newborn and there
B Accessory duct (dorsal rudiment) Pyloric antrum is a smooth continuation between the body and the tail. The inferior
Stomach border of the head of the pancreas is found at the level of the second
lumbar vertebra. The body and tail pass cranially and to the left, and
Biliary duct the tail is in contact with the spleen (see Fig. 14.6).
Liver
The liver is one of the most precocious embryonic organs and is the
Cystic duct Dorsal pancreas main centre for haemopoiesis in the fetus. It develops from an endo
dermal evagination of the foregut and from septum transversum mes
enchyme, which is derived from the proliferating coelomic epithelium
in the protocardiac region. The development of the liver is intimately
related to the development of the heart. The vitelline veins, succeeded
by the umbilical veins passing to the sinus venosus, are disrupted by
Bile duct the enlarging septum transversum to form a hepatic plexus, the forerun
ner of the hepatic sinusoids. (See Collins (2002b) for a detailed account
Portal vein of hepatic development.)
Principal duct (ventral rudiment)
Early liver development
Fig. 60.4 Development of the pancreas in a human embryo. A, An early
As the head fold and early intraembryonic coelom form, the ventral
stage, 7.5 mm embryo: lateral view. B, A later stage, 14.5 mm embryo:
ventral view. parietal wall of the pericardial cavity gives rise to populations of cells
termed precardiac or cardiac mesenchyme. Hepatic endoderm is
induced to proliferate by this mesenchyme, although all portions of the
the body of the pancreas extends into the dorsal mesoduodenum and early heart tube, truncus arteriosus, atria, ventricle, both endocardium
then cranially into the dorsal mesogastrium. As the stomach rotates, and myocardium, have hepatic induction potency that is tissuespecific
this portion of the dorsal mesogastrium is directed to the left, forming but not speciesspecific. As the heart and foregut become separated by
the posterior wall of the lesser sac. The posterior layer of this portion the accumulation of the cardiac mesenchyme, the mesenchyme itself is
of dorsal mesogastrium fuses with the parietal layer of the coelom wall renamed septum transversum. It is seen as a ventral mass, caudal to the
(peritoneum), and the pancreas becomes mainly retroperitoneal (see heart, which passes dorsally on each side of the developing gut to join
Fig. 60.7C). The region of fusion of the dorsal mesogastrium does not the mesenchyme proliferating from the walls of the pericardioperito
extend so far left as to include the tail of the pancreas, which passes neal canals. The majority of the cells within the septum transversum
into the splenorenal (lienorenal) ligament. The anterior border of the are destined to become hepatic mesenchyme. For details of the molecu
pancreas later provides the main line of attachment for the posterior lar signalling of early hepatic development, see Lemaigre (2009).
leaves of the greater omentum. In the stage 11 embryo, the location of the hepatic endoderm has
been identified at the superior boundary of the rostral intestinal portal.
Cellular development of the pancreas
By stage 12, the hepatic endodermal primordium is directed ventrally
The early specification of pancreatic endoderm involves the proximity and begins to proliferate as a diverticulum. There are two parts: a caudal
of the notochord to the dorsal endoderm, which locally represses the part, which will produce the cystic duct and gallbladder; and a cranial
expression of Shh transcription factor. Endoderm caudal to the pancre part, which forms the liver biliary system (see Fig. 60.3; Fig. 60.5A).
atic region does not respond to notochordal signals. The ventral pan The cells start to express liverspecific molecular markers and glycogen
creatic endoderm does not seem to undergo the same induction. storage.
Pancreatic mesenchyme is derived from two regions. The mesenchyme Around the cranial portion of the hepatic diverticulum, the basal
that surrounds the dorsal pancreatic bud proliferates from the splanch lamina is progressively disrupted and individual epithelial cells migrate
nopleuric coelomic epithelium of the medial walls of the pericardio into the surrounding septum transversum mesenchyme. The previously
peritoneal canals, whereas the ventral pancreatic bud is invested by smooth contour of the diverticulum merges into columnar extensions
septum transversum mesenchyme and by mesenchyme derived from of endoderm, the epithelial trabeculae, which stimulate the hepatic
the lower ventral walls of the pericardioperitoneal canals. mesenchymal cells to form blood islands and endothelium. The
The primitive endodermal ductal epithelium provides the stem cell advance of the endodermal epithelial cells promotes the conversion of
population for all the secretory cells of the pancreas. Initially, these progressively more hepatic mesenchyme into endothelium and blood
endocrine cells are located in the duct walls or in buds developing from cells, and only a little remains to form the scanty liver capsule and
them; later, they accumulate in pancreatic islets. The remaining primi interlobular connective tissue. This invasion by the hepatic epithelium
tive duct cells will differentiate into definitive ductal cells. In the fetus, is completed in stage 13, when it approaches the caudal surface of the
they develop microvilli and cilia but lack the lateral interdigitations pericardial cavity, and is separated from it only by a thin lamina of
seen in the adult. Branches of the main duct become interlobular mesenchyme that will give rise to part of the diaphragm. | 1,469 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Postpharyngeal foregut
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A Cranial B
Foregut
Pericardial cavity
Oesophagus Lung
Lungs
Dorsal mesogastrium
Septum transversum Pericardio- Ventral mesogastrium
peritoneal canals
Dorsal aorta
Liver developing within
Hepatic trabeculae
septum transversum
Spleen
Putative common bile duct
Gallbladder
Biliary duct system
Dorsal
Fig. 60.5 Early development of the liver and the supra-umbilical peritoneal
cavities. A, The hepatic endodermal primordium proliferates ventrally into
Ventral
the septum transversum mesenchyme. The endodermal cells forming the
hepatic trabeculae will become hepatocytes; the septum transversum
mesenchymal cells will become the endothelium of the liver sinusoids
and early blood cells. The developing lung buds can be seen expanding
C Oesophagus Stomach
into the pericardioperitoneal cavities. B, The septum transversum
Spleen mesenchyme and the stomach become enclosed by the right and left
pericardioperitoneal canals (shown on transverse section). The apposition
of the medial pericardioperitoneal walls forms the dorsal and ventral
Developing liver mesogastria. The proximity of the lung buds to the developing stomach
Ventral
can be seen. The pleural and supra-umbilical peritoneal cavities are
pancreatic
bud transiently, and bilaterally, symmetrical above the umbilicus. C, The lower
border of the ventral mesogastrium denotes the connection between the
supra-umbilical peritoneal cavities: pleuroperitoneal canals, which can be
Dorsal
pancreatic identified by the position of the ventral pancreatic bud and common bile
bud duct. The white arrows in B and C indicate the direction of movement of
the dorsal and ventral mesogastria.
During this early phase of development, the liver is far more highly diverticulum gives rise to the liver hepatocytes, the intrahepatic large
vascularized than the rest of the gut. The hepatic capillary plexus is bile ducts (right and left hepatic ducts, segmental ducts, area ducts and
connected bilaterally with the right and left vitelline veins. Dorsolater their first branches) and the small bile ducts (septal bile ducts, inter
ally, they empty by multiple channels into enlarged hepatocardiac chan lobular ducts and bile ductules). The portal and hepatic veins arise
nels, which lead to the right and left horns of the sinus venosus (see together from the vitelline veins. Early in development, the accumula
Fig. 60.9); usually, the channel on the right side is most developed. tion of mesenchyme around these veins is similar, whereas later mes
Both left and right channels bulge into the pericardioperitoneal canals, enchyme increases around the portal veins. This is a prerequisite for
forming sites for the exchange of fluid from the coelom into the vascular bile duct development. Primitive hepatocytes surround the portal vein
channels. The growth of the hepatic tissue in these regions is sometimes branches and associated mesenchyme, and form a sleeve of cells termed
referred to as the left and right horns of the liver. the ductal plate. Individual cells of the ductal plate are termed cholan
The liver remains proportionately large during its development and giocytes. Local hepatoblasts that are adjacent to the cholangiocytes
constitutes a sizeable organ dorsal to the heart at stage 14, then more arrange themselves to delineate a bile duct lumen and then also switch
caudally placed by stage 16. By this stage, hepatic ducts can be seen to a cholangiocyte lineage (Lemaigre 2009). As the bile ducts develop,
separating the hepatic epithelium from the extrahepatic biliary system, angiogenic mesenchymal cells form blood vessels that connect to the
but, even at stage 17, the ducts do not penetrate far into the liver. hepatic artery from 10 weeks. Thus, the portal triads are patterned by
the portal vein radicles, which initially induce bile duct formation and
Maturation of the liver
then artery formation. The development of the biliary system extends
At 3 months’ gestation, the liver almost fills the abdominal cavity and from the hilum to the periphery. Anomalies of the biliary tree are associ
its left lobe is nearly as large as its right. When the haemopoietic activity ated with abnormalities of the branching pattern of the portal vein. The
of the liver is assumed by the spleen and bone marrow, the left lobe developing bile ducts remain patent throughout development; the solid
undergoes some degeneration and becomes smaller than the right. The stage of ductal development previously promulgated has been refuted.
liver remains relatively larger than in the adult throughout the remain Atresia of the extrahepatic bile ducts has been noted, often in associa
der of gestation. In the neonate, it constitutes 4% of the body weight, tion with extrahepatic atresia. The cause of this condition is not clear;
compared to 2.5–3.5% in adults. It is in contact with the greater part inflammatory process may be involved, although some cases have fea
of the diaphragm and extends below the costal margin anteriorly, and, tures of ductal plate malformation (Howard 2002).
in some cases, to within 1 cm of the iliac crest posteriorly. The left lobe
Development of extrahepatic biliary ducts
covers much of the anterior surface of the stomach and constitutes
nearly onethird of the liver (see Fig. 14.6). Although its haemopoietic The caudal part of the hepatic endodermal diverticulum forms the
functions cease before birth, its enzymatic and synthetic functions are extrahepatic biliary system, the common hepatic duct, gallbladder,
not completely mature at birth. Hepatocytes remain a heterogeneous cystic duct and common bile duct.
population with different gene expressions and metabolic functions The bile duct, which originated from the ventral wall of the foregut
within different hepatic lobule locations. This metabolic zonation (now duodenum), migrates with the ventral pancreatic bud, first to the
becomes fully established after birth (Lemaigre 2009). right and then dorsomedially into the dorsal mesoduodenum. The right
and left hepatic ducts arise from the cranial end of the common hepatic
Development of intrahepatic biliary ducts
duct from 12 weeks’ gestation.
The development of the intrahepatic biliary ducts follows the branching Atresia of the extrahepatic bile ducts in neonates occurs alone or in
pattern of the portal vein radicles (Collins 2002b). The cranial hepatic conjunction with a range of other anomalies, including situs inversus, | 1,470 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
DEvEloPmEnT of THE PERiTonEAl CAviTy, gAsTRoinTEsTinAl TRACT AnD iTs ADnExAE
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malrotation, polysplenia and cardiac defects. In such cases, the intra sure; these hernias usually resolve without treatment. Exomphalos is a
hepatic bile ducts have a mature tubular shape but also show features ventral wall defect with midline herniation of the intraabdominal
of ductal plate malformation. contents into the base of the umbilical cord. Herniated viscera are
In the neonate, the gallbladder has a smaller peritoneal surface than covered by the peritoneum internally and amnion externally. The
in the adult, and its fundus often does not extend to the liver margin. omphalocele so formed ranges in size from a large umbilical hernia to
It is generally embedded in the liver and, in some cases, may be covered a very large mass containing most of the visceral organs. Even after the
by bands of liver. After the second year, the gallbladder assumes the exomphalos has been repaired, these babies will still have a deficient
relative size it has in the adult. anterior abdominal wall.
Gastroschisis is a paraumbilical defect of the anterior abdominal
wall associated with evisceration of the abdominal organs. The organs
MIDGUT are not enclosed in membranes; thus, gastroschisis can be detected by
prenatal ultrasonography and differentiated from exomphalos (see Fig.
14.5B). Gastroschisis is thought to result from periumbilical ischaemia,
The midgut forms the third and fourth parts of the duodenum, jejunum,
caused by vascular compromise of either the umbilical vein or arteries.
ileum and twothirds of the way along the transverse colon; its develop
The incidence of this condition appears to be increasing, especially in
ment produces most of the small, and a portion of the large, intestine.
babies born to young women less than 20 years old (Whittle 1999,
In embryos of stages 10 and 11, it extends from the cranial to the caudal
Ionescu et al 2014).
intestinal portals and communicates directly with the yolk sac over its
Congenital volvulus arises if the midgut loop does not rotate appro
entire length. Although it has a dorsal wall, the lateral walls have not
priately. A number of types of this condition are identified. Leftsided
yet formed at these stages. By stage 12, the connection with the yolk
colon occurs if the midgut loop has not rotated at all; mixed rotation
sac has narrowed, such that the midgut has ventral walls cranially and
results in the caecum lying inferior to the pylorus; and failure of appro
caudally. This connection is reduced to a yolk stalk containing the vitel
priate attachment of the peritoneum may result in the small intestine
lointestinal duct during stage 13, at which time the yolk sac appears as
being attached at only two points on the posterior abdominal wall. All
a sphere in front of the embryo. Posterior to the midgut, the splanch
of these arrangements lead to a risk of volvulus, which may result in
nopleuric coelomic epithelia converge, forming the dorsal mesentery.
necrosis of the gut.
Ventrolaterally, the intraembryonic coelom is in wide communication
The position and configuration of the duodenal loop are of particu
with the extraembryonic coelom. At stage 14, the midgut has increased
lar importance in children. The normal duodenal loop has a Ushaped
in length more than the axial length of the embryonic body and, with
configuration. The suspensory ligament of the duodenum (ligament of
elongation of the dorsal mesentery, it bulges ventrally, deviating from
Treitz) is usually found to the left of the body of the first or second
the median plane. For all these stages, see Figure 60.3.
lumbar vertebral body after normal gut rotation; any other position of
this ligament may indicate some degree of gut malrotation. On barium
PRIMARY INTESTINAL (OR MIDGUT) LOOP studies, the duodenojejunal flexure should, thus, lie to the left of the
upper lumbar spine at the level of the pylorus.
If the caecum has remained in the right upper quadrant, it may
The midgut loop can first be seen at stage 15, when a bulge – the caecal
become fixed in that position by peritoneal attachments passing to the
bud – can be discerned on the lower limb of the loop, caudal to the
right, the socalled Ladd’s bands. These may compress the underlying
yolk stalk (which arises from the apex or summit of the loop). Later,
duodenum and give rise to duodenal stenosis. The high positioning of
the original proximal limb of the loop moves to the right and the distal
the caecum close to the duodenal jejunal flexure – in some cases, in the
limb to the left (see Fig. 60.3C). The longest portion of the dorsal
midline – is associated with later development of volvulus.
mesentery is at the level of the yolk stalk; there is less relative lengthen
The identification of intestinal malrotation can be made by Xray
ing near the caudal end of the duodenum or the cranial half of the
investigation. However, ultrasonography has the advantage of showing
colon. The midgut extends into the umbilical coelom, having already
the position of the superior mesenteric vein and artery. The vein should
rotated through an angle of 90° (anticlockwise, viewed from the ventral
lie to the right of the artery. Most cases of volvulus will show inversion
aspect). This relative position is approximately maintained so long as
of this normal relationship but malrotation can occur with apparently
the protrusion persists, during which time the proximal limb that forms
normally related vessels, particularly in malrotation with bowel obstruc
the small intestine elongates greatly. It becomes coiled, and its adjacent
tion due to Ladd’s bands and not volvulus.
mesentery adopts a pleated appearance. The origin of the root of the
mesentery is initially both median and vertical, while, at its intestinal
attachment, it is elongated like a ruffle and folded along a horizontal UMBILICAL CORD
zone. The mesenteric sheet and its contained vessels have spiralled
through 90°. The distal, colic, part of the loop elongates less rapidly
During the period when the midgut loop protrudes into the umbilical
and has no tendency to become coiled. By the time the fetus has
coelom, the edges of the ventral body wall are becoming relatively
attained a length of 40 mm (10 weeks), the peritoneal cavity has
closer, forming a more discrete root for the umbilical cord. Somatic
enlarged and the relative size of the liver and mesonephros is much
mesenchyme, which will form the ventral body wall musculature,
less. The reentry of the gut occurs rapidly and in a particular sequence,
migrates into the somatopleuric mesenchyme and passes ventrally
during which it continues the process of rotation. The proximal loop
towards the midline. The umbilical cord forms all of the ventral body
returns first, with the jejunum mainly on the left and the ileum mainly
wall between the pericardial bulge and the developing external genita
on the right of the subhepatic abdominal cavity. As they reenter the
lia. It encloses a portion of the extraembryonic coelom, the umbilical
abdominal cavity, the coils of jejunum and ileum slide inwards over the
coelom, into which midgut loop protrudes. When the midgut loop is
right aspect of the descending mesocolon, and so displace the descend
abruptly returned to the abdominal cavity, the more recognizable
ing colon to the left. The transverse colon passes superiorly to the origin
umbilical cord forms. The vitellointestinal duct and vessels involute.
of the root of the mesentery (Fig. 60.6). The caecum is the last to
The cranial end of the allantois becomes thinned and its lumen partially
reenter and, at first, lies on coils of ileum on the right. Later develop
obliterated, and it forms the urachus. The mesenchymal core of the
ment of the colon leads to its elongation and to the establishment of
umbilical cord is derived by coalescence from somatopleuric amniotic
the hepatic and splenic flexures. A timetable for intestinal rotation in
mesenchyme, splanchnopleuric vitellointestinal (yolk sac) mesen
staged human embryos is given by Kim et al (2003).
chyme and splanchnopleuric allantoic (connecting stalk) mesenchyme.
These various layers become fused and are gradually transformed into
Anomalies of midgut rotation the viscid, mucoid, connective tissue (Wharton’s jelly) that characterizes
the more mature cord. The changes in the circulatory system result in
If the midgut loop fails to return to the abdominal cavity at the appro a large, cranially orientated, left umbilical vein (the right umbilical vein
priate time, a range of ventral defects can result. Failure of obliteration regresses), and two spirally disposed umbilical arteries (see Fig. 52.19).
of the vitellointestinal duct connecting the midgut to the yolk sac results
in Meckel’s diverticulum. This may present as a short segment of vitel
MATURATION OF THE SMALL INTESTINE
line duct attached to the original ventral side of the ileum; it may
remain attached to the umbilicus as a fistula; or it may remain as a liga
Mucosa
mentous attachment to the umbilicus.
An umbilical hernia occurs when loops of gut protrude into a
widened umbilical cord at term. The degree of protuberance may The exact timing of the cellular morphogenesis of the gut is difficult
increase when the infant cries, which raises the intraabdominal pres to establish, especially as it undergoes a proximodistal gradient in | 1,471 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
midgut
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Gut tube Oesophagus Stomach
A Ventral mesogastrium Dorsal mesogastrium B Spleen
Dorsal Septum transversum
aorta
Septum transversum
Biliary duct system
Umbilical vein Dorsal
mesentery
Yolk sac
Dorsal
pancreatic
bud
Umbilical Ventral
coelom pancreatic
bud
Allantois
Rotation
Umbilical artery Midgut loop entering beginning
umbilical coelom
Caecum
Liver Lesser Gastrosplenic
C omentum ligament D
Falciform ligament
Splenorenal
ligament
Gallbladder
Gallbladder
Caecum Early epiploic foramen
Expanding
greater
omentum
Ventral
pancreatic
Colon
bud
Jejunum
and ileum
Superior mesenteric artery
(axis of midgut rotation)
Fig. 60.6 The major developmental sequences of the subdiaphragmatic embryonic and fetal guts, together with their associated major glands,
peritoneum and mesenteries: left anterolateral aspect. A–F, The development sequence spans 1.5 months to the perinatal period. A–B, The top white
arrows show the relative movements of the dorsal and ventral mesogastria that result in the longitudinal rotation of the stomach and limited entry to the
lesser sac (see also Fig. 60.5). C–D, The lower white arrows associated with the midgut indicate the relative movements and rotation of the midgut loop
within the umbilical coelom, and as it returns to the abdominal cavity.
Continued
maturation. Developmental differences between parts of the small ner’s glands are present in the duodenum from 15 weeks and the mus
intestine or colon have not yet been correlated with age. The endoder cularis mucosa can be seen in the small intestine from 18 weeks.
mal cells of the small intestine proliferate and form a layer some three Whereas mitotic figures are initially seen throughout the endoder
to four cells thick, with mitotic figures throughout. From 7 weeks, blunt mal layer of the small intestine prior to villus formation, by 10–12 weeks
projections of the endoderm have begun to form in the duodenum and they are limited to the intervillous regions and the developing crypts.
proximal jejunum; these are the developing villi, which increase in It is believed that an ‘adult’ turnover of cells may exist when roundedup
length until, in the duodenum, the lumen becomes difficult to discern. cells can be observed at the villus tips, in position for exfoliation. The
The concept of occlusion of the lumen and recanalization, which is absorptive enterocytes have microvilli at their apical borders before
described in many accounts of development, does not match the cyto 9 weeks. An apical tubular system appears at this time, and is com
differentiation that occurs in the gut epithelia. Thus, it is no longer posed of deep invaginations of the apical plasma membrane and
thought that there is secondary recanalization of the gut lumen. By membranebound vesicles and tubules; many lysosomal elements
9 weeks, the duodenum, jejunum and proximal ileum have villi, and (meconium corpuscles) appear in the apical cytoplasm. These latter
the remaining distal portion of ileum develops villi by 11 weeks. The features are more developed in the ileum than jejunum, are most
villi are covered by a simple epithelium. Primitive crypts, epithelial prominent at 16 weeks, and diminish by 21 weeks. There are abundant
downgrowths into the mesenchyme between the villi, appear between deposits of glycogen in the fetal epithelial cells, and it has been sug
10 and 12 weeks and similarly follow a craniocaudal progression. Brun gested that, prior to the appearance of hepatic glycogen, the intestinal | 1,472 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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E F
Duodenum is
retropositioned
Caecum
Layers of
greater
omentum
Arrows here indicate
gut undergoing
continued rotation Caecum
Transverse colon
G H
Duodenum Root of greater omentum
Spleen
Transverse
mesocolon
Ascending Ascending
colon now colon
retroperitoneal
Jejunoileal Transverse
mesentery mesocolon
Descending
Descending
colon now
colon
retroperitoneal
Sigmoid mesocolon
Sigmoid colon
Caecum
Pelvic mesocolon
Fig. 60.6, cont’d The major developmental sequences of the subdiaphragmatic embryonic and fetal guts, together with their associated major glands,
peritoneum and mesenteries: left anterolateral aspect. E–F, The lower white arrows associated with the midgut indicate the relative movements and
rotation of the midgut loop within the umbilical coelom, and as it returns to the abdominal cavity. G–H, The approximate disposition in the adult
abdomen of the gut (G) and the mesenteric roots, showing their lines of attachment and principal contained vessels (H).
epithelium serves as a major glycogen store. Goblet cells are present in contains vernix and cellular debris, salivary, biliary, pancreatic and
small numbers by 8 weeks, Paneth’s cells differentiate at the base of the intestinal secretions, and sloughed enterocytes. As the mixture passes
crypts in weeks 11 and 12, and enteroendocrine cells appear between along the gut, water and solutes are removed and cellular debris and
weeks 9 and 11. M cells (membrane or microfold cells) are present proteins concentrated. Meconium contains enzymes from the pancreas
from 14 weeks. and proximal intestine in higher concentrations in preterm than in
Intestinal subepithelial myofibroblasts (ISEMFs) have been described fullterm babies.
within the villus cores and adjacent to the intervillous space at the base
of the crypts from week 21. They are arranged as a syncytium between
Muscularis layer
the epithelium and the muscularis mucosae, where they contribute to
the extracellular matrix. They demonstrate αsmooth muscle actin
(SMA) expression (McLin et al 2009). It is not clear whether these cells The muscularis layer is derived from the splanchnopleuric mesenchyme,
derive from splanchnopleuric mesenchyme fibroblasts, smooth muscle as it is in other parts of the gut. Smooth muscle myoblasts are character
precursors or neural crest. They migrate from the crypts to the villous ized by expression of αSMA. Longitudinal muscle can be seen from
axis in a manner similar to enterocytes. 12 weeks. At 26–30 weeks, the gut shows contractions without regular
Meconium can be detected in the lumen of the intestine by the periodicity; from 30–33 weeks, repetitive groups of regular contractions
sixteenth week. It is derived from swallowed amniotic fluid, which have been seen in preterm neonates. | 1,473 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Primitive hindgut
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Serosa MATURATION OF THE LARGE INTESTINE
The small intestine possesses only a dorsal mesentery. The movement The similarity of development of the small and large intestines is further
of the root of this dorsal mesentery, and the massive lengthening of its mirrored in their cytological differentiation. Fetal gut, from 11 weeks,
enteric border in order to match the longitudinal growth of the gut tube, shows dipeptidase activity in the colon as well as in the small intestine.
reflect the spiralizing of the midgut loop in the umbilical coelom. Throughout preterm development, meconium corpuscles are seen in
the colon and in the small intestine; they are believed to be the phago
Small intestine at birth cytosed remains of neighbouring cells that have died as a result of
programmed cell death.
There is little direct evidence of colonic function in the human fetus
The radial patterning of the small intestine is completed before birth,
and neonate. However, the specific results of mammalian studies are
with differentiation of the crypt–villous axis. Specification of the space
being correlated to human studies where possible. A number of distinct
between villi, crypt depth and villous length is a dynamic process
and important differences between the function of adult and fetal colon
dependent on the establishment of the intestinal microbiota. In the
have been reported.
neonate, the small intestine forms an ovalshaped mass with its greater
diameter transversely orientated in the abdomen, rather than vertically
Mucosa
as in the adult. The mass of the small intestine inferior to the umbilicus
is compressed by the urinary bladder, which is anterior at this point.
The small intestine is 300–350 cm long at birth and its width, when The absorption of glucose and amino acids does not take place through
empty, is 1–1.5 cm. The ratio between the length of the small and the the colonic mucosa in adult life, but there is evidence of direct absorp
length of the large intestine at birth is similar to the adult ratio. The tion of these nutrients during development. At birth, the normal cycle
mucosa and submucosa are fairly well developed and villi are present of bile acids is not mature. In the adult, bile is secreted by the liver,
throughout the small intestine; however, some epithelial differentiation stored in the gallbladder and then secreted into the intestine, where it
is incomplete. The muscularis is very thin, particularly the longitudinal is absorbed by the jejunum and ileum. In the fetus and neonate, the
layer, and there is little elastic tissue in the wall. There are few or no transport of bile acids by an active process from the ileum does not
circular folds in the small intestine, and the jejunum and ileum have occur, and so bile salts pass on into the colon. In the adult, the presence
little fat in their mesentery. of bile salts in the colon stimulates the secretion of water and electrolytes,
which results in diarrhoeal syndrome; however, the fetal and neonatal
colon seems protected from this effect. The colon is not considered a
PRIMITIVE HINDGUT site of significant nutrient absorption in the adult, and yet neonates are
unable to assimilate the full lactose load of a normal breast feed from
the small intestine and a large proportion of it may be absorbed from
Just as the foregut has an extensive ventral endodermal diverticulum,
the colon. Thus, it appears that the colon fulfils a slightly different role
which contributes to a system separate from the gut, so, too, the hindgut
in the preterm and neonatal period, conserving nutrient absorption and
has a ventral diverticulum – the allantois – destined for a different
minimizing fluid loss until the neonate has adjusted to extrauterine life,
system. However, unlike the respiratory diverticulum of the foregut, the
oral feeding and the establishment of the symbiotic bacterial flora.
allantois is formed very early in development, prior even to formation
of the embryonic endoderm and tailfolding. With the reorganization
of the caudal region of the embryo at stage 10, part of the allantois is Muscularis
drawn into the body cavity. The early embryonic hindgut thus consists
of a dorsal tubular region extending from the caudal intestinal portal The muscularis is present and functioning by the eighth week, when
to the cloacal membrane, and a ventral blindending allantois extend peristaltic waves have been observed. The specific orientation of the
ing from the cloacal region into the connecting stalk. The slightly longitudinal muscle layer into taeniae coli occurs in the eleventh to
dilated cavity, lined by endoderm, that cranially receives the enteric twelfth weeks, when haustra appear. The enteric nerves are present in
hindgut proper and the root of the allantoenteric diverticulum is termed Meissner’s and Auerbach’s plexuses at 8 and 12 weeks, respectively;
the endodermal cloaca. It is closed ventrally by the cloacal membrane there is a craniocaudal migration of neurones into the gut wall. A
(endoderm opposed to proctodeal ectoderm), and it also has, tran normal distribution of ganglion cells has been noted in preterm babies
siently, a small recess of endoderm in the root of the tail, the postanal of 24 weeks, although there is a region devoid of ganglia just above the
gut. As elsewhere, the hindgut, allantois and endodermal cloaca are anal valves. Anomalous migration of neural crest cells to the gut may
encased in splanchnopleuric mesenchyme. Proliferation of the mesen give rise to Hirschsprung’s disease (see below). Puborectalis appears in
chyme and endoderm in the angle of the junction of hindgut and 20–30 mm embryos, following opening of the anal membrane.
allantois produces a urorectal septum (see Fig. 72.4B). Continued pro
liferation of the urorectal septum and elongation of the endodermal Serosa
structures thrust the endodermal epithelium towards the cloacal mem
brane, with which it fuses centrally, separating the presumptive rectum
The development of the serosa of the intestine is considered with the
and upper anal canal (dorsally) from the presumptive urinary bladder
development of the peritoneal cavity (see below).
and urogenital sinus (ventrally) (see Fig. 72.4C). The cloacal membrane
is thus divided into anal (dorsal) and urogenital (ventral) membranes.
The nodal centre of division is the site of the future perineal body, the Colon at birth
functional centre of the perineum.
In the neonate, the colon is typically 66 cm long and averages 1 cm in
width. The caecum is relatively smaller than in the adult; it tapers into
ENTERIC HINDGUT
the vermiform appendix. The ascending colon is shorter in the neonate,
reflecting the shorter lumbar region. The transverse colon is relatively
The development of the large intestine, whether derived from mid or long, whereas the descending colon is short, but twice the length of the
hindgut, seems to be similar. The proximal end of the colon can be first ascending colon (see Fig. 14.6B). The sigmoid colon may be as long as
identified at stage 15, when an enlargement of a local portion of gut the transverse colon; it often touches the inferior part of the anterior
on the caudal limb of the midgut loop defines the developing caecum. body wall on the left and, in about half of neonates, part of the sigmoid
An evagination of the distal portion of the caecum forms the vermiform colon lies in the right iliac fossa. The muscularis, including the taeniae
appendix at stage 17 (see Fig. 60.3E). Apart from the embryonic studies coli, is poorly developed in the colon, as it is in the small intestine.
of Streeter (1942), there is little information about the development of Appendices, epiploicae and haustra are not present, which gives a
the large intestine in humans. The early endodermal lining of the colon smooth external appearance to the colon. Haustra appear within the
appears stratified, and mitoses occur throughout the layers. A series of first 6 months. The rectum is relatively long; its junction with the anal
longitudinal folds arise initially at the rectum and caecum, and later in canal forms at nearly a right angle.
the regions of colon between these two points. The folds segment into
villi with new villi forming between. The developing mucosa invagi
nates into the underlying mesenchyme between the villi to form glands ANAL CANAL
that increase in number by splitting longitudinally from the base
upwards. The villi gradually diminish in size and are absent by the time Mesenchymal proliferation occurs around the rim of the ectodermal
of birth. aspect of the anal membrane, which thus comes to lie at the bottom | 1,474 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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of a depression, the proctodeum (see Fig. 72.7E). With the absorption clear whether these cells migrate in from distant sources or differentiate
and disappearance of the anal membrane, the anorectum communi from the investing mesenchyme. The endodermal epithelium overlying
cates with the exterior. The lower part of the anal canal is formed from the lymphoid aggregates is often distorted into a dome shape. The cells
the proctodeal ectoderm and underlying mesenchyme, but its upper within the dome are a mixed population of enterocytes, endocrine cells,
part is lined by endoderm. The line of union corresponds with the goblet cells and M cells. M cells are specialized to provide a mechanism
edges of the anal valves in the adult. The dual origin of the anal canal for the transport of microorganisms and intact macromolecules across
is reflected in its innervation: the endodermal portion is innervated by the epithelium to the intraepithelial space and lamina propria. They
autonomic nerves, and the ectodermal proctodeum is innervated by have been observed in the fetus by 17 weeks; it is believed that they are
spinal nerves. formed by a specialized epithelial–mesenchymal interaction of the
In the fourth and fifth weeks, a small part of the hindgut, the post endoderm and underlying lymphoidtype mesenchyme.
anal gut, projects caudally beyond the anal membrane (see Fig. 60.3B); There are similarly specialized epithelial cells between the entero
it usually disappears before the end of the fifth week. cytes. Intraepithelial leukocytes typically account for 15% of the epithe
Imperforate anus is a term used to describe many different anorectal lial cells of the gut in the adult. They have been observed at 11 weeks,
anomalies. The most common is anal agenesis, which is found in with a distribution of 2–3 intraepithelial leukocytes per 100 gut epithe
almost half of all cases of imperforate anus. The condition is usually lial cells. Both T and B lymphocytes have been described in the develop
associated with a fistula, which opens into the vulva (females) or into ing gut wall. For an account of the development of the immune cells
the urethra (males). It is more rare for the anal membrane to fail to of the gut, consult Butzner and Befus (1989). The neonatal gut becomes
perforate. The condition cannot reliably be diagnosed prenatally by colonized by a range of bacterial flora; some of these exist in a symbiotic
ultrasound diagnosis, and it may be confused with Hirschsprung’s relationship with their host, and some of them may be considered
disease (see below) and colonic atresia. The prognosis is good for low pathogenic.
lesions of the anal canal. The principal concern, in all cases, is the
degree of bowel control, urinary control and, in some cases, sexual
ULTRASOUND ANTENATAL IMAGING OF
function, which is compromised by the condition. Anorectal anomalies
may be indicators of other anomalies, e.g. those forming the ‘VATER’ THE FETAL GUT
syndrome (vertebral, anal, tracheooesophageal and renal anomalies).
The abdominal circumference, routinely estimated at 20 weeks, is cal
culated from the anteroposterior diameter and the transverse abdomi
ENTERIC NERVOUS SYSTEM nal diameter perpendicular to it, taken at the widest part of the
abdomen. The section usually includes one entire rib and the stomach
Enteric neurones are derived from cranial (vagal) neural crest cells at cavity (termed stomach bubble) and can be confirmed on the left side
somite levels 1–7 and from 28 onwards (see Fig. 17.19 and p. 251). of the body (see Fig 14.4G). Anteriorly, the connection of the umbilical
After neurulation, the crest cells begin their ventral migration and invade cord can be confirmed (see Fig 14.4H). Anomalies of the anterior body
the gut via the dorsal mesentery (see Fig. 17.11). Glial cells associated wall, exomphalos and gastroschisis, are readily detected. In exompha
with the gut have been identified as arising from similar levels. It is los, a mass of peritoneal organs herniate through the base of the umbili
thought that the vagal and sacral neural crest cells have intrinsic differ cal ring; in gastroschisis, loops of small intestine and colon float free
ences in their ability to colonize the gut. The local splanchnopleuric in the amniotic fluid (see Fig. 14.5B) (Ionescu 2014).
mesenchyme patterns the crest cells, such that those that enter the gut
layers attain an enteric fate, whereas those that remain outside the gut
FUNCTIONAL MATURITY OF THE GUT AT BIRTH
become committed as parasympathetic postganglionic neurones. The
enteric neurones also migrate to the glands of the gut, e.g. the pancreas.
Migrating vagal neural crest cells reach the midgut by week 5 and the The postnatal maturation of the gut is dependent on the establishment
entire length of the gut is colonized by week 7. Maturation of the of an intestinal microbiota, which, in turn, is affected by gestational
myenteric plexus follows a craniocaudal progression. The submucosal age, mode of delivery, type of feeding and any medical interventions.
plexus arises from centripetally migrating cells from the myenteric plexus In cases of chorioamnionitis, preterm infants ingest bacterial products
2–3 days later (Burns et al 2009). Interstitial cells of Cajal, which derive from the amniotic fluid; it has been suggested that this may be associ
from splanchnopleuric mesenchyme, do not mature in a craniocaudal ated with preterm labour (Neu and Mai 2012). Normal, term, vaginal
progression. They are seen around the myenteric ganglia along the entire delivery establishes the initial colonization of the neonatal gut with
gut from weeks 12–14 (Burns et al 2009). There is evidence that mucosal maternal vaginal and intestinal flora. Twoway interactions between
enteric glial cells, which move into the mucosa after birth, interact with enteric microbes in a biofilm within the luminal glycocalyx of entero
the colonizing intestinal flora, suggesting a microbiotadriven homeo cytes modify intestinal permeability, increase T and B lymphocyte
static mechanism for gut function (Kabouridis et al 2015). numbers within the mucosal lamina propria and mesenteric lymph
nodes, and stimulate postnatal immune development (Vaarala 2012,
Wynn and Neu 2012, Martin et al 2012, Patel et al 2012, Gritz and
Hirschsprung’s disease
Bhandari 2015). Delivery by caesarean section results in the establish
ment of skin microbiota, different intestinal microbes and low micro
Hirschsprung’s disease (commonly called megacolon) is usually charac biota diversity. Failure to develop an appropriate, dynamic, microbiota
terized by an aganglionic portion of gut that does not display peristalsis, is thought to be associated with allergic and inflammatory conditions
and a dilated segment of structurally normal colon proximal to this site. in later life (Wynn and Neu 2012). (For further reading, see Neu (2012),
Histologically, there is either an absence or a reduction in the number Bäckhed et al (2015), Rodríguez et al (2015).)
of ganglia and postganglionic neurones in the myenteric plexus of the The onset of feeding also contributes to gut maturity. Breast milk is
affected segment of gut; postganglionic innervation of the muscle layers a source of epidermal growth factor, which promotes postnatal mucosal
is also often defective. It is believed that the condition is caused by a development and helps mucosal repair. Breast feeding also affects the
failure of neural crest cells to colonize the gut wall appropriately production of immunoglobulin A (IgA) in the gut mucosa (Vaarala
(Gershon 2010). A variable length of large intestine may be affected; the 2012). Undernutrition leads to villous atrophy and, in the preterm
lower and midrectum are the most common sites but, in severe cases, infant, parenteral nutrition is associated with changes in intestinal
the rectum, sigmoid, descending and even proximal colon can be agan structure and function that may lead to increased intestinal permeabil
glionic. Occasionally, aganglionosis affects only a very short length of ity (Martin et al 2012). Antibiotic therapy within the neonatal period
rectum proximal to the anorectal junction and the degree of functional can lead to changes in, and the establishment of, the normal intestinal
obstruction is minimal; in these cases of ‘ultrashortsegment Hirschs microbiota (Martin et al 2012).
prung’s disease’, clinical anomalies arise later in life. Infants with Hir The first passage of faeces of the newborn is termed meconium. This
schsprung’s disease show delay in the passage of meconium, constipation, is a dark, sticky, viscid substance formed from the passage of amniotic
vomiting and abdominal distension. fluid, sloughed mucosal cells, digestive enzymes and bile salts along the
fetal gut. Meconium becomes increasingly solid as gestation advances
but does not usually pass out of the fetal body while in utero. Fetal
GUT-ASSOCIATED LYMPHOID TISSUE distress produced by anoxia may induce the premature defecation of
meconium into the amniotic fluid, with the risk of its inhalation. At
Individual lymphocytes appear in the lamina propria of the gut from birth, the colon contains 60–200 g of meconium. The majority of
approximately week 12 of development, and lymphoid aggregates – neonates defecate within the first 24 hours after birth. Delayed passage
Peyer’s patches – have been noted between 15 and 20 weeks; it is not of stool beyond this time is associated with Hirschsprung’s disease (see | 1,475 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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above) or imperforate anus. The normal passage of meconium contin Mesenteries of the developing gut
ues for the first 2 or 3 days after birth, and is followed by a transition
to faecal stools by day 7.
The cervicothoracic oesophagus develops between the pericardioperito
neal canals. It is encased in prevertebral, retrotracheal and retrocardiac
mesenchyme. As the pericardioperitoneal canals expand with the devel
PERITONEAL CAVITY oping lung buds, and the diaphragm forms immediately below them;
the oesophagus, at this level, has no true dorsal or ventral mesentery.
The early development of the intraembryonic coelom, which gives rise At superior and intermediate thoracic levels, parts of the lateral aspects
to the peritoneal cavity, is described on page 185. Figure 12.2 shows a of the oesophagus are closely related to the secondary, mediastinal,
scheme of the shape of the early peritoneal cavity and indicates the parietal pleura. In the lower thorax, the oesophagus inclines ventrally
mesenchymal populations derived from its epithelial walls. Initially, the anterior to the descending thoracic aorta. The dorsocaudally sloping
peritoneal cavity associated with the lower end of the foregut has sepa midline diaphragm between oesophageal and aortic orifices may be
rate right and left components: the pleuroperitoneal canals (see Fig. homologized with part of a dorsal mesooesophagus, and is used in
60.1). At the level of the midgut, the pleuroperitoneal canals join a that context in descriptions of diaphragmatic development. A ventral
confluent cavity surrounding the developing gut, which transitorily is midline diaphragmatic strip may also be considered to be a derivative
in communication with the extraembryonic coelom. of a ventral mesooesophagus; however, this region is more usually
The description of the development of the peritoneal cavity that thought of as septum transversum.
follows pertains to changes that occur as a consequence of the differ The alimentary tube, from the diaphragm to the start of the rectum,
ential growth of the gut. initially possesses a sagittal dorsal mesentery. Its line of continuity with
the dorsal parietal peritoneum (i.e. its ‘root’ or ‘line of reflection’) is,
initially, also midline.
The abdominal foregut, from the diaphragm to the future hepato
PERITONEUM
pancreatic duodenal papilla, also has a ventral mesentery. This extends
from the ventrolateral margins of the abdominal oesophagus and as yet
Peritoneum develops from a specific portion of the intraembryonic
‘unrotated’ primitive stomach and proximal duodenum, cranially to the
coelomic walls. Initially, the intraembryonic coelomic epithelium is a
future diaphragm and anteriorly to the ventral abdominal wall (to the
pseudostratified germinal layer from which cellular progeny with dif
level of the cranial rim of the umbilicus). Caudally, between umbilicus
ferent fates arise in specific sites and at specific developmental times.
and duodenum, it presents a crescentic free border.
The portion that will give rise to the peritoneum is derived from the
The midgut and hindgut have no ventral mesentery; thus, the pleural
lower portion of the pericardioperitoneal canals and the somatopleure
and supraumbilical peritoneal cavities are, initially and transiently,
and splanchnopleure associated with the lower foregut, midgut and
bilaterally symmetrical above the umbilicus. Below the umbilicus, the
upper portions of the hindgut (see Figs 12.2, 60.1).
peritoneal cavity is freely continuous across the midline ventral to the
The proliferative splanchnopleuric epithelium produces cell popula
gut (see Fig. 60.5A).
tions for the mucosa and muscularis of the gut, and also for the lamina
propria and epithelium of the visceral peritoneum (the serosa of the Foregut mesenteries
gut wall). The somatopleuric epithelium gives rise to the lamina propria
and epithelium of the parietal peritoneum. The visceral and parietal
The ventral and dorsal foregut mesenteries are relatively large compared
peritoneal layers constitute a mesothelium, which denotes their origin
with the slender endodermal tubes they encase; they are composed
from the intraembryonic mesoderm of the coelomic wall.
of mesenchyme sandwiched between two layers of splanchnopleuric
As the gut grows, splanchnic mesenchyme accumulates around the
coelomic epithelium. A complex series of recesses develop in the
endodermal epithelium and the whole unit generally moves ventrally.
splanchnopleuric mesenchyme and become confluent. As a result of
There is a concomitant enlargement of the caudal ends of the develop
foregut rotation, differential growth of the stomach, liver, pancreas
ing pericardioperitoneal (pleuroperitoneal) canals and developing peri
and spleen, and the completion of the diaphragm, the territories of
toneal cavity. The medial walls of the intraembryonic coelom move
the greater sac and lesser sac (omental bursa) are delimited, and the
closer and there is a relative decrease in the mesenchyme between them.
mesenteric complexes of these organs (omenta and ‘ligaments’) are
The regions where the medial portions of the intraembryonic coelom
defined (see Figs 60.6–60.7).
come together are termed mesenteries. They are composed of two layers
of peritoneum with intervening mesenchyme and contain the neuro
Consequences of rotation of the stomach
vascular structures that pass to and from the gut. At the caudal ends of
the pleuroperitoneal canals, the gut has both ventral and dorsal
mesenteries, whereas, caudal to this, there is only a dorsal mesentery A number of processes occur concurrently, which, conceptually, can be
(see Fig. 60.6; Fig. 60.7). visualized as the movement of the right pleuroperitoneal canal to a
The mesenteries attached to the gut lengthen to permit large move position posterior to the stomach, such that its communication with
ments or rotations of the gut tube. Later, when part or the whole of the the remainder of the peritoneal cavity is reduced. These processes
mesentery lies against the parietal peritoneum, their apposed surfaces include the differential growth of the walls of the stomach, the forma
fuse and are absorbed, i.e. they become sessile. Only those viscera tion and specific local extension of the omenta (dorsal and ventral
developed in direct apposition to one of the primary coelomic regions, mesogastria), and the growth of the liver and, particularly, of the vessels
or a secondary extension of the latter, retain a partial or almost com and ducts that enter and leave the liver. These developments permit
plete visceral serous cover. Thus, the original line of reflection of stomach expansion both anteriorly and posteriorly when food is
mesenteries becomes altered, or, in some cases, the organ may become ingested, and free movement of peristalsis. The right pleuroperitoneal
retroperitoneal. These mechanisms are significant throughout the sub canal forms a discrete region of the peritoneal cavity, the lesser sac, and
diaphragmatic gut, but are predominant in the small and large intestine. the remaining left pleuroperitoneal canal and the remainder of the
All serous membranes may vary their thickness, lines of reflection, peritoneal cavity form the greater sac. The entrance to the original right
disposition, ‘space’ enclosed and their channels of communication, by pleuroperitoneal canal (lesser sac) becomes reduced in size. It is called
a process of areal and thickness growth on one aspect, combined with the epiploic foramen, foramen of Winslow, or the aditus of the omental
cavitation (leading to expanding embryonic recess formation) on the bursa (bursa omentalis).
other.
Early stages of lesser sac development
Although all of the gut tube and its derived glands are associated
with mesenteries formed as described above, the nomenclature for
some portions of the gut and glands is different. Thus, the mesenteries The lesser sac is first indicated by the appearance of multiple clefts
of the stomach are called omenta and the reflections of peritoneum in the paraoesophageal mesenchyme on both left and right aspects
around the liver, which develop from a confluence of splanchnopleuric, of the oesophagus. Although they may become confluent, the left clefts
somatopleuric and septum transversumderived portions, are called are transitory and soon atrophy. The right clefts merge to form the
ligaments. right pneumatoenteric recess that extends from the oesophageal end of
The movements of the developing viscera within the peritoneal the lesser curvature of the stomach as far as the caudal aspect of the
cavity occur with associated movements of the mesothelia that sur right lung bud. At its gastric end, it communicates with the general
round them. The descriptions of peritoneal cavity development that peritoneal cavity and lies ventrolateral to the gut; more rostrally it
follow are thus describing a sequence of changes that affect a complex lies directly lateral to the oesophagus. It is not, as commonly stated,
space and its boundaries. a simple progressive excavation of the right side of the dorsal | 1,476 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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A(i) A(ii)
Oesophagus
Extends cranially into pneumatoenteric recess
Right lung bud
Right pneumatoenteric recess Hepatoenteric Parietal
recess (lesser Inferior vena cava peritoneum
Inferior vena cava in caval fold omental recess)
in caval fold
Epiploic foramen
Hepatoenteric recess
Perigastric,
retrogastric and
greater omental Secondary dorsal mesogastrium
recesses
Lesser omentum, free border Retrogastric and perigastric recesses
B(i) B(ii)
Kidney
Infracardiac bursa Suprarenal gland Line of fusion
Diaphragm
Pneumatoenteric
recess (caudal part)
Inferior vena cava
Liver (early caudate lobe)
Caval fold
Spleen
Hepatoenteric recess
Stomach Spleen
Pancreaticoenteric recess
Pancreas (body) Stomach
C(i) C(ii)
Upper part of lesser sac:
pneumatoenteric and
hepatoenteric regions, Prerenal, retroperitoneal, body of pancreas Kidney
covered by lesser omentum
Entrance via epiploic
foramen and canal
Junction between upper
and lower parts of lesser sac
Lesser omentum Gastrosplenic ligament
Tail of pancreas in splenorenal ligament
Lower part of lesser sac: perigastric,
retrogastric and greater omental
D Lesser omentum Diaphragm E
Liver Aorta
Liver Gastrosplenic ligament
Spleen
Falciform ligament
Splenorenal ligament
Gallbladder
Pancreas
(body)
Entrance to early
epiploic foramen Expanding greater omentum
Fig. 60.7 A–C, Stages of development of the subdiaphragmatic foregut and the right and left pericardioperitoneal/pleuroperitoneal canals, with particular
reference to the terminal oesophagus, stomach, duodenum, spleen, the lesser sac of the peritoneum and the omenta, seen in semicoronal section (left
column) and transverse section at the levels indicated by the arrows (right column). D–E, The lesser sac and dorsal and ventral mesogastria.
mesogastrium. The right pneumatoenteric recess undergoes further mesooesophagus; the much larger ventral mesogastrium, and the
extension, subdivision and modification (see Fig. 60.7 A(i), B(i)). most caudal free border, is from the ventral mesoduodenum. As dif
From its caudal end, a second process of cleft and cavity formation ferential growth of the duodenum occurs, the biliary duct is reposi
occurs, which produces the hepatoenteric recess. This thins and tioned and most of the duodenum becomes sessile. The duodenal
expands the splanchnopleure between the liver and the stomach and attachment of the free border and a continuous neighbouring strip of
proximal duodenum, and reaches the diaphragm (see Fig. 60.7A(i), the lesser omentum become confined to the upper border of a short
C(i)). The resulting, structurally bilaminar, mesenteric sheet is the segment of its superior part. The contrasting growth and positioning of
lesser omentum. It is derived, cranially to caudally, from the small its attached viscera cause the free border to change gradually from the | 1,477 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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horizontal to the vertical. It carries the bile duct, portal vein and meet and blend. It provides a mesenchymal route for the upper abdom
hepatic artery, and its hepatic end is reflected around the porta hepatis. inal, transdiaphragmatic and transpericardial parts of the inferior vena
An alternative name for this part of the lesser omentum is the hepa cava, and it is also prominent in the development of parts of the liver,
toduodenal ligament; it forms the anterior wall of the epiploic lesser sac of peritoneum, and certain mesenteries. The left fold regresses
foramen. The floor of the foramen is the initial segment of the superior whereas the right fold enlarges rapidly (see Fig. 60.7A).
part of the duodenum, its posterior wall is the peritoneum covering The pneumatoenteric recess continues to expand to the right into
the immediately subhepatic part of the inferior vena cava, and its roof the substance of the caval fold. It stops near the left margin of the
the peritonealized caudate process of the liver. The major part of the hepatic part of the inferior vena cava, which remains extraperitoneal
lesser omentum from the lesser gastric curvature passes in an approxi and crosses the base of the now roughly triangular bare area of the liver
mately coronal plane to reach the floor of the increasingly deep groove and this new expanded line of reflection. With closure of the pleuro
for the ductus venosus on the hepatic dorsum; this part is sometimes peritoneal canals, the rostral part of the right pneumatoenteric recess is
called the hepatogastric ligament. sequestered by the diaphragm but often persists as a small serous sac
in the right pulmonary ligament. The remaining caval fold mesen
Ligaments of the liver
chyme to the left of the inferior vena cava – which forms the right wall
The liver is precociously large during development because of its early of the upper part of the lesser sac – becomes completely invaded by
role in haemopoiesis. Thus, the liver mass projects into the abdominal embryonic hepatic tissue and is transformed into the caudate lobe of
cavity with equal growth on the two sides of the peritoneal cavity. The the liver. This smooth, vertically elongated, mass projects into the
ligaments associated with the liver develop from the ventral mesogas cavity of the lesser sac; both its posterior, and much of its anterior,
trium – which passes from the foregut to the ventral abdominal wall, surfaces become peritonealized as a result of the increasing depth of
down to the cranial rim of the intestinal portal – and from the reflec the groove for the ductus venosus and the attachment of the lesser
tions of peritoneum from the liver to the diaphragm. omentum to its floor.
The medial portions of the germinative coelomic epithelial walls,
containing splanchnopleuric mesenchyme, septum transversum mesen
Later stages of lesser sac development
chyme and developing liver, constitute the early ventral mesogastrium
(see Fig. 60.5). The mesenchyme between these layers is continuous
superiorly with the septum transversum mesenchyme of the diaphragm. The lower (inferior) part of the lesser sac can be first seen in embryos
The coelomic epithelial layers of the ventral mesogastrium almost touch of 8–9 mm crown–rump length, and the early pneumatoenteric and
anterior and posterior to the liver, and are separated by a slender lamina hepatoenteric recesses are well established. Progressive differential
of mesenchyme. They form the falciform ligament and the lesser gastric growth produces an elliptical transverse sectional profile, with a
omentum, respectively, and where they are in contact with the liver rightsided lesser curvature, which corresponds to the original ventral
directly, they form visceral peritoneum (see Fig. 60.7D). border of the gastric tube. The lesser omental gastric part of the ventral
When the diaphragm is formed above the liver, local cavities coalesce mesogastrium remains attached to this border. The greater curvature of
and open into the general coelomic cavity as extensions of the greater the stomach is a new, rapidly expanding, region; its convex profile
(and lesser) sacs. In this way, almost all the ventrosuperior, visceral and projects mainly to the left, but also cranially and caudally (see Fig.
some of the posterior aspects of the liver become peritonealized. The 60.7A(i), B(i), C(i)). The original dorsal border of the gastric tube now
process of extending the greater sac continues over the right lobe and traverses the dorsal aspect of the expanding rudiment, curving along a
stops when the future superior and inferior layers of the coronary liga line near the lesser curvature. The primitive dorsal mesogastrium is
ment and the right triangular ligament are defined. Those, plus a medial transiently attached to it, and blends with the thick layer of compound
boundary provided by an extension of the lesser sac, enclose the ‘bare gastric mesenchyme clothing the posterior aspect and greater curvature
area’ of the liver, where loose areolar tissue of septum transversum of the miniature stomach. Because of its thickness, the mesenchyme
origin persists. Later in development, when the haemopoietic function projects cranially, caudally and, particularly, to the left, beyond the
of the liver declines, the left lobe becomes relatively smaller than the ‘new’ greater curvature of the endodermal lining of the stomach.
right; this, presumably, accounts for the smaller size of the left triangu The processes already described in relation to the ventral mesenteries
lar ligament. now supervene. Multiple clefts appear at various loci in the mesen
Where the superior layers of the coronary and left triangular liga chyme, and there are local mesenchyme to epithelial transitions. The
ments meet, they continue as a (bilaminar) ventral mesentery attached groups of clefts rapidly coalesce to form transiently isolated closed
to the ventrosuperior aspects of the liver. Its somewhat arched umbilico spaces, which soon join with each other and with the preformed upper
hepatic free caudal border carries the left umbilical vein. As the ventral part of the lesser sac; the newly formed epithelia join the coelomic
body wall develops, this falciform ligament, which initially attaches to epithelium. In sequence, the initial loci occur in the compound poste
the early cranial intestinal portal, is drawn to the diminishing cranial rior gastric mesenchyme nearer the lesser curvature and along its zone
rim of the umbilicus. It may be considered the final ventral part of the of blending with the primitive dorsal mesogastrium; in the dorsal meso
ventral mesogastrium, although its free border has a ventral mesoduo duodenum; and independently, in the caudal rim, where greater curva
denal origin. Its passage to the ventral body wall becomes increasingly ture mesenchyme and dorsal mesogastrium blend. As these cavities
oblique, curved and falciform (sickleshaped) as the umbilicus becomes become confluent and their ‘reniform’ expansion follows, matches and
more defined. then exceeds that of the gastric greater curvature, there are several major
In the early embryo, the connection between one pericardioperito sequelae. The primitive dorsal mesogastrium increases in area by intrin
neal canal and the other was directly across the ventral surface of the sic growth, and, as cavitation proceeds, by incorporating substantial
cranial midgut, immediately caudal to the developing primitive ventral contributions from the dorsal lamella separated by cleavage of the
mesogastrium. By stage 14, the passage from one side of the falciform posterior gastric mesenchyme; it is now called the secondary dorsal
ligament to the other necessitates passing below the greatly enlarged mesogastrium (see Fig. 60.7A(ii)). The gastric attachment of the second
liver, or the curved lower edge of the falciform ligament, or the lesser ary dorsal mesogastrium changes progressively. It may be regarded as a
omentum. The position of the falciform ligament is of clinical interest set of somewhat spiral lines, longitudinally disposed, that move with
in the neonate in diagnosing pneumoperitoneum because it is silhouet time to the left, from near the lesser curvature, towards and finally
ted by air on abdominal Xrays. reaching the definitive greater curvature. The parietal mesogastrial and
(cleaving) mesoduodenal attachment remains in the dorsal midline for
Caval fold a time, but it later undergoes profound changes. With the confluence
The caval fold is a linear eminence, with divergent cranial and caudal of the cavities that collectively form the lower part of the lesser sac, its
ends, which passes from the upper abdominal to the lower thoracic communication with the upper part (which corresponds to the lesser
region and protrudes from the dorsal wall of the pleuroperitoneal canal. gastric curvature and right and left gastropancreatic folds) becomes
Cranially, it becomes continuous, lateromedially, with the root of the better defined. Ventral to the lower part of the cavity, postcleavage
pulmonary anlage and pleural coelom, the uppermost portion of the splanchnopleure covers the posteroinferior surface of the stomach and
septum transversum mesenchyme, and the retrocardiac mediastinal a short proximal segment of the duodenum. This ventral wall is con
mesenchyme. Caudally, it forms an arch with dorsal and ventral horns. tinued beyond the greater curvature and duodenum as the splanchno
The dorsal horn merges with the primitive dorsal mesentery and the pleuric strip of visceral attachment of the secondary dorsal mesogastrium
mesonephric ridge and associated gonad and suprarenal (adrenal) and mesoduodenum. The radial width of the strip is relatively short
gland. The ventral horn is confluent with the dorsal surface of the septal cranially (gastric fundus) and gradually increases along the descending
mesenchyme. left part of the greater curvature. It is longest throughout the remaining
Thus, the caval fold is a zone where intestinal, mesenteric, intermedi perimeter of the greater curvature as far as the duodenum; this promi
ate, hepatic, pericardial, pulmonary and mediastinal mesenchymes nent part shows continued marginal (caudoventral and lateral) growth | 1,478 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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with extended internal cavitation (its walls constitute the expanding vein, portal vein, left renal vessels, the caudal pole of the left suprar
greater omentum; see Fig. 60.6H). The margins of the cavity of the enal gland, a broad ventral band on the left kidney and various
inferior part of the lesser sac are limited by the reflexed edges of the muscles). The intervening peritoneal mesothelia fuse and atrophy, and
ventrally placed strata derived from the secondary dorsal mesogastrium the mesenchymal cores form fascial sheaths and septa. The pancreas is
just described. These converge to form the splanchnopleuric dorsal wall, now sessile. The peritoneum covering the upper left part of its head,
which is initially ‘free’ throughout, except at its midline dorsal root. At neck and the anterosuperior part of its body forms the central part of
roughly midgastric levels, the pancreatic rudiment grows obliquely the dorsal wall of the lesser sac. The pancreatic tail remains perito
encased in this dorsal wall; its tail ultimately reaches the left limit of nealized by a persisting part of the secondary dorsal mesogastrium as
the lesser sac at the level of the junction between gastric fundus and it curves from the ventral aspect of the left kidney towards the hilum
body (see Fig. 60.7C(ii)). of the spleen. The infracolic parts of the pancreas are covered with
greater sac peritoneum. In the greater omental subregion of the lower
Greater omentum part of the lesser sac, two contrasting forms of mesenteric adhesion
The greater omentum continues to grow, both laterally and, particularly, occur. The posterior ‘returning’ bilaminar stratum of the omentum
caudoventrally. It covers and is closely applied to the transverse meso undergoes partial fusion with the peritoneum of the transverse colon
colon, transverse colon and inframesocolic and infracolic coils of small at the taenia omentalis and with its mesocolon. The layers remain
intestine (see Fig. 60.6D–G). At this stage, the quadrilaminar nature of surgically separable; no anastomosis occurs between omental and
the dependent part of the greater omentum is most easily appreciated. colic vessels.
‘Simple’ mesenteries are bilaminar: they possess two mesothelial sur The original dorsal midline attachment to the parietes of the
faces derived from splanchnopleuric coelomic epithelium, which foregut dorsal mesentery is profoundly altered during the develop
enclose a connective tissue core derived from splanchnopleuric mesen ment of the lesser sac and its associated viscera. However, despite the
chyme. In the greater omentum, the gastric serosa covering its postero extensive areas of fusion, virtually the whole of the gastric greater cur
inferior surface (single mesothelium) and the anterosuperior serosa vature (other than a small suboesophageal area) and its topographical
(single mesothelium) converge to meet at the greater curvature and continuation (the inferior border of the first 2–3 cm of the duode
initial segment of the duodenum. The resulting bilaminar mesentery num) retain true mesenteric derivatives of the secondary dorsal mes
continues caudoventrally as the ‘descending’ stratum of the omentum. ogastrium and its continuation, the dorsal mesoduodenum. Although
This, on reaching the omental margins, is reflexed and now passes regional names are used to assist identification and description, it is
cranio dorsally to its parietal root as the ‘ascending’ posterior bilaminar important to emphasize that they are all merely subregions of one
stratum. The two bilaminar strata are, initially, in fairly close contact continuous sheet.
caudally, but are separated by a fine, fluidcontaining, cleftlike exten The upper (oesophagophrenic) part of the lesser omentum arches
sion of the lower part of the lesser sac. The posterior mesothelium of across the diaphragm. As this bilaminar mesentery approaches the
the posterior stratum makes equally close contact with the anterosupe oesophageal hiatus, its laminae diverge, skirting the margins of the
rior surface of the transverse colon, starting at the taenia omentalis, and hiatus. They then descend for a limited distance and with variable
with its transverse mesocolon. inclination, to enclose reciprocally shaped areas on the dorsum of the
gastric fundus and diaphragm. The area may be roughly triangular to
quadrangular; it contains areolar tissue and constitutes the bare area
Maturation of the lesser sac
of the stomach or, when large, the left extraperitoneal space. Its right
lower angle is the base of the left gastropancreatic fold, and its left
At this stage, and subsequently, it is convenient to designate the lower lower angle reconstitutes the bilaminar mesentery. The root of the
part of the lesser sac as consisting of three subregions: retrogastric, peri latter arches downwards and to the left across the diaphragm and
gastric and greater omental (Fig. 60.7C(ii)). The names are self suprarenal gland, and gives the gastrophrenic ligament to the gastric
explanatory but their confines are all modified by various factors. Two fundus. It continues to arch across the ventral surface of the upper
phenomena are particularly prominent: namely, gastric ‘descent’ rela part of the left kidney, and its layers part to receive the pancreatic tail;
tive to the liver, and fusion of peritoneal layers with altered lines of they initially extend to the hilum of the spleen as the splenorenal liga
reflection, adhesion of surfaces and loss of parts of cavities. ment (see Figs 60.6C, 60.7D). The left half of this bilaminar ‘liga
After the third month, hepatic growth, particularly of the left lobe, ment’ provides an almost complete peritoneal tunic for the spleen. It
diminishes and the whole organ recedes into the upper abdomen. then reunites with its fellow at the opposite rim of the splenic hilum,
Meanwhile, the stomach elongates and some descent occurs, despite and continues to the next part of the gastric greater curvature as the
its relatively fixed cranial and caudal ends. This produces the angular gastrosplenic ligament. The remaining part (perhaps twothirds) of
flexure of the stomach, which persists postnatally. The concavity of the the gastric greater curvature and its short duodenal extension provide
lesser curvature is now directed more precisely to the right; the lesser attachment for the anterior, ‘descending’, bilaminar stratum of the
omentum is more exactly coronal and its free border vertical. Ventral greater omentum. Its returning, posterior, bilaminar stratum continues
to the liver, the free border of the falciform ligament passes steeply to its parietal root (which extends from the inferior limit assigned to
craniodorsally from umbilicus to liver (see disposition in the neonate the splenorenal ligament), and curves caudally and to the right along
in Figs 14.6–14.7). The mesenchymal dorsal wall of the lower part of the anterior border of the body of the pancreas, immediately cranial
the lesser sac, which is crossed obliquely by the growing pancreas, has, to the line of attachment of the transverse mesocolon. Crossing the
up to this point, remained free and retained its original dorsal midline neck of the pancreas, the same curve is followed for a few centimetres
root. Substantial areas now fuse with adjacent peritonealized surfaces on to its head; the omental root then sharply recurves cranially and to
of retroperitoneal viscera, the parietes, or another mesenteric sheet or the left, to reach the inferior border of the duodenum. Thus, it reaches
fold. Where sheets fuse, there is a variable loss of apposed mesothelia that part of the lesser sac provided by cleavage of the dorsal mesoduo
and some continuity of their mesenchymal cores, but they remain denum from the greater sac. It enters the epiploic foramen, traverses
surgically separable and no vascular anastomosis develops across the the epiploic canal between the caudate hepatic process and proximal
interzone. Above the pancreas, the posterior secondary dorsomesogas duodenum, then crosses the right gastropancreatic fold, and descends
trial wall of the sac becomes closely applied to the peritoneum behind the proximal duodenum to enter the right marginal strip
covering the posterior abdominal wall and its sessile organs, the dia enclosed by the greater omentum. The definitive origins of the perito
phragm, much of the left suprarenal gland, the ventromedial part of neum from the posterior abdominal wall are shown in the adult in
the upper pole of the left kidney, the initial part of the abdominal Figures 63.1, 68.5, 63.6B.
aorta, the coeliac trunk and its branches, and other vessels, nerves
and lymphatics. Their peritoneal surfaces fuse. However, albeit with Peritoneum associated with the
some tissue loss, a single mesothelium remains covering these struc
mid- and hindgut
tures, intercalated as a new secondary dorsal wall for this part of the
lesser sac.
The pancreas grows from the duodenal loop, penetrating the sub It is convenient to consider the mesenteries of the small and large
stance of the dorsal mesoduodenum and secondary dorsal mesogas intestine after rotation and the principal growth patterns have been
trium; their mesenchymes and mesothelia initially clothe its whole achieved, and the developing pancreas is becoming retroperitoneal.
surface, except where peritoneal lines of reflection exist. Its posterior
Small intestine
peritoneum becomes closely applied to that covering all the posterior
abdominal wall structures it crosses (the inferior vena cava, abdomi Most of the duodenal loop encircles the head of the pancreas and is
nal aorta, splenic vein, superior mesenteric vessels, inferior mesenteric retroperitoneal. The peritoneum principally covers its ventral and | 1,479 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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RETPAHC
convex aspects. Areas not covered are a short initial segment of the eleventh ribs by a phrenicocolic ligament. The latter sometimes
superior (first) part, which is more completely peritonealized because blends with a presplenic fold that radiates from the gastrosplenic liga
it gives attachment to the right margins of the greater and lesser omenta; ment. The descending colon becomes sessile. The process of fusion and
the sites where the transverse colon is closely apposed to the descending obliteration of both ascending and descending mesocolons starts later
(second) part, or where the latter is crossed by the root of the transverse ally and progresses medially.
mesocolon; and the sites where the mesentery crosses the transverse
(third) part, and descends across the ascending (fourth) part from its Sigmoid colon
upper extremity at the duodenojejunal flexure. These regions are illus The sigmoid colon is most variable in its length and disposition. It
trated in the adult in Figure 63.2. In addition, one or more of up to six retains its dorsal mesocolon, but the initial midline dorsal attachment
different duodenal recesses may develop (p. 1108). of its root is considerably modified in its definitive state.
From a mesenteric standpoint, the succeeding small intestine, from
the duodenojejunal flexure to the ileocaecal junction, undergoes less Rectum
modification of its embryonic form than other gut regions. Its early The rectum continues from the ventral aspect of the third sacral vertebra
dorsal mesentery is a continuous, single (but structurally bilaminar) to its anorectal (perineal) flexure anteroinferior to the tip of the coccyx;
sheet, with a midline parietal attachment (line of reflection, or ‘root’). the distance changes with age. All aspects of the rectum are encased by
The attachment of the root becomes an oblique narrow band from the mesenchyme, and the early, dorsally placed, mass is named, by some
left aspect of the second lumbar vertebra to the cranial aspect of the authorities, the dorsal mesorectum. However, the latter does not form
right sacroiliac joint (see Figs 60.6H, 63.2). a true mesentery; with progressive skeletal development, it is reduced
to a woven fibroareolar sheet that displays patterned variations in thick
Ascending colon ness and fibre orientation. The sheet is closely applied to the ventral
The caecum and vermiform appendix arise as a diverticulum from the concavity of the sacrum and coccyx, and encloses numerous fibromus
antimesenteric border of the caudal limb of the midgut loop; conse cular and neurovascular elements. The rectum, therefore, becomes
quently, the caecum does not possess a primitive mesocaecum. These sessile, and visceral peritoneum is restricted to its lateral and ventral
regions of the gut undergo long periods of growth, often asymmetrical, surfaces (see Fig. 72.4).
and their final positions, dimensions and general topography show With the disappearance of the postanal gut by the end of the fifth
considerable variation. The vermiform appendix is almost wholly week, the ventrolateral peritoneum reaches the superior surface of the
clothed with visceral peritoneum, derived from the diverging layers of pelvic floor musculature; this condition persists until late in the fourth
its rather diminutive mesoappendix. The latter should perhaps be month. In the male, the ventral rectal peritoneum is reflected over the
regarded as a direct derivative of the primitive dorsal mesentery, and posterior surface of the prostate, bladder trigone and associated struc
perhaps a similar status for the vascular fold of the caecum should be tures. In the female, the ventral peritoneum initially receives a reflection
considered. that covers almost the whole posterior aspect of the vagina, and is
The colonic gut retains its primitive dorsal mesentery, the mesoco continued over the uterus. Subsequently, the closely apposed walls of
lon, until the differential growth, rotation and circumabdominal dis these deep peritoneal pouches fuse over much of their caudal extent,
placement of this part of the gut tube near completion. Its original their mesothelia are lost, and the viscera are separated by an interven
root is still vertical in the dorsal midline, although the mesocolon ing, bilaminar (surgically separable), fibrous stratum. In the male, this
diverges from it widely as an incomplete, flattened pyramid, to reach becomes the rectovesical fascia and posterior wall of the prostatic
its colonic border at the future taenia mesocolica. During the fourth sheath (see Fig. 72.10). In the female, it becomes the rectovaginal
and fifth months, substantial areas of the primitive mesocolon adhere septum between the lower part of the vagina and the rectum (see Fig.
to, then fuse with, the parietal peritoneum. In this way, some colonic 72.9). The proximal third of the rectum is covered by peritoneum ven
segments become sessile while others have a shorter mesocolon with trolaterally; the lateral extensions of this tunic are triangular and deep
an often profoundly altered parietal line of attachment. The mesoco proximally, but taper to an acute angle by the middle third of the
lon of the transverse and sigmoid segments normally persists, while rectum. The middle third of the rectum is covered by peritoneum only
the ascending colon, right (hepatic) flexure and descending colon on its ventral surface, where it forms the posterior wall of the shallower
become sessile; the ascending or descending, or both, colonic seg rectovesical or rectovaginouterine pouch. The remaining rectum and
ments may also retain a mesocolon, which varies from a localized anal canal are extraperitoneal.
‘fold’ to a complete mesocolon. When sessile, the ventral, medial and
lateral aspects of the ascending or descending colon are clothed with
NEONATAL PERITONEAL CAVITY
peritoneum, and the protrusion of the viscus produces medial and
lateral peritoneal paracolic gutters on each side. This form of apposi
The fully formed peritoneal cavity, although complex topographically,
tion to underlying structures (zygosis) proceeds from the ascending
remains a single cavity with numerous intercommunicating regions,
colon to include the right colic (hepatic) flexure; from there, it contin
pouches and recesses (see Fig. 14.7). The only small peritoneal sacs to
ues anteroinferiorly to the left, so involving the rightsided initial
separate completely from the main cavity are the infracardiac bursa and
segment of the transverse colon.
the tunica vaginalis testis (see Fig. 72.17).
In fetal life, the greater omental cavity extends to the internal
Transverse colon
aspect of the lateral and caudal edges of the omentum. Postnatally, a
The right extremity of the transverse colon is sessile, and is separated
slow but progressive fusion of the internal surfaces occurs, with oblit
by fibroareolar tissue from the anterior aspect of the descending
eration of the most dependent part of the cavity; this proceeds ros
(second) part of the duodenum and the corresponding aspect of most
trally and, when mature, the cavity does not usually extend appreciably
of the head of the pancreas. The remainder of the transverse colon, up
beyond the transverse colon. Transverse mesocolon–greater omentum
to and including the left (splenic) colic flexure, is almost completely
fusion begins early while the umbilical hernia of the midgut has not
peritonealized by the diverging layers of the transverse mesocolon.
returned. It starts between the right margin of the early greater
The root of the latter reaches the neck and whole extent of the ante
omentum and near the root of the presumptive mesocolon, and later
rior border of the body of the pancreas. The long axis of the definitive
spreads to the left.
pancreas lies obliquely. The splenic colonic flexure is considerably
In the neonate, the peritoneal cavity is ovoid (see Fig. 14.6). It is
more rostral than the hepatic flexure and, consequently, the root of
fairly shallow from anterior to posterior because the bilateral posterior
the mesocolon curves obliquely upwards as it crosses the upper
extensions on each side of the vertebral column, which are prominent
abdomen from right to left. As it expands, the posteroinferior wall of
in the adult, are not present. Two factors lead to the protuberance of
the greater omental part of the lesser sac gradually covers, and becomes
the anterior abdominal wall in the neonate and infant. The diaphragm
closely applied to, the transverse mesocolon and its contained colon,
is flatter in the newborn, which produces a caudal displacement of the
finally projecting beyond the latter. Craniocaudal adherence now
viscera. The pelvic cavity is very small in the neonate, which means that
occurs between the omental wall and the pericolonic and mesoco
organs that are normally pelvic in the adult, i.e. urinary bladder, ovaries
lonic layers.
and uterus, all extend superiorly into the abdomen (see Figs 14.7,
72.9–72.10). The pelvic cavity is joined to the abdominal cavity at less
Descending colon
of an acute angle in the neonate because there is no lumbar vertebral
The left colic flexure receives much of its peritoneal covering from the curve and only a slight sacral curve.
left extremity of the transverse mesocolon. It is also often connected The peritoneal attachments are similar to the adult. However, the
to the parietal peritoneum of the diaphragm over the tenth and greater omentum is relatively small; its constituent layers of peritoneum | 1,480 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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may not be completely fused, and it does not extend much below the The most common anomaly of suprarenal gland development is
level of the umbilicus. Generally, the length of the mesentery of the congenital hyperplasia, which occurs in 1 : 5000 to 1 : 15,000 births.
small intestine and of the transverse and sigmoid mesocolons is greater This condition is caused by a group of autosomal recessive disorders,
than in the adult, whereas the area of attachment of the ascending and in which there are deficiencies in enzymes required for the synthesis of
descending colons is relatively smaller. The peritoneal mesenteries and cortisol. In 90% of cases, the cause is deficiency of the enzyme
omenta contain little fat. 21hydroxylase, producing an accumulation of 17hydroxyprogesterone,
which is converted to androgens. The levels of androgens increase by
several hundred times, causing female embryos and fetuses to undergo
SPLEEN
external genital masculinization ranging from clitoral hypertrophy to
formation of a phallus and scrotum; masculinization of the brain has
The spleen appears about the sixth week as a localized thickening of also been suggested. In male embryos, the levels do not cause any
the coelomic epithelium of the dorsal mesogastrium near its cranial end changes in external genitalia. Signs of androgen excess may appear in
(see Figs 60.6–60.7). The proliferating cells invade the underlying ang childhood with precocious masculinization and accelerated growth
iogenetic mesenchyme, which becomes condensed and vascularized. (Lewis et al 1999).
The process occurs simultaneously in several adjoining areas, which
soon fuse to form a lobulated spleen of dual origin (from coelomic
epithelium and from mesenchyme of the dorsal mesogastrium). SUPRARENAL GLANDS IN THE NEONATE
The vascular reticulum is well developed at 8–9 weeks, and contains
immature reticulocytes and numerous closely spaced, thinwalled, vas The suprarenal glands are relatively very large at birth (see Figs 14.6C,
cular loops. From 11 weeks, the development of the spleen has been 72.8) and constitute 0.2% of the entire body weight, compared with
described in four stages: stage 0 has erythrocyte precursors, few macro 0.01% in the adult. The left gland is heavier and larger than the right,
phages and fewer lymphocytes; at stage I, lymphocytes begin coloniza as it is in the adult. At term, each gland usually weighs 4 g; the average
tion and arterial vascular lobules are seen; at stage II, T and B weight of the two glands is 9 g (average in the adult is 7–12 g). Estima
lymphocytes form periarteriolar clusters with B cells aggregated around tion of the suprarenal gland volume can provide an estimate of fetal
the peripheral branches of splenic arterioles and T cells centrally; at weight; a volume of greater than 420 mm3/kg is relevant in predicting
stage III, before birth, the lobular arrangement is no longer discernible preterm birth within 5 days of measurement (Turan et al 2012, Turan
(Steiniger et al 2007). et al 2007). Within the first 2 weeks of postnatal life, the glands shrink
From week 17, αSMApositive reticulum cells are found around to normal infantile size. The average weight of both glands is 5 g by the
arterioles. These increase in number and form a reticular framework end of the second week, and 4 g by 3 months; gland birth weight is not
from 20 to 23 weeks, when a primitive white pulp can be observed regained until puberty. This rapid involution of the glands occurs
around arterioles. By 24 weeks, T and B lymphocytes become segre regardless of gestational age. It is thought that parturition is the stimu
gated, with T cells within the SMApositive reticular framework, and B lus for suprarenal involution (BenDavid et al 2007). The cortex of the
cells aggregating close to the periarticular lymphoid sheath, where they suprarenal gland is thicker than in the adult and the medulla of the
form lymphoid follicles (Satoh et al 2009). gland is small. With normal involution, the fetal zone cells of the post
Initially, the splenic capsule consists of cuboidal cells bearing cilia natal gland become smaller and they assume the appearance and organ
and microvilli. The enlarging spleen projects to the left, so that its sur ization typical of zona fasciculata.
faces are covered by the peritoneum of the mesogastrium on its left
aspect, which forms a boundary of the general extrabursal (greater) sac.
When fusion occurs between the dorsal wall of the lesser sac and the INFERIOR VENA CAVA, PORTAL CIRCULATION
dorsal parietal peritoneum, it does not extend to the left as far as the
AND UMBILICAL VESSELS
spleen, which remains connected to the dorsal abdominal wall by a
short splenorenal ligament. Its original connection with the stomach
persists as the gastrosplenic ligament. The earlier lobulated character of INFERIOR VENA CAVA
the spleen disappears, but is indicated by the presence of notches on
its upper border in the adult. The inferior vena cava of the adult is a composite vessel that develops
The spleen displays various developmental anomalies, including on the posterior abdominal wall dorsal to the developing peritoneal
complete agenesis, multiple spleens or polysplenia, isolated small addi cavity. It forms as a consequence of the temporal remodelling of suc
tional spleniculi and persistent lobulation. Asplenia and polysplenia cessive venous complexes (see Fig. 13.4). The precise mode of develop
are associated with other anomalies, especially those involving the ment of its postrenal segment (caudal to the renal vein) is still somewhat
cardiac and pulmonary systems. Accessory spleens are very common in uncertain. Its function is initially carried out by the right and left post
neonates, located in the greater omentum. At birth, the spleen weighs, cardinal veins (Fig. 60.8; see also Fig. 13.4), which receive the venous
on average, 13 g (see Fig. 14.6). It doubles its weight in the first post drainage of the lower limb buds and pelvis, and run in the dorsal part
natal year and triples it by the end of the third year. of the mesonephric ridges, receiving tributaries from the body wall
(intersegmental veins) and from the derivatives of the mesonephroi. It
should be remembered that descriptions of venous development are
SUPRARENAL GLANDS
very largely based on studies on animals, where the dimensions and
final disposition of visceral organs differ from those found in humans.
The suprarenal (adrenal) cortex is formed during the second month by Many of the changes seen in the development of the infrahepatic caval
a proliferation of the coelomic epithelium. Cells pass into the underly and azygos systems in the human may result from lateral to medial
ing mesenchyme between the root of the dorsal mesogastrium and the movement of the vessels as a consequence of the growth of the abdomi
mesonephros (see Fig. 17.11). The proliferating tissue, which extends nal viscera (Hikspoors et al 2015).
from the level of the sixth to the twelfth thoracic segments, is soon The early postcardinal veins communicate across the midline via an
disorganized dorsomedially by invasion of neural crest cells from interpostcardinal anastomosis. This remains as an oblique transverse
somite levels 18–24, which form the medulla, and also by the develop anastomosis between the iliac veins, and becomes the major part of the
ment of venous sinusoids. The latter are joined by capillaries, which definitive left common iliac vein. It diverts an increasing volume of
arise from adjacent mesonephric arteries and penetrate the cortex in a blood into the right longitudinal veins, which accounts for the ultimate
radial manner. When proliferation of the coelomic epithelium stops, disappearance of most of those on the left.
the cortex is enveloped ventrally, and later dorsally, by a mesenchymal The supracardinal veins receive the larger venous drainage of the
capsule that is derived from the mesonephros. The subcapsular nests of growing body wall. The right supracardinal vein persists and forms
cortical cells are the rudiment of the zona glomerulosa; they proliferate the greater part of the postrenal segment of the inferior vena cava. The
cords of cells that pass deeply between the capillaries and sinusoids. continuity of the vessel is maintained by the persistence of the anasto
The cells in these cords degenerate in an erratic fashion as they pass mosis between the right supracardinal and the right subcardinal in the
towards the medulla, becoming granular, eosinophilic and, ultimately, renal collar. The left supracardinal disappears, but some of the renal
autolysed. These cords of cells constitute the fetal cortex, which under collar formed by the left supracardinal–subcardinal anastomosis per
goes rapid involution during the first 2 years after birth. The fascicular sists in the left renal vein. Both supracardinal veins drain cranially into
and reticular zones of the adult cortex are proliferated from the glomer the subcardinal veins. On the right side, the subcardinal vein comes
ular zone after birth. Serial ultrasound measurements of the length of into intimate relationship with the liver. An extension of the vessel takes
fetal suprarenal glands at 4week intervals from the fifteenth week of place in a cranial direction and meets and establishes continuity with
gestation have been published (van Vuuren et al 2012). a corresponding new formation that is growing caudally from the right | 1,481 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Brachiocephalic veins
A B Superior
intercostal vein
Internal jugular veins
Oblique vein
Superior
and ligament
vena cava
of left atrium
Azygos vein IVC hepatic
Postcardinal vein
segment
IVC subhepatic
segment
Hemiazygos vein
IVC subcardinal
Remains of intersubcardinal segment
anastomosis (renal collar)
Left suprarenal vein
Left supracardinal vein Left renal vein
Oblique transverse anastomosis
Left gonadal vein
IVC supracardinal
segment
Postcardinal vein
Supracardinal vein (thoracolumbar line vein) Common iliac veins
Azygos line vein (medial sympathetic line vein)
Subcardinal vein
Hepatic segment of inferior vena cava
(and right vitelline vein)
Subhepatic segment of IVC
Fig. 60.8 The inferior vena cava (IVC) develops within the posterior abdominal wall. It is a composite vessel formed by temporal remodelling of
successive somatic venous anastomoses. A, The progressive asymmetry of the developing venous system. B, The definitive venous arrangement. (For
early venous development, see Fig. 13.4.)
vitelline hepatocardiac (common hepatic) vein. In this way, on the right embryonic arrangement occur with the growth of the foregut, liver and
side, a more direct route is established to the heart and the prerenal paired viscera, i.e. kidneys and suprarenal glands.
(cranial) segment of the inferior vena. In summary, the inferior vena The early development of the ventral splanchnic arteries is outlined
cava is formed from below upwards by the confluence of: the common in Chapter 13. Three main arterial trunks – the coeliac trunk, superior
iliac veins, a short segment of the right postcardinal vein, the mesenteric and inferior mesenteric arteries – supply the fore, mid and
postcardinal–supracardinal anastomosis, part of the right supracardinal hindgut, respectively. From the gastric terminal segment of the future
vein, the right supracardinal–subcardinal anastomosis, right subcardi oesophagus to the upper rectum, the developing endodermal epithe
nal vein, a new anastomotic channel of double origin (the hepatic lium is surrounded by splanchnopleuric mesenchyme permeated by a
segment of the inferior vena cava), and the cardiac termination of the capillary plexus that drains into an anastomosing network of veins. This
right vitelline hepatocardiac vein (common hepatic vein). plexus is particularly dense ventrally where it is associated with the
Only the supracardinal part of the inferior vena cava receives central midgut region; here, for a while, it receives a network of small
intersegmental venous drainage. The postrenal (caudal) segment of the veins from the definitive yolk sac. Later, in normal development, these
inferior vena cava is on a plane that lies dorsal to the plane of the vessels atrophy as the yolk sac diminishes. More rostrally, the splanch
prerenal (cranial) segment. Thus, the right phrenic, suprarenal and nopleuric capillaries associated with the foregut and upper portions of
renal arteries, which represent persistent mesonephric arteries, pass the yolk sac form longitudinal channels anterolateral to the gut and
behind the inferior vena cava, whereas the testicular or ovarian artery, these become increasingly well defined as the embryonic abdominal
which has a similar developmental origin, passes anterior to it. vitelline veins. Entering the septum transversum, the right and left vitel
In some animals, the right postcardinal vein constitutes a large part line veins incline slightly, becoming parallel to the lateral aspects of the
of the postrenal segment of the inferior vena cava. In these cases, the gut. They establish connections with capillary plexuses in the septal
right ureter, on leaving the kidney, passes medially dorsal to the vessel mesenchyme, and then continue, finally curving to enter the medial
and then, curving round its medial side, crosses its ventral aspect. part of the cardiac sinual horn of their corresponding side. The parts of
Rarely, a similar condition is found in humans, and indicates the per the gut closely related to the presinual segments of the vitelline veins
sistence of the right postcardinal vein and failure of the right supracar are the future subdiaphragmatic end of the oesophagus, primitive
dinal to play its normal part in the development of the inferior vena stomach, the superior (first) and descending (second) regions of the
cava. duodenum, and the remainder of the duodenal tube.
The principal ascending vitelline veins flanking the sides of the
abdominal part of the foregut receive venules from its splanchnopleuric
PORTAL CIRCULATION capillaries and those of the septal mesenchyme. Within these venular
nets, enlarged (but still plexiform) anastomoses connect the two vitel
The heart first differentiates in splanchnopleure that, after headfold line veins (Fig. 60.9; see Fig. 13.1C). A subdiaphragmatic intervitelline
formation, forms the dorsal wall of the primitive pericardial cavity anastomosis develops in the rostral septal mesenchyme, lying a little
(floor of the rostral foregut) and may, therefore, be considered a highly caudal to the cardiac sinuatrial chamber, connecting the veins near their
specialized vitelline vascular derivative. At the caudal extremity of the sinual terminations. (The channel is sometimes termed suprahepatic
splanchnopleuric gut tube (the future lower rectum and upper anal because of the position of the hepatic primordium; with expansion of
canal), the vitelline venous drainage makes connections with the inter the latter, it becomes partly intrahepatic.) The presumptive duodenum
nal iliac radicles of the postcardinal complex. is crossed by three transverse duodenal intervitelline anastomoses. Their
The development of the gut occurs contemporaneously with changes relation to the gut tube alternates so that the most cranial, the subhe
to the early symmetrical embryonic circulation (Ch. 13). A symmetrical, patic, is ventral, the intermediate is dorsal and the caudal is ventral (Fig.
segmental system of somatic arteries remains and supplies the body 60.9B). It has become customary to describe the paraduodenal vitelline
wall of the trunk. The underlying arrangement of these vessels is only veins and their associated anastomoses as forming a figure eight. At this
slightly modified by subsequent development. The main changes to the early stage, when left and right embryonic veins are still symmetrical, | 1,482 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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A Common sinuatrial chamber B Parts that persist, expand and
modify into main permanent
Sinus venosus: right horn channels
Right New connections forming further main
precardinal vein permanent channels
Site of hepatic rudiment, which expands
Right common
cardinal vein INTERVITELLINE and invades neighbouring anastomoses,
ANASTOMOTIC vitelline and umbilical veins
Right VEINS
postcardinal vein 1 Subdiaphragmatic Oxygenated blood
(suprahepatic)
Early ductus venosus Deoxygenated blood
Right 2 Subhepatic, ventral
Right vitelline duodenal
umbilical vein vein
3 Intermediate, dorsal
Region of future duodenal
duodenum
4 Caudal, central
duodenal
Fig. 60.9 Development of the vitelline, umbilical and terminal cardinal vein complexes: the early symmetrical condition. A, The early symmetrical
arrangement of cardinal and umbilical veins entering the sinus venosus; blood from the yolk sac passes, via vitelline veins, through anastomoses forming
in the septum transversum mesenchyme (green). B, The developing duodenum is surrounded by transverse duodenal intervitelline anastomoses.
Changes in the developing gut and umbilical veins cause shifts in the routes taken by venous blood flowing to the sinus venosus.
Right half of subdiaphragmatic anastomosis
Progressive inflection of sinuatrial wall
Right precardinal and common cardinal veins
Left precardinal and common cardinal veins
Right postcardinal vein Postcardinal vein
Hepatocardiac part of right umbilical vein
Hepatocardiac part of left umbilical vein
Left venae revehentes
Right hepatocardiac vein (termination of Hepatocardiac part of left vitelline vein
right vitelline vein – future inferior vena cava)
Hepatic terminals of left vitelline vein
Left venae advehentes
Hepatic terminal right umbilical vein Hepatic terminals of left umbilical vein
Vitelline vein segments and ventral anastomosis New venous connections
Left umbilical vein
Presumptive splenic vein Merge to form root of
Presumptive superior mesenteric vein definitive hepatic portal vein
Parts that persist, expand and modify into
main permanent channels
New connections forming further main permanent channels
Oxygenated blood
Deoxygenated blood
Fig. 60.10 Development of the vitelline, umbilical and terminal cardinal vein complexes: a mid-stage of asymmetry has been reached between the early
symmetrical condition (see Fig. 60.9) and the definitive late prenatal state. The extent of the liver within the septum transversum mesenchyme is shown
in green.
the cranial duodenal anastomosis becomes connected with the subdia CHANGES IN THE VITELLO-UMBILICAL VEINS
phragmatic anastomosis by a median longitudinal channel, the primi
tive median ductus venosus, which is dorsal to the expanding hepatic Progressive changes in the vitelloumbilical veins are rapid, profound
primordium but ventral to the gut. The further development of the and closely linked with regional modifications in shape and position
vitelline veins and anastomoses is, as indicated, closely interlocked, of the gut, expansion and invasion of venous channels by hepatic tissue,
with rapid hepatic expansion and gut changes, and umbilical vein dis asymmetry of the heart and cardiac venous return. The principal events
position and modification is closely involved. are summarized in Figures 60.9–60.11. | 1,483 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Superior vena cava Left atrium Fig. 60.11 The condition of some main upper
abdominal and intrathoracic right atrial terminal
Coronary sinus
veins in the later prenatal months. The rotation of
Right atrium Secondary upper left hepatic vein the stomach and movement of the duodenum
produce relative changes in the final arrangement
Inferior vena cava of the duodenal intervitelline anastomoses that
form the hepatic portal vein.
Upper right hepatic vein
Ductus venosus
Lower right hepatic vein
Persistent left afferent hepatic veins
Left umbilical vein
Portal vein formed from the
Splenic vein
final arrangement of anterior,
left and posterior anastomoses
around the duodenum Superior mesenteric vein
Duodenum
Oxygenated blood
Deoxygenated blood
From the cranial portion of the early hepatic evagination of the fibrous tags attached to the inferior wall of the coronary sinus. The right
foregut, interconnected sheets and ‘cords’ of endodermal cells, the pre vitelline hepatocardiac vein continues enlarging and, ultimately, forms
sumptive hepatocytes, penetrate the septum transversum mesenchyme. the terminal segment of the inferior vena cava. The latter receives the
Hepatic mesenchyme is composed of a mixed population of cells with right efferent hepatic veins and new channels draining the territories of
endothelial/angiogenic and connective tissue lineages. Capillary plex the left efferent hepatic veins. These collectively form the upper and
uses develop within this mesenchyme and, possibly under the influence lower groups of right and (secondary) left hepatic veins. The terminal
of the endodermal hepatic sheets, the plexuses become more profuse caval segment also shows the orifice of the right half of the intervitelline
by further addition of angioblastic septal mesenchyme, which also subdiaphragmatic anastomosis, and a large new connection with the
forms masses of perivascular intrahepatic haemopoietic tissue. These right subcardinal vein.
processes extend along the plexiform connections of the vitelline, and The hepatic terminals of the right and left duodenal parts of the
later the umbilical, veins until their intrahepatic (transseptal) zones vitelline veins are destined to form the corresponding branches of the
themselves become largely plexiform. Initially capillary in nature, they hepatic portal vein, the left branch incorporating the cranial ventral
transform into a mass of rather wider, irregular, sinusoidal vessels with intervitelline anastomosis. With rotation of the gut and formation of
a discontinuous endothelium containing many phagocytic cells. The the duodenal loop, segments of the original vitelline veins and the
lengths of vitelline veins involved in these processes are the intermedi caudal transverse anastomosis atrophy (indicated in Figs 60.10–60.11),
ate parts of the segments extending from the subhepatic (cranioventral while new splanchnopleuric venous channels – the superior mesenteric
duodenal) to the suprahepatic (subdiaphragmatic) transverse intervitel and splenic veins – converge and join the left end of the dorsal inter
line anastomoses, and the corresponding lengths of the umbilical veins. mediate anastomosis. The numerous other radicles of the portal vein
Thus, at this early stage, the liver sinusoids are perfused by mixed blood and its principal branches, including the inferior mesenteric vein, are
reaching them through a series of branching vessels collectively called later formations.
the venae advehentes, or afferent hepatic veins: they are deoxygenated For a period, placental blood returns from the umbilicus via right
from the gut splanchnopleure via vitelline vein hepatic terminals, and and left umbilical veins, both discharging through afferent hepatic veins
oxygenated from the placenta via hepatic terminals of the umbilical into the hepatic sinusoids, where admixture with vitelline blood occurs.
veins (see Fig. 60.10). Blood leaves the liver through four venae reve At approximately 7 mm crown–rump length, the right umbilical vein
hentes (efferent hepatic veins); two on each side reach and open into retrogresses completely. The left umbilical vein retains some vessels
their respective cardiac sinual horns. This full complement of four discharging directly into the sinusoids, but new enlarging connections
hepatocardiac veins is only transient and becomes reduced to one with the left half of the subhepatic intervitelline anastomosis emerge.
dominant, rapidly enlarging channel. The originally bilaterally sym The latter is the start of a bypass channel for the majority of the pla
metrical cardinal vein complexes, both rostral and caudal, develop cental blood, which continues through the median ductus venosus and,
transverse or oblique anastomoses so that the cardiac venous return is finally, the right half of the subdiaphragmatic anastomosis, to reach the
ultimately restricted to the definitive right atrium. termination of the inferior vena cava (see Fig. 60.11).
These cardiac and concomitant hepatoenteric changes are accompa The left and right hepatic portal veins and the ductus venosus are
nied by events in supra, intra and subhepatic parts of the vitello routinely observed in the second trimester ultrasound scan at the plane
umbilical veins. Some vessels enlarge, persisting as definitive vessels to to estimate abdominal circumference (see Fig. 14.4G).
maturity; in places, they are joined later by other channels that become
defined in already established capillary plexuses. Other vessels retro
FETAL/NEONATAL UMBILICAL VESSELS
gress, either disappearing completely or remaining as vestigial tags and,
occasionally, vessels of fine calibre. Some vessels of crucial importance
Umbilical arteries
in the circulatory patterns of embryonic and fetal life become obliter
ated postnatally and transformed to substantial fibrous cords. Both
right and left umbilical hepatocardiac and the left vitelline hepatocar The fetal umbilical arteries are in direct continuation with the internal
diac veins continue, for a time, to discharge blood into their sinual iliac arteries. Their lumen is 2–3 mm in diameter at their origin, when
horns; however, they begin to retrogress (see Figs 60.9–60.10). The right distended. This narrows as they approach the umbilicus, where there is
umbilical channel atrophies completely. The left channels also disap a reciprocal thickening of the tunica media, as a result, in particular, of
pear, but their cardiac terminals may, on occasion, be found as conical an increase in the number of longitudinal smooth muscle fibres and | 1,484 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Table 60.1 Key anatomical reference points for umbilical arterial catheterization Umbilical vein
Structure Vertebral level
The umbilical vein in the neonate is 2–3 cm long and 4–5 mm in
Ductus arteriosus T4–5
diameter when distended. It passes from the umbilicus, within the layers
Coeliac artery T12 of the falciform ligament, superiorly and to the right, to the porta hepatis.
Superior mesenteric artery T12–L1 Here, it gives off several large intrahepatic branches to the liver and then
Renal artery L1 joins the left branch of the portal vein and the ductus venosus. The
Inferior mesenteric artery L3 umbilical vein is thinwalled; it possesses a definite internal lamina of
Aortic bifurcation L4–5 elastic fibres at the umbilical ring but not in its intraabdominal course.
The tunica media contains smooth muscle fibres, collagen and elastic
fibres. When the cord is severed, the umbilical vein contracts, but not
elastic fibres. Before birth, there is a proliferation of connective tissue so vigorously as the arteries. The rapid decrease in pressure in the umbili
within the vessel wall. The umbilical vessels constrict in response to cal vein after the cord is clamped means that the elastic tissue at the
handling, stretching, cooling and altered tensions of oxygen and carbon umbilical ring is sufficient to arrest any retrograde flow along the vessel.
dioxide. Umbilical vessels are muscular, but devoid of a nerve supply Before birth, there is a subintimal proliferation of connective tissue.
in their extraabdominal course. After the cord is severed, the umbilical After birth, the contraction of the collagen fibres in the tunica media
arteries contract, preventing significant blood loss; thrombi often form and the increased subintimal connective tissue contribute to the trans
in the distal ends of the arteries. The arteries obliterate from their distal formation of the vessel into the ligamentum teres. Obliteration occurs
ends until, by the end of the second or third postnatal month, involu from the umbilical ring towards the hepatic end. No thrombi are formed
tion has occurred at the level of the superior vesical arteries. The proxi in the obliteration process. For up to 48 hours after birth, the intra
mal parts of the obliterated vessels remain as the medial umbilical abdominal portion of the umbilical vein can be easily dilated. In most
ligaments. adults, the original lumen of the vein persists through the ligamentum
teres and can be dilated to 5–6 mm in diameter.
Umbilical arterial catheterization
Insertion of an umbilical catheter is undertaken to provide direct access Ductus venosus
to the arterial circulation. Arterial blood can be withdrawn repeatedly The ductus venosus is a direct continuation of the umbilical vein and
for measurement of oxygen and carbon dioxide partial pressures, pH, arises from the left branch of the portal vein, directly opposite the
base excess and many other parameters of blood biochemistry and termination of the umbilical vein. It passes for 2–3 cm within the layers
haematology. The indwelling catheter also enables the continuous of the lesser omentum, in a groove between the left lobe and caudate
measurement of arterial blood pressure. lobe of the liver, before terminating in either the inferior vena cava, or
The catheter is inserted directly into either the cut end or the side of in the left hepatic vein immediately before it joins the inferior vena
one of the two umbilical arteries in the umbilical cord stump that cava. The tunica media of the ductus venosus contains circularly
remains attached to the baby after transection of the umbilical cord at arranged smooth muscle fibres, an abundant amount of elastic fibres
the time of delivery. The catheter tip is then advanced along the length and some connective tissue.
of the umbilical artery, through the internal iliac artery, into the The ductus venosus is already closed in about onethird of newborn
common iliac artery and, from there, into the aorta. In order to keep infants. It shuts down by an unknown mechanism. Obliteration begins
the catheter patent, a small volume of fluid is continuously infused at the portal vein end in the second postnatal week and progresses to
through it. It is important for the tip of the catheter to be located well the vena cava; the lumen has been completely obliterated by the second
away from arteries branching from the aorta, to avoid potentially or third month after birth. The fibrous remnant of the ductus venosus
harmful perfusion of these arteries with the catheter fluid. Thus, umbili is the ligamentum venosum.
cal arterial catheter tips are placed in the descending aorta either in a
Umbilical vein catheterization
‘high’ position, above the coeliac artery but well below the ductus arte
riosus, or in a ‘low’ position, below the renal and inferior mesenteric The umbilical vein may be catheterized in the neonate to enable
arteries but above the point where the aorta bifurcates into the two exchange and transfusion of blood, for central venous pressure meas
common iliac arteries. The length of catheter to be inserted can be urement and, usually in an emergency, for vascular access. The catheter
estimated from charts relating the required catheter length to external is inserted into the cut end of the umbilical vein and is advanced along
body measurements, or from birth weight. Positioning of the catheter the length of the vein, through the ductus venosus and into the inferior
is assessed by means of radiographs of the abdomen or chest: a ‘high’ vena cava; the tip is placed between the ductus venosus and the right
catheter tip should be located in the descending aorta somewhere atrium. Positioning of the catheter tip is confirmed radiologically and
between the levels of the sixth and ninth thoracic vertebrae (T6–9), it should be located just above the diaphragm at a point that is level
while a ‘low’ catheter tip should be at a level between the third and with the ninth or tenth thoracic vertebra (T9/T10). As with umbilical
fourth lumbar vertebrae (L3–4). Relevant anatomical reference points arterial catheters, estimation of the required catheter length can be
are given in Table 60.1. determined from standard charts.
KEY REFERENCES
Collins P 2002a Embryology of the pancreas. In: Howard ER, Stringer MD, Lebenthal E 1989 Concepts in gastrointestinal development. In: Lebenthal
Colombani PM (eds) Surgery of the Liver, Bile Ducts and Pancreas in E (ed) Human Gastrointestinal Development. New York: Raven Press;
Children, Part 8. London: Arnold, pp. 479–92. Ch. 1.
Covers pancreatic morphogenesis, the timescale of development, the origin of This chapter is the first in a volume dedicated to the development of
pancreatic cell lines and factors that regulate pancreatic development. structure and function of the gut, liver and pancreas. It includes the
development of the immunological surveillance mechanisms and
Collins P 2002b Embryology of the liver and bile ducts. In: Howard ER, gastrointestinal flora.
Stringer MD, Colombani PM (eds) Surgery of the Liver, Bile Ducts and
Pancreas in Children, Part 3. London: Arnold, pp. 91–102. Neu J (ed) 2012 Gastroenterology and Nutrition: Neonatology Questions
Covers morphogenesis of the liver and early hepatic circulation, the origin of and Controversies, 2nd ed. Philadelphia: Elsevier, Saunders.
hepatic cell lines and the development of the extra- and intrahepatic biliary Contains a comprehensive range of articles on the development and
systems. maturation of the gut.
Gershon MD 2010 Developmental determinants of the independence and O’Rahilly R, Müller F 1987 Developmental Stages in Human Embryos.
complexity of the enteric nervous system. Trends Neurosci 33:446–56. Washington: Carnegie Institution.
This paper reviews the molecular basis of normal and defective enteric Streeter GL 1942 Developmental horizons in human embryos. Descriptions
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Contrib Embryol Carnegie Inst Wash 30:211–45.
Howard ER 2002 Biliary atresia: aetiology, management and complications.
In: Howard ER, Stringer MD, Colombani PM (eds) Surgery of the Liver, Whittle MJ 1999 Gastrointestinal abnormalities. In: Rodeck CH, Whittle MJ
Bile Ducts and Pancreas in Children, Part 3. London: Arnold, (eds) Fetal Medicine: Basic Sciences and Clinical Practice. Edinburgh:
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Reviews the aetiology and clinical presentation of biliary atresia, including the Reviews the diagnosis and treatment of anomalies of the gastrointestinal tract.
congenital, infective and anatomical factors that are related to the condition. | 1,485 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Collins P 2002b Embryology of the liver and bile ducts. In: Howard ER, ship to health and disease. In: Neu J (ed) Gastroenterology and Nutri
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Pancreas in Children, Part 3. London: Arnold, pp. 91–102. Elsevier, Saunders; Ch. 5, pp. 59–65.
Covers morphogenesis of the liver and early hepatic circulation, the origin of O’Rahilly R, Müller F 1987 Developmental Stages in Human Embryos.
hepatic cell lines and the development of the extra- and intrahepatic biliary Washington: Carnegie Institution.
systems.
Patel RM, Neish As, Lin P 2012 The developing intestine as an immune
Gershon MD 2010 Developmental determinants of the independence and organ. In: Neu J (ed) Gastroenterology and Nutrition: Neonatology
complexity of the enteric nervous system. Trends Neurosci 33: 446–56. Questions and Controversies, 2nd ed. Philadelphia: Elsevier, Saunders;
This paper reviews the molecular basis of normal and defective enteric Ch. 6, pp. 67–89.
nervous system development. Rodríguez JM, Murphy K, Stanton C et al 2015 The composition of the gut
Gritz EC, Bhandari V 2015 The human neonatal gut microbiome: a brief microbiota throughout life, with an emphasis on early life. Microb Ecol
review. Front Pediatr 3:17. Health Dis 2015;26 26050 doi: 10.3402/mehd.v26.26050.
Hikspoors JP, Soffers JH, Mekonen HK et al 2015 Development of the Satoh T, Sakurai E, Tada H et al 2009 Ontogeny of reticular framework of
human infrahepatic inferior caval and azygos venous systems. J Anat white pulp and marginal zone in human spleen: immunohistochemical
226:113–25. studies of fetal spleens from the 17th to 40th week of gestation. Cell
Tissue Res 336:287–97.
Hitchcock RJI, Pemble MJ, Bishop AE et al 1992 Quantitative study of the
development and maturation of human oesophageal innervation. Steiniger B, Ulfig N, Risse M et al 2007 Fetal and early postnatal develop
J Anat 180:175–83. ment of the human spleen: from primordial arterial B cell lobules to a
nonsegmented organ. Histochem Cell Biol 128:205–15.
Howard ER 2002 Biliary atresia: aetiology, management and complications.
In: Howard ER, Stringer MD, Colombani PM (eds) Surgery of the Liver, Streeter GL 1942 Developmental horizons in human embryos. Descriptions
Bile Ducts and Pancreas in Children, Part 3. London: Arnold, of age group XI, 13 to 20 somites, and age group XII, 21 to 29 somites.
pp. 103–32. Contrib Embryol Carnegie Inst Wash 30:211–45.
Reviews the aetiology and clinical presentation of biliary atresia, including Turan OM, Turan S, Funai EF et al 2007 Fetal adrenal gland volume: a novel
the congenital, infective and anatomical factors that are related to the method to identify women at risk for impending preterm birth. Obstet
condition. Gynecol 109:855–62.
Ionescu S, Mocanu M, Andrei B et al 2014 Differential diagnosis of abdomi Turan OM, Turan S, Buhimschi IA et al 2012 Comparative analysis of 2D
nal wall defects – omphalocele versus gastroschisis. Chirurgia (Bucur) versus 3D ultrasound estimation of the fetal adrenal gland volume and
109:7–14. prediction of preterm birth. Am J Perinatol 29:673–80.
Kabouridis PS, Lasrado R, McCallum S 2015 Microbiota controls the Vaarala O 2012 The developing gastrointestinal tract in relation to autoim
homeostasis of glial cells in the gut lamina propria. Neuron 85: mune disease, allergy, and atopy. In: Neu J (ed) Gastroenterology and
289–95. Nutrition: Neonatology Questions and Controversies, 2nd ed. Philadel
phia: Elsevier, Saunders; Ch. 7, pp. 91–9.
Kim WK, Kim H, Ahn DH et al 2003 Timetable for intestinal rotation in
staged human embryos and fetuses. Birth Defects Res A Clin Mol Teratol van Vuuren SH, DamenElias HA, Stigter RH et al 2012 Size and volume
67:941–5. charts of fetal kidney, renal pelvis and adrenal gland. Ultrasound Obstet
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ling in stomach and intestine: new roles for hedgehog in gastrointestinal Whittle MJ 1999 Gastrointestinal abnormalities. In: Rodeck CH, Whittle MJ
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Elsevier, Churchill Livingstone; Ch. 54, pp. 703–14.
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structure and function of the gut, liver and pancreas. It includes the systemic inflammation and developmental delays. In: Neu J (ed) Gas
development of the immunological surveillance mechanisms and troenterology and Nutrition: Neonatology Questions and Controver
gastrointestinal flora. sies, 2nd ed. Philadelphia: Saunders; Ch. 19, pp. 293–304. | 1,486 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
CHAPTER
61
Anterior abdominal wall
The anterior abdominal wall constitutes a hexagonal area defined supe- adherent to the linea alba and pubic symphysis. Inferiorly, it fuses
riorly by the costal margins and xiphoid process, laterally by the mid- with the iliac crest, extends superficial to the inguinal ligament and
axillary line, and inferiorly by the iliac crests, pubis and pubic symphysis. fuses with the fascia lata at the inguinal flexure or skin crease of the
It is continuous with the posterior abdominal wall and paravertebral thigh. In the male, it extends on to the dorsum of the penis, forming
tissues, forming a flexible sheet of skin, muscle and connective tissue part of the superficial ligament of the penis, and on to the scrotum,
across the anterior and lateral aspects of the abdomen. These tissues where it becomes continuous with the membranous layer of superfi-
also form the umbilicus and the inguinal canal, which connects the cial fascia of the perineum (Colles’ fascia). In the female, it continues
abdominal cavity to the scrotum in men or to the labia majora in into the labia majora and is continuous with the fascia of the
women. The anterior abdominal wall maintains the shape of the perineum.
abdomen and aids numerous physiological functions. However, its In boys, the testis can frequently be retracted out of the scrotum into
dysfunction is equally notable because hernia repair is the single most the loose areolar tissue between the membranous layer of superficial
common operation performed by general surgeons. fascia over the inguinal canal and the external oblique aponeurosis. This
‘space’ is sometimes called the superficial inguinal pouch.
Deep adipose layer
SKIN AND SOFT TISSUE
The thickness of the deep adipose layer is more variable than the super-
ficial fatty layer. It is thin or absent where the membranous layer fuses
The integument of the anterior abdominal wall comprises skin, soft with bony prominences and the linea alba, and becomes markedly
tissues, and lymphatic and vascular structures, as well as segmental thick in the morbidly obese. Its adipocytes show different metabolic
nerves. The outer layer is formed from the skin and subcutaneous fat. activities to those in the superficial adipose layer (Chopra et al 2011).
The skin is non-specialized and variably hirsute, depending on sex and Liposuction preferentially removes this layer of fat with relative preser-
race. All postpubertal individuals have some extension of the pubic hair vation of the superficial adipose layer in order to avoid skin dimpling
on to the anterior abdominal wall skin, although this is commonly and other skin contour irregularities (Markman and Barton 1987).
most pronounced in males, in whom the hair may extend almost up
to the umbilicus in a triangular pattern. The subcutaneous fat of the
abdominal wall is highly variable in thickness, depending in part on Transversalis fascia
gender and adiposity.
The transversalis fascia is a thin layer of connective tissue lying between
the deep surface of transversus abdominis and the extraperitoneal fat.
SOFT TISSUE
It is part of the general layer of thin fascia between the peritoneum and
the abdominal wall. Posteriorly, it fuses with the anterior layer of the
Superficial fascia
thoracolumbar fascia (p. 1083), and anteriorly, it forms a continuous
sheet. Superiorly, it blends with the fascia covering the inferior surface
The ‘superficial fascia’ of the abdominal wall lies between the dermis of the diaphragm. Inferiorly, it is continuous with the iliac and pelvic
and the muscles, and is conventionally divided into a superficial fatty parietal fasciae, and is attached to the iliac crest between the origins
layer (Camper’s fascia) and a deep membranous layer (Scarpa’s fascia). of transversus abdominis and iliacus, and to the posterior margin of
In reality, there are three layers, with a further layer of adipose tissue the inguinal ligament between the anterior superior iliac spine and the
deep to the membranous layer (Lancerotto et al 2011). These three femoral sheath. Medial to the femoral sheath it is thin and fused to the
layers are particularly well defined in the child. Lying within the super- pubis behind the conjoint tendon. An inferior extension of the trans-
ficial fascia are blood vessels, lymphatics, nerves and, in the region of versalis fascia forms the anterior part of the femoral sheath. The fascia
the groin, superficial inguinal lymph nodes. displays a discrete thickening known as the iliopubic tract (also called
the deep crural arch), which runs parallel to the inguinal ligament
Superficial adipose layer
(Teoh et al 1999); it consists of transverse fibres that fan out laterally
The superficial layer contains a variable amount of fat that is partitioned towards the anterior superior iliac spine to blend with the iliopsoas
by fibrous septa connecting the dermis with the deeper membranous fascia and run medially behind the conjoint tendon to the pubic bone.
layer. Inferiorly, it is continuous with the superficial fascia of the thigh, The iliopubic tract is recognized as an important structure during open
and medially, it is continuous over the linea alba. In the male, this layer and laparoscopic inguinal hernia repair. A further thickening of the
continues over the external genitalia, where it becomes thin and pale transversalis fascia, the interfoveolar ligament, runs inferior to the
red, and contains very little adipose tissue. In the scrotum it also con- inguinal ligament at the medial margin of the deep inguinal ring; it
tains the smooth muscle fibres of the dartos muscle. In the female, it may contain muscle fibres.
continues from the suprapubic region of the abdomen into the labia The transversalis fascia is prolonged as the internal spermatic fascia
majora and perineum. over the structures that pass through the deep inguinal ring (the testicu-
lar vessels and vas (ductus) deferens in the male and the round ligament
Membranous layer of the uterus in the female).
The membranous layer is a variably developed entity composed of
connective tissue and elastic fibres. In the adult, its thickness varies
Extraperitoneal connective tissue
over the anterior abdominal wall, becoming thinner in the upper
abdomen (Lancerotto et al 2011). Measured histologically, it is between
0.5 and 1 mm thick but it appears thicker on computed tomography The extraperitoneal connective tissue lying between the peritoneum and
(CT) scans (Lancerotto et al 2011, Chopra et al 2011). It is loosely con- the fasciae lining the abdominal and pelvic cavities contains a variable
nected to the underlying external oblique aponeurosis and rectus amount of fat. The fat is especially abundant on the posterior wall of
sheath by oblique fibrous septa. Superiorly, it is continuous with the the abdomen around the kidneys (particularly in obese men) and
superficial fascia over the remainder of the trunk. In the midline, it is scanty above the iliac crest and in much of the pelvis. 1069 | 1,487 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Anterior AbdominAl wAll
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Superficial vessels Deep vessels
Subclavian artery and vein
Internal thoracic artery and vein
Intercostal artery and vein
Axillary vein
Lateral thoracic vein
Musculophrenic artery and vein
Superior epigastric artery and vein
Thoracoepigastric vein
Subcostal artery and vein
Inferior epigastric artery and vein
Superficial epigastric artery and vein
Deep circumflex iliac artery and vein
Superficial circumflex iliac artery and vein
External iliac artery and vein
Superficial external pudendal artery and vein
Femoral artery and vein
Long (great) saphenous vein
Fig. 61.1 The blood supply of the anterior abdominal wall.
VASCULAR SUPPLY AND LYMPHATIC DRAINAGE artery also gives small branches to the anterior part of the diaphragm.
On the right, small branches reach the falciform ligament, where they
Understanding the blood supply of the abdominal wall is critical when anastomose with branches from the hepatic artery.
planning incisions, raising myocutaneous flaps and reconstructing the
abdominal wall during ventral hernia repair (Fig. 61.1).
Inferior epigastric artery and veins
Superior epigastric artery and veins
The inferior epigastric artery (often referred to as the deep inferior
The superior epigastric artery is a terminal branch of the internal tho- epigastric artery in clinical practice in order to distinguish it from the
racic artery. It arises at the level of the sixth costal cartilage and descends superficial (inferior) epigastric artery) originates from the medial aspect
between the costal and xiphoid slips of the diaphragm, accompanied of the external iliac artery just proximal to the inguinal ligament (see
by two or more veins that drain to the internal thoracic vein (see Figs 61.1–61.2; Fig. 61.3). Its accompanying veins, usually two, unite
Fig. 61.1; Fig. 61.2). The vessels pass anterior to the lower fibres of to form a single vein that drains into the external iliac vein (Rozen et al
transversus thoracis and the upper fibres of transversus abdominis 2009). It curves forwards in the anterior extraperitoneal tissue and
before entering the rectus sheath, where they run inferiorly behind ascends obliquely along the medial margin of the deep inguinal ring.
rectus abdominis. They anastomose with the inferior epigastric arteries, It lies posterior to the spermatic cord, separated from it by the transver-
usually above the level of the umbilicus, in one of several potential salis fascia. It pierces the transversalis fascia and enters the rectus sheath
branching patterns (Rozen et al 2008). by passing anterior to the arcuate line. In this part of its course, it is
Branches supply rectus abdominis and perforate the anterior lamina visible through the parietal peritoneum of the anterior abdominal wall
of the rectus sheath to supply the abdominal skin. A branch given off and forms the lateral umbilical fold. Disruption of the artery at this site
in the upper rectus sheath passes anterior to the xiphoid process of the by surgical incisions (e.g. insertion of laparoscopic ports or abdominal
sternum and anastomoses with a corresponding contralateral branch. drains) may result in a haematoma that can expand to considerable size
This vessel may give rise to bleeding during surgical incisions that because of the absence of adjacent tissue against which the bleeding
extend up to and alongside the xiphoid process. The superior epigastric can be tamponaded. | 1,488 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Anterior abdominal wall
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The vascular supply to the anterior abdominal wall can be divided
into three zones. Zone I represents the epigastrium and central anterior
abdominal wall within the region of rectus abdominis, and is supplied
by the superior and inferior epigastric vessels. Zone II consists of the
lower anterior abdominal wall below zone I and is predominantly
supplied by the superficial epigastric, superficial external pudendal,
and superficial circumflex iliac arteries. Zone III is lateral to zone I and
is supplied by the musculophrenic, lower intercostal, subcostal and
lumbar arteries.
The distance of the vertically running superior and deep inferior
epigastric vessels from the midline is relevant to siting surgical incisions
(Table 61.1).
Table 61.1 Distances of superior and deep inferior epigastric arteries from midline
Level Left Right
Xiphoid cartilage 4.5 ± 0.1 cm 4.4 ± 0.1 cm
Between xiphoid and umbilicus 5.4 ± 0.2 cm 5.5 ± 0.2 cm
Umbilicus 5.6 ± 0.1 cm 5.9 ± 0.1 cm
Between umbilicus and pubic symphysis 5.3 ± 0.1 cm 5.3 ± 0.1 cm
Pubic symphysis 7.5 ± 0.1 cm 7.5 ± 0.1 cm
Adapted from Saber AA, Meslemani AM, Davis R, Pimentel R 2004 Safety zones for anterior abdominal wall
entry during laparoscopy: a CT scan mapping of epigastric vessels. Ann Surg 239:182–5. | 1,489 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
Skin and soft tissue
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Fig. 61.2 The deep muscles and
arterial supply of the anterolateral
abdominal wall. The greater part of
Internal thoracic artery and vein Serratus anterior the left rectus abdominis has been
removed to show the superior and
inferior epigastric vessels.
Latissimus dorsi
Superior epigastric
artery and vein
Intercostal artery
Innermost intercostal
Linea alba Musculophrenic artery
Rectus abdominis (cut) External oblique (cut)
Cut edge of aponeurosis Internal oblique (cut)
of internal oblique
Transversus abdominis
Arcuate line Deep circumflex iliac artery
Transversalis fascia
Inferior epigastric artery and vein
Inguinal ligament
Superficial epigastric artery and vein External iliac artery and vein
Rectus abdominis (cut) Deep circumflex iliac artery
Inferior epigastric artery and vein
Pyramidalis Superficial epigastric artery and vein
Spermatic cord
Femoral artery and vein
The inferior epigastric arteries ascend and anastomose with their laparoscopic inguinal hernia repair or with pelvic fractures. Muscular
superior counterpart without branching in about 30% of cases branches supply the abdominal muscles and peritoneum, and anasto-
(El-Mrakby and Milner 2002). Branching into two vessels before anas- mose with the circumflex iliac and lumbar arteries. Cutaneous branches
tomosis is the most common pattern, accounting for almost 60% of perforate the aponeurosis of external oblique, supply the skin and
cases, with a trifurcation being present in the remainder. The inferior anastomose with branches of the superficial epigastric artery. These
epigastric arteries have an average diameter of approximately 3 mm musculocutaneous perforators have been mapped in detail because they
at their origin, compared to an average diameter of 1.6 mm at the are particularly important to plastic surgeons undertaking reconstruc-
origin of the superior epigastric arteries, presumably explaining why the tive surgery with (myo)cutaneous flaps (Rozen et al 2008).
inferior epigastric arteries provide the ‘dominant’ supply to rectus Occasionally, the inferior epigastric artery arises from the femoral
abdominis. Preliminary ligation of the inferior epigastric artery is often artery. It then ascends anterior to the femoral vein to follow its usual
performed when preparing a myocutaneous flap using the mid or lower abdominal course. Rarely, it arises from the external iliac artery in
rectus abdominis based on the superior epigastric artery; this encour- common with an aberrant obturator artery or from the obturator artery.
ages the augmentation of the superior epigastric arterial supply. The superior and inferior epigastric arteries are important sources of
Branches of the inferior epigastric artery anastomose with branches collateral blood flow between the internal thoracic artery and the exter-
of the superior epigastric artery within the rectus sheath posterior to nal iliac artery when aortic blood flow is compromised. Small tributar-
rectus abdominis at a variable level above the umbilicus (Rozen et al ies of the inferior epigastric vein draining the skin around the umbilicus
2008). Other branches anastomose with terminal branches of the lower anastomose with terminal branches of the umbilical vein draining the
five posterior intercostal, subcostal and lumbar arteries at the lateral umbilical region via the falciform ligament. These portosystemic anas-
border of the rectus sheath. Inferolaterally, branches anastomose with tomoses may open widely in cases of portal hypertension, when portal
the deep circumflex iliac artery. The inferior epigastric artery ascends venous blood may drain into the systemic circulation via the inferior
along the medial margin of the deep inguinal ring. The vas deferens in epigastric veins. The pattern of dilated superficial veins radiating from
the male, or the round ligament in the female, passes medially after the umbilicus is referred to as the ‘caput medusae’.
hooking around the artery at the deep inguinal ring. The artery forms
the lateral border of Hesselbach’s inguinal triangle, an important land-
Posterior intercostal, subcostal
mark in laparoscopic inguinal hernia repair; the inferior border of the
and lumbar arteries
triangle is formed by the inguinal ligament, and the medial border is
formed by the lateral margin of rectus abdominis.
The inferior epigastric artery also gives off the cremasteric artery, a The tenth and eleventh posterior intercostal arteries, the subcostal
pubic branch, and muscular and cutaneous branches. The cremasteric artery, and the lumbar arteries pierce the posterior aponeurosis of trans-
artery accompanies the spermatic cord in males, supplies cremaster and versus abdominis to enter the neurovascular plane of the abdominal
the other coverings of the cord and anastomoses with the testicular wall deep to internal oblique (Fig. 61.4). The location of these arteries
artery. In females, the artery is small and accompanies the round liga- and their accompanying segmental nerves is of clinical importance
ment. A pubic branch, near the femoral ring, descends posterior to the when creating myofascial flaps during abdominal wall reconstruction.
pubis and anastomoses with the pubic branch of the obturator artery. The arteries on either side run forwards, giving off muscular branches
The pubic branch of the inferior epigastric artery may be larger than the to the overlying internal and external oblique, before anastomosing
obturator artery and supply most of the obturator artery territory in the with the lateral branches of the superior and inferior epigastric arteries
thigh, in which case it is referred to as the aberrant obturator artery (Pai at the lateral border of the rectus sheath (see Fig. 61.4). Perforating
et al 2009). It lies close to the medial border of the femoral ring and cutaneous vessels run vertically through the muscles to supply the
may be damaged in medial dissection of the ring during femoral or overlying skin and subcutaneous tissue. A small contribution to the | 1,490 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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A lower abdominal wall run with the deep circumflex iliac and inferior
epigastric arteries to external iliac nodes.
Inguinal ligament Testicular vessels
Rectus SEGMENTAL NERVES
abdominis
The ventral rami of the sixth to eleventh intercostal nerves, the subcostal
nerve (twelfth thoracic) and first lumbar nerve (iliohypogastric and
Deep ilioinguinal nerves) supply the muscles and skin of the anterior abdom-
inguinal ring inal wall (Rozen et al 2008). The seventh to the twelfth thoracic ventral
rami continue anteriorly from the intercostal and subcostal spaces into
Iliopsoas
the abdominal wall (Fig. 61.5). Approaching the costal margin, the
Femoral seventh to tenth nerves curve medially across the deep surface of
nerve the costal cartilages between the digitations of the diaphragm and
Inferior transversus abdominis. The subcostal nerve gives a branch to the first
External
epigastric
iliac lumbar ventral ramus (dorsolumbar nerve) that contributes to the
vessels
vessels lumbar plexus (Ch. 62). It accompanies the subcostal vessels along the
Femoral ring
inferior border of the twelfth rib, passing behind the lateral arcuate liga-
ment and kidney, and anterior to the upper part of the quadratus
lumborum.
Vas
All these segmental nerves run anteriorly within a thin layer of fascia
deferens
Obturator in the neurovascular plane between transversus abdominis and internal
nerve and oblique, where they branch and interconnect with adjacent nerves
artery (Rozen et al 2008). Muscular branches innervate transversus abdominis
and internal and external oblique. Cutaneous branches supply the
skin of the lateral and anterior abdominal walls. The thoracic nerves
enter the rectus sheath at its lateral margin and pass posterior to
rectus abdominis, where they again intercommunicate. Each nerve then
II
pierces rectus abdominis from its posterior aspect and gives off muscu-
H lar branches to this muscle (and a branch to pyramidalis from the
subcostal nerve), and cutaneous branches that pierce the anterior rectus
sheath to supply overlying skin.
The ninth intercostal nerve supplies skin above the umbilicus, the
tenth supplies skin that consistently includes the umbilicus, and the
eleventh supplies skin below the umbilicus (see Fig. 16.10; Fig. 61.5).
The subcostal nerve supplies the anterior gluteal skin just below the
iliac crest, and the skin of the lower abdomen and inguinal region
(overlapping with the L1 dermatome in this region) (Lee et al 2008).
A typical dermatome map of the anterior abdominal wall is shown in
TT DD Figure 16.10. The ventral rami of the lower intercostal and subcostal
EE
nerves also provide sensory fibres to the costal parts of the diaphragm
and parietal peritoneum.
The transversus abdominis plane (TAP) block is a regional anaes-
B
thetic technique for abdominal surgery. Using ultrasound imaging guid-
ance, local anaesthetic is injected into the neurovascular plane between
Fig. 61.3 A, The deep aspect of the lower part of the anterior abdominal internal oblique and transversus abdominis, targeting the segmental
wall of the left side. The femoral and deep inguinal rings are displayed, nerves of the anterolateral abdominal wall.
together with the vessels and other structures in relation to them and also
the opening into the obturator canal. B, A laparoscopic view showing the Lesions of the intercostal nerves
parietal peritoneum covering the area. Abbreviations: D, vas (ductus)
deferens; E, external iliac vessels; H, orifice of direct inguinal hernia;
I, inferior epigastric vessels; T, testicular vessels. (B, With permission from The anterolateral abdominal wall muscles are innervated by several
Drake RL, Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd segmental nerves and injury to a single nerve does not produce a clini-
ed, Elsevier, Churchill Livingstone. Copyright 2010.) cally detectable loss of muscle tone. The overlap between sequential
dermatomes means that significant cutaneous anaesthesia is appreci-
ated only after sectioning at least two sequential nerves.
supply of the lower abdominal muscles comes from branches of the MUSCLES
deep circumflex iliac arteries.
The anterior abdominal wall is also supplied by branches of the ANTEROLATERAL MUSCLES OF THE ABDOMEN
femoral artery: namely, the superficial epigastric, superficial circumflex
iliac, and superficial external pudendal arteries, and by the deep circum-
Rectus abdominis, pyramidalis, external oblique, internal oblique and
flex iliac artery arising from external iliac artery (see Fig. 78.7A).
transversus abdominis constitute the anterolateral muscles of the
abdomen. They act together to perform a range of functions, some of
Lymphatic drainage
which involve the generation of a positive pressure within one or more
body cavity. Although many of these activities may occur with no
Superficial lymphatic vessels accompany the subcutaneous blood ‘forced assistance’, expiration, defecation and micturition may be aided
vessels immediately below the dermis (Tourani et al 2013). Vessels from by the generation of a positive intra-abdominal pressure. Parturition,
the lumbar and gluteal regions run with the superficial circumflex iliac coughing and vomiting always require such a positive pressure. Under
vessels, and those from the infra-umbilical skin run with the superficial resting conditions, the tone developed within the muscles provides
epigastric vessels. Both drain into superficial inguinal nodes. The supra- support for the abdominal viscera and retains the normal contour of
umbilical region is drained by vessels draining to axillary and paraster- the abdomen. The consequences of diminished muscular support can
nal nodes. be seen in patients who have massive ventral hernias or conditions like
The deep lymphatic vessels accompany the deeper arteries. Laterally, ‘prune belly syndrome’, where there is congenital deficiency or absence
they run either with the lumbar arteries to drain into the lateral aortic of these muscles.
nodes, or with the intercostal and subcostal arteries to posterior media- Active contraction of the muscles provides an important role in the
stinal nodes. Lymphatics in the upper anterior abdominal wall run with maintenance of abdominal wall tone. The compression of the abdomi-
the superior epigastric vessels to parasternal nodes while those in the nal cavity required to increase intra-abdominal pressure is brought | 1,491 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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muscles
Muscular terminal branch
RA
Cutaneous artery
Intercostal artery
Inferior epigastric artery
PPF IOA SCF
PP TF EOA
Perforating cutaneous artery
Subcostal artery
TF IO SCF
PPF TA EO
Lumbar artery
RPF EO SCF
TLF LD
EO External oblique PP Parietal peritoneum SCF Subcutaneous fat
EOA External oblique aponeurosis PPF Preperitoneal fat TA Transversus abdominis
IO Internal oblique RA Rectus abdominis TF Transversalis fascia
IOA Internal oblique aponeurosis RPF Retroperitoneal fat TLF Thoracolumbar fascia
LD Latissimus dorsi
Fig. 61.4 The arrangement of the anterolateral abdominal wall vessels at the level of the mid-abdomen.
about mainly by contraction of the diaphragm. The bony pelvis, spine muscle, fusing with the fibres of the anterior lamina of the rectus sheath.
and lower thoracic cage provide rigidity to part of the abdominal wall. Occasionally, one or two incomplete intersections are present below the
During the generation of positive intra-abdominal pressure, the abdom- umbilicus. The intersections may represent the myosepta delineating
inal muscles act to hold the abdominal wall in a relatively fixed posi- the myotomes that form the muscle.
tion, rather than to generate pressure directly; because the majority of The medial border of each rectus abdominis abuts the linea alba. Its
the abdominal wall is muscular, the anterolateral abdominal wall lateral border may be visible on the surface of the anterior abdominal
muscles must be synchronously contracted to prevent displacement of wall as a gently curved groove, the linea semilunaris, which extends
the viscera and the resultant loss of pressure. The oblique muscles, from the tip of the ninth costal cartilage to the pubic tubercle. In a
acting through their anterior aponeuroses and the rectus sheath, provide muscular individual it is readily visible, even when the muscle is not
the majority of this tension, although transversus abdominis and rectus actively contracting, but in many normal and obese individuals it may
abdominis contribute. be completely obscured.
The anterolateral abdominal muscles contribute little to the move-
ments of the trunk during normal sitting and standing; these move- Attachments Rectus abdominis arises by two tendons. The larger,
ments are controlled predominantly by the paravertebral and spinal lateral tendon is attached to the pubic crest and may extend beyond the
muscles. However, movements of the trunk against resistance or when pubic tubercle to the pectineal line. The medial tendon interlaces with
the individual is supine require the anterolateral abdominal muscles. the contralateral muscle and blends with ligamentous fibres covering
Rectus abdominis is the most important in these situations, producing the front of the pubic symphysis. Additional fibres may arise from the
anterior flexion of the trunk. If the pelvic girdle is fixed, flexion of the lower part of the linea alba. The pubic attachment of the tendon of
thoracic girdle occurs. With a fixed thoracic cage, contraction of rectus rectus abdominis and its anterior sheath run over the anterior surface
abdominis causes the pelvis to tilt and lift. Lateral flexion and rotation of the pubic symphysis and become continuous with the attachments
of the trunk against resistance is provided by unilateral contraction of of gracilis and adductor longus (Norton-Old et al 2013). Superiorly,
the oblique muscles. rectus abdominis is attached by three slips of muscle to the fifth, sixth
and seventh costal cartilages. The most lateral fibres are usually attached
Rectus abdominis
to the anterior end of the fifth rib; occasionally, this slip is absent or it
Rectus abdominis is a paired, long, strap-like muscle that extends along extends to the fourth and third ribs. The most medial fibres are occa-
the entire length of the anterior abdominal wall on either side of the sionally connected to the costoxiphoid ligaments and the side of the
linea alba (Fig. 61.6). It is widest in the upper abdomen. The muscle xiphoid process.
fibres of rectus abdominis are partially interrupted by three fibrous
bands or tendinous intersections, which pass transversely or obliquely Vascular supply Rectus abdominis is supplied principally by the
across the muscle. One is usually situated at the level of the umbilicus, superior and inferior epigastric arteries, the latter being the dominant
another opposite the free end of the xiphoid process and a third about supply. Small terminal branches from the lower three posterior inter-
midway between the other two. They are rarely full-thickness and costal arteries, the subcostal artery, the lumbar arteries and the deep
usually extend only half-way through the anterior thickness of the circumflex iliac artery may contribute, particularly at the lateral edges | 1,492 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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Fig. 61.5 The cutaneous branches of
the lower intercostal and lumbar
Serratus anterior
nerves. Portions of the muscles of
the anterior abdominal wall have
been removed, including most of the
Latissimus dorsi anterior layer of the rectus sheath
and parts of rectus abdominis.
Sixth intercostal nerve Lateral cutaneous branches
of intercostal nerve
Innermost intercostal
Lateral cutaneous branches
Tenth intercostal nerve
Rectus abdominis (cut)
External oblique (cut)
Transversus abdominis
Eleventh intercostal nerve
Anterior cutaneous branch
Subcostal nerve
Arcuate line Iliohypogastric nerve
Ilioinguinal nerve
Transversalis fascia
Rectus abdominis (cut) Internal oblique (cut)
Anterior lamina of Inguinal ligament
rectus sheath
Spermatic cord
and the lower parts of the muscle, where they anastomose with small from all three anterior leaves run obliquely upwards, whereas the pos-
lateral branches of the epigastric arteries. Rectus abdominis provides a terior leaves run obliquely downwards at right angles to the anterior
reliable and versatile myocutaneous flap, either pedicled or free, because leaves. Above the arcuate line, the anterior rectus sheath is composed
of the excellent vascularity provided by the epigastric vessels and of both leaves of the aponeurosis of external oblique and the anterior
because the muscle belly can be separated relatively easily from its leaf of the aponeurosis of internal oblique fused together. The poste-
surrounding sheath. The upper half of the muscle may be used for rior rectus sheath is composed of the posterior leaf of the aponeurosis
breast reconstruction, and the lower half may be transposed to the of internal oblique and both leaves of the aponeurosis of transversus
groin and upper thigh or rotated on its lower attachments and delivered abdominis. Thus, both the anterior and posterior layers of the rectus
into the perineum for reconstruction after radical pelvic and perineal sheath consist of three layers of fibres with the middle layer running
resections. at right angles to the other two. At the midline, the anterior and pos-
terior layers are closely approximated. Fibres from each layer decussate
Innervation Rectus abdominis is innervated segmentally by the ter- to the opposite side of the sheath, forming a continuous aponeurosis
minal branches of the ventral rami of the lower six or seven thoracic with the contralateral muscles. Fibres also decussate anteroposteriorly,
spinal nerves. It may also receive a branch from the ilioinguinal nerve crossing from the anterior sheath to the posterior sheath. The dense
(Rozen et al 2008). fibrous line caused by this decussation is called the linea alba. The
external oblique, internal oblique and transversus abdominis muscles
Actions The recti contribute to flexion of the trunk and the mainte- can therefore be regarded as digastric muscles with a central tendon
nance of abdominal wall tone required during straining. comprising the linea alba (Rizk 1980). The decussating fibres at the
linea alba can be used to identify the midline during surgical incisions.
rectus sheath Below the arcuate line, all three aponeuroses from the oblique and
Rectus abdominis on each side is enclosed by a fibrous sheath (Figs transversus abdominis muscles pass into the anterior rectus sheath (see
61.7–61.10). The anterior portion of this sheath extends the entire Fig. 61.7).
length of the muscle and fuses with periosteum and ligaments at sites
of the muscle’s attachments. The posterior part of the sheath is complete linea alba and umbilicus
behind the upper two-thirds of the muscle but absent below this level, The linea alba is a tendinous raphe extending from the xiphoid process
which corresponds to approximately one-third of the distance between to the pubic symphysis and pubic crest. It lies between the two recti and
the umbilicus and the pubis (Loukas et al 2008). The termination of is formed by the interlacing and decussating aponeurotic fibres of exter-
the posterior rectus sheath is usually gradual but may be abrupt and nal oblique, internal oblique and transversus abdominis. At its lower
marked by a clearly visible curved horizontal line known as the arcuate end, the linea alba has two attachments to the pubis: superficial fibres
line (of Douglas). Below this level, rectus abdominis lies on the trans- are attached to the pubic symphysis, and deeper fibres form a triangular
versalis fascia and extraperitoneal connective tissue. lamella that is attached behind rectus abdominis to the posterior
The rectus sheath is formed from the aponeuroses of all three surface of both pubic crests (adminiculum lineae albae). The fundiform
lateral abdominal muscles: namely, external oblique, internal oblique ligament of the penis and pyramidalis are attached to the suprapubic
and transversus abdominis. Each aponeurosis is bilaminar; the fibres part of the linea alba. The linea alba is visible externally in those who | 1,493 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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muscles
Fig. 61.6 Muscles of the left side of
the trunk. External oblique has been
Pectoralis major (cut) removed to show internal oblique,
but its digitations from the ribs have
been preserved. The sheath of rectus
abdominis has been opened and its
anterior layer removed.
Latissimus dorsi
Linea alba
Digitations of external oblique
Internal intercostal muscle of
tenth intercostal space
Tendinous intersections
Internal oblique
Aponeurosis of internal oblique
Rectus abdominis
Cut edge of aponeurosis
of external oblique
Anterior superior iliac spine
Gluteus medius
Inguinal ligament
Gluteus maximus
Pyramidalis
Spermatic cord
Tensor fasciae latae
Sartorius Rectus femoris
A Rectus abdominis Linea alba External oblique Fig. 61.7 Transverse
sections through the
anterior abdominal wall.
A, Immediately above the
umbilicus. B, Below the
arcuate line. The bilaminar
nature of each muscular
aponeurosis is difficult to
illustrate in cross-section.
Peritoneum Transversalis fascia Internal oblique The fibres appear to fuse
into a single sheet during
Preperitoneal fat Transversus abdominis
formation of the rectus
B Rectus abdominis Linea alba External oblique sheath. Note that rectus is
supported directly by the
transversalis fascia below
the arcuate line.
Peritoneum Transversalis fascia Internal oblique
Preperitoneal fat Transversus abdominis
are lean and muscular, as a shallow midline groove in the anterior consists of skin, a fibrous layer (representing the area of fusion between
abdominal wall. Its width varies along its length: it is wider above the the round ligament of the liver, the median umbilical ligament, and
umbilicus than below, and widest at the level of the umbilicus (Rath two medial umbilical ligaments), the transversalis fascia, the umbilical
et al 1996). It is wider and thinner in women, in adults aged over fascia surrounding the urachal remnant, and peritoneum (Fathi et al
50 years, and in the obese and multiparous (Naraynsingh et al 2012). 2012). Its appearance and position are variable (Fathi et al 2012). In
Its tensile strength is proportional to its thickness and density (Kore- adults, it tends to lie at a relatively lower position with advancing age,
nkov et al 2001). The linea alba is relatively bloodless but it is crossed in men, and in individuals with a higher body mass index.
superficially from side to side by a few small blood vessels. In the fetus, the umbilicus transmits the umbilical vessels, urachus
The umbilicus is a fibrous cicatrix that lies a little below the mid- and, up to the third month of gestation, the vitelline or yolk stalk. It
point of the linea alba, and is covered by an adherent area of skin. It closes a few days after birth, but the vestiges of the vessels and urachus | 1,494 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |
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A A
B Fused aponeuroses B Aponeurosis
of external and of external oblique
internal oblique
Linea alba Linea alba Aponeurosis of
External oblique
transversus
Rectus abdominis Internal oblique Rectus abdominis abdominis
Internal oblique
Transversus
Fused aponeuroses
of internal oblique and abdominis Transversalis Transversus
transversus abdominis fascia abdominis
Left renal vein
Aorta
Fig. 61.8 The rectus sheath. Computed tomography scan (A) and Fig. 61.9 The rectus sheath. Computed tomography scan (A) and
diagram (B) of the anterior abdominal wall, demonstrating the formation of diagram (B) of the anterior abdominal wall, demonstrating the formation of
the rectus sheath above the umbilicus. The anterior rectus sheath is the rectus sheath below the umbilicus. The posterior rectus sheath is
composed of both leaves of the aponeurosis of external oblique and the replaced by the transversalis fascia and extraperitoneal connective tissue.
anterior leaf of the aponeurosis of internal oblique, fused together.
The posterior rectus sheath is composed of the posterior leaf of the
aponeurosis of internal oblique and both leaves of the aponeurosis of
transversus abdominis.
Posterior rectus sheath Fig. 61.10 The concept of bilaminar aponeuroses of the
oblique and transversus abdominis muscles. Note that
Laminae of Posterior lamina of the fibres of the superficial and deep laminae are
transversus abdominis internal oblique approximately at right angles; decussations occur as part
Posterior Anterior of the linea alba.
Transversus abdominis
Internal oblique
Rectus
abdominis External oblique
Anterior lamina of Posterior Anterior
internal oblique
Laminae of
external oblique
Anterior rectus sheath | 1,495 | Gray's Anatomy | temp.pdf | https://archive.org/download/GraysAnatomy41E2015PDF/Grays%20Anatomy-41%20E%20%282015%29%20%5BPDF%5D.pdf | PDFPlumberTextLoader |