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LARgE inTEsTinE 1154 8 nOiTCEs A Rectal mucosa Rectum Rectal circular muscle Terminal branches (superior rectal veins) Longitudinal muscle Submucosal venous plexus Levator ani Ischio-anal fat Puborectalis Anal column External anal sphincter Anal valve Conjoint longitudinal coat Dentate line Inferior rectal vein Anal gland Internal anal sphincter Perineal skin Fibromuscular septum Anal verge Intersphincteric groove Lower anal mucosa B Tip of coccyx Terminal branches (superior rectal veins) Anococcygeal raphe Puborectalis Anorectal junction Attachment to anococcygeal ligament Longitudinal muscle Inferior rectal vein Attachment to transverse perineal muscles Posterior external anal sphincter Decussating fibres of upper external anal sphincter External anal sphincter Fig. 66.44 A, A coronal section through the anal canal; glandular and vascular structures are shown unilaterally for clarity. B, A sagittal section through the anal canal; the anal canal is angled posteriorly and so anterior sphincteric structures appear to be lower than posterior structures. The glandular, vascular and fibromuscular structures have been omitted for clarity. is lined by hair­bearing keratinizing, stratified squamous epithelium, The well­defined muscularis mucosae of the rectum continues into which is continuous with the perianal skin. Dilated veins in the sub­ the upper canal. Some fibres from the conjoint longitudinal muscle of epithelial tissue below the dentate line contribute to an external haem­ the anal canal traverse the internal anal sphincter and turn cranially to orrhoidal venous plexus (see Fig. 66.44); this can be seen on clinical merge with the muscularis mucosae, forming the submucosal muscle examination as a circumferential ring at the anal margin if the subject of the anal canal (also called the musculus submucosae ani, or muscu­ is asked to bear down. lus canalis ani, or Treitz’s muscle). Attachments of the longitudinal The junction between the columnar epithelium above and the squa­ fibres to the submucosal muscle of the anal canal are particularly dense mous epithelium below is referred to as the anal transition zone (ATZ). at the dentate line (the mucosal suspensory ligament (of Parks)), It is variable in length and position but often extends about 1 cm causing the mucosa to be tethered more firmly at this level and approxi­ proximal to the dentate line (Fenger 1987). Nerve endings, including mately marking the watershed between the portal and systemic venous thermoreceptors, exist in the submucosa around the upper anal transi­ drainage of the haemorrhoidal plexuses. The attachments of fibres from tion zone; they probably play a role in continence by providing a the longitudinal muscle layer, the muscularis mucosae of the anal canal, highly specialized ‘sampling’ mechanism to identify the contents of the also create ‘spaces’ within the submucosa: a proximal submucous space, lower rectum when the upper anal canal relaxes (Duthie and Gairns a marginal space extending from the dentate line to the intersphincteric 1960). groove, and a perianal space distally.

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Anal canal 1155 66 RETPAHC Fig. 66.45 A, A mid-coronal MRI endocoil image of the anal canal. B, An anterior coronal MRI endocoil section in a woman showing the transverse perineii (TP) joining the external anal sphincter anteriorly (between arrows). Other abbreviations: EAS, external anal sphincter; IAS, internal anal sphincter; PR, puborectalis. PR PR TP IAS EAS A B Internal anal sphincter The internal anal sphincter is the specialized, white, thickened terminal part of the inner circular muscle of the large intestine. It is thicker in males and in patients with chronic constipation. The muscle fibre arrangement is not truly circular, but rather a tight spiral that shortens COIL and widens with relaxation. It commences at the anorectal junction and ends above the anal verge; its lower border is palpable at the inter­ PR sphincteric groove, which corresponds to the proximal limit of the subcutaneous part of the external anal sphincter. It is traversed by Lm fibres passing medially from the conjoint longitudinal muscle into the Ias submucosa. Eas At rest, it is tonically contracted but it relaxes as a consequence of Tp reflex activity, predominantly during defecation. Transient relaxation of the upper internal anal sphincter occurs in response to rectal distension Cs Eas (the recto­anal inhibitory reflex) and postprandial rectal contractions (the sampling reflex). Relaxation allows the passage of distal rectal 5 cm Bs contents into the upper anal canal, enabling a conscious or subcon­ scious perception of their physical nature; this is accompanied by sus­ tained contraction of the distal internal anal sphincter and contraction of the external anal sphincter to maintain continence. The recto­anal inhibitory reflex is primarily mediated by the enteric nervous system, although spinal pathways may have a modulatory role. It is absent in Fig. 66.46 An MRI endocoil mid-sagittal view of the anal canal in a man. patients with Hirschsprung’s disease. Abbreviations: Bs, bulbospongiosus; Cs, corpus spongiosum; Eas, external anal sphincter; Ias, internal anal sphincter; Lm, longitudinal Vascular supply and innervation muscle; PR, puborectalis; Tp, transverse perineii. The internal anal sphincter is supplied by terminal branches of the superior and inferior rectal vessels, and innervated extrinsically by auto­ nomic nerves. Sympathetic fibres originate in the upper two lumbar spinal segments, and parasympathetic fibres originate in the second to fourth sacral spinal segments, both being distributed via the inferior hypogastric plexus. Stimulation of cholinergic muscarinic receptors (parasympathetic) causes internal anal sphincter relaxation and longitudinal anal muscle contraction, while α­adrenergic receptor stim­ ulation (sympathetic) causes contraction of both the internal anal sphincter and longitudinal muscle. Activation of nitrergic nerves also mediates internal anal sphincter relaxation and is the rationale for using topical nitroglycerine and other drugs that promote nitric oxide release in the treatment of pathological conditions associated with increased resting anal tone. Conjoint longitudinal muscle The conjoint longitudinal muscle of the anal canal is a direct continu­ ation of the outer longitudinal smooth muscle of the rectum, descend­ Fig. 66.47 The endoscopic appearance of the anorectal junction viewed ing between internal and external anal sphincters, and augmented in internally from above. The endoscope is visible in the upper left corner of its upper part by striated muscle fibres from the medial aspect of levator the image. ani (Lunniss and Phillips 1992). The muscle is particularly prominent in the fetus, where it is actually thicker than the internal anal sphincter. With advancing age, there is gradual replacement of muscle by connec­ MUSCLES OF THE ANAL CANAL tive tissue, such that the layer becomes thin in the elderly and few muscle fibres are seen in its distal part. As it passes down the anal canal, The anal canal is surrounded by internal and external anal sphincters, muscle fibres peel off in three directions: internally, through the internal separated by the conjoint longitudinal muscle layer, the whole arrange­ anal sphincter to reach the anal submucosa; inferiorly, through the ment being referred to as the anal sphincter complex (Figs 66.48– striated muscle of the lower subcutaneous part of the external anal 66.49) (Al­Ali et al 2009). The anatomy of this region has been clarified sphincter to insert into the perianal skin (some of these fibres encircling in recent years using endoanal sonography and MRI. the anal orifice); and outwards, through the upper part of the external

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LARgE inTEsTinE 1156 8 nOiTCEs S las Lm las PR Eas PR A B C UUrr TTpp Vag PPPRRR llaass SSccEEaass SSppEEaass E F AAccll D Upper Mid Upper Lower Mid Lower G Fig. 66.48 A–C, Axial views of the anal canal at three levels on endoanal ultrasound in a woman. The endoanal ultrasound probe is the central black structure. A, The upper anal canal. The ‘U’ shape of puborectalis is visible. B, The middle anal canal. The external anal sphincter is now a complete ring anteriorly (arrowhead). C, The lower anal canal. Below the termination of the internal anal sphincter, the longitudinal layer extends through the subcutaneous external anal sphincter (between arrowheads). D–F, An MRI of the anal canal. D, At upper anal canal level, the sling of puborectalis extends anteriorly to the pubic bones. E, At mid anal canal level, the transverse perineii fuse into the external anal sphincter anteriorly. The superficial (middle) external anal sphincter is attached either side of the anococcygeal ligament. F, The low anal canal level, below the internal anal sphincter. G, A key for levels of the anal canal. Abbreviations: Acl, anococcygeal ligament; Eas, external anal sphincter; Ias, internal anal sphincter; Lm, longitudinal muscle; PR, puborectalis; S, subepithelial tissues; ScEas, subcutaneous (lower) part of the external anal sphincter; SpEas, superficial (middle) external anal sphincter; Tp, transverse perineii; Ur, urethra; Vag, vagina. anal sphincter (see Fig. 66.44). The lowermost fibres create a honey­ 1984) and is central to the development of haemorrhoids. Its exten­ comb arrangement in the subcutaneous fat and separate a superficial sions provide pathways for the spread and containment of infection. perianal space from the deeper ischio­anal fossa. Additional ramifica­ External anal sphincter tions of this muscle beyond the external anal sphincter have been described, emphasizing its central role in anorectal stability (Courtney The external anal sphincter forms the bulk of the anal sphincter 1950). complex. It is an oval tube of striated muscle composed mostly of The conjoint longitudinal muscle is innervated by autonomic nerves type I slow twitch muscle fibres adapted for prolonged contraction. The that share their origin with those supplying the internal anal sphincter length and thickness of the external anal sphincter is less in females (see above). Its contraction during defecation shortens and widens the (Rociu et al 2000). The historical concept of the muscle having three anal canal, and everts the anal orifice. Degeneration of the muscle and parts (deep, superficial and subcutaneous) is no longer valid, but upper its gradual replacement by connective tissue occurs with age (Haas et al (deep) and lower (superficial or subcutaneous) parts are described by

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Anal canal 1157 66 RETPAHC Bulbocavernosus Bulbospongiosus Levator ani Conjoint Superficial transverse longitudinal perineal muscle muscle External anal sphincter (lower part) External anal sphincter (upper part) Internal anal sphincter Conjoint longitudinal Anal orifice muscle External anal sphincter * * (lower part) Fig. 66.50 A dissection of the male external anal sphincter in a fresh cadaver, viewed from below. (Courtesy of Dr Robert P Myers.) Fig. 66.49 A transilluminated 2.5 mm thick coronal section of a male pelvis processed for epoxy resin E12 sheet plastination, showing the entire length of the anal canal and its muscular layers: namely, the external anal sphincter, conjoint longitudinal muscle and internal anal entered surgically to provide access in a variety of operations (e.g. inter­ sphincter. Note the continuity of the external anal sphincter with levator sphincteric excision of the rectum and intersphincteric approaches to ani superiorly, consisting of two parts: the upper part and the lower part. fistulae). Within the space lie the intersphincteric anal glands, the The upper part of the conjoint longitudinal muscle is continuous with the source of most anal fistulae (Parks 1961). There is an average of twelve longitudinal muscular layer of the rectum and, inferiorly, its fibres traverse intersphincteric anal glands within the adult anal canal, evenly distrib­ the lower part of the external anal sphincter to blend with or form uted around the circumference. Their function is unknown, but they fibro-fatty, honeycomb-like compartments around the perianal region secrete mucin (different in composition from that secreted by rectal (asterisks). The internal anal sphincter ends above the lower part of the mucosa) and they communicate with the anal lumen via ducts (lined external anal sphincter. (Courtesy of Dr Saad Al-Ali, with permission from by epithelium similar to that of the anal transition zone), which cross Al-Ali S, Blyth P, Beatty S, Duang A, Parry B, Bissett IP. (2009) the internal anal sphincter to open at the level of the anal valves imme­ Correlation between gross anatomical topography, sectional sheet diately above the dentate line (Seow­Choen and Ho 1994). Retrograde plastination, microscopic anatomy and endoanal sonography of the anal passage of bacteria from the anal canal to the gland is understood sphincter complex in human males. J. Anat. 215; 212–220.) to cause infection; inflammatory occlusion of the duct prevents spon­ taneous drainage back into the lumen of the anal canal. Sepsis may then spread along a variety of routes to cause abscesses and fistulae some authors. The upper part surrounds the internal anal sphincter within various spaces (Parks et al 1976). while the lowermost part encircles the anal canal inferior to the internal anal sphincter (Fritsch et al 2002, Al­Ali et al 2009). The upper part of the external anal sphincter is attached to the ano­ VASCULAR SUPPLY AND LYMPHATIC DRAINAGE coccygeal ligament posteriorly and to the perineal body anteriorly; OF THE ANUS some muscle fibres on each side of the sphincter decussate to form a commissure in the anterior and posterior midline. The uppermost fibres Arteries blend with the lower medial fibres of puborectalis and attach to the anococcygeal raphe posteriorly and the transverse perineal muscles The anal canal is supplied by terminal branches of the superior rectal anteriorly. The lower part of the external anal sphincter extends below artery and the inferior rectal branch of the internal pudendal artery, the internal anal sphincter and is traversed by the terminal fibres of the together with a small contribution from the median sacral artery. The conjoint longitudinal muscle (see above). Anteriorly, it is attached to arterial supply to the epithelium of the lower anal canal in the bulbospongiosus and bulbocavernosus (Fig. 66.50) (Shafik et al 2007). midline, particularly posteriorly, is relatively deficient (Klosterhalfen Like the levator ani and internal anal sphincter, the external anal et al 1989); this is further diminished if the internal anal sphincter is sphincter is tonically contracted at rest (the postural reflex). hypertonic (Schouten et al 1996). The epithelium is more firmly teth­ ered to underlying structures in the midline, which may also be a Vascular supply and innervation focal point of pressure in the anal canal. Collectively, these factors are The external anal sphincter is supplied by the inferior rectal vessels, with thought to predispose to the occurrence of acute and chronic anal fis­ a small contribution from the median sacral artery. It is innervated sures, which are most commonly found in the midline, especially bilaterally by the inferior rectal branch of the pudendal nerve (contain­ posteriorly. ing contributions from the second, third and fourth sacral spinal Veins nerves). The pudendal nerve also carries afferent fibres from the lining of the anal canal and perianal skin. The upper external anal sphincter The venous drainage of the anal canal parallels the arterial supply. The may also receive motor fibres from the nerve to levator ani (ventral rami upper canal is drained predominantly by the superior rectal veins, tribu­ of predominantly the third and fourth sacral spinal nerves). taries of the inferior mesenteric vein and the portomesenteric venous system; some blood returns to the internal iliac veins via the middle Intersphincteric space and anal glands rectal veins. The lower part of the anal canal, including the external The intersphincteric ‘space’ is a potential space between the conjoint haemorrhoidal venous plexus, drains via the inferior rectal branches of longitudinal muscle layer and the external anal sphincter. It can be the internal pudendal vein into the internal iliac vein.

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LARgE inTEsTinE 1158 8 nOiTCEs Haemorrhoids and the external anal sphincter, which are tonically contracted at rest, Haemorrhoids develop when the supporting connective tissues of the can be further contracted voluntarily to move stool back up from the anal cushions degenerate, causing downward displacement of the cush­ distal rectum. If the defecatory urge is associated with a conscious ions and abnormal venous dilation (Lohsiriwat 2012). They are associ­ decision to evacuate, distal progression of colonic high­amplitude ated with laxity of the anal canal submucosa and enlargement of the propagating complexes, rectal contractions, raised intra­abdominal terminal branches of the superior rectal artery supplying the anal pressure from voluntary straining (the efficiency of which is influ­ cushions. enced by posture), relaxation of pubor ectalis (which straightens the anorectal angle) and the anal sphincters all combine to enable defeca­ Lymphatic drainage tion. Relaxation of the internal anal sphincter is a reflex response to Lymph from the upper anal canal drains cranially into the submucosal rectal distension, whereas relaxation of the external anal sphincter is and intramural lymphatics of the rectum. Lymphatics around puborec­ voluntary. During defecation, contraction of the conjoint longitudinal talis drain to internal iliac lymph nodes. Lymph from the lower anal muscle shortens and opens the anal canal and flattens the anal cush­ canal and external sphincter drains to inguinal lymph nodes. This ions. Both rectal and a variable quantity of colonic contents are evacu­ pattern of drainage is particularly important when considering lym­ ated. After defecation, the external anal sphincter contracts (the phatic spread of malignant tumours from the lower rectum and anal closing reflex), the internal anal sphincter gradually recovers its resting canal. Blockage of lymph drainage along normal routes can lead to tone, and the postural reflex is reactivated. The conjoint longitudinal unusual patterns of dissemination. muscle relaxes, permitting the anal canal to elongate and the anal cushions to re­expand. Problems with defecation may result from impaired colonic transit DEFECATION or from a variety of functional or mechanical rectal disorders (Lunniss et al 2009). Functional causes include inadequate or ineffective expul­ Defecation is the act of voiding stool from the anus and involves the sive effort, paradoxical contraction of the pelvic floor and external anal coordinated function of the colon and rectum, pelvic floor and anal sphincter (dyssynergia), and lack of normal sensation (rectal hyposen­ sphincter. It is influenced by multiple factors, including colonic transit, sitivity). Mechanical causes include impedance to evacuation when stool volume and consistency, posture, age, gender, psychology and straining (rectal intussusception, obstructing masses or anal stenosis), behaviour, culture and lifestyle (Palit et al 2012). Social behaviour misdirection of force vectors during straining (rectocele), or dissipation entrains defecation to occur at a time of convenience rather than of evacuatory forces (ballooning perineum). simply in response to a defecatory urge. The urge to defecate is pre­ ceded by high­amplitude propagated contractions in the colon, which Anal continence and incontinence result in the antegrade propulsion of intraluminal contents to the As long as anal pressure exceeds rectal pressure, faecal continence will rectum; these contractions increase in frequency and intensity just be maintained. Anal resting tone is derived mainly from sympatheti­ before expulsion. The response to rectal filling involves intact rectal cally mediated tonic contraction of the internal anal sphincter, aug­ afferent nerves, reflex rectal contractions and normal rectal wall bio­ mented by contraction of the external anal sphincter. The anal cushions mechanics. The rectum acts as a reservoir and is able to relax to contribute by providing an effective seal. Anal continence involves accommodate faecal material and gas (adaptive relaxation). Periodic central, spinal and peripheral pathways, somatic, autonomic and enteric sampling within the upper anal canal helps to determine the nature of nerves, intact sacral sensorimotor reflexes, and structurally and func­ the rectal content. If the defecatory urge is inconvenient, puborectalis tionally intact smooth and striated musculature. Intestinal glands Columnar absorptive cell (crypts) Mucosa Neuroendocrine cell and adjacent capillary Submucosa Part of muscularis externa Lymphoid follicle Goblet cell Fig. 66.51 The microstructure of the colonic wall and its epithelial cells. Note the aggregations of lymphocytes (blue) and undifferentiated epithelial cells (white).

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1159 66 RETPAHC Key references Sphincteric causes of faecal incontinence may be structural (disrup­ MICROSTRUCTURE OF THE LARGE INTESTINE tion or atrophy of part of the sphincter musculature) or neuropathic (damage to the nerve supply to the sphincters), or a combination of both. The most common causes of sphincter disruption are obstetric injury, anal surgery (for haemorrhoids, fistula or fissure) and trauma. Available with the Gray’s Anatomy e-book Pudendal neuropathy is most commonly associated with childbirth (prolonged second stage) and chronic straining. The layers of tissue in the large intestinal wall (Fig. 66.51) resemble Although the anus constitutes the final barrier to faecal inconti­ those in the small intestine (Ch. 65), except that villi and circular folds nence, suprasphincteric factors are also essential in maintaining faecal are absent and the glands (crypts) are longer. continence, particularly the rate at which the stool is delivered to the rectum, rectal sensation and compliance, and adaptive relaxation. Thus, even in the presence of structurally and functionally intact sphincter mechanisms, faecal incontinence may occur: for instance, in diarrhoeal states or conditions where there is loss of rectal reservoir function (Scott Bonus e-book image and Lunniss 2007). Conversely, chronic rectal distension with retained faeces may result in passive (overflow) leakage, possibly as a result of a chronically relaxed internal anal sphincter consequent on a persistently activated recto­anal inhibitory reflex, together with blunted rectal sensa­ Fig. 66.29 A CT scan (coronal reformat) showing both right colonic tion causing diminished conscious contraction of the external anal and sigmoid diverticulosis. sphincter. KEY REFERENCES Brookes SJ, Dinning PG, Gladman MA 2009 Neuroanatomy and physiology Lunniss PJ, Gladman MA, Benninga MA et al 2009 Pathophysiology of of colorectal function and defaecation: from basic science to human evacuation disorders. Neurogastroenterol Motil 21:31–40. clinical studies. Neurogastroenterol Motil 21: 9–19. A review of the spectrum and classification of rectal evacuatory disorders. A contemporary review of the neuroanatomy and physiology of colorectal Palit S, Lunniss PJ, Scott SM 2012 The physiology of human defecation. Dig motor function. Dis Sci 57:1445–64. Fenlon HM 2002 Virtual colonoscopy. Br J Surg 89:1–3. A detailed review of contemporary understanding of the normal physiology A description and review of the use of multislice CT to image the colon. of defecation. Fisher DF Jr, Fry WJ 1987 Collateral mesenteric circulation. Surg Gynecol Parks AG 1961 The pathogenesis and treatment of fistula in ano. Br Med J Obstet 164:487–92. 1:463–9. A review of collateral mesenteric circulations that develop during disease An early, full description of the relationship between the anatomy of anal processes. glands and cryptoglandular sepsis. Heald RJ, Husband EM, Ryall RDH 1982 The mesorectum in rectal cancer Scott SM, Lunniss PJ 2007 Risk factors in faecal incontinence In: Ratto C, surgery: the clue to pelvic recurrence? Br J Surg 69:613–16. Doglietto GB (eds) Fecal Incontinence. Diagnosis and Treatment. The original description of the mesorectal plane and its relevance to the London: Springer, pp. 43–66. surgical excision of rectal tumours. A review of both congenital and acquired risk factors in faecal incontinence with descriptions of the underlying pathophysiologies. Klosterhalfen B, Vogel P, Rixen H et al 1989 Topography of the inferior rectal artery: a possible cause of chronic primary anal fissure. Dis Colon Thomson WH 1975 The nature of haemorrhoids. Br J Surg 62:542–52. Rectum 32:43–52. An anatomical and clinical study directed at understanding the nature of A detailed postmortem angiographic study demonstrating the arrangement haemorrhoids. of anal arterial supply.

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Large intestine 1159.e1 66 RETPAHC Mucosa Lamina propria The lamina propria is composed of connective tissue that supports the The mucosa is pale, smooth and, in the colon, raised into numerous epithelium, forming a specialized pericryptal myofibroblast sheath crescent­shaped folds between the sacculi. It is thicker, darker, more around each intestinal gland. Solitary lymphoid follicles within the vascular, and more loosely attached to the submucosa in the rectum. lamina propria, similar to those of the small intestine, are most abun­ dant in the caecum, appendix and rectum, but are also present scattered Epithelium along the rest of the large intestine; efferent lymphatic vessels originate The luminal surface of all but the anorectal junction is lined by colum­ within them. Lymphatic vessels are absent from the intercryptal lamina nar cells, mucous (goblet) cells and occasional microfold (M) cells that propria. are restricted to the epithelium overlying lymphoid follicles. Muscularis mucosae Columnar (absorptive) cells Columnar (absorptive) cells are the The muscularis mucosae of the large intestine is essentially similar to most numerous of the epithelial cell types. Although there is some that of the small intestine. variation in their structure, they all bear apical microvilli which are shorter and less regular than those on enterocytes in the small intestine. Submucosa Typical junctional complexes around their apices limit extracellular diffusion from the lumen across the intestine wall. The submucosa of the large intestine is similar to that of the small intestine. Mucous (goblet) cells Mucous cells have a similar structure to those of the small intestine but they are more numerous. They are Muscularis externa outnumbered by absorptive cells for most of the length of the colon but they are equally frequent towards the rectum, where their numbers The muscularis externa has outer longitudinal and inner circular layers increase. of smooth muscle. The longitudinal fibres form a continuous layer that is aggregated into macroscopically visible longitudinal bands or taeniae Microfold (M) cells Microfold cells are similar to those of the small coli (see Figs 66.3 and 66.13). Between the taeniae coli, the longitudinal intestine. layer is much thinner, less than half the thickness of the circular layer. intestinal glands (crypts) The circular fibres constitute a thin layer over the caecum and colon, and a thicker layer in the walls of the rectum; they form the internal Intestinal crypts are narrow, perpendicular tubular glands that are anal sphincter in the anal canal. Interchange of fascicles between circu­ longer, more numerous and closer together than those of the small lar and longitudinal layers occurs, especially near the taeniae coli. intestine. Their orifices lend a cribriform appearance to the mucosa in Deviation of longitudinal fibres from the taeniae coli to the circular surface view. The glands are lined by low columnar epithelial cells, layer may, in some instances, explain the haustrations of the colon. mainly goblet cells, augmented by columnar absorptive cells and neuroendocrine cells. The latter are situated mainly at the bases of Serosa the glands, and secrete basally into the lamina propria. In general, the glands lack Paneth cells but some may be present in the caecum. Stem cells located at or near the bases of the intestinal glands (crypts) are the The serosa or visceral peritoneum is variable in extent. Small, fat­filled source of the other epithelial cell types in the large intestine. They appendices epiploicae are most numerous on the sigmoid and trans­ provide cells that migrate towards the luminal surface of the intestine; verse colon but generally absent from the rectum. their progeny differentiate, undergo apoptosis and are shed after approximately 5 days.

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LARgE inTEsTinE 1159.e2 8 nOiTCEs REFERENCES Ahmadi O, McCall JL, Stringer MD 2015 Mesocolic lymph node number, Graf O, Boland GW, Kaufman JA et al 1997 Anatomic variants of mesenteric size and density: an anatomical study. Dis Colon & Rectum (in press). veins: depiction with helical CT venography. AJR Am J Roentgenol 168: Akinkuotu A, Samuel JC, Msiska N et al 2011 The role of the anatomy of 1209–13. the sigmoid colon in developing sigmoid volvulus: a case­control study. Haas PA, Fox TA Jr, Haas GP 1984 The pathogenesis of hemorrhoids. Dis Clin Anat 24:634–7. Colon Rectum 27:442–50. Al­Ali S, Blyth P, Beatty S et al 2009 Correlation between gross anatomical Hale SJ, Mirjalili SA, Stringer MD 2010 Inconsistencies in surface anatomy: topography, sectional sheet plastination, microscopic anatomy and the need for an evidence­based reappraisal. Clin Anat 23:922–30. endoanal sonography of the anal sphincter complex in human males. Heald RJ, Husband EM, Ryall RDH 1982 The mesorectum in rectal cancer J Anat 215:212–20. surgery: the clue to pelvic recurrence? Br J Surg 69:613–16. Alatise OI, Ojo O, Nwoha P et al 2013 The role of the anatomy of the The original description of the mesorectal plane and its relevance to the sigmoid colon in developing sigmoid volvulus: a cross­sectional study. surgical excision of rectal tumours. Surg Radiol Anat 35:249–57. Helander HF, Fändriks L 2014 Surface area of the digestive tract – revisited. Barlow A, Muhleman M, Gielecki J et al 2013 The vermiform appendix: a Scand J Gastroenterol 49:681–9. review. Clin Anat 26:833–42. Jackson JE 1999 Vascular anatomy of the gastrointestinal tract. In: Butler P, Batra AP, Kaur J, Parihar D et al 2013 Variations in origin of right colic artery Mitchell AWM, Ellis H (eds) Applied Radiological Anatomy. Cambridge: supplying colon. CIBTech J Surg 2:14–20 (available at http://www. Cambridge University Press. cibtech.org/cjs.htm). Jamieson JK, Dobson JF 1909 The lymphatics of the colon. Ann Surg Bharucha AE 2012 High amplitude propagated contractions. Neurogastro­ 50:1077–90. enterol Motil 24:977–82. Kinugasa Y, Arakawa T, Abe S et al 2011 Anatomical reevaluation of the Bell S, Sasaki J, Sinclair G et al 2009 Understanding the anatomy of lym­ anococcygeal ligament and its surgical relevance. Dis Colon Rectum phatic drainage and the use of blue­dye mapping to determine the 54:232–7. extent of lymphadenectomy in rectal cancer surgery: unresolved issues. Klosterhalfen B, Vogel P, Rixen H et al 1989 Topography of the inferior rectal Colorectal Dis 11:443–9. artery: a possible cause of chronic primary anal fissure. Dis Colon Bissett IP, Fernando CC, Hough DM et al 2001 Identification of the fascia Rectum 32:43–52. propria by magnetic resonance imaging and its relevance to preoperative A detailed postmortem angiographic study demonstrating the arrangement assessment of rectal cancer. Dis Colon Rectum 44:259–65. of anal arterial supply. Brookes SJ, Dinning PG, Gladman MA 2009 Neuroanatomy and physiology Lindsey I, Guy RJ, Warren BF et al 2000 Anatomy of Denonvilliers’ fascia of colorectal function and defaecation: from basic science to human and pelvic nerves, impotence, and implications for the colorectal clinical studies. Neurogastroenterol Motil 21: 9–19. surgeon. Br J Surg 87:1288–99. A contemporary review of the neuroanatomy and physiology of colorectal motor function. Lohsiriwat V 2012 Hemorrhoids: from basic pathophysiology to clinical management. World J Gastroenterol 18:2009–17. Brown G, Richards CJ, Newcombe RG et al 1999 Rectal carcinoma: thin­ Lunniss PJ, Gladman MA, Benninga MA et al 2009 Pathophysiology of section MR imaging for staging in 28 patients. Radiology 211:215–22. evacuation disorders. Neurogastroenterol Motil 21:31–40. Buschard K, Kjaeldgaard A 1973 Investigations and analysis of the positions, A review of the spectrum and classification of rectal evacuatory disorders. fixation, length and embryology of the vermiform appendix. Acta Chir Scand 139:293–8. Lunniss PJ, Phillips RK 1992 Anatomy and function of the anal longitudinal muscle. Br J Surg 79:882–4. Coffey JC 2013 Surgical anatomy and anatomic surgery – clinical and sci­ entific mutualism. Surgeon 11:177–82. Madiba TE, Thomson SR 2002 The management of cecal volvulus. Dis Colon Rectum 45:264–7. Courtney H 1950 Anatomy of the pelvic diaphragm and anorectal muscu­ lature as related to sphincter preservation in anorectal surgery. Am J Surg Murono K, Kawai K, Kazama S et al 2015 Anatomy of the inferior mesenteric 79:155–73. artery evaluated using 3­dimensional CT angiography. Dis Colon Rectum 58:214–9. Culligan K, Walsh S, Dunne C et al 2014 The mesocolon: a histological and electron microscopic characterization of the mesenteric attachment of Murphy JM, Maibaum A, Alexander G et al 2000 Chilaiditi’s syndrome and the colon prior to and after surgical mobilization. Ann Surg 260: obesity. Clin Anat 13:181–4. 1048–56. Narducci F, Bassotti G, Gaburri M et al 1987 Twenty four hour manometric Duthie HL, Gairns FW 1960 Sensory nerve­endings and sensation in the recording of colonic motor activity in healthy man. Gut 28:17–25. anal region of man. Br J Surg 47:585–95. Oliphant M, Berne AS, Meyers MA 1996 The subperitoneal space of the Felson B 1949 Appendiceal calculi: incidence and clinical significance. abdomen and pelvis: planes of continuity. Am J Roentgenol 167: Surgery 25:734–7. 1433–9. Fenger C 1987 The anal transitional zone. Acta Pathol Microbiol Immunol Ouattara D, Kipré YZ, Broalet E et al 2007 Classification of the terminal Scand Suppl 289:1–42. arterial vascularization of the appendix with a view to its use in recon­ structive microsurgery. Surg Radiol Anat 29:635–41. Fenlon HM 2002 Virtual colonoscopy. Br J Surg 89:1–3. A description and review of the use of multislice CT to image the colon. Palit S, Lunniss PJ, Scott SM 2012 The physiology of human defecation. Dig Dis Sci 57:1445–64. Fisher DF Jr, Fry WJ 1987 Collateral mesenteric circulation. Surg Gynecol A detailed review of contemporary understanding of the normal physiology Obstet 164:487–92. of defecation. A review of collateral mesenteric circulations that develop during disease processes. Parks AG 1961 The pathogenesis and treatment of fistula in ano. Br Med J 1:463–9. Fritsch H, Brenner E, Lienemann A et al 2002 Anal sphincter complex: An early, full description of the relationship between the anatomy of anal reinterpreted morphology and its clinical relevance. Dis Colon Rectum glands and cryptoglandular sepsis. 45:188–94. Parks AG, Gordon PH, Hardcastle JD 1976 A classification of fistula­in­ano. García­Armengol J, García­Botello S, Martínez­Soriano F et al 2008 Review Br J Surg 63:1–12. of the anatomic concepts in relation to the retrorectal space and endopelvic fascia: Waldeyer’s fascia and the rectosacral fascia. Colorectal Pollard MF, Thompson­Fawcett MW, Stringer MD 2012 The human ileocae­ Dis 10:298–302. cal junction: anatomical evidence of a sphincter. Surg Radiol Anat 34:21–9. Gaudio E, Riva A, Franchitto A et al 2010 The fascial structures of the rectum and the ‘so­called mesorectum’: an anatomical or a terminological con­ Randal Bollinger R, Barbas AS, Bush EL et al 2007 Biofilms in the large bowel troversy? Surg Radiol Anat 32:189–90. suggest an apparent function of the human vermiform appendix. J Theor Biol 249:826–31. Gourley EJ, Gering SA 2005 The meandering mesenteric artery: a historic review and surgical implications. Dis Colon Rectum 48:996–1000.

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Large intestine 1159.e3 66 RETPAHC Rivkind AI, Shilon E, Muggia­Sullam M et al 1986 Paracecal hernia: a cause Silverstein FE, Tytgat GNJ 1991 Atlas of Gastrointestinal Endoscopy, 2nd ed. of intestinal obstruction. Dis Colon Rectum 29:752–4. London: Gower Medical. Rociu E, Stoker J, Eijkemans MJ et al 2000 Normal anal sphincter anatomy Slack WW 1962 The anatomy, pathology and some clinical features of and age­ and sex­related variations at high­spatial­resolution endoanal diverticulitis of the colon. Br J Surg 50:185–90. MR imaging. Radiology 217:395–401. Søndenaa K, Quirke P, Hohenberger W et al 2014 The rationale behind Sato K, Sato T 1991 The vascular and neuronal composition of the lateral complete mesocolic excision (CME) and a central vascular ligation for ligament of the rectum and the rectosacral fascia. Surg Radiol Anat colon cancer in open and laparoscopic surgery: proceedings of a con­ 13:17–22. sensus conference. Int J Colorectal Dis 29:419–28. Saunders BP, Phillips RK, Williams CB 1995 Intraoperative measurement of Song XY, Chen BN, Zagorodnyuk VP et al 2009 Identification of medium/ colonic anatomy and attachments with relevance to colonoscopy. Br J high threshold extrinsic mechanosensitive afferent nerves to the gas­ Surg 82:1491–3. trointestinal tract. Gastroenterology 137:274–84. Schouten WR, Briel JW, Auwerda JJ et al 1996 Anal fissure: new concepts Thomson WH 1975 The nature of haemorrhoids. Br J Surg 62:542–52. in pathogenesis and treatment. Scand J Gastroenterol Suppl 218: An anatomical and clinical study directed at understanding the nature of 78–81. haemorrhoids. Scott SM, Lunniss PJ 2007 Risk factors in faecal incontinence In: Ratto C, Turmezei TD, Cockburn JF 2009 Digital subtraction angiography of the Doglietto GB (eds) Fecal Incontinence. Diagnosis and Treatment. superior mesenteric artery: identifying arterial branches. Clin Anat London: Springer, pp. 43–66. 22:777–9. A review of both congenital and acquired risk factors in faecal incontinence van Gulik TM, Schoots I 2005 Anastomosis of Riolan revisited: the meander­ with descriptions of the underlying pathophysiologies. ing mesenteric artery. Arch Surg 140:1225–9. Searle AR, Ismail KA, Macgregor D et al 2013 Changes in the length and Veeresh H, Halasagi SS, Shakuntala RP et al 2012 A study of arterial supply diameter of the normal appendix throughout childhood. J Pediatr Surg of caecum in humans. J Evol Med Dent Sci 1:811–16. 48:1535–9. Yamaguchi S, Kuroyanagi H, Milson JW et al 2002 Venous anatomy of the Seow­Choen F, Ho JM 1994 Histoanatomy of anal glands. Dis Colon Rectum right colon: precise structure of the major veins and gastrocolic trunk 37:1215–18. in 58 cadavers. Dis Colon Rectum 45:1337–40. Shafik A, Asaad S, Doss S 2003 Identification of a sphincter at the sig­ Yoshida T, Suzuki S, Sato T 1993 Middle mesenteric artery: an anomalous moidorectal canal in humans: histomorphologic and morphometric origin of a middle colic artery. Surg Radiol Anat 15:361–3. studies. Clin Anat 16:138–43. Zhai LD, Liu J, Li YS et al 2009 Denonvilliers’ fascia in women and its rela­ Shafik A, Shafik IA, el­Sibai O et al 2007 Physioanatomical relationship of tionship with the fascia propria of the rectum examined by successive the external anal sphincter to the bulbocavernosus muscle in the female. slices of celloidin­embedded pelvic viscera. Dis Colon Rectum 52: Int Urogynecol J Pelvic Floor Dysfunct 18:851–6. 1564–71.

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SUBSECTION: Abdominal viscera CHAPTER 67 Liver The liver is the largest of the abdominal viscera, occupying a substantial of proteins and clotting factors; the metabolism of amino acids; and portion of the upper abdominal cavity. It occupies most of the right bile production. It is involved in a plethora of other biochemical reac- hypochondrium and epigastrium, and frequently extends into the left tions. Since the majority of these processes are exothermic, a substantial hypochondrium as far as the left anterior axillary line (Fig. 67.1). As part of the thermal energy production of the body, especially at rest, is the body grows from infancy to adulthood, the liver rapidly increases provided by the liver. The liver is populated by phagocytic macrophages, in size. This period of growth reaches a plateau around 18 years and is components of the mononuclear phagocyte system capable of remov- followed by a gradual decrease in liver weight from middle age. The ing particulates from the blood stream. It is an important site of hae- ratio of liver to body weight decreases with growth from infancy to mopoiesis in the fetus. adulthood. The liver weight is 4–5% of body weight in infancy and An account of the more common eponyms relating to the anatomy decreases to approximately 2% in adulthood. The size of the liver also and surgery of the liver is provided in Stringer (2009). varies according to sex, being smaller in females, and body size, enlarg- ing with fat deposition. It has an overall wedge shape, which is, in part, determined by the form of the upper abdominal cavity into which it SURFACES OF THE LIVER grows. The narrow end of the wedge lies towards the left hypochon- drium, and the anterior edge points anteriorly and inferiorly. The supe- The liver is usually described as having superior, anterior, right, poste- rior and right lateral aspects are shaped by the anterolateral abdominal rior and inferior surfaces, and has a distinct inferior border (Figs 67.2– and chest wall, as well as the diaphragm. The inferior aspect is shaped 67.3). However, the superior, anterior and right surfaces are continuous by the adjacent viscera. The capsule is no longer thought to play an and no definable borders separate them. It is more appropriate to group important part in maintaining the shape of the liver; it is notable that them as the diaphragmatic surface, which is mostly separated from the it allows expansion when the liver hypertrophies in response to disease, inferior, or visceral, surface by a narrow inferior border. At the infraster- surgical resection or contra lateral embolization of the portal vein or nal angle, the inferior border is adjacent to the anterior abdominal wall hepatic artery. and accessible to examination by percussion, but not usually palpable, Throughout life, the liver is reddish brown in colour, although this except on deep inspiration. In the midline, the inferior border of the can vary, depending on the fat content. Obesity is the most common liver is near the transpyloric plane. In women and children, the border cause of excess fat in the liver (steatosis); the liver assumes a more yel- often projects a little below the right costal margin. lowish tinge as its fat content increases and gains a bluish tinge with venous obstruction. The texture of the organ is usually soft to firm, Superior surface The superior surface is the largest and lies imme- although it depends partly on the volume of blood it contains and on diately below the diaphragm, separated from it by peritoneum, except its fat and fibrous tissue content. for a small triangular area where the two layers of the falciform ligament The liver performs a wide range of metabolic activities required for diverge. The majority of the superior surface lies beneath the right homeostasis, nutrition and immune defence. For example, it is impor- dome, but there is a shallow cardiac impression centrally that corre- tant in the removal and breakdown of toxic, or potentially toxic, materi- sponds to the position of the heart above the central tendon of the als from the blood; the regulation of blood glucose and lipids; the diaphragm. The left side of the superior surface lies beneath part of the storage of certain vitamins, iron and other micronutrients; the synthesis left dome of the diaphragm. Stomach (fundus) Inferior vena cava Right cupola of diaphragm Oesophagus Right crus of diaphragm Right suprarenal gland Right kidney Hepatic flexure Duodenum 1160 Fig. 67.1 The ‘bed’ of the liver. The outline of the liver is shaded green. The central bare area is unshaded.

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Liver 1161 76 RETPAHC A B Inferior vena cava Bare area Superior layer of Posterior and coronary ligament anterior layers Posterior of left triangular Superior ligament Porta hepatis Inferior layer of coronary ligament Right triangular ligament Right lobe Left lobe Left lobe Right lobe Fissure for ligamentum C D venosum Superior Inferior border Inferior Falciform Attachment of lesser Right Anterior ligament omentum Gallbladder Ligamentum Gallbladder teres Fissure for ligamentum teres Inferior border Fig. 67.2 The surfaces and external features of the liver. A, Superior view. B, Posterior view. C, Anterior view. D, Inferior view. Spinal area A B Oesophageal area Gastric area Left dome Suprarenal area of diaphragm Cardiac area Left dome D Right dome of diaphragm Spinal area Renal area C Oesophageal area Area related to Suprarenal area right lower lobe of lung Gastric area Area related to Colic area costodiaphragmatic recess Duodenal area Fig. 67.3 Relations of the liver. A, Superior view. B, Posterior view. C, Anterior view. D, Inferior view. Anterior surface The anterior surface is approximately triangular the diaphragm and the seventh and eighth ribs. The diaphragm, the and convex, and is covered by peritoneum, except at the attachment of costodiaphragmatic recess lined by pleura, and the ninth and tenth ribs the falciform ligament. Much of it is in contact with the anterior attach- lie lateral to the middle and lower thirds of the right surface. Lateral to ment of the diaphragm. On the right, the diaphragm separates it from the lower third, the diaphragm and thoracic wall are in direct contact. the pleura and sixth to tenth ribs and cartilages, and on the left, from Rarely, the hepatic flexure and proximal transverse colon lie on a long the seventh and eighth costal cartilages. mesentery over the right, anterior and superior surfaces of the liver; this may lead to misdiagnosis of pneumoperitoneum on a radiograph or Right surface The right surface is covered by peritoneum and lies very rarely cause symptoms (Chilaiditi’s syndrome) (see p. 1144). adjacent to the right dome of the diaphragm, which separates it from the right lung and pleura and the seventh to eleventh ribs. The right Posterior surface The posterior surface is convex, wide on the right lung and basal pleura lie above and lateral to its upper third, between but narrow on the left. A median concavity corresponds to the forward

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LivER 1162 8 NOiTCES convexity of the vertebral column close to the attachment of the liga- of the falciform ligament with no subdivisions. It is substantially mentum venosum. Much of the posterior surface is attached to the thinner than the right lobe, having a thin apex that points into the left diaphragm by loose connective tissue, forming the triangular ‘bare area’. upper quadrant. The inferior vena cava lies in a groove or tunnel in the medial end of the ‘bare area’. To the left of the caval groove, the posterior surface of Quadrate lobe The quadrate lobe is visible as a prominence on the the liver is formed by the caudate lobe, and covered by a layer of peri- inferior surface of the liver, to the right of the groove formed by the toneum continuous with that of the inferior layer of the coronary liga- ligamentum teres (and thus is incorrectly said to arise from the right ment and the layers of the lesser omentum. The caudate lobe is related lobe, although it is functionally related to the left hemi-liver). It lies to the diaphragmatic crura and the right inferior phrenic artery above anterior to the porta hepatis and is bounded by the gallbladder fossa the aortic hiatus, and separated by these structures from the descending to the right, a short portion of the inferior border anteriorly, the fissure thoracic aorta. for the ligamentum teres to the left, and the porta hepatis posteriorly. The fissure for the ligamentum venosum separates the caudate lobe Like the caudate lobe, its morphology varies between individuals (Joshi from the left lobe. The fissure cuts deeply in front of the caudate lobe et al 2009). and contains the two layers of the lesser omentum. The posterior surface of the left lobe bears a shallow impression near the upper end of the Caudate lobe The caudate lobe is visible as a prominence on the fissure for the ligamentum venosum that is caused by the abdominal inferior and posterior surfaces to the right of the groove formed by the oesophagus. The posterior surface of the left lobe to the left of this ligamentum venosum; it lies posterior to the porta hepatis. To its right impression is related to the fundus of the stomach. Together, these is the groove for the inferior vena cava. Above, it continues into the posterior relations make up what is sometimes referred to as the ‘bed’ superior surface on the right of the upper end of the fissure for the liga- of the liver (see Fig. 67.1). mentum venosum. In gross anatomical descriptions, this lobe is said to arise from the right lobe but it is functionally separate. Inferior surface The inferior surface is bounded by the inferior edge of the liver. It blends with the posterior surface in the region of the origin of the lesser omentum, the porta hepatis and the inferior layer FUNCTIONAL ANATOMICAL DIVISIONS of the coronary ligament, and is marked near the midline by a sharp fissure that contains the ligamentum teres (the obliterated fetal left Current understanding of the functional anatomy of the liver is based umbilical vein). The gallbladder usually lies in a shallow fossa but this on Couinaud’s division of the liver into eight (subsequently nine, then is variable; it may have a short mesentery or be completely intrahepatic later revised back to eight) functional segments, based on the distribu- and lie within a cleft in the liver parenchyma. The quadrate lobe lies tion of portal venous branches in the parenchyma (Couinaud 1957). between the fissure for the ligamentum teres and the gallbladder. Further understanding of the intrahepatic biliary anatomy, especially of The inferior surface of the left lobe is related inferiorly to the fundus the right ductal system, was enhanced by contributions from Hjortsjö of the stomach and the upper lesser omentum. The quadrate lobe lies (1951) and Healey and Schroy (1953), who used the biliary system as adjacent to the pylorus, the first part of the duodenum and the lower the main guide for division of the liver (Fig. 67.4). part of the lesser omentum. Occasionally, the transverse colon lies The liver is divided into four portal sectors by the four main branches between the duodenum and the quadrate lobe. To the right of the of the portal vein. These are right lateral, right medial, left medial and gallbladder, the inferior surface is related to the hepatic flexure of the left lateral (sometimes, the term posterior is used in place of lateral, colon, the right suprarenal gland and right kidney, and the first part of and anterior in place of medial). The three main hepatic veins lie the duodenum (see Fig. 67.1). between these sectors as intersectoral veins. These intersectoral planes are also called portal fissures (or scissures). Each sector is subdivided into segments (usually two), based on their supply by tertiary divisions SUPPORTS OF THE LIVER of the vascular biliary (Glissonian) sheaths. The liver is stabilized and maintained in its position in the right upper Fissures of the liver quadrant of the abdomen by both static and dynamic factors. A three- tier classification of supporting structures has been proposed: the sus- pensory attachments at the posterior abdominal wall to the inferior Knowledge of the fissures of the liver is essential for understanding liver vena cava, hepatic veins, coronary and triangular ligaments (primary surgery. Three major fissures (main, left and right portal fissures), not factors); the support provided by the right kidney, right colic flexure visible on the surface, run through the liver parenchyma and contain and duodenopancreatic complex (secondary factors); and the attach- the three main hepatic veins. Three minor fissures (umbilical, venous ment to the anterior abdominal wall and diaphragm by the falciform and fissure of Gans) are visible as physical clefts of the liver surface. The ligament (tertiary factors) (Flament et al 1982). fissure of Gans is also known as Rouvière’s sulcus or the incisura hepatis The surgical implications of these different factors are important for dextra. Accessory fissures are rare. understanding the pathophysiology of blunt liver trauma and when considering the stability of transplanted liver grafts. The inferior vena Main portal fissure The main fissure, sometimes called Cantlie’s cava and the hepatic veins, especially the right hepatic vein, appear to line, extends from the midpoint of the gallbladder fossa at the inferior be the most important anatomical structures that support the bulk of margin of the liver back to the midpoint of the inferior vena cava, and the liver. Other factors that influence the position of the liver within contains the middle hepatic vein. It separates the liver into right the abdominal cavity include positive intra-abdominal pressure and the and left hemi-livers. Segments V and VIII lie immediately to the right, movement of the diaphragm during respiration. and segment IV immediately to the left, of the fissure. Left portal fissure The left portal fissure divides the left hemi-liver GROSS ANATOMICAL LOBES into medial (anterior) and lateral (posterior) sectors. It extends from the midpoint of the inferior edge of the liver between the falciform Historically, the liver has been divided on the basis of its external ligament and the left triangular ligament to the point that marks the appearance into right, left, caudate and quadrate lobes, which are, in confluence of the left and middle hepatic veins. It contains the left part, defined by peritoneal ligamentous attachments. Additional liver hepatic vein and separates the left medial (anterior) and left lateral lobes have been reported but are rare. (posterior) sectors; segment III lies immediately anteriorly and segment Right lobe The right lobe is the largest in volume and contributes to II posteriorly. all surfaces of the liver. It is divided from the left lobe by the falciform ligament anteriorly and superiorly and the ligamentum venosum and Right portal fissure The right portal fissure divides the right hemi- fissure for the ligamentum teres inferiorly. On the inferior surface, to liver into lateral (posterior) and medial (anterior) sectors. The plane of the right of the grooves formed by the ligamentum teres and ligamen- the right fissure is the most variable of the portal fissures and runs tum venosum, there are two prominences separated by the porta approximately diagonally through the anatomical right lobe from the hepatis; the caudate lobe lies posterior, and the quadrate lobe lies lateral end of the inferior border to the termination of the right hepatic anterior. The gallbladder lies in a shallow fossa to the right of the quad- vein. The fissure divides the right anterior sector to its left (segments V rate lobe. and VIII) from the right posterior sector to its right (segments VI and VII), and contains the right hepatic vein. The right fissure traverses the Left lobe The left lobe is the smaller of the two main lobes, although thickest portion of liver parenchyma that is commonly transected it is nearly as large as the right lobe in young children. It lies to the left during liver resection.

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Liver 1163 76 RETPAHC Fig. 67.4 The fissures and sectors of the liver. (Right lateral = right posterior; right medial = right anterior.) II I VII VIII IV III V VI Umbilical fissure Left lateral sector Left portal fissure Main portal fissure Left medial sector Right lateral sector Right portal fissure Right medial sector A B Fig. 67.5 Segments of the liver (after Couinaud). A, Superior view. B, Posterior view. C, Anterior view. D, Inferior view. The segments are usually referred to by VII II II I number (name): I (caudate); II (left lateral VII superior); III (left medial inferior); IV (left medial superior) (sometimes III VIII III subdivided into superior and inferior IV IV parts); V (right medial inferior); VI (right lateral inferior); VII (right lateral superior); V VI VIII (right medial superior). C D II VII VII III II I VIII IV VI III VI V IV V Umbilical fissure The umbilical fissure (or fissure for the ligamen- Venous fissure The venous fissure (or fissure for the ligamentum tum teres) separates segment III from segment IV within the left medial venosum) is in direct continuity with the umbilical fissure on the sector and contains a major branch of the left hepatic vein (the umbili- undersurface of the liver and contains the ligamentum venosum (the cal fissure vein). It is marked anteriorly by the attachment of the falci- obliterated ductus venosus). It lies between the caudate lobe and form ligament and inferiorly by the ligamentum teres, where it may be segment II. covered by a bridge of liver tissue extending between segments III and Fissure of Gans The fissure of Gans (or Rouvière’s sulcus) lies on IV. This liver bridge is usually avascular and can be divided safely with the undersurface of the right lobe of the liver behind the gallbladder diathermy during surgery. The umbilical fissure also contains the umbil- fossa. It often marks the variable site of division of the portal pedicle ical portion of the left portal vein, segmental bile ducts converging to to the right posterior sector. form the left hepatic duct, and the terminal branches of the left branch of the hepatic artery. The umbilical portion of the left portal vein offers Sectors and segments of the liver direct surgical access to the left portal vein; this is important for mobi- lization of the left portal vein in surgery for hilar cholangiocarcinoma and in operations to restore intrahepatic portal blood flow after portal Sectors vein occlusion. A knowledge of the arrangement of the vascular and The sectors of the liver are made up of between one and three segments: biliary structures within the umbilical fissure is also essential when right lateral sector = segments VI and VII; right medial sector = segments splitting the liver for an adult and paediatric recipient and for live donor V and VIII; left medial sector = segments III and IV (and part of I); liver transplantation for a child recipient. left lateral sector = segment II (Fig. 67.5). Segments are numbered

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LivER 1164 8 NOiTCES portion), while in the Far East, right and left subdivisions are recog- nized. The Glissonian sheaths to segment I arise from both right and left main sheaths; the segment therefore receives vessels from both the II left and right branches of the portal vein and hepatic arteries. The IV venous drainage of the caudate lobe is directly into the inferior vena cava by multiple small tributaries that nearly always arise from the lower, and occasionally from the middle, third of the segment, but L rarely from the upper third. The bile ducts draining the segment are VIII M closely related to the confluence of the right and left hepatic ducts (see Chapter 68), such that excision of bile duct tumours affecting the hilum R of the liver usually requires removal of segment I. Segment II Segment II lies posterolateral to the left portal fissure and VII is the only segment in the left lateral sector of the liver. It often has only one Glissonian sheath and drains into the left hepatic vein. Rarely, a separate vein drains directly into the inferior vena cava. Segment III Segment III lies between the umbilical fissure and the A left portal fissure, and is supplied by one to three Glissonian sheaths; it drains into the left hepatic vein. The vein of the falciform ligament can provide an alternative drainage route for segment III. Very rarely, the venous drainage is to the middle hepatic vein and reconstruction is required following a right hepatectomy involving resection of the IV middle hepatic vein and in split liver transplantation (Dar et al 2008). II Segment IV Segment IV lies between the umbilical fissure and the LPV main portal fissure, immediately anterior to segment I. Segment IV is PV supplied by three to five Glissonian sheaths, most of which arise in the umbilical fissure; their origins are often close to those that supply seg- ments II and III. Occasionally, segment IV is supplied by branches from VIII I the main left pedicle. The main venous drainage of segment IV is into the middle hepatic vein but the segment can also drain into the left IVC hepatic vein through the vein of the falciform ligament. Segment IV has been divided into IVa superiorly and IVb inferiorly; this is relevant to transverse hepatectomy, in which segments IVb, V and VI are removed along a transverse portal plane (Sugarbaker 1990). VII Segment V Segment V is the inferior segment of the right medial sector and lies between the middle and the right hepatic veins. Its size B is variable, as are the number of Glissonian sheaths that supply it from the right anterior sheath. Venous drainage is usually into the right and middle hepatic veins, but may be direct into the inferior vena cava via an inferior right hepatic vein. III Segment VI Segment VI forms the inferior part of the right lateral IV sector posterior to the right portal fissure. It is often supplied by two to three branches from the right posterior Glissonian sheath, and occa- sionally the Glissonian sheath to segment VI can arise directly from the right pedicle. Venous drainage is normally into the right hepatic vein but, like in segment V, may be via an inferior right hepatic vein directly V I into the inferior vena cava. RPV Segment VII Segment VII forms the superior part of the right lateral sector and lies behind the right hepatic vein. The sheath to segment VII is often single. The venous drainage is into the right hepatic vein; occa- sionally, the segment can drain directly into the inferior vena cava. VI Segment VIII Segment VIII is the superior part of the right medial sector. The right medial (anterior) sectoral sheath ends in segment VIII C and supplies it, after giving off branches to segment V. Venous drainage is to the right and middle hepatic veins. Fig. 67.6 Segments of the liver seen on axial computed tomography (CT) scan. A, A contrast enhanced CT shows the left (L), middle (M) and right Peritoneal attachments and ligaments (R) hepatic veins at the superior aspect of the liver, marking the left, main of the liver and right portal fissures. B, Inferior to this, the caudate lobe (segment I) lies between the inferior vena cava (IVC) and the portal vein (PV). The left portal vein (LPV) separates segment II superiorly from segment III The liver is attached to the anterior abdominal wall, diaphragm and inferiorly. C, The right portal vein (RPV) divides segments V and VI other viscera by several peritoneal ligaments. inferiorly (C) from segments VII and VIII superiorly (B). Falciform ligament and ligamentum teres The liver is attached to the anterior abdominal wall by the falciform clockwise from below, starting with segment I and ending with segment ligament, derived from the ventral mesogastrium in the embryo. The VIII (see Figs 67.4–67.5; Fig. 67.6). two layers of this ligament pass posteriorly and slightly to the right from the posterior surface of the anterior abdominal wall and the undersur- Segment I Segment I corresponds to the anatomical caudate lobe and face of the diaphragm in the midline, and attach to the anterior and lies posterior to segment IV, with its left half directly adjacent to segment superior surfaces of the liver. On the dome of the superior surface, the II and its medial half wrapped around the retrohepatic segment of the right leaf runs laterally and is continuous with the upper layer of the inferior vena cava to a variable extent. In European literature, it is sub- coronary ligament. The left layer of the falciform ligament turns medi- divided into three parts (caudate process, Spiegel lobe and paracaval ally and is continuous with the anterior layer of the left triangular

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Liver 1165 76 RETPAHC ligament. The ligamentum teres is the obliterated remnant of the left dividing the lesser omentum because an aberrant or accessory left umbilical vein of the fetus; it runs in the lower free border of the falci- hepatic artery may run within it; when present, it invariably extends to form ligament and continues into a fissure on the inferior surface of the liver at the base of the umbilical fissure, and may be identified by the liver. In fetal life, the left umbilical vein opens into the left portal a pulsation in the lesser omentum close to the umbilical fissure. vein. It is supposed to be obliterated in adult life but frequently remains partially patent; in reality, its lumen is usually closed rather than obliter- Ligamentum venosum ated and it can be dissected at the umbilicus, dilated and used to access The ligamentum venosum represents the obliterated venous connection the left portal vein in more than half of individuals. The ligamentum that existed in the fetus between the left branch of the portal vein and teres may reopen in conditions such as portal hypertension, when it the termination of the left hepatic vein (the ductus venosus). It is used forms a sizeable collateral channel. as a guide to gain control of the left hepatic vein outside the liver during The ligamentum teres is important in abdominal surgery for several surgery. By dividing the ligament close to its insertion into the left reasons. It is often divided in upper abdominal surgery to optimize hepatic vein and retracting it laterally, the angle between the left and access to the upper abdominal viscera or as the first step in mobilization the middle hepatic veins may be accessed. of the liver. It is vascularized by numerous small arterial branches This can be helpful in left liver resection with preservation of the (mainly from the artery to segment IV) and para-umbilical veins, and caudate lobe, but if the caudate lobe is to be removed, the left hepatic these anastomose with branches of the superior epigastric artery; it is vein (or, more usually, the confluence of the left and middle hepatic therefore important to ligate or coagulate the ligament during its divi- veins with the inferior vena cava) can be approached more posteriorly sion. The ligamentum teres is a guide to the segment III hepatic duct without division of the ligamentum venosum. in hepaticojejunostomy formation, and to the left portal vein lying in the umbilical fissure during mesenterico-portal bypass (Vellar et al Porta hepatis, hepatoduodenal ligament 1998, di Francesco et al 2014). and hilar plate Coronary ligament The porta hepatis is a deep transverse fissure on the inferior surface of The coronary ligament is formed by the reflection of the peritoneum the liver. It is situated between the quadrate lobe anteriorly and the from the diaphragm on to the superior and posterior surfaces of the caudate process posteriorly, and contains the portal vein, hepatic artery right lobe of the liver. A large triangular area of liver devoid of peritoneal and hepatic nervous plexuses as they ascend into the parenchyma of covering, the so-called ‘bare area’ of the liver, lies between the two layers the liver, and the right and left hepatic ducts and some lymph vessels of the coronary ligament. Here, the liver is attached to the diaphragm that emerge from the liver. The hepatic ducts usually lie anterior to the by areolar tissue, which is in continuity inferiorly with the anterior portal vein and its branches, and the hepatic artery with its branches pararenal space. On the right, the two layers of the coronary ligament lies between the two (Figs 67.7–67.8). However, the right hepatic artery converge laterally to form the right triangular ligament. On the left, the sometimes lies anterior to the common hepatic duct; this variation is two layers become closely applied, and form the left triangular liga- important during bile duct reconstruction by hepaticojejunostomy ment. The upper layer of the coronary ligament is reflected superiorly on to the inferior surface of the diaphragm and inferiorly on to the right and superior surfaces of the liver. The lower layer of the coronary liga- Anterior ment is reflected inferiorly over the right suprarenal gland and right kidney, and superiorly on to the inferior surface of the liver. Surgical Right lobar nerves division of the right triangular and coronary ligaments allows the right Left hepatic duct lobe of the liver to be brought forwards, and exposes the lateral aspect Right hepatic duct Left hepatic artery of the inferior vena cava behind the liver. Right hepatic artery Left lobar lymphatics Triangular ligaments The left triangular ligament is a double layer of peritoneum that extends Left portal vein Right portal vein for a variable length over the superior border of the left lobe of the liver. Medially, the anterior leaf is continuous with the left layer of the falci- Peritoneal envelope form ligament, and the posterior layer is continuous with the left layer of the lesser omentum. The left triangular ligament lies in front of the Posterior abdominal part of the oesophagus and part of the fundus of the Fig. 67.7 A cross-section of the structures at the porta hepatis viewed stomach. Division of the left triangular ligament allows the left lobe of from above. the liver to be mobilized for exposure of the abdominal oesophagus and crura of the diaphragm. The left triangular ligament is an important stabilizing factor for the left lobe after excision of the right lobe of the Common hepatic duct liver. Its division will result in the left lobe being unstable, to the extent that it can rotate and displace into the space created under the right hemidiaphragm, which, in turn, can compromise the venous outflow of the left lobe with consequent liver dysfunction. If it is divided, the left lobe should be stabilized by reattaching the falciform ligament to the anterior abdominal wall. The right triangular ligament is a short structure that lies at the right lateral limit of the ‘bare area’ of the liver and represents the convergence laterally of the two layers of the coronary ligament. Lesser omentum The lesser omentum is a double layer of peritoneum that extends from the lesser curvature of the stomach and proximal duodenum to the inferior surface of the liver. Its free margin contains the portal triad (Ch. 63). Its attachment to the inferior surface of the liver is L-shaped. The vertical component follows the line of the fissure for the ligamentum venosum, the fibrous remnant of the ductus venosus. More inferiorly, the attachment runs horizontally to complete the L in the porta hepatis. At its upper end, the left layer of the lesser omentum is continuous with the posterior layer of the left triangular ligament, and the right layer is continuous with the coronary ligament as it encloses the inferior vena cava. At its lower end, the two layers of the lesser omentum diverge to surround the structures of the porta hepatis. A thin, fibrous condensa- tion of fascia usually runs from the medial end of the porta hepatis into the fissure for the ligamentum teres. This fascia is continuous with the Portal vein Inferior vena cava Hepatic artery lower border of the falciform ligament where the ligamentum teres Fig. 67.8 An axial CT of the porta hepatis. The hepatic ducts lie re-emerges at the inferior border of the liver. Care should be taken when anteriorly, the portal vein posteriorly, and hepatic artery between the two.

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LivER 1166 8 NOiTCES (Michels 1966). All these structures are enveloped within a perivascular A Medial (anterior) division sheath of loose connective tissue that surrounds the vessels and bile VIII ducts as they course through the liver parenchyma, and is continuous III II with the fibrous hepatic capsule (of Glisson). The dense aggregation of VII I vessels, supporting connective tissue, and liver parenchyma just above IV Left hepatic artery the porta hepatis is often referred to as the ‘hilar plate’ of the liver. Understanding the concept of the hilar plate is important in surgical approaches to the hilar structures; division or lowering of the hilar plate is essential for optimum surgical access to the left hepatic duct. The hepatic artery, bile duct and portal vein extend between the VI V Left gastric porta hepatis and the upper border of the duodenum in the free edge artery of the hepatoduodenal ligament, which forms the anterior boundary Lateral (posterior) division Splenic artery of the epiploic foramen. Rapid control of the vessels entering the porta Right hepatic artery hepatis (the hepatic pedicle) can be obtained by compressing them in the free edge of the lesser omentum (a ‘Pringle’ manœuvre); this is Cystic artery conveniently done by dividing the lesser omentum immediately to the Common hepatic artery Hepatic artery ‘proper’ left of these structures and passing a tape around them through the epiploic foramen. Gastroduodenal artery Right gastric artery The left hepatic duct is extrahepatic as it descends obliquely along the undersurface of segment IV (the quadrate lobe) to the confluence B Cystic duct Caudate lobe, of the hepatic ducts. Access to this extrahepatic segment of the left Cystic artery Portal vein anterior surface hepatic duct is particularly useful when performing a biliary-enteric bypass procedure to treat a stricture of the hepatic duct confluence. The Liver, right lobe right hepatic duct is more intrahepatic and extension of a hepatico- Diaphragm, right crus jejunal anastomosis on to the right hepatic duct necessitates incision of the liver parenchyma in the gallbladder fossa. Glissonian sheaths Left gastric Glisson’s capsule of the liver becomes condensed as Glissonian sheaths artery around the branches of the portal triad structures as they enter the liver Inferior vena parenchyma and subdivide into segmental branches. Thus, each bile cava duct, hepatic artery and portal vein is surrounded by a single fibrous Common sheath, which Couinaud called the ‘Valoean sheath’ (after Valoeus, an hepatic artery anatomist from the Middle Ages who first described the liver capsule). Right gastric Within each sheath, the portal vein is surrounded by loose areolar con- artery nective tissue, making dissection of the portal vein relatively easy. The Gastro- fibrous tissue around the bile ducts and hepatic artery is tougher, and duodenal artery dissection of these structures is more difficult. This sheath arrangement facilitates surgical control of the right and left vasculobiliary pedicles of the liver, as well as sectoral and segmental divisions in complex liver resections (Yamamoto et al 2012). Gallbladder, Bile Superior Right gastro- VASCULAR SUPPLY AND LYMPHATIC DRAINAGE fundus duct pancreatico- epiploic artery duodenal artery The blood vessels connected with the liver are the portal vein, hepatic Fig. 67.9 The hepatic artery. A, Branches. B, Usual relations of the artery and hepatic veins. The portal vein and hepatic artery ascend in hepatic artery, bile duct and portal vein to each other in the lesser the lesser omentum to the porta hepatis, where each usually bifurcates. omentum: anterior aspect, portion of the liver removed. The common hepatic duct and lymphatic vessels descend from the porta hepatis alongside the portal vein and hepatic artery (see Fig. 67.8). The hepatic veins leave the liver via its posterior surface and run directly into the inferior vena cava. well to the left of the porta hepatis. The main significance of an early division is that the right branch may pass behind the portal vein Hepatic artery (Lanouis and Jamieson 1993). The segmental arteries of the liver are macroscopically end arteries, although some collateral circulation In adults, the common hepatic artery is intermediate in size between occurs between segments via fine terminal branches. the left gastric and splenic arteries. In fetal and early postnatal life, it is Anatomical variants of the normal arrangement of the hepatic artery the largest branch of the coeliac trunk. The hepatic artery gives off the are found in about one-third of individuals and are important to right gastric and gastroduodenal arteries, as well as branches to the bile re cognize because they are relevant to surgical and interventional radio- duct and gallbladder from its right hepatic branch (Fig. 67.9A). After logical procedures (Covey et al 2002, Michels 1966, López-Andújar originating from the coeliac trunk, the hepatic artery passes anteriorly et al 2007, Saba and Mallarini 2011). An artery that supplies part of the and laterally above the upper border of the pancreas to the upper aspect liver in addition to its normal artery is defined as an accessory artery. A of the first part of the duodenum. It is subdivided into the common replaced hepatic artery is an artery that does not originate from an hepatic artery, from the coeliac trunk to the origin of the gastroduode- orthodox position and provides the sole supply to that part of the liver. nal artery, and the ‘hepatic artery proper’, from that point to its bifurca- The most common anatomical variants are a replaced or accessory tion. It ascends anterior to the portal vein and medial to the bile duct left hepatic artery that arises from the left gastric artery, or a replaced within the free margin of the lesser omentum in the anterior wall of or accessory right hepatic artery that arises from the superior mesenteric the epiploic foramen. It divides into right and left branches at a variable artery, both occurring in 10–20% of individuals. level below the porta hepatis. The right branch of the hepatic artery Variations in the intrahepatic arteries are common and may be surgi- usually crosses posterior (occasionally anterior) to the common hepatic cally important. For example, the segment IV artery most commonly duct (Fig. 67.9B). This close proximity often means that the right arises from the left hepatic artery, but in up to 30% of cases, it arises hepatic artery is involved in bile duct cancer earlier than the left hepatic from the right hepatic artery or the hepatic artery proper (Onishi et al artery. Occasionally, the right hepatic artery crosses anterior to the 2000). The segment IV artery never arises to the right of the common common hepatic duct and is more vulnerable to injury in biliary hepatic duct; thus, if the right hepatic artery is divided to the right of surgery. It almost always divides into an anterior branch supplying seg- the common hepatic duct, this arterial supply to segment IV is not ments V and VIII, and a posterior branch supplying segments VI and endangered. Failure to recognize this variation may compromise the VII. The anterior division also often supplies a branch to segment I and blood supply to segment IV following right hepatectomy, and is espe- the gallbladder. The hepatic artery proper sometimes divides at a low cially important during right lobe donation for live donor liver level close to its origin and, occasionally, it divides at a higher level, transplantation.

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Liver 1166.e1 76 RETPAHC A replaced hepatic artery proper may arise from the superior artery arises from the left gastric artery, entering the liver through the mesenteric artery (Fig. 67.10) and can be suspected at surgery by a rela- umbilical fissure; this artery provides a source of collateral supply in tively superficial portal vein (reflecting the absence of a hepatic artery cases where the arteries at the porta hepatis are occluded, but it may that would normally ascend in front of the vein). More commonly, a also be injured during mobilization of the stomach, as it lies in the replaced or accessory right hepatic artery arises from the superior upper portion of the lesser omentum. Rarely, an accessory left or right mesenteric artery (see Fig. 67.10; Fig. 67.11). In such cases, the variant hepatic artery may arise from the gastroduodenal artery or directly from artery runs in the lesser omentum behind the portal vein and bile duct, the aorta. The presence of replaced arteries can be life-saving in patients and can usually be identified at surgery by palpable pulsation behind with bile duct cancer; because they are further away from the bile duct the portal vein. An accessory right hepatic artery may be injured during they tend to be spared from infiltration by the cancer, making excision resection of the pancreatic head because the artery lies in close proxim- of the tumour feasible. Knowledge of these variations is also essential ity to the portal vein. Occasionally, a replaced or accessory left hepatic when performing whole and split liver transplantation. Replaced left hepatic artery: 10–20% Replaced hepatic artery proper: 4% Fig. 67.10 Common hepatic artery variants. Replaced right hepatic artery: 10–15% Left gastric artery Superior mesenteric artery Superior mesenteric artery or aorta Left hepatic artery Fig. 67.11 Hepatic arteriograms. A, A selective hepatic arteriogram shows normal left hepatic artery branches and small right hepatic artery branches. B, The right hepatic artery is arising from the origin of the superior mesenteric artery. A Gastroduodenal artery Right hepatic artery B

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Liver 1167 76 RETPAHC Veins The main extrahepatic tributaries of the portal vein are the left gastric (coronary) vein, which ends in the left margin of the portal vein, and the posterior superior pancreaticoduodenal vein near the head of the The liver has two venous systems. The portal system conveys venous pancreas. The portal vein divides into right and left branches at the blood from the majority of the gastrointestinal tract and its associated hilum of the liver (Fig. 67.13). The left portal vein has a longer extra- organs to the liver (p. 1039). The hepatic venous system drains blood hepatic course (4–5 cm) than the right portal vein, tends to lie more from the liver parenchyma into the inferior vena cava. horizontal, and is often smaller in calibre. It has a horizontal portion Portal vein that runs along the inferior surface of segment IV and invariably gives The portal vein is formed behind the neck of the pancreas, usually from branches to segment I and sometimes to segment IV. The left branch of the convergence of the superior mesenteric and splenic veins (Fig. the portal vein continues within the liver, giving off a segment II branch 67.12; see also Figs 70.8b, 59.8). Its origin lies in the transpyloric plane laterally before taking a more anterior and vertical course in the umbili- between the lower border of the body of the first lumbar vertebra and cal fissure. Here, it gives off branches to segments III and IV, and receives the upper border of the body of the second lumbar vertebra (Mirjalili the obliterated left umbilical vein (ligamentum teres). The majority of et al 2012). The portal vein is approximately 8 cm long and ascends the portal venous supply to segment IV comes from the left portal vein, obliquely to the right behind the first part of the duodenum, the and only occasionally from the right branch of the portal vein or its common bile duct and gastroduodenal artery, and anterior to the infe- branches to segment V or VIII. The right branch of the portal vein is rior vena cava. It enters the right border of the lesser omentum and only 2–3 cm in length and usually divides into a right medial (anterior) ascends anterior to the epiploic foramen to reach the right end of the sectoral division supplying segments V and VIII, and a right lateral porta hepatis, where it divides into right and left main branches, which (posterior) sectoral division supplying segments VI and VII. The medial enter the liver. In the lesser omentum, the portal vein lies posterior to division may give a branch to segment I. both the bile duct and the hepatic artery. It is surrounded by the hepatic Portal vein variations usually involve the right branch (Covey et al nerve plexus and accompanied by numerous lymphatics and some 2004). If the latter is absent, which occurs in about 10–15% of livers, lymph nodes. The portal vein contains smooth muscle in its wall and, the portal vein usually trifurcates into left portal, right medial and right in experimental animals at least, has well-developed spontaneous con- lateral sectoral veins. This has implications for split liver and live donor tractions with frequencies between 0.01 and 1 Hz (Burt 2003). It is liver transplantation, where its presence might be considered as a rela- typically valveless. tive contraindication. The right lateral sectoral portal vein may arise from the portal vein, or the right medial sectoral portal vein may origi- nate from the left portal vein, a variant that it is important to remember during left-sided liver resection. Rarely, the portal bifurcation is absent, Portal vein in which case the portal vein enters the liver, giving off the right sectoral branches, and then turns left to supply the left lobe, which presents an added complexity in major liver surgery (Chaib 2009). Porto-systemic shunts Increased pressure within the portal venous system may result in dila- tion of portal venous tributaries and reversed flow at sites of porto- systemic anastomoses. Common sites of porto-systemic shunts are listed in Table 67.1. Hepatic veins The liver drains by three major hepatic veins into the suprahepatic part of the inferior vena cava and via numerous minor hepatic veins that drain into the retrohepatic inferior vena cava. The adult retrohepatic inferior vena cava is 6–7 cm long and surrounded, to a variable extent, by segment I (Camargo et al 1996). The three major veins are located between the four sectors of the liver (see Fig. 67.6A; Figs 67.14–67.15). Thus, the right hepatic vein lies between the right medial and lateral sectors, the middle hepatic vein lies between the right and left hemi- livers, and the left hepatic vein lies between the left medial and lateral sectors. During hepatic resection, the surgeon should transect the liver Superior mesenteric vein parenchyma slightly to the left or right of the particular fissure that is Fig. 67.12 A coronal CT of the portal vein and superior mesenteric vein. being opened to avoid the main trunk of a hepatic vein. Fig. 67.13 The main portal vein and its intrahepatic branches. (Right lateral = right posterior; right medial = II right anterior.) I VII VIII IV III V VI Right lateral sectoral vein Left portal vein Right medial sectoral vein Right portal vein

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LivER 1168 8 NOiTCES inf.HV1 RHV MHV8 LHV4 LHV Middle hepatic vein Inferior vena cava Fig. 67.14 A sagittal ultrasound of the middle hepatic vein. The middle inf.HV2 MHV5 MHV5 MHV4 MHV4 MHV4 hepatic vein is seen draining into the inferior vena cava. Fig. 67.15 Modern CT analysis techniques are helpful in demonstrating variations in hepatic venous anatomy and this is very useful for planning live donor surgery for liver transplantation. Abbreviations: inf. HV1, inf. HV2, right inferior hepatic veins; LHV, left hepatic vein; LHV4, left hepatic Table 67.1 Common sites of porto-systemic anastomoses in portal hypertension and associated clinical implications vein branch to segment 4; MHV4, middle hepatic vein branches to segment 4; MHV5, middle hepatic vein branches to segment 5; MHV8, Portal vein tributaries Systemic veins Clinical middle hepatic vein branches to segment 8; RHV, right hepatic vein. presentations (Courtesy of MeVis Medical Solutions AG, Bremen, Germany.) Left gastric vein Distal oesophageal veins Oesophageal and draining into azygos and gastric varices hemiazygos veins Superior rectal veins Middle and inferior rectal Rectal varices the right side of the middle hepatic vein and is sometimes large enough veins draining into internal to be mistaken for the middle hepatic vein. Anteriorly, the middle iliac and pudendal veins hepatic vein drains some of segment V; the sizes of the tributaries drain- Persistent tributaries of left Periumbilical branches of ‘Caput medusae’ ing segments V and VIII are variable. Intrahepatic venous anastomoses branch of portal vein in epigastric and intercostal ligamentum teres veins between the middle and right hepatic veins, particularly in segment Tributaries of right branch of Retroperitoneal veins Dilated retroperitoneal VIII, have been reported in up to one third of adult livers (Hribernik portal vein overlying ‘bare draining into azygos, veins at risk during and Trotovšek 2014). area’ of liver hemiazygos, lumbar, surgery or interventional intercostal and phrenic veins procedures Left hepatic vein Omental and colonic veins near Retroperitoneal veins near May be problematic The left hepatic vein lies between the left medial and left lateral sectors hepatic and splenic flexures hepatic and splenic flexures during surgery of the liver and drains segments II, III and, occasionally, IV. Small veins draining segment II and, occasionally, the superior part of segment IV may drain directly into the inferior vena cava. Usually, a major tributary of the left hepatic vein, the umbilical fissure vein, runs between Right hepatic vein segments III and IV and contributes to their drainage. Occasionally, This is the longest and largest hepatic vein. It is usually single, but the vein draining segment III ends separately in the confluence of occasionally remains as two trunks until it terminates by draining into the left and middle hepatic veins. These variations in venous drainage the inferior vena cava. The right hepatic vein runs in the right portal are of significance in split liver transplantation and live donor liver fissure between the right medial and lateral sectors. It drains the whole transplantation. of segments VI and VII, and variable proportions of segments V and VIII, depending on the extent to which these segments drain into the Minor hepatic veins middle hepatic vein. The right hepatic vein is formed anteriorly near Segment I veins drain directly into the inferior vena cava and vary in the inferior border of the liver and lies in a coronal plane through most number from one to five. Since this segment has an independent venous of its course. It drains into the inferior vena cava near the upper border drainage from the rest of the liver, in patients with Budd–Chiari syn- of the caudate lobe. Of the three major hepatic veins, the right hepatic drome, in which the major hepatic veins are blocked, segment I often vein is most variable in its size, not only due to the variable contribu- continues to drain effectively and undergoes compensatory hypertro- tion of the middle hepatic vein to the drainage of segments V and VIII phy. There may be an accessory inferior or middle right hepatic vein, as but also due to the existence of an accessory right inferior (30%) and/ well as several smaller ‘retrohepatic’ veins that drain the right lobe or middle hepatic vein (10%) (Fang et al 2012). The hepatic venous directly into the inferior vena cava. When present, they are of surgical anatomy is particularly important in right lobe living donation and can importance, especially if greater than 5 mm in diameter; they drain be assessed preoperatively by computed tomography (CT) or magnetic segments V and VI independently of the three major hepatic veins and, resonance imaging (MRI) and/or by intraoperative ultrasound. therefore, a tumour involving the latter can be resected safely as long as venous drainage from the accessory veins is preserved. In live donor Middle hepatic vein and split liver transplantation, larger accessory veins must be individu- The middle hepatic vein lies in the main portal fissure between the right ally anastomosed to the recipient inferior vena cava to ensure adequate and left hemi-livers. It usually joins the left hepatic vein and terminates venous drainage. in the inferior vena cava as a short common trunk (about 5 mm long); it ends as a single trunk in the inferior vena cava in fewer than 10% of Transjugular intrahepatic porto-systemic shunt individuals. The middle hepatic vein drains the central part of the liver (TiPS) procedure for portal hypertension and receives constant tributaries from segments IV, V and VIII. The vein from segment IV lies in a sagittal plane and enters the middle hepatic Available with the Gray’s Anatomy e-book vein on its left side. The vein from segment VIII runs transversely into

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Liver 1168.e1 76 RETPAHC In extreme cases of chronic portal hypertension, a large-calibre anasto- mosis between the portal and systemic circulations may be created within the liver parenchyma by inserting a stent between a large portal and hepatic vein within the liver. The stent is introduced through a catheter inserted into the internal jugular vein and guided into the liver under radiological control. This large shunt relieves the severe portal hypertension but tends to worsen incipient hepatic encephalopathy.

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Liver 1169 76 RETPAHC Segmental anatomy of the liver in relation area’ and superior surface; distension or disruption of the liver capsule to hepatic resection causes quite well-localized, sharp pain. Hepatic plexus The hepatic plexus receives preganglionic parasympathetic fibres from Available with the Gray’s Anatomy e-book the anterior and, to a lesser extent, the posterior vagus, and postgangli- onic sympathetic fibres via the coeliac and superior mesenteric plexuses. Lymphatic drainage Nerve fibres accompany the branches of the portal triad into the liver, penetrating as far as the hepatocytes. Aminergic, cholinergic, peptider- gic and nitrergic nerve fibres have been identified and appear to be Lymph from the liver is rich in protein and is mostly a product of the involved in hepatic metabolism and the control of sinusoidal blood hepatic sinusoids (Ohtani and Ohtani 2008). It passes, via deep and flow (McCuskey 2004); however, the transplanted, denervated liver superficial pathways, to nodes above and below the diaphragm (Trut- indicates that this role is not essential. Multiple fine branches from the mann and Sasse 1994). Obstruction of hepatic venous drainage plexus supply the extrahepatic bile ducts and gallbladder; the vagal increases the flow of lymph in the thoracic duct. fibres are motor to the muscle of the bile ducts and gallbladder, and Superficial hepatic lymphatics inhibitory to the sphincter of the bile duct. Branches from the plexus Superficial lymphatics run in subserosal areolar tissue over the surface also run inferiorly with the right gastric artery to contribute to the of the liver and drain in four directions. Lymphatics from most of the supply of the pylorus; with the gastroduodenal artery and its branches posterior surface, including the caudate lobe, drain into nodes along- to reach the pylorus, proximal duodenum and pancreas; and with the side the inferior vena cava; a few lymphatics from the posterior surface right gastroepiploic artery to provide a small contribution to the nerve of the left lobe pass towards the oesophageal hiatus and nodes around supply of the stomach. the cardia. Lymphatics in the coronary and right triangular ligaments Referred pain may pass directly to the thoracic duct. Lymphatics from most of the inferior, anterior and superior surfaces drain into hepatic nodes at the Pain arising from the parenchyma of the liver is poorly localized. In porta hepatis. A few lymphatics from the right superior surface accom- common with other structures of foregut origin, pain is referred to the pany the inferior phrenic artery across the right diaphragmatic crus to epigastrium. Stretch or irritation of the liver capsule by inflammation drain into coeliac nodes. or neoplasia produces well-localized ‘somatic’ pain. Pathology involv- ing the diaphragmatic surface of the liver may be referred via the phrenic Deep hepatic lymphatics nerve to the right shoulder region (C3,4,5 dermatomes). Fine lymphatics within the portal triads and around interlobular veins merge to form larger vessels. Some ascend through the parenchyma to pass through the vena caval opening in the diaphragm and drain into MICROSTRUCTURE inferior mediastinal nodes, but most drain to lymph nodes at the porta hepatis. The liver is essentially an epithelial-mesenchymal outgrowth of the caudal part of the foregut, with which it remains connected via the biliary tree (see Ch. 60). Most of the surface of the liver is covered by INNERVATION a typical serosa, the visceral peritoneum. Beneath this, and enclosing the whole organ, is a thin (50–100 µm) capsule of connective tissue, The liver has a dual innervation. The parenchyma is supplied by nerves from which extensions pass into the liver as septa and trabeculae. arising from the hepatic plexus, which contains sympathetic and para- Branches of the hepatic artery and hepatic portal vein, together with sympathetic (vagal) fibres; they all enter the liver at the porta hepatis. bile ductules and ducts, run within these connective tissue trabeculae, The capsule is supplied by fine branches of the lower intercostal nerves, which are termed portal tracts. The combination of the two types which also supply the parietal peritoneum, particularly around the ‘bare of vessel and a bile duct is termed a portal triad (Fig. 67.19); these A B Fig. 67.19 The structural organization of human liver tissue. A, Lobules bordered by delicate connective tissue septa (arrows), in which run branches of the hepatic portal vein, hepatic artery and bile duct, grouped as portal triads. A central vein drains each lobule. B, A portal triad containing branches of the hepatic portal vein (PV; generally the largest profile), the hepatic artery (A) PV and a bile duct (B), with typical round epithelial nuclei. Other small bile ductule and arteriolar branches are also visible. C, A functional view, in which the territories of the hepatic lobules are A shown as regular hexagons (unlike their real B appearance, which is highly variable). Functionally, the liver microarchitecture is better considered in terms of acini extending between adjacent central venules and divided into three zones as shown. (A, With permission from Dr JB Kerr, Monash C Central vein Portal triad: branches of Terminal branches of hepatic University, from Kerr JB 1999 Atlas of Functional (tributary of hepatic vein) hepatic artery, bile duct arteriole and portal vein and hepatic portal vein Histology. London: Mosby. B, Courtesy of Mr Peter Helliwell and the late Dr Joseph Mathew, Department of Histopathology, Royal Cornwall Hospitals Trust, UK.) 1 2 3 Classic hepatic lobule Portal lobule Liver acinus Metabolic zonation within liver acinus

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Liver 1169.e1 76 RETPAHC In 1888, Rex described the midline division of the liver, and in the A 1950s Claude Couinaud’s detailed description of the segmental anatomy of the liver formed the basis for subsequent advances in liver Left hepatic vein imaging and surgery. Goldsmith and Woodburne also published a detailed description of liver anatomy in 1957 but used a different ter- Left posterior sector minology; confusion in hepatic nomenclature has persisted for several decades. Couinaud divided the right and left hemi-livers into two sectors each, according to the secondary divisions of the portal vein. In the right hemi-liver, the anteromedial and posterolateral sectors were each sub- Left portal fissure divided into a superior and an inferior segment, producing a total of four segments. In the left hemi-liver, the medial sector was divided into two segments separated by the falciform ligament and ligamentum Umbilical teres, while the lateral sector consisted of a single segment (II). The fissure smallest segment, which Couinaud designated segment I, was located in the central and posterior part of the liver between the bifurcation of the portal vein and the inferior vena cava, and had independent hepatic Left anterior sector vein and portal vein tributaries. Couinaud, therefore, described eight B liver segments, numbered I to VIII: segments II, III and IV made up the left hemi-liver and segments V, VI, VII and VIII made up the right hemi-liver. In 1994, he added segment IX to describe the small region of the right hemi-liver lying adjacent to the right side of the inferior vena cava, but later recognized that this was better considered as part of segment I. In 1982, Henri Bismuth used Couinaud’s anatomical descriptions with some modifications as the basis for developing anatomical liver resections (Bismuth 2013). Couinaud’s studies had been based on cor- rosion casts of injected cadaveric livers that had undergone slight post- mortem flattening from resting on a firm surface. Bismuth renamed Couinaud’s anteromedial and posterolateral sectors in the right hemi- liver as anterior and posterior, and also challenged Couinaud’s subdivi- Fig. 67.16 A, The umbilical fissure that divides the anterior sector of the sion of the left liver. Couinaud had described two sectors: a lateral sector left lobe into two segments is, in fact, an artificial scissure. B, When it is consisting of a single segment, and a medial sector consisting of two suppressed, the anterior sector appears as a single segment. (Redrawn segments separated by a branch of the left portal vein lying in continuity with permission from Bismuth H. Surgical anatomy and anatomical with the round ligament. Bismuth considered that this went against surgery of the liver. World J Surg 1982;6:3–9, Springer.) Couinaud’s own description of individual segments containing a major branch of the portal vein, and suggested that the left medial sector also Middle segment Left segment consisted of a single segment, i.e. segments III and IV were, in fact, ‘half-segments’ (Fig. 67.16). This scheme created a single sector con- taining two segments within the left hemi-liver. To avoid confusion, Bismuth chose to retain the segment numbers III and IV, albeit recog- nizing them as half-segments. The Bismuth classification recognized two hemi-livers, three sectors (right posterior, right anterior and left) and seven segments: segments 6 and 7 in the right posterior sector, segments 5 and 8 in the right anterior sector, half-segments 3 and 4 and segment 2 in the left sector, and segment 1 (numbering was changed from Roman to Arabic). In 1986, Ken Takasaki described a different basis for subdividing the gross architecture of the liver, in which the portal vein had three branches (right, middle and left) and there were just two hepatic veins (right and middle, the left hepatic vein being a tributary of the middle hepatic vein; Fig. 67.17). Takasaki had divided the liver into three parts of almost equal volume, based on the three branches of the portal vein and the two hepatic veins. Apart from the terms used, Takasaki’s descrip- tion is similar to Bismuth’s modification of Couinaud’s anatomy in that the liver is considered to consist of three, and not four, territories. It fails to take into account the division of the left side of the liver by the falciform and round ligaments. The major advantage of Takasaki’s description is the individualization of the middle part, facilitating the concept of central hepatectomy. Three secondary branches of the Right segment Glissonian pedicle Fig. 67.17 The liver is divided into three segments and a caudate area, according to the ramification of the Glissonian pedicles. (Redrawn based on Takasaki K, Koabayashi S, Tanaka S, et al 1986 Highly selected hepatic resection by Glissonian sheath-binding method. Dig Surg 3: 121.)

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LivER 1169.e2 8 NOiTCES In 1998, the International Hepato-Pancreato-Biliary Association 1957), bisegmentectomy (Couinaud 1957), resection of half a segment (IHPBA) developed an international committee on nomenclature of (Takasaki et al 1986), and left lateral sectionectomy (Terminology hepatic anatomy and resections, and this reported to the IHPBA General Committee of the IHPBA 2000). To avoid confusion, the term lobec- Assembly in Brisbane in 2000 (Terminology Committee of the IHPBA tomy is no longer used but Bismuth has argued for a return to classical 2000). The chairman of the committee, Steven M. Strasberg, highlighted anatomy and the use of the term left lobectomy. He has also argued the confusion that arose from applying multiple terms to the same that all hepatectomies should be defined by the specific segments that anatomical structure or operative procedure, and from using the same are resected. Thus, removal of a single segment should be described as term to describe more than one structure or operation. For example, in ‘segmentectomy n’ where n is the specific number of the segment 1997, there were 13 terms in use for the plane that defined the water- removed. Resection of two segments is a ‘bisegmentectomy n + n1’, and shed between the right and left hemi-livers (called the midplane of the that of three segments a trisegmentectomy n + n1 + n2 (Bismuth 2013). liver by the committee), and the terms ‘lobe’, ‘lobectomy’, ‘segment’ Masatoshi Makuuchi, a member of the IHPBA Brisbane 2000 com- and ‘segmentectomy’ were being used to describe different parts of the mittee on nomenclature, has recently questioned the current status, liver and associated procedures, depending on whether the surgeon was pointing out that the differences in portal vein branching patterns in European or North American. The anatomical basis for the Brisbane the left and right hemi-livers have been the major obstacle in consist- 2000 nomenclature was the usual branching pattern of the hepatic ently classifying liver territories to satisfy what is known about hepatic arteries and bile ducts within the liver. The ramification of the portal embryology, as well as descriptive and surgical anatomy. Makuuchi vein was said to follow an identical pattern in the right hemi-liver but (2013) has commented that, in the embryo, the right and left hemi- to be different in the left hemi-liver. Three orders of branching resulted livers develop synchronously and that the right and left umbilical veins in successive division of the liver into two hemi-livers, four sections and initially join the right and left branches of the portal vein, respectively. eight segments. Watershed areas between territories subserved by At 4–5 weeks’ gestation, the right umbilical vein is resorbed so that the branches of the hepatic artery and bile duct were demarcated by the volume of the left side of the liver increases compared to the right, but midplane of the liver, a right and left intersectional plane, and several after occlusion of the left umbilical vein after birth, the left hemi-liver intersegmental planes. The terminology of liver resections was based gradually shrinks and the right side enlarges. Makuuchi argues that directly on the anatomical terminology, and individual resections were the left lateral sector (segment II) and right lateral sector (segments termed hemihepatectomy (or hepatectomy), sectionectomy and seg- VI and VII) were so named by Couinaud because the portal vein mentectomy; an extended resection of three sections was called a trisec- branches to both sectors are the first large branches arising from the tionectomy (Fig. 67.18). There has been a clear trend towards adoption left and right divisions of the portal vein. These two sectors also share of this terminology since 2000 but it has not been universal, not least the characteristic of having a major hepatic vein running on their because the classification has some anatomical deficiencies. In particu- medial border. This is contrary to the views of both Bismuth and Taka- lar, Couinaud’s segments II and III became the left lateral section saki, who maintain that segment II should be amalgamated with seg- (which meant that removal became a left lateral sectionectomy) but this ments III and IV into a single sector, and of the IHPBA Brisbane 2000 does not accurately represent the anatomical division. The introduction nomenclature committee, who considered segment IV to be a full of the term ‘section’, as opposed to ‘sector’, was intended to introduce sector. Makuuchi postulates that the left lateral sector shrinks after birth simpler terms for segments II and III (left lateral section) and segment and, if segment IV is determined to be a sector, then the right medial IV (left medial section) that would mirror the arrangement in the right sector of the liver should be demarcated by a plane that corresponds to hemi-liver (right anterior and posterior sections). the embryonic right umbilical vein. As the main portal pedicle should Bismuth argued that classification of the lateral part of the left hemi- be located at the centre of the sector and not at its border, if the left liver was particularly problematic. According to Couinaud, individual and right hemi-livers are each divided into two sectors, it is more logical liver territories contain portal vein branches but are separated by the to regard segment II as a sector, as suggested by Couinaud, rather than major hepatic veins. However, the lateral part of the left hemi-liver is segment IV. demarcated by the falciform and round ligaments. Resection of this part Makuuchi also discussed the use of the term ‘extended’, as proposed of the liver remains one of the most commonly performed hepatecto- by Bismuth and the IHPBA Brisbane 2000 nomenclature committee. mies. In classical anatomy, the term lobe relates to part of an organ He suggested that ambiguity could be eliminated by adopting the defined by an external fissure; removal of the part of the liver to the wording ‘extended into segment X’, where X is the specific segment left of the falciform and round ligaments was originally called a left number identified by Couinaud. Further revision of the nomenclature lobectomy. According to subsequent classifications, this resection has is likely in the future (Strasberg and Phillips 2013). been termed a left lateral segmentectomy (Goldsmith and Woodburne

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Liver 1169.e3 76 RETPAHC Fig. 67.18 Resectional terminology. (Redrawn with Anatomical term Couinaud segments Term for surgical resection Diagram permission from Terminology Committee of the (pertinent area is shaded) International Hepato-Pancreato-Biliary Association. The Brisbane 2000 terminology of liver anatomy and resections. HPB 2000;2:333–9.) 2 8 Right liver Sg 5-8 Right hepatectomy 7 4 3 or or Hemi-liver Right hemihepatectomy 6 5 2 8 Left liver Sg 2-4 Left hepatectomy 7 4 3 or or Hemi-liver Left hemihepatectomy 6 5 2 8 Right anterior Sg 5,8 Right anterior sectionectomy 7 4 3 section 5 6 2 8 Right posterior Sg 6,7 Right posterior sectionectomy 7 4 3 section 5 6 2 8 7 4 3 Left medial Sg 4 Left medial sectionectomy section 5 6 2 8 Left lateral Sg 2,3 Left lateral sectionectomy 7 4 3 section 5 6 2 8 Segments 1-8 Any one of Sg 1-8 Segmentectomy 7 4 3 (e.g. segmentectomy 6) 5 6 2 8 Two contiguous Any two of Sg 1-8 Bisegmentectomy 7 4 3 segments in continuity (e.g. bisegmentectomy 5,6) 5 6 Extended resections (Trisectionectomy) 2 Right trisectionectomy (preferred term) 8 or 7 4 3 Sg 4-8 Extended right hepatectomy 5 or 6 Extended right hemihepatectomy Left trisectionectomy (preferred term) 2 8 or 7 4 3 Extended left hepatectomy Sg 2,3,4,5,8 or 5 6 Extended left hemihepatectomy

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LivER 1170 8 NOiTCES structures are usually accompanied by one or more lymphatic vessels can be divided into three zones: zone 1 (periportal) is nearest to the and nerves. terminal branches of afferent vessels; zone 2 is the intermediate zone; The liver parenchyma consists of a complex network of epithelial and zone 3 is the area closest to the central vein. cells, supported by connective tissue, and perfused by a rich blood supply from the portal vein and hepatic artery. The epithelial cells, Blood supply hepatocytes, carry out the major metabolic activities, but additional cell types possess storage, phagocytic and mechanically supportive func- Preterminal hepatic arterioles within the acini convey arterial blood to tions. In the mature liver, hepatocytes are arranged mainly in plates (or the sinusoids, mostly via a fine capillary plexus that drains to branches cords when seen in two-dimensional sections) that are usually only one of the portal veins; a small proportion of arterial blood passes directly cell thick and are separated by venous sinusoids, which anastomose to the hepatic sinusoids, bypassing these capillary plexuses. Sinusoids with each other via gaps in the plates (Fig. 67.20; see Fig. 67.22). Until thus contain mixed venous and arterial blood. Central veins from adja- about 7 years of age, plates are normally two cells thick. This pattern cent lobules form interlobular veins that unite as hepatic veins and recurs in liver regeneration, when a mixture of hyperplasia and hyper- drain to the inferior vena cava. trophy results in cell plates that are several cells thick and composed of larger multinucleated hepatocytes, reverting over the course of about a Hepatic plates (cords) year to single cell thickness. Bile is secreted by hepatocytes and collected in a network of minute tubes (canaliculi). The hepatocytes can therefore be regarded as exo- The endothelium of the sinusoids is fenestrated and lacks a basal crine cells, secreting bile into the alimentary tract via the extrahepatic lamina, which enables it to act as a dynamic blood filter (Fraser et al bile ducts. Their other metabolic functions involve complex biochemi- 1995). The sinusoids are separated from the plates of hepatocytes by a cal exchanges with the blood. narrow gap, the perisinusoidal space of Disse, which is normally The fetal liver is a major haemopoietic organ; erythrocytes, leuko- 0.2–0.5 µm wide but which distends in hypoxic states. The space con- cytes and platelets develop from mesenchyme covering the sinusoidal tains interstitial fluid, the microvilli of adjacent hepatocytes, hepatic endothelium. stellate cells, fine collagen fibres (mostly type III, with some types I and IV), and occasional non-myelinated nerve terminals. Lobulation of the liver A network of minute, interconnecting biliary canaliculi (approxi- mately 1 µm in diameter) runs between the hepatic plates. The canal- iculi are formed by the apposed plasma membranes of adjacent The structural unit of the liver is the lobule: a roughly hexagonal hepatocytes sealed by tight junctions. They conduct bile to the canals arrangement of plates of hepatocytes, separated by intervening sinu- of Hering, trough-like structures lined by cholangiocytes and hepato- soids that radiate outwards from a central vein, with portal triads at the cytes within the liver lobules. Each canal collects bile from multiple vertices of each hexagon (Fig. 67.21; see Fig. 67.19). The central veins canaliculi and empties into a bile ductule (lined by cholangiocytes), drain into the hepatic veins. In some species, the classic lobular units which in turn drains into an interlobular bile duct within the portal are delimited microscopically by distinct connective tissue septa. tracts (Roskams et al 2004). The flow of bile is thus towards the periph- However, the lobular organization of the human liver is not immedi- ery of the lobule, in the opposite direction to the blood flow, which is ately evident in histological sections; the lobules do not have distinct centripetal. boundaries, and connective tissue is sparse. The plates do not pass straight to the periphery of a lobule like the spokes of a wheel but run Cells of the liver irregularly as they anastomose and branch. Detailed studies of human liver, using three-dimensional reconstruc- tion and morphometric analysis combined with histopathological Resident cells of the liver include hepatocytes, hepatic stellate cells (also observations, have revealed a highly ordered arrangement of functional known as fat-storing Ito cells), sinusoidal endothelial cells, macro- units: the hepatic (portal) acini. Each acinus is an approximately ovoid phages (Kupffer cells), the epithelial cells of the biliary tree (cholangio- mass of tissue, orientated around a terminal branch of a hepatic arteri- cytes), hepatic stem cells, natural killer lymphocytes (pit cells), and ole and portal venule, and with its long axis defined by two adjacent connective tissue cells of the capsule and portal tracts (see Fig. 67.19B). central veins (see Fig. 67.19). It includes the hepatic tissue served by these afferent vessels and is bounded by adjacent acini. Hepatocytes About 80% of the liver volume and 60% of its cellular The acinar definition of hepatic microarchitecture has clarified the population is made up of hepatocytes (parenchymal cells) (see Fig. interpretation of liver histopathology, particularly in relation to zones 67.21; Fig. 67.22). They are polyhedral, with 5–12 sides, and measure of hypoxic damage, glycogen deposition and removal, and toxic injury, 20–30 µm across. Their nuclei are round, euchromatic and often tetra- all of which are related to the direction of blood flow. There are also ploid, polyploid or multiple, with two or more in each cell. Their real metabolic differences between hepatocytes within the acini, which cytoplasm typically contains a considerable amount of rough and Central vein Interlobular septum Central vein Hepatocyte Kupffer cells Sinusoid Bile canaliculi Hepatic artery Bile duct Hepatic portal vein Bile duct Hepatic artery Hepatic portal vein Portal triad Bile ductules Fig. 67.21 The hepatic microstructure. Sinusoidal endothelial cells are not shown.

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Liver 1170.e1 76 RETPAHC Fig. 67.20 Scanning electron micrographs of a CV resin corrosion cast of the human liver demonstrating the three-dimensional arrangement of the hepatic sinusoids. A, A portal vein (PV) branch within a portal triad × 33 100 µm. B, Sinusoids and central veins (CV) × 37 100 µm. C, A sinusoidal network ×330 10 µm. D, Sinusoidal CV endothelial cells × 7000 1 µm. (Courtesy of Professor Greg Jones, University of Otago, New Zealand). PV A B C D

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Liver 1171 76 RETPAHC Fig. 67.22 A schematic illustration of a hepatocyte and adjacent sinusoids. (Redrawn from O’Grady J, Lake JR, Howdle PD. Comprehensive Clinical Fenestrae Hepatology, Mosby 2000.) Kupffer cell Endothelial cells Sinusoid Space of Disse Stellate cell Smooth endoplasmic Vacuole reticulum Mitochondrion Tight junction Golgi apparatus Biliary canaliculus Nucleus (chromatin) Nucleolus Peroxisome Rough endoplasmic reticulum Gap junction Lipid Desmosome Lysosome Collagen fibres Sinusoid smooth endoplasmic reticulum, many mitochondria, lysosomes and homeostasis and regeneration. Hepatic stellate cells also play a major well-developed Golgi apparatus, all features that indicate a high meta- role in pathological processes (Yin et al 2013). In response to liver bolic activity. Glycogen granules and lipid vacuoles are usually promi- damage, they become activated and predominantly myofibroblast-like. nent. Numerous large peroxisomes and vacuoles containing enzymes, They are responsible for the replacement of damaged hepatocytes with e.g. urease in distinctive crystalline forms, indicate the complex metab- collagenous scar tissue, a process called hepatic fibrosis, that is seen olism of these cells. Their role in iron metabolism is reflected by initially in zone 3, around central veins. Fibrosis can progress to cir- the presence of storage vacuoles containing crystals of ferritin and rhosis, where the parenchymal architecture and pattern of blood flow haemosiderin. within the liver are destroyed, with major systemic consequences. The surfaces of hepatocytes facing the sinusoids exhibit numerous microvilli, approximately 0.5 µm long, creating a large surface area Sinusoidal endothelial cells Hepatic venous sinusoids are gener- (approximately 70% of the hepatocyte surface) exposed to blood ally wider than blood capillaries and are lined by a thin but highly plasma. Elsewhere, hepatocytes are linked by numerous gap junctions fenestrated endothelium that lacks a basal lamina. The endothelial cells and desmosomes. Lateral plasma membranes of adjacent hepatocytes are typically flattened, each with a central nucleus, and are joined to form microscopic channels, the bile canaliculi, which are specialized each other by junctional complexes. The fenestrae are grouped in clus- regions of intercellular space formed by apposing grooves in hepatocyte ters with a mean diameter of 100 nm, allowing plasma direct access to plasma membranes, sealed from extraneous interstitial space by the basal plasma membranes of hepatocytes. Their cytoplasm contains tight junctions. Four types of transmembrane molecules (occludins, numerous transcytotic vesicles. claudins, junctional adhesion molecules and coxsackie virus and aden- ovirus receptors) constitute the core units of the functional protein Kupffer cells Kupffer cells are hepatic macrophages derived from complexes of the tight junctions (Lee 2012) (see Fig. 1.19). Individual circulating blood monocytes and originate in the bone marrow. They tight junction complexes, either alone or in combination, are involved are long-term hepatic residents and lie within the sinusoidal lumen in signalling pathways in health and disease. Numerous membrane- attached to the endothelial surface. Kupffer cells are irregular in shape bound exocytotic vesicles cluster near the lumen of the canaliculi and have long processes that extend into the sinusoidal lumen. They because the secretion of bile is targeted at the canalicular plasma mem- form a major part of the mononuclear phagocyte system, which is brane. The tight junctions surrounding the biliary canaliculi prevent responsible for removing cellular and microbial debris from the circula- bile from entering the interstitial fluid or blood plasma, thereby creat- tion, and for secreting cytokines involved in defence. They remove ing a blood–bile barrier. aged and damaged red cells from the hepatic circulation, a function normally shared with the spleen but fulfilled entirely by the liver after Hepatic stellate cells Hepatic stellate cells are much less numerous splenectomy. than hepatocytes. They are irregular in outline and lie within the per- isinusoidal space of Disse between the sinusoids and the hepatocyte Hepatic stem cells Hepatic stem cells are undifferentiated, pluripo- plates. They are thought to be mesenchymal in origin and are character- tential cells and are understood to reside around the canals of Hering; ized by numerous cytoplasmic lipid droplets. These cells secrete most they are derived from the ductal plate in fetal livers. Their progeny are of the intralobular matrix components, including collagen type III small epithelial cells (8–18 µm) with a large oval nucleus and scanty (reticular) fibres. They store the fat-soluble vitamin A in their lipid cytoplasm, expressing both biliary epithelial and hepatocyte markers droplets and are a significant source of growth factors involved in liver (Roskams et al 2010).

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LivER 1172 8 NOiTCES Bonus e-book images Fig. 67.10 Common hepatic artery variants. scissure. B, When it is suppressed, the Fig. 67.18 Resectional terminology. anterior sector appears as a single segment. Fig. 67.11 Hepatic arteriograms. Fig. 67.20 Scanning electron micrographs of Fig. 67.17 The liver is divided into three a resin corrosion cast of the human liver Fig. 67.16 A, The umbilical fissure that segments and a caudate area, according to demonstrating the three-dimensional divides the anterior sector of the left lobe the ramification of the Glissonian pedicles. arrangement of the hepatic sinusoids. into two segments is, in fact, an artificial KEY REFERENCES Bismuth H 1982 Surgical anatomy and anatomical surgery of the liver. Lanouis B, Jamieson GG 1993 Modern operative techniques in liver surgery. World J Surg 6:5–9. Clinical Surgery International 18. Edinburgh: Elsevier, Churchill Bismuth H 2013 Revisiting liver anatomy and terminology of hepatec- Livingstone. tomies. Ann Surg 257:383–6. Makuuchi M 2013 Could we or should we replace the conventional nomen- Couinaud C 1957 Le Foie: études anatomiques et chirurgicales. Paris: clature of liver resections? Ann Surg 237:387–9. Masson. Takasaki K, Koabayashi S, Tanaka S et al 1986 Highly selected hepatic resec- Couinaud’s original descriptive studies of liver segmentation, later updated tion by Glissonian sheath-binding method. Dig Surg 3:121 (abstract). and translated into English in 1989 as Surgical Anatomy of the Liver Terminology Committee of the International Hepato-Pancreato-Biliary Revisited. Association 2000 The Brisbane 2000 terminology of liver anatomy and Goldsmith NA, Woodburne RT 1957 Surgical anatomy pertaining to liver resections. HPB 2:333–9. resection. Surg Gynecol Obstet 195:310–18. Stringer MD 2009 Eponyms in Surgery and Anatomy of the Liver, Bile Ducts Healey JE, Schroy PC 1953 Anatomy of the biliary ducts within the human and Pancreas. London: Royal Society of Medicine. liver: analysis of the prevailing pattern of branchings and the major A concise illustrated account of the derivation and individuals behind the variations of the biliary ducts. Arch Surg 66:599–616. more common eponyms associated with liver anatomy and surgery.

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Liver 1172.e1 76 RETPAHC REFERENCES Bismuth H 1982 Surgical anatomy and anatomical surgery of the liver. Lee NP 2012 The blood–biliary barrier, tight junctions and human liver World J Surg 6:5–9. diseases. Adv Exp Med Biol 763:171–85. Bismuth H 2013 Revisiting liver anatomy and terminology of hepatec- López-Andújar R, Moya A, Montalvá E et al 2007 Lessons learned from tomies. Ann Surg 257:383–6. anatomic variants of the hepatic artery in 1,081 transplanted livers. Liver Burt RP 2003 Phasic contractions of the rat portal vein depend on intracel- Transpl 13:1401–4. lular Ca2+ release stimulated by depolarization. Am J Physiol Heart Circ McCuskey RS 2004 Anatomy of efferent hepatic nerves. Anat Rec A Discov Physiol 284:H1808–17. Mol Cell Evol Biol 280:821–6. Camargo AM, Teixeira GG, Ortale JR 1996 Anatomy of the ostia venae Makuuchi M 2013 Could we or should we replace the conventional nomen- hepaticae and the retrohepatic segment of the inferior vena cava. J Anat clature of liver resections? Ann Surg 237:387–9. 188:59–64. Michels NA 1966 Newer anatomy of the liver and its variant blood supply Couinaud C 1957 Le Foie: études anatomiques et chirurgicales. Paris: and collateral circulation. Am J Surg 112:337–47. Masson. Mirjalili SA, McFadden SL, Buckenham T et al 2012 Anatomical planes: are Couinaud’s original descriptive studies of liver segmentation, later updated we teaching accurate surface anatomy? Clin Anat 25:819–26. and translated into English in 1989 as Surgical Anatomy of the Liver Ohtani O, Ohtani Y 2008 Lymph circulation in the liver. Anat Rec 291: Revisited. 643–52. Chaib E 2009 Absence of bifurcation of the portal vein. Surg Radiol Anat Onishi H, Kawarada Y, Das BC et al 2000 Surgical anatomy of the medial 31:389–92. segment (S4) of the liver with special reference to bile ducts and vessels. Covey AM, Brody LA, Getrajdman GI et al 2004 Incidence, patterns, and Hepatogastroenterology 47:143–150. clinical relevance of variant portal vein anatomy. AJR Am J Roentgenol Rex H 1888 Beiträge zur Morphologie der Säugerleber. Morph Jahrb 183:1055–64. 14:517–616. Covey AM, Brody LA, Maluccio MA et al 2002 Variant hepatic arterial Roskams T, Katoonizadeh A, Komuta M 2010 Hepatic progenitor cells: an anatomy revisited: digital subtraction angiography performed in 600 update. Clin Liver Dis 14:705–18. patients. Radiology 224:542–7. Roskams TA, Theise ND, Balabaud C et al 2004 Nomenclature of the finer Dar FS, Faraj W, Heaton ND et al 2008 Variation in the venous drainage of branches of the biliary tree: canals, ductules, and ductular reactions in left lateral segment liver graft requiring reconstruction of segment III human livers. Hepatology 39:1739–45. vein with donor iliac artery. Liver Transpl 14:576–9. Saba L, Mallarini G 2011 Anatomic variations of arterial liver vascularization: di Francesco F, Grimaldi C, de Ville de Goyet J 2014 Meso-Rex bypass – a an analysis by using MDCTA. Surg Radiol Anat 33:559–68. procedure to cure prehepatic portal hypertension: the insight and the Strasberg SM, Phillips C 2013 Use and dissemination of the Brisbane 2000 inside. J Am Coll Surg 218:e23–36. nomenclature of liver anatomy and resections. Ann Surg 257:377–82. Fang CH, You JH, Lau WY et al 2012 Anatomical variations of hepatic veins: Stringer MD 2009 Eponyms in Surgery and Anatomy of the Liver, Bile Ducts three-dimensional computed tomography scans of 200 subjects. World and Pancreas. London: Royal Society of Medicine. J Surg 36:120–4. A concise illustrated account of the derivation and individuals behind the Flament JB, Delattre JF, Hidden G 1982 The mechanisms responsible for more common eponyms associated with liver anatomy and surgery. stabilising the liver. Anat Clin 4:125–35. Sugarbaker PH 1990 En bloc resection of hepatic segments 4B, 5 and 6 by Fraser R, Dobbs BR, Rogers GW 1995 Lipoproteins and the liver sieve: the transverse hepatectomy. Surg Gynecol Obstet 170:250–2. role of the fenestrated sinusoidal endothelium in lipoprotein metabo- lism, atherosclerosis, and cirrhosis. Hepatology 21:863–74. Takasaki K, Koabayashi S, Tanaka S et al 1986 Highly selected hepatic resec- tion by Glissonian sheath-binding method. Dig Surg 3:121 (abstract). Goldsmith NA, Woodburne RT 1957 Surgical anatomy pertaining to liver resection. Surg Gynecol Obstet 195:310–18. Terminology Committee of the International Hepato-Pancreato-Biliary Association 2000 The Brisbane 2000 terminology of liver anatomy and Healey JE, Schroy PC 1953 Anatomy of the biliary ducts within the human resections. HPB 2:333–9. liver: analysis of the prevailing pattern of branchings and the major variations of the biliary ducts. Arch Surg 66:599–616. Trutmann M, Sasse D 1994 The lymphatics of the liver. Anat Embryol (Berl) 190:201–9. Hjortsjö CH 1951 The topography of the intrahepatic duct systems. Acta Anat (Basel) 11:599–615. Vellar ID, Banting SW, Hardy KJ 1998 The anatomical basis for segment III cholangiojejunostomy with analysis of 13 cases. Aust N Z J Surg 68: Hribernik M, Trotovšek B 2014 Intrahepatic venous anastomoses with a 498–503. focus on the middle hepatic vein anastomoses in normal human livers: anatomical study on liver corrosion casts. Surg Radiol Anat 36:231–7. Yamamoto M, Katagiri S, Ariizumi S et al 2012 Glissonean pedicle transec- tion method for liver surgery (with video). J Hepatobiliary Pancreat Sci Joshi SD, Joshi SS, Athavale SA 2009 Some interesting observations on the 19:3–8. surface features of the liver and their clinical implications. Singapore Med J 50:715–19. Yin C, Evason KJ, Asahina K et al 2013 Hepatic stellate cells in liver develop- ment, regeneration, and cancer. J Clin Invest 123:1902–10. Lanouis B, Jamieson GG 1993 Modern operative techniques in liver surgery. Clinical Surgery International 18. Edinburgh: Elsevier, Churchill Livingstone.

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CHAPTER 68 Gallbladder and biliary tree The biliary tree consists of the system of ducts that collect and The gallbladder is described as having a fundus, body and neck. deliver bile from the liver to the second part of the duodenum. It is The neck lies at the medial end, close to the porta hepatis, and almost conventionally divided into intrahepatic and extrahepatic biliary trees. always has a short peritoneal attachment (mesentery) to the liver, The intrahepatic ducts are formed from bile ductules that join to form which usually contains the cystic artery. The mucosa at the medial segmental ducts. These merge to form right and left hepatic ducts close end of the neck is obliquely ridged, forming a crescentic fold that is to the porta hepatis. The extrahepatic biliary tree consists of the extra- continuous with the spirally arranged mucosal folds in the cystic duct hepatic segments of the right and left hepatic ducts, the common (Dasgupta and Stringer 2005). At its lateral end, the neck widens out hepatic duct, the cystic duct and gallbladder, and the common bile duct to form the body of the gallbladder; when this widening is clearly (Fig. 68.1). demarcated as a result of gallstone disease, it is referred to as ‘Hart- mann’s pouch’. The neck usually lies anterior to the second part of the duodenum. The body of the gallbladder normally lies in contact with GALLBLADDER the visceral surface of the liver. When the neck possesses a mesentery, this rapidly shortens along the length of the body as it lies in the gall- The gallbladder is a flask-shaped, blind-ending diverticulum attached bladder fossa. The body lies anterior to the second part of the duode- to the bile duct by the cystic duct (Fig. 68.2). It stores and concentrates num and the right end of the transverse colon. The bulbous fundus lies bile. In life, it is grey–blue in colour and is usually firmly attached at the lateral end of the body and usually projects past the inferior by connective tissue to the inferior surface of the right lobe of the border of the liver to a variable extent. Here, it frequently lies in contact liver, between segments IV and V at the lower limit of the principal with the anterior abdominal wall behind the ninth costal cartilage, plane. In the adult, the gallbladder is between 7 and 10 cm long, where the lateral edge of the right rectus abdominis crosses the costal with a resting volume of about 25 ml and a capacity of up to 50 ml margin. This is where enlargement of the gallbladder is best sought on (Di Ciaula et al 2012). It usually lies in a shallow fossa (the gallbladder clinical examination. The fundus commonly lies adjacent to the trans- bed) on the visceral surface of the right lobe of the liver, covered verse colon. by peritoneum continued from the liver surface. This attachment can The gallbladder varies in size and shape. The fundus may be elon- vary widely. Rarely, the gallbladder is almost completely buried within gated and highly mobile. Rarely, the fundus is folded back on the body the liver (intrahepatic gallbladder; Guiteau et al 2009), or suspended of the gallbladder, the so-called Phrygian cap; on ultrasound, this may from the liver by a peritoneal mesentery (when it is at risk of torsion; be wrongly interpreted as an apparent septum within an otherwise Gupta et al 2009), or connected to the duodenum by an extension of normal gallbladder. Other anatomical variants of the gallbladder the free edge of the lesser omentum (cystoduodenal ligament; Ashaolu include duplication, with or without a double cystic duct; agenesis; et al 2011). internal septation; and an ectopic location (most commonly left-sided) (Gross 1936, Faure et al 2008); although rare, these congenital anoma- lies are particularly important if the patient requires surgery for gall- bladder or gallstone disease (Lamah et al 2001, Singh et al 2006, Right anterior (medial) Castorina et al 2014, Chowbey et al 2004). sectoral duct VIII Right posterior (lateral) V sectoral duct INTRAHEPATIC BILIARY TREE VII Right hepatic SEGMENTAL AND SECTORAL DUCTS duct I I II The segmental ducts of the left hemi-liver have a relatively constant VI pattern, although more than one segmental duct may drain each particular segment. The left hepatic duct is formed by the union of III segment II and III ducts, most often behind or to the left of the umbili- IV Left hepatic duct cal portion of the left portal vein (see Fig. 68.1). The biliary drainage of segment IV is more variable but is usually by a single duct into the Common hepatic duct left hepatic duct. The right hepatic duct is formed by the union of Cystic duct the right anterior (medial) and posterior (lateral) sectoral ducts. The right anterior (medial) sectoral bile duct drains segments V and VIII, Supraduodenal and the right posterior (lateral) sectoral duct drains segments VI and common bile duct VII. The right posterior sectoral duct usually curves around the posterior aspect of the right anterior duct before fusing with its medial aspect; Retroduodenal bile duct this is known as Hjortsjö’s crook and is an important technical consid- eration when performing liver resection (Fig. 68.3). The bile ducts Retropancreatic draining the caudate lobe (segment I) usually join the origin of the bile duct left hepatic duct or may drain into both hepatic ducts near the hilar confluence. The right hepatic duct and its branches are more often subject to variation than the left ductal system (Cucchetti et al 2011, Chaib et al Fig. 68.1 The overall arrangement of the intrahepatic and extrahepatic 2014). These variations have been classified into six main types (Table biliary tree. The segmental ducts often branch just before they enter the 68.1, Fig. 68.4). Left intrahepatic ductal variations mostly relate to the main ducts, or are multiple as they enter the main ducts, but for clarity drainage pattern of segment IV; this segmental bile duct usually drains are shown here as single ducts. Note that segment I often drains via both into the left hepatic duct but it may open into a segment II or III bile right and left hepatic ducts. The level of the liver parenchyma at the porta duct, the right anterior sectoral duct, or even the common hepatic duct hepatis is shown by the dashed line. (Chaib et al 2014). 1173

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Gallbladder and biliary tree 1173.e1 86 retPaHC An oblique groove on the inferior surface of the liver posterior to the gallbladder bed is present in 70–80% of livers. It is variably known as the fissure of Gans, Rouviere’s sulcus or the incisura hepatis dextra (Ch. 67). It overlies the division of the right posterior (lateral) portal pedicle, where it gives off the inferior segment VI branch. It has been increasingly recognized as a useful anatomical landmark during hepatic resection and in laparoscopic cholecystectomy (since the cystic duct and artery lie anterosuperior to the sulcus while the common bile duct lies posteroinferior) (Dahmane et al 2013).

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Gallbladder and biliary tree 1174 8 nOitCeS Neck Cystic duct variants Body Cystic duct V Fundus Right and left hepatic ducts Common A1 Low entry A2 Medial side entry A3 Common drainage A4 Accessory bile hepatic duct with right anterior duct (segment V) sectoral duct draining directly to gallbladder or Intrahepatic bile duct variants cystic duct Spiral II II folds VIII VIII I I V III V III IV Common VII VII IV bile duct VI VI Fig. 68.2 The interior of the gallbladder and bile ducts. Type 1 Normal Type 4 Low drainage of the right posterior Table 68.1 Major variations of the intrahepatic duct drainage patterns sectoral duct into the common hepatic duct Type Approximate % Description VIII II VIII II of population I I 1 60* Normal anatomy V III V III 2 15 No right hepatic duct. The common hepatic duct is formed by the VII IV VII IV union of right anterior sectoral, right posterior sectoral and left hepatic ducts (trifurcation pattern) 3 15 One of the right sectoral ducts (more often the posterior) joins VI VI the left hepatic duct 4 10 Low drainage of one of the right sectoral ducts (more often the Type 2 Absence of right hepatic duct Rare type. Right posterior sectoral duct posterior) into the common hepatic duct draining into the cystic duct Rare <5 The segment V duct or the right posterior sectoral duct drains VIII II into the cystic duct or gallbladder I V III (Data from Cucchetti et al 2011 and Chaib et al 2014.) *This figure is higher in men and lower in women, i.e. women are more likely to have variant intrahepatic VII IV bile duct anatomy. N.B. The percentage of different types varies between populations. VI Type 3 Right posterior sectoral duct draining into the left hepatic duct EXTRAHEPATIC BILIARY TREE CYSTIC DUCT Fig. 68.4 Variations in the anatomy of the cystic and intrahepatic bile ducts. The cystic duct variations are labelled A1–A4 and the intrahepatic bile duct variations as types 1–4 (see Table 68.1). The cystic duct drains the gallbladder into the common bile duct. In adults, it is usually between 2 and 4 cm long and has a luminal diameter of 2–3 mm (Dasgupta and Stringer 2005). It passes posteriorly and medially from the neck of the gallbladder, often in a tortuous fashion, rather than regulate the flow of bile, as is commonly stated (Dasgupta to unite with the common hepatic duct and form the common bile and Stringer 2005). duct. The anatomy of the junction between the cystic duct and common hepatic duct is variable (see Fig. 68.4). In most individuals, the cystic duct joins the middle third of the combined lengths of the common HEPATIC DUCTS hepatic and common bile ducts (Shaw et al 1993), but it may drain into the distal common bile duct or into a more proximal duct such as The right and left hepatic ducts emerge from the liver and unite near the proximal common hepatic duct or right hepatic duct; it usually joins the right end of the porta hepatis to form the common hepatic duct. the right lateral aspect of the common hepatic duct but may merge The extrahepatic right duct is short (0.5–2.0 cm in adults) and nearly medially, anteriorly or posteriorly; and it usually forms an oblique vertical, while the left is longer (1.5–3.5 cm) and more horizontal, and angle with the common hepatic duct but can spiral around it or run lies along the inferior border of segment IV. The accessibility of the parallel to it in the free edge of the lesser omentum for a variable dis- extrahepatic segment of the left hepatic duct is exploited when perform- tance before merging (Lamah et al 2001). Irrespective of the site or type ing a surgical biliary bypass in patients with benign hilar bile duct of union, the terminal part of the cystic duct is frequently adherent to strictures (Myburgh 1993). the common hepatic duct for a variable distance. In adults, the common hepatic duct descends approximately 3 cm Rarely, the cystic duct is double or absent (when the gallbladder before being joined obliquely on its right by the cystic duct to form drains directly into the bile duct), or receives an anomalous hepatic the common bile duct. The common hepatic duct lies to the right of duct from segment V of the liver. These variations in cystic duct anatomy the hepatic artery and anterior to the portal vein in the free edge of the are of considerable importance during surgical excision of the gallblad- lesser omentum. In adults, the luminal diameter of the normal common der (cholecystectomy). The cystic duct must be identified passing to the hepatic duct, as measured by ultrasound, is less than 5 mm. neck of the gallbladder and must be occluded some distance away from the bile duct to prevent injury to the latter. A preliminary operative cholangiogram is essential if the anatomy is unclear or anomalous. COMMON BILE DUCT The mucosa of the cystic duct has 2–10 crescentic folds that project into the lumen and form a spiral; these are continuous with those in The common bile duct is formed near the porta hepatis, by the junction the neck of the gallbladder. The function of these spiral folds is unknown of the cystic and common hepatic ducts (Figs 68.5–68.6). In adults, it but they may help to preserve the patency of this narrow, tortuous duct is usually between 6 and 8 cm long and its luminal diameter, as

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Gallbladder and biliary tree 1174.e1 86 retPaHC A small bile duct from segment V of the liver may traverse the gall- Right anterior (medial) bladder fossa and join the right hepatic duct or its anterior sectoral sectoral duct Hjortsjö’s crook branch or the common hepatic duct. This is often known as Luschka’s duct and its importance lies in the fact that it may be injured during Right posterior (lateral) cholecystectomy, causing a postoperative bile leak (Spanos and Syrakos sectoral duct 2006). Postmortem studies have identified such a duct in up to one- third of individuals but many of these are small and relatively insignifi- cant; if larger ducts (1–2 mm) are considered, the prevalence is nearer 5% (Ko et al 2006). These ducts are more likely to be injured if the gallbladder is not dissected close to its wall. Luschka did not describe Left hepatic duct a duct draining directly into the gallbladder; this is referred to as a cystohepatic or cholecystohepatic duct and should not be confused with a hepatocystic duct (which is present when the common bile duct Portal vein is absent and both hepatic ducts drain directly into the gallbladder Hepatic artery which drains in turn via the cystic duct into the duodenum) (Losanoff Common hepatic duct et al 2002). Fig. 68.3 Hjortsö’s crook. The right posterior (lateral) sectoral bile duct usually hooks around the right anterior (medial) sectoral pedicle, rendering it vulnerable to injury when performing an extended left hepatectomy that includes segments V and VIII of the liver (left trisectionectomy).

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extrahepatic biliary tree 1175 86 retPaHC Gallbladder Cystic duct wall of the second part of the duodenum and anterior to the right renal vein. The posterior superior pancreaticoduodenal branch of the gas- troduodenal artery descends anterior to the retroduodenal portion of the common bile duct (at the superior border of the pancreas) before spiralling around the right side of the bile duct to reach the posterior surface of the head of the pancreas (Bertelli et al 1996). Hepatopancreatic ampulla As it descends behind the head of the pancreas medial to the second part of the duodenum, the common bile duct approaches the right end of the pancreatic duct. The two ducts usually enter the duodenal wall together in a Y configuration to form a short common channel measur- ing between 2 and 10 mm in length (Flati et al 1994). This common channel often contains a dilation known as the hepatopancreatic ampulla (of Vater) and it opens via a single orifice on to the medial wall of the second part of the duodenum at the major duodenal papilla (Fig. 68.5B). In clinical practice, the whole region is often termed the pancreaticobiliary junction. Occasionally, the common bile duct and pancreatic duct unite outside the duodenal wall to form an abnormally long common channel or the two ducts are separated by a septum or drain into the duodenum separately (Kamisawa and Okamoto 2008). The mucosa of the terminal 5–10 mm of the common bile and pan- creatic ducts has a complex arrangement of circumferentially arranged folds (Purvis et al 2013) (Fig. 68.7). Their distribution and orientation impede reflux of duodenal contents into the bile and pancreatic ducts, A and they may sometimes cause difficulty cannulating the major duode- nal papilla during endoscopic retrograde cholangiopancreatography (ERCP). Common bile Endoscope Pancreatic A complex arrangement of smooth muscle with prominent circular duct duct fibres surrounds the distal common bile duct (bile duct sphincter) and Fig. 68.5 A, An endoscopic retrograde cholangiopancreatogram. hepatopancreatic ampulla (sphincter of Oddi); to a lesser extent, it also (B, continued online) surrounds the terminal part of the main pancreatic duct (pancreatic duct sphincter) (Boyden 1957, Didio and Anderson 1968). The whole sphincter muscle complex lies mostly within the wall of the duodenum Gallbladder Right hepatic duct Left hepatic duct Common hepatic duct and, in adults, measures approximately 15–20 mm in length; it con- tains a high pressure zone that can be detected by manometry (Teilum 1991, Habib et al 1988). The smooth muscle of the ampullary sphincter is developmentally and anatomically distinct from the adjacent duo- denal muscle. The sphincter regulates the flow of bile and pancreatic secretions into the duodenum and impedes reflux of duodenal contents into the ductal system (Guelrud et al 1990); it is inhibited by chole- cystokinin (CCK), which not only relaxes the sphincter but also causes gallbladder contraction (Woods et al 2005). Division of the upper part of the ampullary sphincter (sphincterotomy) may be required to allow access to the common bile duct during ERCP. The pancreaticobiliary junction is clinically important because it may be affected by various congenital and acquired disorders. An anom- alous union between the bile and pancreatic ducts, particularly one resulting in an abnormally long common channel, may be associated with congenital bile duct dilation, recurrent pancreatitis, and/or gall- bladder cancer (Kimura et al 1985, Misra and Dwivedi 1990, Stringer et al 1995). Acquired pathology in this region also includes gallstone obstruction and peri-ampullary tumours. Hepatobiliary triangle The triangular region formed between the cystic duct, the common hepatic duct and the inferior surface of the liver is the hepatobiliary triangle (Fig. 68.8). It is often mistakenly referred to as Calot’s triangle, which is an isosceles triangle based on the common hepatic duct, with Duodenum Cystic duct Common bile duct Pancreatic duct the cystic artery and cystic duct forming its sides (Stringer 2009). The hepatobiliary triangle is bridged by the double layer of peritoneum that Fig. 68.6 A magnetic resonance cholangiopancreatogram. forms the short and variable mesentery of the cystic duct. Between these two layers there is a variable amount of fatty connective tissue, lymphat- ics, the cystic lymph node, autonomic nerves, and usually the cystic measured by ultrasound, is no more than 7 mm (Perret et al 2000); the artery as it runs from the right hepatic artery to the gallbladder; occa- diameter increases slightly with advancing age from a mean of 3.6 mm sionally, there may also be an accessory bile duct (see above). Under- below 60 years to a mean of 4 mm after 80 years. The common bile duct standing the variations in biliary and arterial anatomy as they relate to can be divided into supraduodenal, retroduodenal and pancreatic seg- the triangle is of considerable importance during excision of the gall- ments. The supraduodenal segment descends posteriorly and slightly bladder in order to avoid injury to the common hepatic or common to the left, anterior to the epiploic foramen and inferior vena cava, in bile duct or right hepatic artery (Suzuki et al 2000, Talpur et al 2010). the free right border of the lesser omentum, where it lies anterior and to the right of the portal vein and to the right of the hepatic artery. This part of the common bile duct is the most accessible at surgery. The retroduodenal segment lies behind the first part of the duodenum with GALLSTONES the gastroduodenal artery on its left. The pancreatic segment runs in a groove on the posterior surface of the head of the pancreas, embedded Gallstones are relatively common and usually form in the gallbladder. in the gland to a variable degree; it lies up to 2 cm away from the medial Gallbladder contraction may move a gallstone towards the narrow cystic

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Gallbladder and biliary tree 1175.e1 86 retPaHC Undersurface of right Cystic artery Line of common hepatic duct lobe of the liver B Endoscopic grasper on Metallic clip across Cystic duct neck of gallbladder cystic duct Fig. 68.5 B, Endoscopic image of the major duodenal papilla (arrow) on Fig. 68.8 A view of the hepatobiliary triangle (dashed line) at laparoscopic the medial wall of the descending duodenum. cholecystectomy. In this patient, the cystic artery can be seen crossing the triangle superficially en route to the gallbladder. (Courtesy of Richard Flint, Christchurch Hospital.) Fig. 68.7 A scanning electron micrograph showing mucosal folds (arrows) lining the wall the hepatopancreatic ampulla. Abbreviations: I, inferior; L, lateral; M, medial; S, superior.

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Gallbladder and biliary tree 1176 8 nOitCeS duct, where it can cause obstruction and pain (biliary colic). If the stone the common hepatic duct within the hepatobiliary triangle, where it continues to occlude the cystic duct, it will lead to inflammation of the lies superior to the cystic duct. On reaching the superior aspect of the gallbladder (acute cholecystitis) or a sterile distension of the gallbladder neck of the gallbladder, it divides into a superficial branch that runs (mucocele); providing the gallbladder has not been inflamed previ- along the peritoneal (inferior) surface of the gallbladder, and a deep ously, it will be non-fibrotic and distensible, and the fundus often branch that runs between the gallbladder and its fossa; the branches becomes palpable below the costal margin. A gallstone lodged in the anastomose over the surface of the body and fundus. The cystic artery cystic duct or neck of the gallbladder may also produce an inflammatory is usually less than 3 mm in diameter, and a larger artery in the swelling that compresses the common hepatic duct, resulting in partial hepatobiliary triangle is more likely to be the right branch of the obstruction to the flow of bile and the development of jaundice (the hepatic artery. so-called ‘Mirizzi syndrome’; Stringer 2009). If the gallstone passes The origin of the cystic artery is variable (Fig. 68.10). The most through the cystic duct, it may become impacted in the distal common common variant is an origin from the hepatic artery proper, when it bile duct or at the pancreaticobiliary junction, causing obstructive jaun- often crosses anterior to the common bile duct or common hepatic duct dice, cholangitis and/or acute pancreatitis. to reach the gallbladder. Rarely, it may arise from the left hepatic, gas- troduodenal, superior pancreaticoduodenal, coeliac, right gastric or superior mesenteric arteries; in these cases, the cystic artery may not ENDOSCOPIC CHOLANGIOPANCREATOGRAPHY traverse the hepatobiliary triangle. The cystic artery frequently bifurcates close to its origin, giving rise to two vessels. Alternatively, an accessory The common bile duct and/or pancreatic duct may be accessed endo- cystic artery may arise from the hepatic artery or one of its branches. scopically from the duodenum for diagnostic cholangiography and/or There appear to be racial differences in the frequency of these variants pancreatography, and for therapeutic interventions such as the relief of (Saidi et al 2007). Small arterial branches from the parenchyma of biliary obstruction by insertion of an internal stent. The acute angle segment IV or V of the liver may contribute to the supply of the body between the distal common bile duct and pancreatic duct may make of the gallbladder, particularly when it is substantially intrahepatic; direct cannulation of the bile duct difficult. In such cases, the upper these help to protect the gallbladder from ischaemic necrosis if inflam- part of the major duodenal papilla may be incised (pre-cut sphincter- mation results in thrombosis of the cystic artery. otomy) to facilitate cannulation of the common bile duct. This incision, The cystic artery also gives rise to multiple fine branches that con- and the more extensive sphincterotomy that may be performed to tribute to the blood supply of the extrahepatic bile ducts. release an impacted gallstone (Sakai et al 2012), are occasionally com- plicated by arterial bleeding. The risk may be reduced by making the ductal arteries incision in the 10–11 o’clock region of the sphincter (Mirjalili and The common bile duct and hepatic ducts are supplied by a fine network Stringer 2011). Endoscopic sphincterotomy can result in uncontrolled of arteries arising from several sources. The common bile duct is fre- reflux of duodenal contents into the distal common bile duct and quently supplied by 2–4 small-calibre arteries that form a long, tortu- ascending biliary infection. ous, anastomotic network along its length; these narrow vessels tend to be concentrated at the 3 and 9 o’clock positions around the circumfer- ence of the duct (Northover and Terblanche 1979). The network is fed BILIARY DRAINAGE by arteries from the right branch of the hepatic artery above, reinforced by fine branches from the cystic artery. Branches from three main arte- The proximity of the fundus of the gallbladder to the anterior abdomi- rial sources often supply the duct from below: the posterior superior nal wall facilitates ultrasound-guided percutaneous drainage of a dis- pancreaticoduodenal artery, the retroduodenal artery (both of which tended, obstructed gallbladder. Because of the small calibre of the cystic originate from the gastroduodenal artery and cross anterior to the duct and its spiral folds, drainage of the gallbladder is rarely sufficient to decompress the biliary tree when the common bile duct is obstructed. In such cases, temporary or permanent biliary drainage may be achieved by the endoscopic insertion of a biliary stent through the obstruction via the major duodenal papilla, surgical bile diversion, or percutaneous transhepatic drainage. The latter involves image-guided puncture of a dilated intrahepatic bile duct and the insertion of an external drain or an internal stent through the biliary obstruction. VASCULAR SUPPLY AND LYMPHATIC DRAINAGE Cystic artery The cystic artery usually arises from the right branch of the hepatic A Hepatic artery proper B Low origin from hepatic artery artery (Fig. 68.9, but see Fig. 68.10) and most often passes posterior to Right hepatic artery Left hepatic artery Cystic artery C Gastroduodenal artery D Superior pancreaticoduodenal, Deep superior branch coeliac or right gastric arteries Superficial inferior branch Hepatic artery ‘proper’ E Left hepatic artery F Multiple cystic arteries Fig. 68.9 Normal anatomy of the cystic artery. Fig. 68.10 Variant anatomy of the cystic artery.

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Microstructure 1177 86 retPaHC retroduodenal segment of the bile duct), and a retroportal artery arising resembles that of the small intestine. The mucosa is yellowish brown from the superior mesenteric artery or coeliac trunk and passing to the and elevated into minute rugae with a honeycomb appearance (see Fig. right on the posterior surface of the portal vein (Chen et al 1999). The 68.2). In section, projections of the mucosa into the gallbladder lumen supraduodenal segment of the bile duct is relatively less well vascular- resemble intestinal villi, but they are not fixed structures and the surface ized than the retroduodenal and pancreatic segments, and excessive flattens as the gallbladder fills with bile. The epithelium is a single layer dissection of this segment may result in an ischaemic bile duct of columnar cells with apical microvilli; basally, the spaces between stricture. epithelial cells are dilated (Fig. 68.11). Many capillaries lie beneath the The hilar ducts are supplied by a fine network of periductal arteries basement membrane. The epithelial cells actively absorb water and that arise from the right and left branches of the hepatic artery and form solutes from the bile and concentrate it up to ten-fold. There are no an anastomotic plexus within the connective tissue of the hilar plate. goblet cells in the epithelium. The thin fibromuscular layer is composed The intrahepatic ducts are supplied by segmental branches of the of fibrous tissue mixed with smooth muscle cells arranged loosely in hepatic artery arising within the Glissonian sheaths (Stapleton et al longitudinal, circular and oblique bundles. 1998, Vellar 1999). The dependence of the intrahepatic bile ducts on their hepatic arterial blood supply is well recognized in liver transplan- tation since hepatic artery thrombosis may lead to diffuse intrahepatic BILE DUCTS biliary strictures despite preservation of portal venous blood flow. The walls of the large biliary ducts consist of external fibrous and inter- Cystic veins nal mucosal layers (Fig. 68.12). The outer layer is fibrous connective The venous drainage of the gallbladder is rarely by a single cystic vein. tissue containing a variable amount of longitudinal, oblique and circu- There are usually multiple small veins. Those arising from the superior lar smooth muscle cells. The mucosa is continuous with that in the surface of the body and neck lie in areolar tissue between the gallblad- der and liver, and drain into segmental portal veins within the liver. The remainder of the organ drains by one or two small cystic veins into either portal vein branches within the liver or portal venous tributaries draining the hepatic ducts and upper bile duct (Sugita et al 2000). Only rarely does a single or double cystic vein drain directly into the right branch of the portal vein. lymphatic drainage Lymph from the gallbladder and cystic duct drains via several pathways: to the cystic node, which usually lies above the cystic duct in the hepa- tobiliary triangle, and from here via nodes in the free edge of the lesser omentum and along the common hepatic artery to coeliac lymph nodes; via lymphatics that descend along the common bile duct to the superior retropancreaticoduodenal node (which communicates with para-aortic nodes); and directly to superior mesenteric nodes (Sato et al 2013). Lymphatics on the hepatic aspect of the gallbladder connect directly with intrahepatic lymph vessels. Lymphatic vessels accompanying the hepatic ducts and upper bile duct drain to hepatic nodes at the porta hepatis and then via lymph nodes in the free edge of the lesser omentum to coeliac nodes. Lymphat- ics from the lower common bile duct also drain to the latter but some pass directly to retropancreatic and superior mesenteric nodes. INNERVATION The gallbladder and the extrahepatic biliary tree are innervated by branches from the hepatic plexus. Gallbladder contraction occurs in response to cholecystokinin (CCK) and parasympathetic (vagal) stimu- Fig. 68.11 A low-power micrograph showing the gallbladder wall, with a mucosal projection that flattens in the full gallbladder, and the thin lation. Postganglionic sympathetic nerve fibres from the coeliac and muscular layer. superior mesenteric ganglia are inhibitory to gallbladder smooth muscle. Sympathetic afferents from the gallbladder convey pain sensa- tion; they travel with the greater and lesser splanchnic nerves and have their cell bodies in the T7–9 spinal cord segments. Visceral pain from the gallbladder is referred to the right hypochondrium and epigastrium NN and may radiate around the back below the right scapula. Inflammation of the parietal peritoneum overlying the gallbladder produces localized right upper quadrant pain. A diverse range of neurotransmitters have CC been identified within intrinsic neurones of the gallbladder (Balemba et al 2004). The common bile duct and smooth muscle of the hepatopancreatic ampulla are also innervated by the vagi, either directly or via the hepatic plexus, and by sympathetic nerves. NN SSMM MICROSTRUCTURE GALLBLADDER MM The fundus of the gallbladder is completely covered by a serosa, and LL the inferior surfaces and sides of the body and neck of the gallbladder are usually covered by a serosa. If the gallbladder possesses a mesentery, Fig. 68.12 A low-power micrograph showing the structure of a human the serosa extends around the sides of the body and neck on to the common bile duct. Shown are the lumen (L), mucosal lining (M), smooth superior surface and continues into the serosa of the mesentery, whereas muscle coat (SM) and outer connective tissue (C), with numerous nerve the serosa is limited to the inferior surfaces only if the gallbladder is fibre bundles (N). (Courtesy of Mr Peter Helliwell and the late Dr Joseph intrahepatic. Beneath the serosa is subserous loose connective and Mathew, Department of Histopathology, Royal Cornwall Hospitals adipose peritoneal tissue. The gallbladder wall microstructure generally Trust, UK.)

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Gallbladder and biliary tree 1178 8 nOitCeS hepatic ducts, gallbladder and duodenum. The epithelium is columnar Bonus e-book images and there are numerous tubulo-alveolar (or tubulo-acinar) mucous glands in the duct walls. Expulsion of gallbladder contents is under neuroendocrine control. Fat in the duodenum causes the release of CCK by intestinal neuro- Fig. 68.3 Hjortsö’s crook. endocrine cells, which stimulates the gallbladder to contract because muscle cells in its walls bear surface receptors for CCK. When the pres- Fig. 68.5 B, Endoscopic image of the major duodenal papilla sure exceeds 100 mmHO of bile, the sphincter of Oddi relaxes and bile (arrow) on the medial wall of the descending duodenum. 2 enters the duodenum. The termination of the united bile and pancreatic Fig. 68.7 A scanning electron micrograph showing mucosal folds ducts is packed with villous, valvular folds of mucosa that contain lining the wall the hepatopancreatic ampulla. muscle cells in their connective tissue cores. Contraction is thought to result in retraction and clumping of these folds, so preventing reflux of Fig. 68.8 A view of the hepatobiliary triangle at laparoscopic duodenal contents and controlling the exit of bile. cholecystectomy. KEY REFERENCES Cucchetti A, Peri E, Cescon M et al 2011 Anatomic variations of intrahepatic Stringer MD 2009 Eponyms in Surgery and Anatomy of the Liver, Bile Ducts bile ducts in a European series and meta-analysis of the literature. and Pancreas. London: Royal Society of Medicine Press. J Gastrointest Surg 15:623–30. A short reference book that contains illustrated accounts of the original An analysis of 200 cholangiograms from liver donors, coupled with a descriptions of eponyms cited in this chapter, along with a brief biography of detailed literature review exploring intrahepatic bile duct anatomy in the person after whom the structure is named. different racial groups. Suzuki M, Akaishi S, Rikiyama T et al 2000 Laparoscopic cholecystectomy, Dasgupta D, Stringer MD 2005 Cystic duct and Heister’s ‘valves’. Clin Anat Calot’s triangle, and variations in cystic arterial supply. Surg Endosc 18:81–7. 14:141–4. A review of cystic duct anatomy and the significance of its spiral mucosal An article that documents a consecutive series of 244 laparoscopic folds. cholecystectomies, in which the cystic artery was not present in the hepatobiliary triangle in 11%, and a further 7% of patients had an Gross R 1936 Congenital anomalies of gallbladder. A review of one hundred accessory cystic artery or other arterial variants. and forty eight cases with a report of double gall-bladder. Arch Surg 32:131–62. Talpur KA, Laghari AA, Yousfani SA et al 2010 Anatomical variations and A seminal paper on congenital anomalies of the gallbladder. congenital anomalies of extrahepatic biliary system encountered during laparoscopic cholecystectomy. J Pak Med Assoc 60:89–93. Lamah M, Karanjia ND, Dickson GH 2001 Anatomical variations of the An analysis of anatomical variants encountered in 300 adults undergoing extrahepatic biliary tree: review of the world literature. Clin Anat cholecystectomy for gallstone disease. Variants were recorded in 20% of 14:167–72. patients and predominantly involved the cystic artery (11%), cystic duct A literature review of anatomical variations affecting the extrahepatic bile (4%), right hepatic artery (3%) and gallbladder (2%). ducts.

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Gallbladder and biliary tree 1178.e1 86 retPaHC REFERENCES Ashaolu JO, Ukwenya VO, Adenowo TK 2011 Cystoduodenal ligament as an Losanoff JE, Jones JW, Richman BW et al 2002 Hepaticocystic duct: a rare abnormal fold and the accompanying anatomical and clinical implica- anomaly of the extrahepatic biliary system. Clin Anat 15:314–15. tions. Surg Radiol Anat 33:171–4. Mirjalili SA, Stringer MD 2011 The arterial supply of the major duodenal Balemba OB, Salter MJ, Mawe GM 2004 Innervation of the extrahepatic papilla and its relevance to endoscopic sphincterotomy. Endoscopy biliary tract. Anat Rec A Discov Mol Cell Evol Biol 280:836–47. 43:307–11. Bertelli E, Di Gregorio F, Bertelli L et al 1996 The arterial blood supply of Misra SP, Dwivedi M 1990 Pancreaticobiliary ductal union. Gut 31: the pancreas: a review. II. The posterior superior pancreaticoduodenal 1144–9. artery. An anatomical and radiological study. Surg Radiol Anat 18:1–9. Myburgh JA 1993 The Hepp–Couinaud approach to strictures of the bile Boyden EA 1957 The anatomy of the choledochoduodenal junction in man. ducts. I. Injuries, choledochal cysts, and pancreatitis. Ann Surg Surg Gynecol Obstet 104:640–52. 218:615–20. Castorina S, Scilletta R, Domergue J 2014 Gallbladder agenesis: laparoscopic Northover JMA, Terblanche J 1979 A new look at the arterial supply views of a significant diagnostic challenge. Surg Radiol Anat 36: of the bile duct in man and its surgical implications. Br J Surg 66: 619–20. 379–84. Chaib E, Kanas AF, Galvão FH et al 2014 Bile duct confluence: anatomic Perret RS, Sloop GD, Borne JA 2000 Common bile duct measurements in variations and its classification. Surg Radiol Anat 36:105–9. an elderly population. J Ultrasound Med 19:727–30. Chen WJ, Ying DJ, Liu ZJ et al 1999 Analysis of the arterial supply of Purvis NS, Mirjalili SA, Stringer MD 2013 The mucosal folds at the pancrea- the extrahepatic bile ducts and its clinical significance. Clin Anat ticobiliary junction. Surg Radiol Anat 35:943–50. 12:245–9. Saidi H, Karanja TM, Ogengo JA 2007 Variant anatomy of the cystic artery Chowbey PK, Wadhwa A, Sharma A et al 2004 Ectopic gallbladder: laparo- in adult Kenyans. Clin Anat 20:943–5. scopic cholecystectomy. Surg Laparosc Endosc Percutan Tech 14:26–8. Sakai Y, Tsuyuguchi T, Sugiyama H et al 2012 Current situation of endo- Cucchetti A, Peri E, Cescon M et al 2011 Anatomic variations of intrahepatic scopic treatment for common bile duct stones. Hepatogastroenterol bile ducts in a European series and meta-analysis of the literature. 59:1712–16. J Gastrointest Surg 15:623–30. Sato T, Ito M, Sakamoto H 2013 Pictorial dissection review of the lymphatic An analysis of 200 cholangiograms from liver donors, coupled with a pathways from the gallbladder to the abdominal para-aortic lymph detailed literature review exploring intrahepatic bile duct anatomy in nodes and their relationships to the surrounding structures. Surg Radiol different ethnic groups. Anat 35:615–21. Dahmane R, Morjane A, Starc A 2013 Anatomy and surgical relevance Shaw MJ, Dorsher PJ, Vennes JA 1993 Cystic duct anatomy: an endoscopic of Rouviere’s sulcus. Scientific World Journal 2013:254287. doi: perspective. Am J Gastroenterol 88:2102–6. 10.1155/2013/254287. Singh B, Ramsaroop L, Allopi L et al 2006 Duplicate gallbladder: an unusual Dasgupta D, Stringer MD 2005 Cystic duct and Heister’s ‘valves’. Clin Anat case report. Surg Radiol Anat 28:654–7. 18:81–7. Spanos CP, Syrakos T 2006 Bile leaks from the duct of Luschka (subvesical A review of cystic duct anatomy and the significance of its spiral mucosal duct): a review. Langenbecks Arch Surg 391:441–7. folds. Stapleton GN, Hickman R, Terblanche J 1998 Blood supply of the right and Di Ciaula A, Wang DQ, Portincasa P 2012 Gallbladder and gastric motility left hepatic ducts. Br J Surg 85:202–7. in obese newborns, pre-adolescents and adults. J Gastroenterol Hepatol Stringer MD 2009 Eponyms in Surgery and Anatomy of the Liver, Bile Ducts 27:1298–305. and Pancreas. London: Royal Society of Medicine Press. Didio JA, Anderson MC 1968 Biliary and Pancreatic Ducts: The ‘Sphincters’ A short reference book that contains illustrated accounts of the original of the Digestive System. Baltimore: Williams & Wilkins, pp. 129–51. descriptions of eponyms cited in this chapter, along with a brief biography of Faure JP, Doucet C, Scepi M et al 2008 Abnormalities of the gallbladder, the person after whom the structure is named. clinical effects. Surg Radiol Anat 30:285–90. Stringer MD, Dhawan A, Davenport M et al 1995 Choledochal cysts: lessons Flati G, Flati D, Porowska B et al 1994 Surgical anatomy of the papilla of from a 20 year experience. Arch Dis Child 73:528–31. Vater and the biliopancreatic ducts. Am Surg 60:712–18. Sugita M, Ryu M, Satake M et al 2000 Intrahepatic inflow areas of the Gross R 1936 Congenital anomalies of gallbladder. A review of one hundred drainage vein of the gallbladder: analysis by angio-CT. Surgery 128: and forty eight cases with a report of double gall-bladder. Arch Surg 417–21. 32:131–62. Suzuki M, Akaishi S, Rikiyama T et al 2000 Laparoscopic cholecystectomy, A seminal paper on congenital anomalies of the gallbladder. Calot’s triangle, and variations in cystic arterial supply. Surg Endosc Guelrud M, Mendoza S, Rossiter G et al 1990 Sphincter of Oddi manometry 14:141–4. in healthy volunteers. Dig Dis Sci 35:38–46. An article that documents a consecutive series of 244 laparoscopic cholecystectomies, in which the cystic artery was not present in the Guiteau JJ, Fisher M, Cotton RT et al 2009 Intrahepatic gallbladder. J Am hepatobiliary triangle in 11%, and a further 7% of patients had an Coll Surg 209:672. accessory cystic artery or other arterial variants. Gupta V, Singh V, Sewkani A et al 2009 Torsion of gall bladder, a rare entity: a case report and review article. Cases J 2:193. Talpur KA, Laghari AA, Yousfani SA et al 2010 Anatomical variations and congenital anomalies of extrahepatic biliary system encountered during Habib FI, Corazziari E, Biliotti D et al 1988 Manometric measurement of laparoscopic cholecystectomy. J Pak Med Assoc 60:89–93. human sphincter of Oddi length. Gut 29:121–5. An analysis of anatomical variants encountered in 300 adults undergoing Kamisawa T, Okamoto A 2008 Pancreatographic investigation of pancreatic cholecystectomy for gallstone disease. Variants were recorded in 20% of duct system and pancreaticobiliary malformation. J Anat 212:125–34. patients and predominantly involved the cystic artery (11%), cystic duct Kimura K, Ohto M, Saisho H et al 1985 Association of gallbladder carci- (4%), right hepatic artery (3%) and gallbladder (2%). Anatomical noma and anomalous pancreaticobiliary ductal union. Gastroenterol variants were associated with a slightly increased incidence of postoperative 89:1258–65. morbidity. Ko K, Kamiya J, Nagino M et al 2006 A study of the subvesical bile duct Teilum D 1991 In vitro measurement of the length of the sphincter of Oddi. (duct of Luschka) in resected liver specimens. World J Surg Endoscopy 23:114–6. 30:1316–20. Vellar ID 1999 The blood supply of the biliary ductal system and its rele- Lamah M, Karanjia ND, Dickson GH 2001 Anatomical variations of the vance to vasculobiliary injuries following cholecystectomy. Aust N Z J extrahepatic biliary tree: review of the world literature. Clin Anat Surg 69:816–20. 14:167–72. Woods CM, Mawe GM, Toouli J et al 2005 The sphincter of Oddi: A literature review of anatomical variations affecting the extrahepatic bile understanding its control and function. Neurogastroenterol Motil ducts. 17:31–40.

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CHAPTER 69 Pancreas The pancreas is one of the largest digestive glands. The major part of duodenum and is continuous with the uncinate process. The anterior the gland is exocrine, secreting enzymes involved in the digestion of surface of the head is covered by peritoneum and related to the origin lipids, carbohydrates and proteins. It has an additional endocrine func- of the transverse mesocolon (Fig. 69.3B). Posteriorly, the common bile tion derived from clusters of cells scattered throughout the substance duct is partially embedded within the head of the gland just proximal of the gland, which take part in glucose homeostasis and the control to where it joins the pancreatic duct near the major duodenal papilla of upper gastrointestinal motility and function. (Burgard et al 1991, Nagai 2003). The posterior surface of the pancreatic The healthy pancreas is creamy pink in colour, with a soft to head is also related to the inferior vena cava, the right crus of the dia- firm consistency and lobulated surface. It is divided into a head, neck, phragm and the termination of the right gonadal vein (Ch. 76; see Fig. body, tail and uncinate process on the basis of its anatomical relations 76.5). Near the midline, the head of the pancreas becomes continuous (Figs 69.1–69.3A). In adults, the gland measures 12–15 cm in length with the neck. and is shaped as a flattened ‘tongue’ of tissue lying in the retroperito- neum, thicker at its medial end (head) and thinner towards the lateral end (tail). The head lies within the ‘C’ loop of the duodenum and the NECK remainder of the gland extends transversely and slightly cranially across the retroperitoneum and posterior to the stomach to the hilum of the The neck of the pancreas is approximately 2 cm wide and links the head spleen. It is ‘draped’ over the vertebral column and other retroperitoneal and body. It is often the most anterior part of the gland and may be structures, forming a distinct shallow curve, with the neck and medial defined as that part of the pancreas lying anterior to the formation of body lying most anteriorly. In adults, it has an average volume of the portal vein (usually the union of the superior mesenteric and 70–80 cm3, although this varies considerably between individuals (with splenic veins) in the transpyloric plane (Fig. 69.4D,E). This is a crucial a range of 40–170 cm3) and tends to be greater in males (Djuric- relationship when evaluating pancreatic cancer because malignant Stefanovic et al 2012). Pancreatic volume increases with age, to reach a involvement of these vessels may make resection impossible. The supe- peak in the fourth decade. From about 60 years of age, the gland atro- rior mesenteric vein and portal vein groove the posterior aspect of the phies and fatty connective tissue replaces exocrine tissue (Caglar et al neck. The inferior mesenteric vein joins the confluence of the superior 2012, Saisho et al 2007). mesenteric vein and splenic vein in one-third of individuals (Kimura The ventral surface of the pancreas is covered by parietal peritoneum 2000; see Fig. 69.7). The anterior surface of the pancreatic neck is and is crossed by the root of the transverse mesocolon. A loose connec- covered by peritoneum and lies adjacent to the pylorus. The anterior tive tissue layer immediately posterior to the pancreas, sometimes superior pancreaticoduodenal branch of the gastroduodenal artery known the fusion fascia of Treitz in the region of the pancreatic head descends in front of the gland at the junction of the head and neck. and the fusion fascia of Toldt in the region of the body and tail, contains vessels that supply the pancreas (Kimura 2000). BODY HEAD The body of the pancreas is the longest part of the gland and runs from the neck to the tail, becoming progressively thinner. It is slightly trian- The head of the pancreas lies to the right of the midline, anterior gular in cross-section, and has anterior and posterior surfaces and supe- and to the right of the vertebral column, within the curve of the duo- rior and inferior borders. denum. It is the thickest and broadest part of the pancreas but is still flattened in the anteroposterior plane. Superiorly, it lies adjacent to the Anterior surface The anterior surface is covered by peritoneum, first part of the duodenum; close to the pylorus, however, where the which is reflected anteroinferiorly from the surface of the gland to duodenum is on a short mesentery, it overlaps the upper part of be continuous with the posterior layer of the greater omentum and the head anteriorly. The duodenal border of the head is flattened, the transverse mesocolon (see Fig. 63.4). The two layers of the trans- slightly concave and adherent to the second part of the duodenum, verse mesocolon diverge along this surface (see Fig. 69.3B). Above the particularly around the duodenal papillae. The superior and inferior attachment of the transverse mesocolon, the anterior surface of the pancreaticoduodenal arteries lie adjacent to this region. The inferior pancreas is separated from the stomach by the lesser sac. Inferiorly, it border of the pancreatic head lies superior to the third part of the lies within the infracolic compartment, and its anterior relations include Inferior vena cava Tail Bile duct Body Left kidney Duodenum Neck Main pancreatic duct Accessory pancreatic duct Head Superior mesenteric artery Superior mesenteric vein Uncinate process Hepatopancreatic ampulla Fig. 69.1 Relations of the pancreas. 1179

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Pancreas 1180 8 nOITces the fourth part of the duodenum, the duodenojejunal flexure and coils of jejunum. Tail Posterior surface The posterior surface of the pancreas is devoid of A peritoneum. It lies on fascia (the fusion fascia of Toldt) anterior to the aorta and the origin of the superior mesenteric artery, the left Body crus of the diaphragm, left suprarenal gland, the upper pole of the left kidney surrounded by perirenal fascia, and left renal vein (Kimura 2000; see Figs 69.1, 69.4A–G). The splenic vein runs from left to right Neck directly on this surface of the gland and indents the parenchyma to a variable extent, ranging from a shallow groove to almost a tunnel. Superior border To the right, the superior border of the body of the Head pancreas is blunt but it becomes narrower and sharper to the left. An Uncinate process Spleen (anterior border) Body of pancreas Tail of pancreas Liver Portal vein Pancreatic duct Stomach Spleen B Body Pylorus D1 Antrum Jejunal loops Attachment of the leaves of the transverse mesocolon Attachment of the leaves Proximal transverse of the greater omentum colon SMV SMA Ileal loops Fig. 69.3 A, Regions and anterior surfaces and borders of the pancreas. Head of pancreas Jejunum B, Anterior relations of the pancreas. Areas covered in peritoneum are shown in blue and structures overlying these areas are separated from Second part of duodenum Neck of pancreas Left kidney the pancreas by peritoneal ‘spaces’. The spleen lies anterior to the Fig. 69.2 A coronal reformat computed tomogram (CT) of the pancreas anterior leaf of the splenorenal ligament and not in direct contact showing its relations in the upper abdomen. (Courtesy of the Department with pancreatic tissue. Abbreviations: D1, first part of the duodenum; of Radiology, Global Hospital, Chennai, India.) SMA, superior mesenteric artery; SMV, superior mesenteric vein. Neck of pancreas Duodenum (fourth part) Inferior vena cava Head of pancreas Superior mesenteric vein A F D B B Superior mesenteric vein Superior mesenteric artery Duodenum Uncinate process (second part) Duodenum Inferior vena cava (fourth part) Aorta Gonadal arteries Inferior pole of left kidney C Duodenum (second part) Aorta Uncinate process Superior mesenteric artery Fig. 69.4 A, Posterior relations of the pancreas, with planes of section labelled as shown in B, D and F. B, Diagrammatic cross-section taken at the mid level of the uncinate process, and equivalent CT axial slice (C). Continued

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Pancreas 1181 96 reTPaHc Superior mesenteric vein Body of pancreas Duodenum (second part) Neck of pancreas Splenic vein D Neck and body of pancreas Portal vein Duodenum Superior (second part) mesenteric artery Splenic vein Inferior vena cava Left renal vein Aorta Left crus Left kidney E Inferior vena cava Left renal vein Superior mesenteric artery Coeliac trunk Body of pancreas Stomach Tail of pancreas F Origin of coeliac trunk Tail of pancreas Inferior vena cava Splenic Aorta vein Spleen Left kidney G Inferior vena cava Aorta Splenic vein Upper pole of left kidney Spleen Fig. 69.4, cont’d Diagrammatic cross-sections and equivalent CT axial slices taken at the head and neck (D–E), and tail (F–G) of the pancreas. omental tuberosity usually projects from the right end of the superior ligament. It may terminate at the base of the splenorenal ligament or border above the level of the lesser curvature of the stomach. The supe- extend up to the splenic hilum, when it is at risk of injury at splenec- rior border is related to the coeliac artery and its branches; the common tomy during ligation or stapling of the splenic vessels. The splenic artery hepatic artery runs to the right just above the gland, and the splenic and its branches, and the splenic vein and its tributaries, lie posterior artery passes to the left in a tortuous manner, projecting above the to the tail (see Fig. 69.4F,G). superior border at several points. Inferior border At the medial end of the inferior border, adjacent to the neck of the pancreas, the superior mesenteric vessels emerge from UNCINATE PROCESS behind the gland. Laterally, the inferior mesenteric vein runs behind the inferior border to join the splenic vein or the confluence of the The uncinate process is a hook-shaped continuation of the inferomedial splenic and superior mesenteric veins. This is a useful site for identifica- part of the head of the gland. Embryologically, it is separate from the tion of the inferior mesenteric vein on computed tomographic (CT) rest of the gland (p. 1051). The superior mesenteric vein and, occasion- imaging and during left-sided colonic resections. ally, the superior mesenteric artery descend on its anterior surface before running forwards into the root of the mesentery of the small intestine. The uncinate process extends medially anterior to the abdominal aorta TAIL above the third part of the duodenum, which may be compressed by a pancreatic tumour at this site. On sagittal cross-sectional imaging, the The tail of the pancreas is the narrowest, most lateral portion of the left renal vein, uncinate process, and third part of duodenum can be gland and is continuous medially with the body. It is between 1.5 and seen lying between the superior mesenteric artery anteriorly and the 3.5 cm long in adults and lies between the layers of the splenorenal abdominal aorta posteriorly.

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Pancreas 1182 8 nOITces A in calibre within the body of the gland as it receives further lobular ducts that join it almost at right angles to its axis, forming a ‘herring- bone pattern’. In adults, the duct can often be demonstrated on ultra- Accessory duct sound, measuring approximately 3 mm in diameter in the head, 2 mm in the body and 1 mm in the tail; the calibre of the duct increases from Main duct about the fifth decade onwards (Glaser et al 1987). As it reaches the neck of the gland, it turns inferiorly and posteriorly towards the bile duct, which lies on its right side. The two ducts unite to form a short common channel, which enters the wall of the descending part of the duodenum obliquely; it may contain a dilation known as the hepatopancreatic ampulla (of Vater) (p. 1175). The terminal part of the main pancreatic duct contains a few mucosal folds that impede reflux of pancreatic juice (Purvis et al 2013). The length of the common pan- B creaticobiliary channel is variable and measures up to 5–7 mm in normal individuals (Horaguchi et al 2014). The accessory (dorsal) pancreatic duct (of Santorini) drains the upper part of the anterior portion of the pancreatic head. Much smaller Accessory duct in calibre than the main duct, it is formed within the substance of the Main duct head from several lobular ducts and usually communicates with the main pancreatic duct near the neck of the gland or near its first inferior branch (Kamisawa and Okamoto 2008, Kamisawa 2004). The accessory duct usually opens on to a small, rounded minor duodenal papilla, which lies about 2 cm proximal to the major papilla (see Fig. 69.5A). If the duodenal end of the accessory duct fails to develop, the lobular ducts drain via small channel(s) into the main duct (Hernandez-Jover et al 2011). The anatomy of the main and accessory pancreatic ducts may vary, reflecting anomalies in the development and fusion of the C dorsal and ventral pancreatic ducts. VASCULAR SUPPLY AND LYMPHATIC DRAINAGE Main duct Arteries The pancreas has a rich arterial supply via branches from the coeliac trunk and superior mesenteric artery (Figs 69.6A–C; see also Fig. 65.4). The head and adjoining duodenum are supplied mainly by four arter- ies: two from the coeliac trunk via the gastroduodenal artery (anterior and posterior superior pancreaticoduodenal arteries), and two from the superior mesenteric artery via the inferior pancreaticoduodenal artery (anterior and posterior inferior pancreaticoduodenal arteries). The two D anterior arteries supply the ventral aspects of the duodenum, pancreatic head and uncinate process, and join to form the anterior pancreati- coduodenal arcade. The two posterior arteries supply the dorsal aspect of the pancreatic head, adjacent duodenum and distal bile duct, and may join to form a posterior pancreaticoduodenal arcade. Main duct The body and tail of the pancreas are supplied by multiple branches from the splenic artery, including the dorsal pancreatic artery. Small arteries characteristically run along the superior and inferior borders of the gland, lying in a deep groove or within the parenchyma. They are fed along their length by the pancreaticoduodenal and splenic arteries. Bleeding from these vessels is avoided by ligating the upper and lower borders of the pancreas prior to transection. Posterior superior pancreaticoduodenal artery Fig. 69.5 Variations in the ductal anatomy of the pancreas. A, Normal. The posterior superior pancreaticoduodenal artery usually arises as the The main pancreatic duct is formed by fusion of the dorsal and ventral first branch of the gastroduodenal artery at the superior edge of the first bud ducts, and communicates with the accessory pancreatic duct. part of the duodenum. It runs to the right, anterior to the supraduode- B, Normal. There is no communication between the main duct and nal portion of the bile duct, before spiralling posteriorly around the a normally sited accessory duct. C, Pancreas divisum. The majority common bile duct and descending on the posterior surface of the pan- of the pancreas drains via a dominant dorsal duct that enters the creatic head. It gives branches to the duodenum, head of the pancreas, duodenum at the minor papilla. A short ventral duct is seen draining, and bile duct before anastomosing with the posterior inferior pancrea- along with the bile duct, into the major duodenal papilla. D, Absence of ticoduodenal artery to form the posterior pancreaticoduodenal arcade. accessory duct. (E–G, continued online) The posterior superior pancreaticoduodenal artery may also give origin to the retroduodenal and supraduodenal arteries, which supply the duodenum (Bertelli et al 1996a). The spiral course of the posterior superior pancreaticoduodenal artery reflects its embryonic develop- ment: it is the artery to the anterior aspect of the ventral pancreatic bud PANCREATIC DUCTS and the bile duct, which subsequently rotate clockwise behind the duodenum and dorsal pancreatic bud (Bertelli et al 1997). The exocrine pancreatic tissue drains into multiple small lobular ducts. The arrangement of the main ducts draining the pancreas is subject to anterior superior pancreaticoduodenal artery variation but the most common arrangement is a single main and a The anterior superior pancreaticoduodenal artery usually arises as the single accessory duct (Fig. 69.5). This arrangement reflects the embryo- smaller terminal branch of the gastroduodenal artery, together with the logical development of the dorsal and ventral pancreatic ducts (p. 1051; right gastroepiploic artery. It originates behind the first part of the duo- see Figs 60.3–60.4). The main pancreatic duct (of Wirsung) usually runs denum and runs inferiorly on the anterior aspect of the pancreatic head within the substance of the gland from left to right. It lies midway at a variable distance medial to the groove between the descending between the superior and inferior borders of the pancreas, usually duodenum and pancreatic head. It passes inferiorly around the right or slightly more towards the posterior surface of the gland. It is formed by inferior border of the pancreatic head, often piercing the gland to reach the junction of several lobular (secondary) ducts in the tail and increases the posterior surface of the uncinate process, where it joins the anterior

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Pancreas 1182.e1 96 reTPaHc An abnormally long common channel may occur in isolation or with congenital choledochal dilation, and is associated with pancreatico- biliary reflux and an increased risk of gallbladder cancer (Kamisawa et al 2010a). Patients who develop acute pancreatitis are more likely to have a poorly developed minor papilla; if this were not so, the patent accessory duct system might act as a secondary drainage mechanism for the main ductal system and so prevent elevation of intraductal pressures likely to cause acute pancreatitis (Kamisawa et al 2010b). One clinically impor- tant variation is ‘pancreas divisum’, seen in 5–10% of individuals (Rana et al 2012; see Fig. 69.5C, G). In this condition, there is a failure of normal duct fusion and the accessory pancreatic duct drains the entire pancreas via the minor papilla, except that part of the head and unci- nate process that develop from the ventral bud. The relatively small size of the minor papilla might impair pancreatic drainage, leading to recur- rent pancreatitis. Catheter in Bile duct Pancreatic duct cystic duct (dorsal duct origin) Pancreatic duct (dorsal duct origin) F E Common bile duct Major duodenal Pancreatic duct Area of fusion of embryonic papilla (ventral duct origin) dorsal and ventral ducts Accessory pancreatic duct Pancreatic duct (dorsal duct origin) (ventral duct portion) Minor duodenal papilla Gallbladder Dorsal pancreatic duct Interconnecting channel G Duodenum Biliopancreatic channel Common bile duct Major duodenal papilla Ventral pancreatic duct Fig. 69.5, cont’d Variations in the ductal anatomy of the pancreas. E, Intraoperative cholangiogram visualizing the main pancreatic duct opening into the duodenum through the major duodenal papilla, the accessory duct opening through the minor duodenal papilla and its communicating branch. F, Normal magnetic resonance cholangiopancreatogram (MRCP). The dorsal duct joins with the distal ventral duct in the head of the pancreas. G, Pancreas divisum. MRCP reconstruction shows that the dorsal duct is dominant and enters the duodenum at the minor duodenal papilla. A short ventral pancreatic duct is seen draining with the bile duct into the major papilla.(Figs 69.5E–G, courtesy of Mohamed Rela, Global Hospitals, Chennai, India.)

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Pancreas 1183 96 reTPaHc A Right gastroepiploic artery Splenic artery Gastroduodenal artery Arteria caudae pancreatis (Artery to the tail of the pancreas) Posterior superior pancreaticoduodenal artery Arteria pancreatica magna (Greater pancreatic artery) Left branch, dorsal pancreatic artery Anterior superior pancreaticoduodenal artery Right branch, dorsal pancreatic artery Jejunal branches Anterior inferior pancreaticoduodenal artery Posterior inferior pancreaticoduodenal artery Superior mesenteric artery RHA GDA LGA PB C LHA CHA SA Gastroduodenal artery Bile duct Communicating artery Duodenum Pancreatic duct B Inferior pancreaticoduodenal PSPD RGE PIPD First jejunal TPA ASPD AIPD IPD artery DPA Anterior superior artery Superior mesenteric artery pancreaticoduodenal artery Posterior pancreaticoduodenal arcade Anterior pancreaticoduodenal arcade Fig. 69.6 A, The arterial supply of the pancreas. B, A CT angiographic reconstruction. The black arrow shows the coeliac trunk, and the white arrow shows the superior mesenteric artery. Anastomotic arcades, both ventral and dorsal, can be seen coursing around the head of the pancreas. The body and tail of the pancreas are supplied by multiple pancreatic branches (PB) from the splenic artery and the dorsal pancreatic artery (DPA), which, in this example, arises from the superior mesenteric artery, and gives origin to the transverse pancreatic artery (TPA). Other abbreviations: AIPD, anterior inferior pancreaticoduodenal artery; ASPD, anterior superior pancreaticoduodenal artery; CHA, common hepatic artery; GDA, gastroduodenal artery; IPD, inferior pancreaticoduodenal artery; LGA, left gastric artery; LHA, left hepatic artery; PIPD, posterior inferior pancreaticoduodenal artery; PSPD, posterior superior pancreaticoduodenal artery; RGE, right gastroepiploic artery; RHA, right hepatic artery; SA, splenic artery. C, The anterior and posterior pancreaticoduodenal arterial arcades and a typical communicating artery. (Adapted with permission from Mirjalili SA, Stringer MD. The arterial supply of the major duodenal papilla and its relevance to endoscopic sphincterotomy. Endoscopy 2011; 43(4): 307–11.) inferior pancreaticoduodenal artery to form the anterior pancreaticoduo- artery gives off a jejunal branch and then runs posterior to both the denal arcade (Bertelli et al 1995). superior mesenteric artery and vein before dividing into its terminal branches. Occasionally, the inferior pancreaticoduodenal artery is Inferior pancreaticoduodenal artery absent and the anterior and posterior inferior pancreaticoduodenal An inferior pancreaticoduodenal artery is present in most individuals. arteries arise separately from the superior mesenteric artery. It usually arises either directly from the superior mesenteric artery at The smaller anterior inferior pancreaticoduodenal artery runs to the the inferior border of the pancreas or as a common vessel with the first right on the posterior surface of the uncinate process to join the anterior jejunal artery (a pancreaticoduodenojejunal trunk) from the posterior superior pancreaticoduodenal artery and form the anterior pancreati- or left aspect of the superior mesenteric artery (Horiguchi et al 2008, coduodenal arcade. The larger posterior inferior pancreaticoduodenal Bertelli et al 1996b). It runs to the right, posterior to the superior artery runs on the posterior surface of the head of the pancreas, parallel mesenteric vein, to reach the posterior surface of the uncinate process, and superior to the anterior inferior pancreaticoduodenal artery. It joins where it divides into anterior and posterior inferior pancreaticoduode- the posterior superior pancreaticoduodenal artery to form the posterior nal arteries. When arising as a pancreaticoduodenojejunal trunk, the pancreaticoduodenal arcade (Bertelli et al 1997).

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Pancreas 1184 8 nOITces communicating arteries Multiple small arteries run between the anterior and posterior pancrea- ticoduodenal arcades, either via the pancreaticoduodenal groove or Portal vein Veins directly draining body and tail through the substance of the gland. The largest and most consistent of these is the communicating artery (sometimes known as the middle pancreaticoduodenal arcade), which passes between the main and accessory pancreatic ducts and connects the anterior pancreaticoduode- Veins directly nal arterial arcade and the posterior superior pancreaticoduodenal draining head artery (Yamaguchi et al 2001; Fig. 69.6C; see also Fig. 65.4). This artery and neck gives rise to the majority of small arteries that supply the major duo- denal papilla (Mirjalili and Stringer 2011). Splenic vein Other arterial arcades in the head of the pancreas Kirk’s arcade is formed by a right branch of the dorsal pancreatic artery that emerges on to the anterior surface of the head of the Inferior gland and anastomoses with a branch of either the gastroduodenal mesenteric or the anterior pancreaticoduodenal arcade (Woodburne and Olsen vein 1951). It supplies blood to the ventral surface of the head and neck of the gland. Gastrocolic venous trunk splenic artery The splenic artery arises from the coeliac trunk and runs behind the Superior mesenteric vein superior border of the pancreas to the splenic hilum (see Fig. 69.6A). It gives multiple small branches along its course that penetrate and Inferior pancreaticoduodenal supply the pancreatic parenchyma. Prominent among these are the vein dorsal pancreatic artery (see below); great pancreatic artery (arteria Superior pancreaticoduodenal veins pancreatica magna), arising approximately two-thirds of the way along (anterior and posterior) the gland; and the artery to the tail of the pancreas (arteria caudae pancreatis), arising near the tail. These branches lie on or within the Fig. 69.7 Venous drainage of the pancreas. (Adapted from Drake RL, posterior aspect of the gland and often anastomose with the transverse Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd ed, Elsevier, pancreatic artery. Anatomical variations are not unusual; the dorsal, Churchill Livingstone. Copyright 2010.) great or transverse pancreatic arteries may be dominant in any one individual (Wu et al 2011). veins (the gastrocolic trunk of Henle) or the right gastroepiploic vein Dorsal pancreatic artery alone, to drain into the superior mesenteric vein at the inferior border The dorsal pancreatic artery commonly arises from the initial 2 cm of of the neck of the pancreas (Mourad et al 1994, Lange et al 2000). The the splenic artery, although it may take origin from the common hepatic posterior superior pancreaticoduodenal vein drains cranially into the or superior mesenteric artery or the coeliac trunk (Horiguchi et al portal vein. Both anterior and posterior inferior pancreaticoduodenal 2008). The artery is short and gives off numerous branches, including veins usually drain directly into the superior mesenteric vein. Veins a terminal left branch near the inferior border of the gland. Several from the body and tail of the gland drain directly into the splenic vein. right-sided branches run to the head of the pancreas, passing either A transverse (or inferior) pancreatic vein may be present, running along behind or in front of the superior mesenteric vein to supply the poste- the inferior border of the pancreas to join the inferior mesenteric vein. rior or anterior surface of the pancreatic head, respectively; they anas- A few pancreatic veins communicate with systemic veins in the retro- tomose with arteries of the pancreaticoduodenal arcade (Tsutsumi et al peritoneum (veins of Retzius); these may form retroperitoneal varices 2014). The terminal left branch anastomoses with the transverse pan- in portal hypertension. creatic artery. Lymphatic drainage The length and course of the dorsal pancreatic artery depend prima- rily on its site of origin. When it arises from the splenic artery, common The lymphatic drainage of the pancreas is extensive (see Fig. 64.14B), hepatic artery or coeliac trunk, the artery runs inferiorly on the dorsal which, in part, explains the poor prognosis of pancreatic cancer. Lym- surface of the pancreas, whereas if it arises from the superior mesenteric phatic vessels commence within the connective tissue septa within the artery, it runs superiorly. The artery uniformly terminates near the infe- gland and join to form larger lymphatics that follow local arteries (Deki rior border of the pancreas close to the confluence of the splenic and and Sato 1988, O’Morchoe 1997). Lymphatics from the tail and body superior mesenteric veins (Bertelli et al 1998). drain mostly into nodes along the splenic artery and inferior border of the gland, and from there to pre-aortic nodes between the coeliac trunk Transverse pancreatic artery and superior mesenteric artery. Lymphatics from the neck and head The transverse pancreatic artery, also called the inferior pancreatic drain more widely into nodes along the pancreaticoduodenal, superior artery, commonly originates from the left terminal branch of the dorsal mesenteric and hepatic arteries, and, ultimately, into pre-aortic nodes pancreatic artery. It runs to the left on the posterior surface of the (Donatini and Hidden 1992). There is no evidence of lymphatic chan- gland close to its inferior border, gives multiple branches to the body nels within the pancreatic islets. and tail, and anastomoses with other pancreatic branches of the splenic artery. INNERVATION OF THE PANCREAS The transverse pancreatic artery may occasionally originate from the gastroduodenal artery or the anterior superior pancreaticoduodenal artery, crossing the anterior surface of the pancreatic head to reach the The pancreas has a rich autonomic nerve supply (Love et al 2007). inferior border of the neck of the gland and then the tail. In such cases, Parasympathetic afferents convey sensory information from pancreatic it may be the dominant artery to the pancreatic body, and its injury or ducts, acini and islets via the vagus nerve. Preganglionic vagal efferents deliberate ligation during pancreaticoduodenectomy may cause ischae- have their cell bodies in the dorsal motor nucleus of the vagus and mia of the remnant pancreas. reach the pancreas via hepatic, gastric and coeliac branches of the nerve. They synapse with postganglionic parasympathetic pancreatic arterial segmentation of the pancreas neurones, which are distributed singly or clustered in ganglia in the interlobular connective tissue, lobules and islets. Pancreatic ganglia Available with the Gray’s Anatomy e-book are most abundant in the head and neck of the gland. The ganglia contain neurones that are dominantly cholinergic but nitrergic, pepti- dergic and dopaminergic neurones are also present. These pancreatic Venous drainage of the pancreas neurones receive input not only from vagal efferents but also from Multiple veins drain the pancreas into the portal, superior mesenteric enteric neurones from the stomach and duodenum, sympathetic and splenic veins (Mourad et al 1994; Fig. 69.7). Although variations efferents and other pancreatic neurones. Their nerve fibres ramify in are common, the anterior superior pancreaticoduodenal vein typically the interacinar spaces and supply acinar cells and islets, modulating joins either the confluence of the right gastroepiploic and right colic both exocrine and endocrine secretion (see Fig. 69.10). A network of

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Pancreas 1184.e1 96 reTPaHc The pancreas may be divided into two arterial ‘segments’ that are sepa- rated by a relatively avascular plane; there is disagreement on the defini- tion of these segments. One view is that the two segments are separated by a plane passing to the left of the superior mesenteric artery, such that the head and neck are supplied by branches of the gastroduodenal and superior mesenteric arteries, and the body and tail are supplied by branches of the splenic artery (Busnardo et al 1988). An alternative view holds that the anterior segment consists of the superior part of the pancreatic head, neck, body and tail of the gland (derived from the dorsal pancreatic bud), and the posterior segment consists of the infe- rior part of the head and the uncinate process (derived from the ventral pancreatic bud) (Sakamoto et al 2000). In both schemes, the main pancreatic duct crosses between the segments. Currently, segmental anatomy is of limited practical surgical significance.

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Pancreas 1185 96 reTPaHc interstitial cells (of Cajal) provides an additional link between auto- pancreatic islets, forming the endocrine component, are embedded nomic nerves and pancreatic acini. (Figs 69.8–69.10). Visceral afferents transmit pain and other sensory information to cell bodies in the sixth to twelfth thoracic dorsal root ganglia via the coeliac Exocrine pancreas plexus and thoracic splanchnic nerves. The cell bodies of preganglionic sympathetic nerves are located in the intermediolateral columns of the spinal cord (T6–12); their axons travel in the thoracic splanchnic nerves The exocrine pancreas is a branched acinar gland (see Fig. 2.6), sur- and synapse in the coeliac and superior mesenteric ganglia. Postgangli- rounded and incompletely lobulated by delicate loose connective onic sympathetic nerves innervate the blood vessels, ganglia and ducts tissue. Individual acini are composed of roughly spherical clusters of within the pancreas, causing vasoconstriction and inhibiting exocrine pyramidal cells that secrete digestive enzymes, water and bicarbonate. secretion. A narrow intralobular duct lined by flattened or cuboidal centro-acinar Perineural invasion is relatively common in pancreatic cancer and cells originates from within each secretory acinus. Intralobular ducts not only adversely affects prognosis but may also be a factor in the pain unite to form larger interlobular ducts lined by taller cuboidal and, associated with this disease (Bapat et al 2011). eventually, columnar epithelium. The latter are surrounded by connec- tive tissue septa, containing smooth muscle, autonomic nerves and fat. Referred pain Neuroendocrine cells are present among the columnar ductal cells, and Pain arising in the pancreas is poorly localized. In common with other mast cells are numerous in the surrounding connective tissue. A network foregut structures, the majority of pain arising from the pancreas is of intralobular arteries, arterioles and capillaries form capillary net- referred to the epigastrium. Inflammatory or infiltrative processes works around the terminal ducts, acini and the richly vascularized arising from the gland rapidly involve the tissues of the retroperito- endocrine islets (Love et al 2007). neum that are innervated by somatic nerves; pain is then localized to the lower thoracic spine. Intractable pain from chronic pancreatitis or Acinar cells Acinar cells have a basal nucleus surrounded by abun- inoperable pancreatic tumours can be temporarily controlled by dant basophilic rough endoplasmic reticulum and an apical region thermal or chemical ablation of the coeliac plexus. containing dense eosinophilic secretory zymogen granules. A promi- nent supranuclear Golgi complex is associated with large, membrane- bound granules containing the protein constituents of pancreatic MICROSTRUCTURE secretion, including enzymes that are only active after release. Gangli- onic neurones and cords of undifferentiated epithelial cells are also The pancreas is composed of exocrine and endocrine tissues. The main found within the acini. The structure of the exocrine pancreas and its tissue mass is exocrine, forming 98% of the pancreas, in which functional regulation are summarized in Figure 69.8. SPHINCTERIC TONE BICARBONATE IONS AND WATER TRANSPORT (Ductal and centro-acinar cells) Neural control Parasympathetic fibres Neural control Mainly vagal cholinergic fibres Sympathetic fibres Hormonal control Mainly secretin (duodenum and jejunum) Pancreatic islet Islet hormones modulate acinar secretion via local capillaries Insulo-acinar portal system Acinar secretion is controlled by duodenal neuroendocrine cell secretion Adrenergic Acinar cell vasoconstrictor terminals Centro-acinar cell Secretion of granule contents (including proteases, esterase, Intercalated amylase and lipase) duct cell Postganglionic parasympathetic neurone Zymogen granule (enzyme storage) Preganglionic cholinergic fibres Cholinergic nerve terminal ENZYME SECRETION (Acinar cells) Neural control Mainly vagal cholinergic fibres Hormonal control Mainly duodenal cholecystokinin (CCK) Fig. 69.8 The microstructure of the exocrine pancreas and the mechanisms by which its secretion is controlled. Pancreatic stellate cells (see text) are not shown.

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Pancreas 1186 8 nOITces Cell types Secretion A (Alpha cells) Glucagon B (Beta cells) Insulin D (Delta cells) Somatostatin, gastrin F cells Pancreatic polypeptide Pancreatic acinus Pancreatic duct Neuroendocrine cells (white) are incorporated into exocrine pancreatic tissue Fig. 69.10 The microstructure and control of function of the endocrine pancreas. telsi citaercnaP Acinus Islet Fig. 69.9 Microstructure of the pancreas. The exocrine tissue consists of acini with pyramid-shaped columnar cells arranged in spherical clusters. Acinar secretions drain into intralobular ducts, which, in turn, join larger interlobular ducts, present in connective tissue septa containing blood vessels. Interspersed between the acini are islets of Langerhans, which appear as clusters of pale-staining cells surrounded by a network of capillaries, seen as narrow clear spaces. Adipocytes may also be present. Haematoxylin and eosin. (Courtesy of Dr Mukul Vij, Global Hospital, Chennai, India.) Small duct Large duct Stimulation of insulin synthesis and secretion Ganglion cell Preganglionic Discontinuous vagal fibre tight junctions Secretomotor terminals Sympathetic Parasympathetic Fenestrated Neuroinsular Gap junction capillaries complex Postganglionic sympathetic vasomotor terminal Direct receptor Indirect stimulation via stimulation vagus and gastrointestinal by glucose hormones after ingestion Gap junction Somatostatin released by D cell inhibits glucagon (and B cell insulin) release locally... ...and also passes into vessels to exert distant effects Neural modulation of endocrine cell activity

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1187 96 reTPaHc Key references Stellate cells Pancreatic stellate cells are myofibroblast-like cells dis- ACUTE PANCREATITIS tributed in the exocrine part of the pancreas, mainly in the peri-acinar space, where their long cytoplasmic processes encircle the base of the acinus, and in perivascular and periductal regions of the pancreas. They Available with the Gray’s Anatomy e-book are usually in a quiescent state but, when activated, they have been implicated in the pathogenesis of chronic pancreatitis and pancreatic cancer (Omary et al 2007, Masamune and Shimosegawa 2013). CHRONIC PANCREATITIS Endocrine pancreas Available with the Gray’s Anatomy e-book Pancreatic islets (of Langerhans) constitute the endocrine component of the pancreas. The human pancreas may contain more than a million PANCREATIC TUMOURS islets distributed throughout the gland but most numerous in the tail. Each islet consists of a highly vascularized cluster of polyhedral cells arranged in a trabecular pattern, closely approximated to a dense Available with the Gray’s Anatomy e-book network of fenestrated capillaries, which enables bidirectional transport of substrates between the islet cells and the circulation (In’t Veld and Marichal 2010). Islets are also supplied by autonomic nerve fibres, PANCREATIC TRANSPLANTATION which travel with the blood vessels and end blindly in the pericapillary space. True synaptic contact between these nerve fibres and islet cells has not been demonstrated, though their role in islet function has been Available with the Gray’s Anatomy e-book suggested (Rodriguez-Diaz et al 2012). Specialized staining techniques are necessary to distinguish various islet cells, designated alpha, beta, delta, epsilon and pancreatic polypeptide (PP) or F cells. Beta cells secrete insulin and are the most abundant (nearly 50% in human islets), followed by glucagon-secreting alpha cells (30–40%). Delta cells Bonus e-book images and PP cells are less common and secrete somatostatin and pancreatic polypeptide, respectively. Epsilon cells secrete ghrelin. Unlike mouse islets, where beta cells form the core of the islet and are surrounded by Fig. 69.5 E–G Variations in the ductal anatomy of the pancreas. alpha cells, human islets do not show cell-type specific localization. The various cell types are uniformly distributed along the microvasculature Fig. 69.11 An intraoperative photograph taken during and have extensive interlinkages with other islet cells. Their general pancreaticoduodenectomy. organization is shown in Figure 69.10. KEY REFERENCES Busnardo AC, DiDio LJ, Thomford NR 1988 Anatomicrosurgical segments Nagai H 2003 Configurational anatomy of the pancreas: its surgical rele- of the human pancreas. Surg Radiol Anat 10:77–82. vance from ontogenetic and comparative-anatomical viewpoints. A description explaining the segmental vascularity of the pancreas and the J Hepatobil Pancreat Surg 10:48–56. watershed area near the neck of pancreas. A well-illustrated description of the arrangement of vascular and other structures around the duodenum and head of pancreas, with explanations In’t Veld P, Marichal M 2010 Microscopic anatomy of the human islet of based on the embryological development of the pancreas, foregut and midgut. Langerhans. Adv Exp Med Biol 654:1–19. A detailed description of the human islet of Langerhans. Omary MB, Lugea A, Lowe AW et al 2007 The pancreatic stellate cell: a star on the rise in pancreatic diseases. J Clin Invest 117:50–9. Kamisawa T, Okamoto A 2008 Pancreatographic investigation of pancreatic A detailed review of the pancreatic acinar cell, which is the focus of research duct system and pancreaticobiliary malformation. J Anat 212:125–34. into its possible role in a multitude of pancreatic disorders. A review of the pancreatic ductal system. Saisho Y, Butler AE, Meier JJ et al 2007 Pancreas volumes in humans from Kimura W 2000 Surgical anatomy of the pancreas for limited resection. birth to age one hundred taking into account sex, obesity, and presence J Hepatobil Pancreat Surg 7:473–9. of type-2 diabetes. Clin Anat 20:933–42. A beautifully illustrated description of the surgical anatomy of the pancreas. A description of pancreatic volumes and the ratio of parenchymal and fat components in humans, with an account of how it changes with age and Kimura W, Nagai H 1995 Study of surgical anatomy for duodenum- gender. preserving resection of the head of the pancreas. Ann Surg 221:359–63. Woodburne RT, Olsen LL 1951 The arteries of the pancreas. Anat Rec A detailed description of the vascular anatomy of the head of the pancreas 111:255–70. and duodenum. One of the earliest comprehensive reviews of pancreatic arterial anatomy.

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Pancreas 1187.e1 96 reTPaHc Acute inflammation of the pancreas occurs in response to a variety of pancreatic insults, including gallstone obstruction of the hepatopancre- atic ampulla, which causes reflux of bile and pancreatic juice into the pancreatic duct. This precipitates intraparenchymal activation of inac- tive digestive enzymes, leading to cell injury, an inflammatory cascade and destruction of pancreatic tissue. The regional anatomy of the pancreas explains most of the clinical D complications of acute pancreatitis. Irritation of the stomach contrib- utes to gastric stasis and vomiting; inflammation of the superior mesenteric plexus may contribute to paralytic ileus; and vascular inflam- mation may cause superior mesenteric or portal vein thrombosis, arte- rial bleeding or pseudoaneurysms, and ischaemia of the transverse colon. Haemorrhagic fluid may accumulate in the loose retroperitoneal E B tissues around the pancreas and track laterally to the flanks (Grey Turner’s sign), down to the inguinal ligaments (Fox’s sign), or via the lesser omentum and ‘bare area’ of the liver to the falciform ligament CC and the skin around the umbilicus (Cullen’s sign), manifesting as AA diffuse bruising. Peripancreatic acute fluid collections frequently resolve spontane- ously as the inflammation in the pancreas subsides. Accumulation of fluid anterior to the pancreas, just beneath the posterior wall of the lesser sac, can result in a ‘pseudocyst’ containing amylase-rich fluid and debris but lacking a true epithelial lining (Banks et al 2013). A large Fig. 69.11 An intraoperative photograph taken during pseudocyst bulges forwards into the lesser sac in contact with the pos- pancreaticoduodenectomy. This patient had coeliac artery stenosis and terior wall of the stomach, lesser omentum and gastrosplenic ligament. consequently hypertrophied pancreaticoduodenal arcade arteries (A) provided the arterial supply to the liver. The pancreatic head and If it does not resolve spontaneously, the pseudocyst can be drained duodenum were resected, preserving the arcade. Note the cut stump at internally through the posterior wall of the stomach by endoscopic or the proximal body of the pancreas (B) and the exposed portal/superior open surgery, or externally by means of a percutaneous drain inserted mesenteric vein (C). The arcade communicates with the hepatic artery (E) under radiological guidance. to supply the liver (D). (Courtesy of Mohamed Rela, Global Hospitals, Sustained injury to the pancreas can cause permanent damage, Chennai, India.) leading to parenchymal fibrosis and calcification within the paren- chyma and the pancreatic ducts. This often causes chronic pain, diabe- and Nagai 1995). Stenosis of the coeliac artery is common in elderly tes mellitus and pancreatic exocrine insufficiency with steatorrhoea and individuals with atherosclerosis. Here, the arterial blood supply to the malnutrition. Fibrosis can involve the bile duct in the head of the pan- liver is provided by the superior mesenteric artery through hypertro- creas, leading to obstructive jaundice, and/or the splenic vein, causing phied arteries of the anterior and posterior pancreaticoduodenal splenic vein thrombosis and ‘left-sided’ portal hypertension. arcades. Care should be taken to avoid ligation of these branches during The vast majority of pancreatic tumours are ductal adenocarcinomas pancreatic surgery since this could cause hepatic ischemia (Fig. 69.11). derived from exocrine ductal epithelium. Up to two-thirds of such The pancreas is usually transplanted along with the kidney (this is tumours are located in the head of the pancreas. Tumours in the head termed a simultaneous pancreas–kidney transplant) in patients with of the pancreas often obstruct the pancreatic segment of the bile duct end-stage renal disease caused by diabetes mellitus. In selected patients, early in the course of disease, leading to obstructive jaundice. The the pancreas alone can be transplanted to treat poor glycaemic control appearance of a dilated common bile duct and main pancreatic duct and hypoglycaemia unawareness (White et al 2009). on cross-sectional imaging (the ‘double duct’ sign) is a characteristic Donor pancreas is recovered from deceased donors, usually as part sign in tumours of the pancreatic head. Advanced tumours may invade of a multi-organ recovery procedure. The entire pancreas, along with the adjacent duodenum, causing gastric outlet obstruction and/or the the duodenal C loop (attached to the head of pancreas) and spleen portal or superior mesenteric veins posterior to the neck of the pancreas. (closely related to the tail of the pancreas), is recovered to prevent A tumour in the body or tail of the gland often grows to a large size damage to the vascular arcades in the pancreaticoduodenal groove and before presenting as an abdominal mass or with back pain and weight minimize handling of the pancreas during organ recovery (Abu-Elmagd loss (Yeo et al 2002). Tumours of the uncinate process can cause et al 2000). The arterial supply for the pancreas graft is based on the early involvement of the superior mesenteric vessels and duodenum splenic artery and the superior mesenteric artery, both of which should (O’Sullivan et al 2009). Peripancreatic and pre-aortic lymph nodes may be carefully preserved during the donor operation. Both arteries are be involved, together with hepatic nodes, in pancreatic head tumours, reconstructed to a Y-shaped deceased donor iliac artery graft to enable and splenic hilar nodes may be involved in pancreatic tail tumours. a single arterial anastomosis in the recipient. The venous drainage is Surgery for pancreatic head tumours usually involves combined through the portal vein. The pancreas graft is implanted heterotopically resection of the pancreatic head and duodenum (pancreaticoduodenec- in the pelvis (not in its normal anatomical position, i.e. the upper tomy) because of their shared blood supply. The resectability of the retroperitoneum). The reconstructed artery is anastomosed to the exter- tumour depends on the presence and extent of major vascular involve- nal iliac artery. The portal vein of the graft can be anastomosed to either ment, particularly the portal vein and superior mesenteric vessels. An the iliac vein or the superior mesenteric vein of the recipient. Though accessory or replaced right hepatic artery (p. 1166) running cranially on portal and systemic venous drainage each has its own supporters, there the posterior surface of the pancreatic head and behind the supraduo- is no evidence regarding the superiority of one technique versus the denal segment of the bile duct is at risk of injury during such procedures other (Bazerbachi et al 2012). Drainage of the pancreas exocrine secre- (Turrini et al 2010). Recognition of this variation and preservation of tions is into the ileum through a duodeno-ileal anastomosis or into the the artery are essential to maintain the arterial supply to the right lobe recipient urinary bladder through a duodeno-cystic anastomosis. Com- of the liver. In distal or total pancreatectomy, spleen-preserving resec- plications of the procedure are primarily a result of the damage the tions are generally undertaken if the underlying pathology does not delicate pancreas sustains during the organ recovery, storage and trans- involve the splenic vein lying in the groove on the posterior surface of plantation process. Complications include graft pancreatitis, graft the gland, taking care to control the multiple small pancreatic venous necrosis leading to bleeding, thrombosis of vascular anastomoses and tributaries. In duodenum-preserving resection of the pancreatic head, sepsis (Delis et al 2004, Troppmann 2010). However, in the majority of which is sometimes undertaken for chronic pancreatitis and benign patients, pancreas transplantation provides the potential for an insulin- pancreatic tumours, it is important to preserve an adequate duodenal free life and retards the development of diabetes-related complications blood supply from the pancreaticoduodenal arterial arcades (Kimura (Gruessner et al 2012).

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Pancreas 1187.e2 8 nOITces REFERENCES Abu-Elmagd K, Fung J, Bueno J et al 2000 Logistics and technique for pro- Kamisawa T, Okamoto A 2008 Pancreatographic investigation of pancreatic curement of intestinal, pancreatic, and hepatic grafts from the same duct system and pancreaticobiliary malformation. J Anat 212:125–34. donor. Ann Surg 232:680–7. A review of the pancreatic ductal system. Banks PA, Bollen TL, Dervenis C et al 2013 Classification of acute Kamisawa T, Suyama M, Fujita N et al 2010a Pancreatobiliary reflux and the pancreatitis–2012: revision of the Atlanta classification and definitions length of a common channel. J Hepatobil Pancreat Surg 17:865–70. by international consensus. Gut 62:102–11. Kamisawa T, Takuma K, Tabata T et al 2010b Clinical implications of acces- Bapat AA, Hostetter G, Von Hoff DD et al 2011 Perineural invasion and sory pancreatic duct. World J Gastroenterol 16:4499–503. associated pain in pancreatic cancer. Nat Rev Cancer 11:695–707. Kimura W 2000 Surgical anatomy of the pancreas for limited resection. Bazerbachi F, Selzner M, Marquez MA et al 2012 Portal venous versus sys- J Hepatobil Pancreat Surg 7:473–9. temic venous drainage of pancreas grafts: impact on long-term results. A beautifully illustrated description of the surgical anatomy of the pancreas. Am J Transplant 12:226–32. Kimura W, Nagai H 1995 Study of surgical anatomy for duodenum- Bertelli E, Di Gregorio F, Bertelli L et al 1995 The arterial blood supply of preserving resection of the head of the pancreas. Ann Surg 221: the pancreas: a review. I. The superior pancreaticoduodenal and the 359–63. anterior superior pancreaticoduodenal arteries. An anatomical and A detailed description of the vascular anatomy of the head of the pancreas radiological study. Surg Radiol Anat 17:97–106, 1–3. and duodenum. Bertelli E, Di Gregorio F, Bertelli L et al 1996a The arterial blood supply of the pancreas: a review. II. The posterior superior pancreaticoduode- Lange JF, Koppert S, van Eyck CH et al 2000 The gastrocolic trunk of Henle nal artery: an anatomical and radiological study. Surg Radiol Anat in pancreatic surgery: an anatomo-clinical study. J Hepatobili Pancreat 18:1–9. Surg 7:401–3. Bertelli E, Di Gregorio F, Bertelli L et al 1996b The arterial blood supply of Love JA, Yi E, Smith TG 2007 Autonomic pathways regulating pancreatic the pancreas: a review. III. The inferior pancreaticoduodenal artery. An exocrine secretion. Auton Neurosci 133:19–34. anatomical review and a radiological study. Surg Radiol Anat 18: Masamune A, Shimosegawa T 2013 Pancreatic stellate cells–multi-functional 67–74. cells in the pancreas. Pancreatology 13:102–5. Bertelli E, Di Gregorio F, Bertelli L et al 1997 The arterial blood supply of Mirjalili SA, Stringer MD 2011 The arterial supply of the major duodenal the pancreas: a review. IV. The anterior inferior and posterior pancrea- papilla and its relevance to endoscopic sphincterotomy. Endoscopy ticoduodenal aa., and minor sources of blood supply for the head of 43:307–11. the pancreas. An anatomical review and radiologic study. Surg Radiol Mourad N, Zhang J, Rath AM et al 1994 The venous drainage of the pancreas. Anat 19:203–12. Surg Radiol Anat 16:37–45. Bertelli E, Di Gregorio F, Mosca S et al 1998 The arterial blood supply of Nagai H 2003 Configurational anatomy of the pancreas: its surgical rele- the pancreas: a review. V. The dorsal pancreatic artery. An anatomic vance from ontogenetic and comparative-anatomical viewpoints. review and a radiologic study. Surg Radiol Anat 20:445–52. J Hepatobil Pancreat Surg 10:48–56. Burgard G, Gilly F, Braillon G et al 1991 Anatomic basis of the surgical A well-illustrated description of the arrangement of vascular and other approach to the retropancreatic common bile duct. Surg Radiol Anat structures around the duodenum and head of pancreas, with explanations 13:352–3. based on the embryological development of the pancreas, foregut and Busnardo AC, DiDio LJ, Thomford NR 1988 Anatomicrosurgical segments midgut. of the human pancreas. Surg Radiol Anat 10:77–82. Omary MB, Lugea A, Lowe AW et al 2007 The pancreatic stellate cell: a star A description explaining the segmental vascularity of the pancreas and the on the rise in pancreatic diseases. J Clin Invest 117:50–9. watershed area near the neck of pancreas. A detailed review of the pancreatic acinar cell, which is the focus of research Caglar V, Songur A, Yagmurca M et al 2012 Age-related volumetric changes into its possible role in a multitude of pancreatic disorders. in pancreas: a stereological study on computed tomography. Surg Radiol O’Morchoe CC 1997 Lymphatic system of the pancreas. Microsc Res Tech Anat 34:935–41. 37:456–77. Deki H, Sato T 1988 An anatomic study of the peripancreatic lymphatics. O’Sullivan AW, Heaton N, Rela M 2009 Cancer of the uncinate process of Surg Radiol Anat 10:121–35. the pancreas: surgical anatomy and clinicopathological features. Hepa- Delis S, Dervenis C, Bramis J et al 2004 Vascular complications of pancreas tobiliary Pancreat Dis Int 8:569–74. transplantation. Pancreas 28:413–20. Purvis NS, Mirjalili SA, Stringer MD 2013 The mucosal folds at the pancrea- Djuric-Stefanovic A, Masulovic D, Kostic J et al 2012 CT volumetry of normal ticobiliary junction. Surg Radiol Anat 35:943–50. pancreas: correlation with the pancreatic diameters measurable by the Rana SS, Gonen C, Vilmann P 2012 Endoscopic ultrasound and pancreas cross-sectional imaging, and relationship with the gender, age, and body divisum. JOP 13:252–7. constitution. Surg Radiol Anat 34:811–17. Rodriguez-Diaz R, Speier S, Molano RD et al 2012 Noninvasive in vivo Donatini B, Hidden G 1992 Routes of lymphatic drainage from the pan- model demonstrating the effects of autonomic innervation on pan- creas: a suggested segmentation. Surg Radiol Anat 14:35–42. creatic islet function. Proc Nat Acad Sci USA 109:21456–61. Glaser J, Hogemann B, Krummenerl T et al 1987 Sonographic imaging of Saisho Y, Butler AE, Meier JJ et al 2007 Pancreas volumes in humans from the pancreatic duct: new diagnostic possibilities using secretin stimula- birth to age one hundred taking into account sex, obesity, and presence tion. Dig Dis Sci 32:1075–81. of type-2 diabetes. Clin Anat 20:933–42. Gruessner AC, Sutherland DE, Gruessner RW 2012 Long-term outcome after A description of pancreatic volumes and the ratio of parenchymal and fat pancreas transplantation. Curr Opin Organ Transplant 17:100–5. components in humans, with an account of how it changes with age and Hernandez-Jover D, Pernas JC, Gonzalez-Ceballos S et al 2011 Pancreato- gender. duodenal junction: review of anatomy and pathologic conditions. Sakamoto Y, Nagai M, Tanaka N et al 2000 Anatomical segmentectomy of J Gastrointest Surg 15:1269–81. the head of the pancreas along the embryological fusion plane: a feasi- Horiguchi A, Ishihara S, Ito M et al 2008 Multislice CT study of pancreatic ble procedure? Surgery 128:822–31. head arterial dominance. J Hepatobil Pancreat Surg 15:322–6. Troppmann C 2010 Complications after pancreas transplantation. Curr Horaguchi J, Fujita N, Kamisawa T et al 2014 Pancreatobiliary reflux in Opin Organ Transplant 15:112–18. individuals with a normal pancreaticobiliary junction: a prospective Tsutsumi M, Arakawa T, Terashima T et al 2014 Morphological analysis of multicenter study. J Gastroenterol 49:875–81. the branches of the dorsal pancreatic artery and their clinical signifi- In’t Veld P, Marichal M 2010 Microscopic anatomy of the human islet of cance. Clin Anat 27:645–52. Langerhans. Adv Exp Med Biol 654:1–19. Turrini O, Wiebke EA, Delpero JR et al 2010 Preservation of replaced or A detailed description of the human islet of Langerhans. accessory right hepatic artery during pancreaticoduodenectomy for Kamisawa T 2004 Clinical significance of the minor duodenal papilla and adenocarcinoma: impact on margin status and survival. J Gastrointest accessory pancreatic duct. J Gastroenterol 39:605–15. Surg 14:1813–19.

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Pancreas 1187.e3 96 reTPaHc White SA, Shaw JA, Sutherland DE 2009 Pancreas transplantation. Lancet Yamaguchi H, Wakiguchi S, Murakami G et al 2001 Blood supply to the 373:1808–17. duodenal papilla and the communicating artery between the anterior Woodburne RT, Olsen LL 1951 The arteries of the pancreas. Anat Rec and posterior pancreaticoduodenal arterial arcades. J Hepatobil Pan- 111:255–70. creat Surg 8:238–44. One of the earliest comprehensive reviews of pancreatic arterial anatomy. Yeo TP, Hruban RH, Leach SD et al 2002 Pancreatic cancer. Curr Probl Cancer 26:176–275. Wu ZX, Yang XZ, Cai JQ et al 2011 Digital subtraction angiography and computed tomography angiography of predominant artery feeding pan- creatic body and tail. Diabetes Technol Ther 13:537–41.

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CHAPTER 70 Spleen The spleen is a large, encapsulated, complex mass of vascular and lym- 1993, Üngör et al 2007). The average adult weight is dependent on the phoid tissue situated in the upper left quadrant of the abdominal cavity volume of contained blood; emptied of blood, it weighs between 70 between the fundus of the stomach and the diaphragm. It is mainly and 120 g, whereas in vivo its weight ranges from 150 to 350 g (Naka- concerned with phagocytosis and immune responses. Although docu- mura et al 1989, Petroianu 2011, Skandalakis et al 1993). mented for more than 3,000 years, there are many aspects of the spleen The shape of the spleen is also variable and mostly determined by that remain poorly understood. It plays important roles in immuno- its relations to neighbouring structures during development; it often logical defence, metabolism and maintenance of circulating blood ele- appears as a slightly curved wedge. The superolateral aspect is shaped ments (Petroianu 2011, Tarantino et al 2013; Table 70.1). In the fetus, by the left dome of the diaphragm, and the inferomedial aspect mostly it is also a major site of haemopoiesis and can resume this role post- by the neighbouring stomach, left kidney and splenic flexure of the natally in certain pathological conditions (Üngör et al 2007). However, colon. In the fetus, the spleen is lobulated (Ch. 60; Coetzee 1982, Faller it is not essential for life; if the spleen is removed, many of its functions 1985, Gupta et al 1976, Petroianu 2011, Scothorne 1985, Skandalakis can be assumed by the liver and other tissues of the mononuclear et al 1993, Üngör et al 2007); the adult spleen usually only retains a phagocytic system. notch on its anterior border, although additional surface notches may The most common clinical manifestations of splenic disorders are persist (Mikhail et al 1979). splenomegaly and a decrease in the number of cellular elements in the A splenic lobule that fails to coalesce with the developing spleen can blood (cytopenias). Other clinical manifestations include infections, persist as a supernumerary or accessory spleen (also known as a sple- lassitude and abdominal discomfort (Coetzee 1982, Oguro et al 1993, nunculus; Gupta et al 1976). This fully functional island of splenic Petroianu 2011, Tarantino et al 2013). Chronic splenomegaly in chil- tissue is found in approximately 10% of individuals and may be located dren may be associated with growth retardation (Petroianu 2003, in any part of the abdomen, or even outside it, but is most commonly Petroianu 1996). The most serious long-term consequence of removal present near the splenic hilum within the gastrosplenic ligament or of the spleen is severe sepsis, which carries a 2% mortality in otherwise greater omentum (Faller 1985, Petroianu 2011; Fig. 70.1). healthy adults and an even greater risk of death in children, the elderly, A normal adult spleen is not palpable on abdominal examination. and patients with chronic diseases. In living supine healthy adults, it is most frequently located between the tenth and twelfth ribs, with its long axis along the eleventh rib (Gupta et al 1976, Mirjalili et al 2012). Its posterior border is approxi- GROSS ANATOMY mately 4 cm from the midline at the level of the tenth thoracic vertebral spine and it extends about 3 cm anterior to the mid-axillary line. In the The size and weight of the spleen vary with age and sex, and can also absence of long peritoneal ligaments, it has to triple in size before it vary slightly in the same individual under different conditions. The becomes palpable below the left costal margin (Mikhail et al 1979, adult spleen is usually 9–14 cm long, 6–8 cm wide and 3–5 cm thick, Üngör et al 2007). and fits comfortably in the individual’s cupped hand. It reaches its largest dimension in puberty and diminishes thereafter (DeLand 1970, Jakobsen and Jakobsen 1997). Although its weight increases during RELATIONS puberty, it is comparatively largest in the young child and tends to diminish in size and weight in old age (Coquet et al 2010, DeLand The spleen has superolateral diaphragmatic and inferomedial visceral 1970, Jakobsen and Jakobsen 1997, Scothorne 1985, Skandalakis et al surfaces (Fig. 70.2), anterosuperior and posteroinferior borders, and Table 70.1 Summary of splenic functions Superior pole Gastric impression Segmental branches General functions Specific functions (posterior extremity) of splenic artery Haematological and immunological Haemopoiesis Maturation of blood elements Anterosuperior Immunoglobulin activation border (notched) Recirculation of T and B lymphocytes Production Leukocytes Peptides Immunoglobulins (mainly IgM) Opsonins Tuftsin Properdin Complement factors Stem cells Storage Leukocytes Platelets All metals Clearance Microorganisms Vein leaving hilum Parasites Circulating antigens Renal impression Altered circulating cells Circulating foreign bodies Posteroinferior border Synthesis Precursor of hepatic functions Inferior pole Metabolism Lipids Cholesterol Bilirubin Amino acids Pancreatic Control Bone marrow Colic impression impression Mononuclear phagocytic function Somatic growth 1188 Fig. 70.2 The visceral surface of the spleen.

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Spleen 1188.e1 07 RETPAHC Spleens in men are proportionally heavier than those in women. In pathological conditions, the spleen may expand and retain blood; weights rarely exceed 700 g but gigantic spleens exceeding 10 kg have been reported (Coquet et al 2010, DeLand 1970, Jakobsen and Jakobsen 1997, Skandalakis et al 1993). Splenomegaly compresses and displaces adjacent organs, causing abdominal discomfort, dyspepsia, respiratory restriction and difficulty walking (Coetzee 1982, Petroianu 2011). Fig. 70.1 A supernumerary spleen located in the greater omentum (arrow). Supernumerary spleens are usually isolated and may be connected to the spleen or splenic pedicle by thin vessels.

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Spleen 1189 07 RETPAHC of the spleen is a long fissure pierced by the splenic vessels, nerves and Central tendon lymphatics, and lies on the visceral surface closer to the posteroinferior border (Petroianu 2011). The anterosuperior border separates the diaphragmatic surface from the gastric impression and is usually convex. Inferiorly, it may bear one or two notches that have persisted from the lobulated form of the spleen in early fetal life (p. 1064). However, the notch may be Left cupola of diaphragm absent and is not a completely reliable guide to identification of the spleen during clinical examination. The posteroinferior border sepa- rates the renal impression from the diaphragmatic surface and is more Tail of pancreas rounded and blunt than the anterosuperior border. The superior pole corresponds to the posterior extremity and usually faces the vertebral column. The inferior pole is longer and less angulated than the superior pole and connects the anterosuperior and posteroinferior borders Phrenicocolic ligament anteriorly; it is related to the colic impression and often lies adjacent Splenic flexure to the splenic flexure and phrenicocolic ligament (Petroianu 2011). The inferior pole of the spleen is particularly at risk of injury from blunt abdominal trauma or during surgical procedures on the stomach, pancreatic tail, left kidney, left suprarenal gland and left colon. Excessive traction of the stomach, transverse colon or greater omentum may tear the splenic capsule and superficial parenchyma by way of their perito- neal attachments, causing bleeding that may be difficult to control (Merchea et al 2012). SPLENIC LIGAMENTS Fig. 70.3 The posterior relations (‘bed’) of the spleen. (Adapted from The spleen develops between the two leaves of the dorsal mesogastrium Drake, RL, Vogl, AW, Mitchell, A (eds), Gray’s Anatomy for Students, 2nd (see Figs 60.6–60.7) and so is almost entirely invested in visceral peri- ed, Elsevier, Churchill Livingstone. Copyright 2010.) toneum that is firmly adherent to its capsule (Üngör et al 2007). The dorsal mesogastric attachments persist as peritoneal ligaments. Thus, the superior pole of the spleen is connected to the stomach via the 1 2 gastrosplenic ligament, and to the posterior abdominal wall by a vari- ably developed phrenicosplenic ligament. The inferior pole of the spleen is connected to the posterior abdominal wall by the splenorenal ligament and to the splenic flexure of the colon. The phrenicocolic liga- ment lies just inferior to the lower pole (Fig. 70.5). Each of these liga- ments is made up of two layers of peritoneum containing fat, blood and lymphatic vessels and nerves (Petroianu 2011, Skandalakis et al 1993). The phrenicosplenic ligament runs between the spleen and the peritoneum of the undersurface of the diaphragm. The anterior layer of the splenorenal ligament is continuous with the peritoneum of the posterior wall of the lesser sac over the left kidney, and with the poste- rior layer of the gastrosplenic ligament at the splenic hilum. The poste- rior layer of the splenorenal ligament is continuous with the peritoneum over the inferior surface of the diaphragm and anterior surface of the left kidney. The terminal portions of the splenic artery and vein, and, more inferiorly, the tail of the pancreas, lie between the two peritoneal layers of the splenorenal ligament. The tail of the pancreas may be injured during dissection when ligating and dividing the splenic vessels, 3 4 5 6 resulting in bleeding, local pancreatitis and pancreatic fistula formation (Petroianu 2011, Skandalakis et al 1993). Fig. 70.4 The gross appearance of the spleen in situ. An intra-abdominal image of the spleen (1) and its relation with the stomach (4), liver (3), The gastrosplenic ligament is continuous with the phrenicosplenic colon (6), diaphragm (2) and greater omentum (5). ligament, the splenic capsule, the gastric serosa and the greater omentum. It contains the short gastric and superior polar arteries, and the left gastroepiploic artery, all of which arise from the splenic artery, and their corresponding veins. During splenectomy or mobilization of superior and inferior poles. The convex, smooth diaphragmatic surface the fundus of the stomach, the short gastric vessels must not be ligated faces mostly superiorly and laterally, although the posterior part may too close to the stomach in order to avoid the risk of local gastric face posteriorly (Mirjalili et al 2012). The diaphragmatic surface is sepa- necrosis, perforation and their consequences. rated from the left pleural costodiaphragmatic recess, lower lobe of the The phrenicocolic ligament connects the splenic flexure of the colon left lung and the tenth to twelfth left ribs by the underside of the left to the diaphragm and runs inferior and lateral to the lower pole of the dome of the diaphragm (Figs 70.3–70.4); splenic inflammation or spleen. It is continuous with the peritoneum of the lateral end of the surgery may lead to a left-sided basal pleural effusion and left lower transverse mesocolon at the end of the pancreatic tail, and the spleno- lobe atelectasis (Petroianu 2011). renal ligament at the hilum of the spleen (Merchea et al 2012, The visceral surface is irregular, faces inferomedially towards the Skandalakis et al 1993). When the phrenicocolic ligament is being abdominal cavity and is marked by gastric, renal and colic impressions. divided, particularly when electrocautery is used, the colon is at risk The gastric impression faces anteromedially and is broad and concave of injury. where the spleen lies adjacent to the posterior aspect of the fundus, upper body and upper greater curvature of the stomach. It is separated Mobile spleen The length of the peritoneal ligaments associated from the stomach by a peritoneal recess, limited by the gastrosplenic with the spleen vary; longer ligaments afford the spleen greater mobil- ligament. The renal impression is slightly concave and lies on the pos- ity, which can stretch its vascular pedicle. This facilitates surgical mobi- teroinferior part of the visceral surface, separated from the gastric lization but may render the spleen more susceptible to injury from impression above by a ridge of splenic tissue and the splenic hilum. It shear forces during trauma. faces inferomedially and slightly backwards, and is related to the upper A floating or wandering spleen is characterized by excessive mobility lateral area of the anterior surface of the left kidney and sometimes to and migration of the organ outside the left hypochondrium. In such the superior pole of the left suprarenal gland. The colic impression is cases, the spleen may undergo torsion or cause bladder or rectal symp- usually flat; it lies at the inferior pole of the spleen and is related to the toms from local pressure; imaging usually confirms the diagnosis (Fig. splenic flexure of the colon and the phrenicocolic ligament. The hilum 70.6). If surgical treatment is necessary, the spleen is freed from local

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Spleen 1189.e1 07 RETPAHC Operating on a normal-sized spleen is a relatively straightforward procedure for most surgeons. Mobilization of the spleen requires divi- sion of the phrenicocolic, gastrosplenic and phrenicosplenic ligaments. Undue traction on the phrenicocolic ligament during mobilization of the splenic flexure may tear the splenic capsule, causing bleeding (Merchea et al 2012). This is less likely if the phrenicocolic ligament is retracted laterally rather than inferiorly and medially (Merchea et al 2012). The anterosuperior border and anterior diaphragmatic surface of the spleen are often adherent to the greater omentum and care must be taken when retracting the latter. The diaphragmatic surface of the spleen is occasionally adherent to the peritoneum on the undersur- face of the diaphragm; these adhesions may follow inflammation of the spleen or be congenital in origin (Petroianu 2011, Skandalakis et al 1993).

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SPlEEn 1190 8 nOITCES A Phrenicosplenic ligament 1988, Liu et al 1996, Pandey et al 2004, Sylvester et al 1995). Almost always, the splenic artery arises from the coeliac trunk, in common with Outline of spleen the left gastric and common hepatic arteries. However, it may originate from the common hepatic artery or the left gastric artery, or rarely directly from the aorta either in isolation or as a splenomesenteric trunk (Cortés and Pellico 1988, García-Porrero and Lemes 1988, Liu et al 1996, Pandey et al 2004, Torres 1998, Trubel 1985). From its origin, the artery runs a little way inferiorly before turning Inferior diaphragmatic peritoneum to the left behind the stomach to run horizontally posterior to the upper border of the body and tail of the pancreas. Multiple loops or even coils Origin of splenorenal ligament of the artery appear above the superior border of the pancreas (McFee et al 1995, Pandey et al 2004). The splenic artery courses anterior to Posterior peritoneal layer of lesser sac the left kidney and left suprarenal gland, and runs in the splenorenal ligament behind or above the tail of the pancreas. In its course, it gives off numerous branches to the pancreas (dorsal pancreatic, greater pan- Splenocolic ligament creatic artery, and arteries to the tail) and, near its termination, it gives Phrenicocolic ligament off the short gastric arteries and the left gastroepiploic artery (Gürleyik et al 2000, Liu et al 1996, Mikhail et al 1979, Pandey et al 2004, Skan- Pancreaticocolic ligament dalakis et al 1993, Trubel et al 1985, Trubel et al 1988). Additional branches include a posterior gastric artery in 40% of individuals and small retroperitoneal branches. Lateral colonic The splenic artery varies between 8 and 32 cm in length and its peritoneal fold calibre usually exceeds that of the common hepatic and left gastric arteries, ranging from 3 to 12 mm. Splenic artery blood flow is approxi- mately 3 ml/sec/100 g, corresponding to approximately 7% of cardiac output (Cortés and Pellico 1988, García-Porrero and Lemes 1988, Nakamura et al 1989, Pandey et al 2004, Petroianu 2011, Skandalakis et al 1993, Torres 1998, Trubel et al 1985). B The splenic artery usually divides into two, or occasionally three, branches before entering the hilum of the spleen. The superior and inferior branches are sometimes known as superior and inferior polar arteries; as they enter the hilum they divide into four or five segmental arteries that each supply a segment of splenic tissue. There is relatively Anterior border of spleen little arterial collateral circulation between segments, which means that occlusion of a segmental vessel often leads to infarction of part of the spleen (Cortés and Pellico 1988, García-Porrero and Lemes 1988, Gupta et al 1976, Liu et al 1996, Mikhail et al 1979, Pandey et al 2004, Torres 1998, Trubel al 1985, Trubel et al 1988). Segmental arteries Gastrosplenic ligament divide within the splenic trabeculae and give rise to follicular arterioles, which are surrounded by a thick lymphoid sheath of white pulp. These Peritoneal reflection at splenic hilum feed the sinusoids of the red pulp. There is considerable communica- tion between arterioles (García-Porrero and Lemes 1988, Liu et al 1996, Mikhail et al 1979, Skandalakis et al 1993, Sow et al 1991, Trubel et al 1988). The superior pole of the spleen gains an additional arterial supply, distinct from the splenic hilar vessels, from the short gastric arteries in the gastrosplenic ligament. These vessels connect the superior pole of the spleen to the gastric fundus and preserve viability of this region of the spleen after ligation of the splenic pedicle (García-Porrero and Lemes 1988, Gürleyik et al 2000, Liu et al 1996, Petroianu 2011, Petroianu and Petroianu 1994, Petroianu et al 1989, Skandalakis et al 1993, Torres 1998, Trubel et al 1988). Veins Fig. 70.5 The peritoneal connections of the spleen. A, The posterior Blood from the parenchyma of the spleen is collected by trabecular peritoneal connections, seen as if the spleen has been removed, with the veins. They join to form segmental veins that drain individual splenic folds fixed in their ‘normal’ positions. B, The anterior peritoneal connections, segments. In general, there are no anastomoses between intrasegmental seen with the spleen in place, as if the stomach and greater omentum have venous tributaries. Segmental veins join to form two (superior and been removed, with the folds fixed in their ‘normal’ positions. (Adapted from inferior) or three (superior, middle and inferior) ‘lobar’ veins that Drake, RL, Vogl, AW, Mitchell, A (eds), Gray’s Anatomy for Students, 2nd ed, Elsevier, Churchill Livingstone. Copyright 2010.) emerge from the length of the splenic hilum and unite to form the splenic vein within the splenorenal ligament (see Fig. 70.2; Fig. 70.8). Communicating veins may interconnect lobar veins (DeLand 1970, Gupta et al 1980, Liu et al 1996, Par et al 1965, Sow et al 1991). adhesions and returned to the left hypochondrium, the surgeon short- The splenic vein runs medially below the splenic artery and posterior ening and suturing its ligaments to the diaphragm (McFee et al 1995, to the tail and body of the pancreas (see Fig. 69.4 D–G) (Gürleyik et al Petroianu 2011, Üngör et al 2007). 2000, Par et al 1965). It crosses the posterior abdominal wall anterior to the left kidney, renal hilum and abdominal aorta, separated from the left sympathetic trunk and left crus of the diaphragm by the left renal VASCULAR SUPPLY AND LYMPHATIC DRAINAGE vessels, and from the abdominal aorta by the superior mesenteric artery and left renal vein (Gupta et al 1976, Gupta et al 1980, Liu et al 1996, Arteries Par et al 1965). It ends posterior to the neck of the pancreas, where it joins the superior mesenteric vein to form the portal vein. Along its The spleen is supplied by the splenic artery, one of the most tortuous course it receives the short gastric veins, left gastroepiploic veins, retro- arteries in the body (Fig. 70.7). The pathophysiology of the tortuosity peritoneal veins (Retzius’s retroperitoneal venous plexus), pancreatic of this vessel, which may become more pronounced with advancing veins, posterior gastric vein, left gastric vein (occasionally) and the age, is not understood, although several theories have been proposed inferior mesenteric vein. Approximately 60% of portal vein blood flow (Borley et al 1995, Cortés and Pellico 1988, García-Porrero and Lemes is derived from the gut and the remainder from the spleen and pancreas

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Spleen 1190.e1 07 RETPAHC 2 7 1 55 6 4 S 33 33 A A 3 2 1 4 B Fig. 70.6 A mobile enlarged spleen located in the left side of the pelvis. A, A computed tomography (CT) scan showing the abnormal location of B an enlarged spleen (S). B, A surgical view of the same spleen, which appears congested due to partial obstruction of its venous drainage at the splenic hilum (arrow). Note the lack of restraining peritoneal ligaments. C Fig. 70.7 A, A three-dimensional reconstructed contrast-enhanced CT scan. Key: 1, spleen; 2, liver; 3, kidneys; 4, splenic vein; 5, superior polar vein; 6, portal vein; 7, aorta. B, A splenic digital subtraction arteriogram showing the splenic artery (1) and its branches. Note the primary division of the splenic artery (2) into superior (3) and inferior branches (4). C, An excised spleen demonstrating the hilar vessels.

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SPlEEn 1190.e2 8 nOITCES Portal vein Splenic vein Spleen A Superior mesenteric vein Portal vein Splenic vein B Fig. 70.8 A, A splenoportogram. B, An axial oblique CT slice showing the portal and splenic veins.

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Spleen 1191 07 RETPAHC (Dawson et al 1986, Gupta et al 1980, Gürleyik et al 2000, Liu et al Fibrous framework 1996, Oguro et al 1993, Par et al 1965). Obstruction to portal or splenic venous drainage leads to reversed The serosa of the peritoneum covers the entire spleen, except at its venous flow through the splenic vein and its tributaries, resulting in hilum and where the peritoneal ligaments are attached. The connective splenomegaly and widespread varices (Petroianu 1988, Petroianu 1992, tissue capsule, deep to the serosa, is approximately 1.5 mm thick and Petroianu 2011, Petroianu et al 1989, Re et al 1985, Skandalakis et al contains abundant type I collagen fibres and some elastin fibres. It is 1993). composed of an outer and inner lamina in which the directions of the collagen fibres differ, so increasing its strength. Numerous trabeculae Lymphatic drainage extend from the capsule into the substance of the spleen, where they branch to form a connective tissue scaffold (Faller 1985, Scothorne Lymphatic drainage begins in the white pulp. Lymphatics travel with 1985). The largest trabeculae enter at the hilum and divide into branches the blood vessels towards a lymphatic subcapsular plexus, which drains in the splenic pulp, providing conduits for the splenic vessels and nerves via larger lymphatic channels to lymph nodes at the splenic hilum and (see Fig. 70.10; Figs 70.11–70.12). Within the spleen, these branches around the tail of the pancreas (Fig. 70.9). From here, lymph drains to become continuous with a delicate network of type III (reticular) col- suprapancreatic, infrapancreatic and omental lymph nodes, and from lagen fibres that pervades both red and white pulps and is maintained there to coeliac nodes and the cisterna chyli. by fibroblasts within its interstices (Gupta et al 1976, Krieken and Velde 1988, Scothorne 1985). INNERVATION White pulp The spleen is innervated by both components of the autonomic nervous In an adult, white pulp accounts for between 5% and 20% of the splenic system; the sympathetic supply is dominant. Postganglionic sympa- tissue. Branches of the splenic artery radiate out into the parenchyma thetic nerves from the coeliac plexus and parasympathetic nerves from of the spleen from the hilum, ramifying within trabeculae. In their the vagal trunks travel with the splenic vessels (see Fig. 70.9). Sympa- terminal few millimetres, their connective tissue adventitia is replaced thetic fibres innervate arteries at least to the trabecular level and have by a sheath of T lymphocytes, the peri-arteriolar lymphatic sheath the potential to influence blood flow within the human spleen (Kudoh (PALS). This is expanded in places by aggregations of B lymphocytes, et al 1979). Unlike in some animals, the motor innervation of the lymphoid follicles measuring 0.25–1 mm in diameter and visible to the human splenic capsule is largely vestigial; it contains minimal quanti- naked eye on the freshly cut surface of the spleen as white semi-opaque ties of smooth muscle and therefore does not contract. In contrast, the dots, in contrast to the surrounding deep reddish purple of the red pulp. capsule and parenchyma are innervated by sensory fibres that convey Follicles are usually situated near the terminal branches of arterioles pain. Mild to moderate splenomegaly is often painless but splenic and typically protrude to one side of a vessel, which consequently inflammation from infection, infarction (e.g. sickle cell disease, emboli- appears eccentrically placed within the follicle. Arterioles branch later- zation) or abrupt distension of the capsule (e.g. haematoma) may cause ally within follicles to form a series of parallel terminal arterioles, peni- severe pain, intensified by inflammation of the overlying parietal peri- cillar arterioles (Krieken and Velde 1988, Scothorne 1985; see Figs toneum. Referred pain from the splenic pulp is poorly localized to the 70.10–70.12). epigastrium (Petroianu 2011). Like peri-arteriolar sheaths, follicles are centres of lymphocyte aggre- gation and proliferation. After antigenic stimulation, they become sites MICROSTRUCTURE of intensive B-cell proliferation, developing germinal centres similar to those found in lymph nodes; antigen presentation by follicular den- dritic cells is involved in this process. Germinal centres regress when The spleen contains the largest single mass of lymphoid tissue in the the stimulus abates. Follicles tend to atrophy with advancing age and body in direct continuity with the circulation. Splenic parenchyma may be absent in the very elderly (Krieken and Velde 1988, Petroianu is divided into two principal regions – white pulp and red pulp – 2011, Scothorne 1985; see Figs 70.10–70.12). named according to the appearance of the cut surface of a fresh spleen (Fig. 70.10). Red pulp The red pulp constitutes up to 90% of the total splenic volume and is a unique filtration device that enables the spleen to clear particulate material from the blood as it perfuses the organ (Krieken and Velde T 1988, Petroianu 2011, Scothorne 1985; see Fig. 70.11). It contains large numbers of venous sinusoids that ultimately drain into tributaries of the splenic vein. The sinusoids are separated from each other by a C fibrocellular network of small bundles of collagen fibres, the reticulum, numerous reticular fibroblasts and splenic macrophages. Seen in two dimensions, these intersinusoidal regions appear as strips of tissue, the W splenic cords (see Figs 70.11–70.12), whereas in reality they form a three-dimensional continuum around the venous spaces (Chen 1978, Krieken and Velde 1988, Scothorne 1985, Weiss 1983). Venous sinusoids are elongated ovoid vessels, approximately 50 µm R in diameter, supported externally by circumferential and longitudinal reticular fibres (Krieken and Velde 1988, Scothorne 1985, Weiss 1983), and lined by a characteristic, discontinuous endothelium that is unique T T to the spleen. The long, narrow endothelial cells are aligned with the long axis of the sinusoid; they are also called stave cells because they W resemble the planks in a barrel (see Fig. 70.12). Stave cells are attached to their neighbours at intervals along their length by short stretches of intercellular junctions that alternate with intercellular slits that allow T blood cells to squeeze into the lumen of the sinusoid from the sur- rounding splenic cords. A discontinuous basal lamina is present on the abluminal aspect of the sinus. Large, stellate fibroblasts – reticular cells – lie around the sinusoids. They synthesize the matrix components of the reticulum, including Fig. 70.10 A section through the spleen. White pulp (W) is present as ovoid areas of basophilic tissue. Red pulp (R) lies between white pulp collagen and proteoglycans, and their cytoplasmic processes help to tissue and consists of splenic sinusoids and intervening cellular cords. compartmentalize the reticular space. Blood from the open ends of the Part of the capsule (C) is seen top right, from which trabeculae (T) capillaries that originate from penicillar arterioles percolates through extend into the splenic tissue. (Courtesy of Mr Peter Helliwell and the reticular spaces within the splenic cords. Macrophages in the spaces the late Dr Joseph Mathew, Department of Histopathology, Royal remove blood-borne particulate material, including ageing and damaged Cornwall Hospitals Trust, UK.) erythrocytes. If the number of damaged erythrocytes increases, the

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Spleen 1191.e1 07 RETPAHC Gastrosplenic ligament Short gastric vessels Superior polar vessel Phrenicosplenic ligament Spleen Left gastric artery Lymph nodes of the splenic hilum Posterior vagal trunk Segmental artery Sympathetic nerves Segmental vein Common Division of the hepatic artery splenic artery Portal vein Inferior polar vessels Splenic artery Splenic vein Inferior mesenteric vein Phrenicocolic ligament Superior mesenteric vein Fig. 70.9 The lymph nodes related to the spleen. The pancreas has been rendered partially transparent to visualize the major blood vessels lying posteriorly. The greater curvature of the stomach has been reflected superiorly to expose its posterior surface and the peritoneal lining of the posterior wall of the lesser sac removed. (Courtesy of Dr Andy Petroianu and Dr Iriam Starling.) In malignant neoplasms of the greater curvature of the stomach, distal pancreas or distal transverse colon, it may be necessary to remove the spleen and tail of the pancreas to achieve a radical resection. In leukaemias and lymphomas, lymphadenopathy of splenic hilar nodes may be found along with splenomegaly during staging investigations (Petroianu 2011).

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SPlEEn 1192 8 nOITCES A B C D Fig. 70.11 The microstructure of the spleen (haematoxylin and eosin staining). A, Red pulp covered by the splenic capsule (arrow). B, Trabeculae (arrows) inside the red pulp. Trabecular arterioles (1) and venules (2), containing erythrocytes, are also shown. C, Red pulp (1), marginal or perifollicular zone (2), and white pulp (3) containing a follicular arteriole surrounded by a peri-arteriolar lymphatic sheath (arrow). D, Red pulp containing several sinusoid capillaries (*) with discontinuous endothelial cells and surrounded by macrophages containing phagocytosed particles within their cytoplasm (arrows). Capsule Venous drainage Sinusoids in red pulp Trabeculae Closed circulation Open circulation Stave cell Reticular fibres White pulp Fig. 70.12 The main features of splenic structure, not to scale. The capsule, trabeculae, reticular fibres and cells, the perivascular lymphoid sheaths and follicles (white pulp), and the cellular cords and venous sinusoids of the red pulp are shown. The ‘open’ and ‘closed’ theories of splenic circulation are illustrated; it is likely that most of the circulation is of the open form. The venous sinusoids are lined by specialized endothelial ‘stave’ cells; the intercellular gaps of these have been over-emphasized for clarity.

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1193 07 RETPAHC Key references reticular cells proliferate and the red pulp expands, causing the spleen removing abnormal and effete cells, blood cell particles, bacteria, para- to enlarge (Kudoh et al 1979, Scothorne 1985). sites and foreign antigens. Perifollicular zone IMAGING The perifollicular (marginal) zone lies at the interface between the white and red pulp; it is the site where blood is delivered into the red Available with the Gray’s Anatomy e-book pulp and where many lymphocytes leave the circulation to migrate to their respective T- and B-lymphocyte aggregations in the white pulp. These lymphocytes are more loosely arranged than they are in the white SPLENOMEGALY pulp, and are held in a dense network of reticular fibres and cells. The arterioles leaving the white pulp are also surrounded by a small aggrega- tion of macrophages: the peri-arteriolar macrophage sheath (Krieken Available with the Gray’s Anatomy e-book and Velde 1988, Petroianu 2011, Scothorne 1985; see Fig. 70.11C). Splenic microcirculation SPLENIC TRAUMA Segmental splenic arteries ramify in the trabeculae (trabecular arteries) The spleen is one of the most frequently damaged organs in blunt before tapering to become arterioles that pass through the white pulp abdominal trauma (Table 70.2, Fig. 70.15). It is particularly prone to and give off penicillar arterioles (García-Porrero and Lemes 1988, injury during rapid deceleration or compression, and its peritoneal liga- Gupta et al 1976, Scothorne 1985). These exit the white pulp and ments render it vulnerable to shearing injuries of the parenchyma and traverse the perifollicular marginal zone before entering the red pulp. splenic vessels. Fractures of the lower left ribs may be associated with Evidence supports a dominantly ‘open’ circulation in humans, in which blunt injuries (Buntain et al 1988). Traction on peritoneal ligaments or blood empties into and percolates slowly through the reticular tissue adhesions may lead to inadvertent capsular tears during surgical proce- of the splenic cords before re-entering the vascular lumen through slits dures such as splenic flexure mobilization. There is insufficient evidence in the walls of the venous sinusoids (Cavalli et al 1982, Chen 1978; see to know whether enlarged spleens are at a significantly greater risk of Fig. 70.12). From the venous sinusoids, blood collects in venules that trauma (Skandalakis et al 1993), but this is frequently postulated. unite to form small veins that run within the trabeculae and drain into segmental splenic veins (Cavalli et al 1982, Chen 1978, Petroianu 2011, Scothorne 1985). Some blood probably takes an alternative, ‘closed’ SPLENECTOMY route and enters the venous sinusoids directly from arterioles and capil- laries in the marginal zone. Either way, the blood is exposed to macro- Available with the Gray’s Anatomy e-book phages and the filtering mechanism of the spleen responsible for Bonus e-book images Fig. 70.1 A supernumerary spleen located in Fig. 70.8 A, A splenoportogram. B, An axial Fig. 70.15 Splenic trauma. A, A CT scan the greater omentum. oblique CT slice showing the portal and showing multiple splenic tears. B, Suture splenic veins. repair of a ruptured spleen. C, Complete Fig. 70.6 A mobile enlarged spleen located splenic rupture. D, Subtotal splenectomy in the left side of the pelvis. A, A computed Fig. 70.9 The lymph nodes related to the after treatment of the patient illustrated tomography (CT) scan showing the spleen. in C. abnormal location of an enlarged spleen. B, A surgical view of the same spleen, Fig. 70.13 Splenic imaging. A, An ultrasound Fig. 70.16 Partial splenectomy and which appears congested due to partial scan with colour Doppler. B, A magnetic autotransplantation. A, Partial splenectomy obstruction of its venous drainage at the resonance scan. C, A radioisotope scan preserving the superior pole supplied by the splenic hilum. (99mTc sulphur colloid). short gastric vessels. B, Partial splenectomy preserving the inferior pole supplied by the Fig. 70.7 A, A three-dimensional Fig. 70.14 Examples of different pathologies left gastroepiploic vessels. C, A splenic reconstructed contrast-enhanced CT scan. causing splenomegaly. A, Portal segment removed after total splenectomy B, A splenic digital subtraction arteriogram hypertension. B, Gaucher’s disease. and sliced into 1–2 cm cubes. D, The showing the splenic artery and its branches. C, Myelofibrosis. D, Thalassaemia. same slices in C sutured on to the greater C, An excised spleen demonstrating the E, Sarcoma. F, Lymphoma. omentum. hilar vessels. KEY REFERENCES Coetzee T 1982 Clinical anatomy and physiology of the spleen. South Afr Skandalakis PN, Colborn GL, Skandalakis LJ et al 1993 The surgical anatomy Med J 61:737–46. of the spleen. Surg Clin North Am 73:747–68. A classic reference paper on splenic anatomy and physiology. One of the most complete descriptions of splenic anatomy. García-Porrero JA, Lemes A 1988 Arterial segmentation and subsegmenta- Sylvester PA, Stewart R, Ellis H 1995 Tortuosity of the human splenic artery. tion in the human spleen. Acta Anat 131:276–83. Clin Anat 8:214–18. A detailed description of the relation between the arterial distribution and A description of the tortuosity of the splenic artery, demonstrating its spleen segmentation. importance in anatomical and surgical approaches. Liu DL, Xia S, Xu W et al 1996 Anatomy of vasculature of 850 spleen speci- mens and its application in partial splenectomy. Surgery 119:27–33. A detailed description of the vascular anatomy of the spleen and its role in surgical procedures on the spleen.

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Spleen 1193.e1 07 RETPAHC Imaging demonstrates the gross morphology and vascular supply of the spleen, and can also be used to assess splenic function. Imaging modali- ties include ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), arteriography, splenoportography and scin- tigraphy (Buntain et al 1988, Merran et al 2007, Nakamura et al 1989, Spleen Xu et al 2009; see Figs 70.7–70.8; Fig. 70.13). Cross-sectional imaging is particularly useful for assessing tumours and infiltrations of the spleen. Percutaneous drainage of splenic and perisplenic fluid collec- tions is routinely performed under image guidance, and percutaneous splenic biopsy is being increasingly utilized in diagnosis. Arteriography Splenic is essential for selective embolization and the insertion of an arterial artery stent to treat splenic artery aneurysm. Scintigraphy can be used to investigate splenic phagocytic function by quantifying the uptake of radioactive labelled agents (e.g. 99mtechnetium sulphur colloid or heat- damaged erythrocytes) (Hermann and Winkel 1977, Merran et al 2007, Splenic Petroianu 2011, Xu et al 2009). vein The numerous causes of splenomegaly may broadly be classified into haematological (e.g. lymphoproliferative, myeloproliferative, erythro- A cyte disorders); vascular (e.g. portal hypertension); infectious (e.g. viral, bacterial, other); autoimmune; and infiltrative (e.g. storage disorders and tumours) (Cavalli et al 1982, Petroianu 1988, Petroianu 2011, Re et al 1985; Fig. 70.14). Contrast-enhanced CT imaging is particularly useful in the assess- Thoracic aorta ment of splenic trauma. The majority of splenic injuries from blunt abdominal trauma are successfully treated by conservative manage- Liver ment. Extensive burst injuries with persistent bleeding or major injuries to the hilar vessels may require splenectomy but various repair tech- niques are available. With hilar injuries, a subtotal splenectomy, pre- Spleen serving the short gastric vessels and superior pole only, is one option. Minor intraoperative capsular tears may be controlled by the topical Kidneys application of haemostatic agents and sutures, although direct suture repair is challenging because the splenic pulp is fragile. Arteriography and embolization are additional techniques that can be used to control bleeding or treat vascular lesions (Petroianu 2011). Most surgical procedures performed on the spleen should start with ligation of the splenic artery at the superior border of the pancreatic B tail. This can be difficult in patients with portal hypertension, splenic artery aneurysm, retroperitoneal fibrosis, regional lymphadenopathy or inflammatory conditions. After splenic artery ligation, the spleen becomes softer because most of its contained blood returns to the cir- culation. Despite the interruption of splenic artery inflow, the superior pole of the spleen continues to be perfused by the short gastric arteries, and the inferior pole may be supplied retrogradely via the left gastroepi- ploic artery. Ligation and division of the splenic vein should be the last step before removal of the spleen to maximize autotransfusion of blood from the spleen (Liu et al 1996, Petroianu 2011, Petroianu and Petroi- anu 1994, Petroianu et al 1989, Skandalakis et al 1993, Sow et al 1991). In partial or subtotal splenectomy, the vessels that supply the part Liver of the spleen to be removed are ligated and divided close to the organ. The devascularized region turns dark blue, demarcating it from the Spleen residual viable splenic tissue; the organ is then divided in this plane (Christo and DiDio 1997, Gürleyik et al 2000, Liu et al 1996, Petroianu and Petroianu 1994, Sow et al 1991). Wedge excision leaves two flaps of splenic capsule that can be sutured or stapled to cover the remaining raw parenchyma, after suture of any visible bleeding vessels (Petroianu 2011, Petroianu 1993, Petroianu et al 1989, Petroianu 1988; Fig. 70.16). If total splenectomy is required to treat splenic trauma, autotrans- plantation of splenic tissue into the greater omentum or mesentery of the bowel can preserve useful splenic function (see Fig. 70.16). Approxi- C mately 20% of the original splenic mass needs to be transplanted and venous drainage of this tissue must be to the portal venous system to Fig. 70.13 Splenic imaging. A, An ultrasound scan with colour Doppler. maintain the metabolic and immunological functions of the splenic B, A magnetic resonance scan. C, A radioisotope scan (99mTc sulphur tissue (Oguro et al 1993, Petroianu 2011). colloid). Contrast-enhanced CT imaging, digital subtraction angiography Total splenectomy has numerous potential consequences. Intraop- and a splenoportogram are shown in Figures 70.7–70.8. eratively, bleeding or damage to the pancreas, stomach or colon may occur. Early postoperative complications include left-sided basal pul- monary atelectasis and pleural effusion, subphrenic abscess, transient leukocytosis and thrombocytosis with the risk of thrombotic complica- Table 70.2 Buntain’s classification of splenic injury tions. In the longer term, there is an increased risk of infection (espe- cially from encapsulated bacteria), which may be fatal (Petroianu 2011). Grade Description of injury Conservative management of splenic trauma and partial splenec- Grade I Subcapsular haematoma or localized capsular disruption without significant tomy now enable splenic function to be preserved in situations where injury to the parenchyma splenectomy would once have been routinely performed. Furthermore, Grade II Single or multiple capsular and parenchymal disruptions that do not involve most surgical procedures on the spleen can now be performed laparo- the hilar vessels scopically, which readily affords inspection of the spleen from all per- Grade III Deep fractures in the hilum involving the vessels spectives (Poulin and Thibaut 1993, Sow et al 1991). Grade IV Shattered or fragmented spleen or hilar avulsion (Reproduced from Buntain WL, Gould HR, Maull KI. Predictability of splenic salvage by computed tomography. J Trauma. 1988; 28:24–34.)

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SPlEEn 1193.e2 8 nOITCES A B C D E F Fig. 70.14 Examples of different pathologies causing splenomegaly. A, Portal hypertension. B, Gaucher’s disease. C, Myelofibrosis. D, Thalassaemia. E, Sarcoma. F, Lymphoma.

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Spleen 1193.e3 07 RETPAHC A B Tear C D Fig. 70.15 Splenic trauma. A, A CT scan showing multiple splenic tears. B, Suture repair of a ruptured spleen. C, Complete splenic rupture. The splenic hilum has been clamped to control bleeding. D, Subtotal splenectomy after treatment of the patient illustrated in C. A B C D Fig. 70.16 Partial splenectomy and autotransplantation. A, Partial splenectomy preserving the superior pole supplied by the short gastric (‘splenogastric’) vessels (arrow). B, Partial splenectomy preserving the inferior pole supplied by the left gastroepiploic vessels (arrow). C, A splenic segment removed after total splenectomy and sliced into 1–2 cm cubes. D, The same slices in C sutured on to the greater omentum.

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SPlEEn 1193.e4 8 nOITCES REFERENCES Borley NR, Mc Farlane JM, Ellis H 1995 A comparative study of the tortuos- Nakamura T, Moriyasu F, Ban N et al 1989 Quantitative measurement of ity of the splenic artery. Clin Anat 8:219–21. abdominal arterial blood flow using image-directed Doppler ultra- Buntain WL, Gould HR, Maull KI 1988 Predictability of splenic salvage by sonography. J Clin Ultrasound 17:261–8. computed tomography. J Trauma 28:24–34. Oguro A, Taniguchi H, Koyama H et al 1993 Relationship between liver Cavalli G, Re G, Casali AM et al 1982 The microvascular architecture of function and splenic blood flow. Ann Nucl Med 7:251–5. spleen in congestive splenomegaly. Pathol Res Pract 174:131–46. Pandey SK, Bhattacharya S, Mishra RN et al 2004 Anatomical variations of Chen L-T 1978 Microcirculation of the spleen. Science 201:157–9. the splenic artery and its clinical implications. Clin Anat 17:497–502. Christo MC, DiDio LJ 1997 Anatomical and surgical aspects of splenic Par MM, Barry P, Autissier JM et al 1965 Considérations sur la morphologie segmentectomies. Ann Anat 179:461–74. de la veine splénique et de ses affluents. Soc Nac Med 1:539–47. Coetzee T 1982 Clinical anatomy and physiology of the spleen. South Afr Petroianu A 1988 Treatment of portal hypertension by subtotal splenectomy Med J 61:737–46. and central splenorenal shunt. Postgrad Med J 64:38–41. A classic reference paper on splenic anatomy and physiology. Petroianu A 1993 Subtotal splenectomy and portal variceal disconnection in the treatment of portal hypertension. Can J Surg 36:251–4. Coquet B, Sandoz B, Savoie PH et al 2010 Anthropometric characterization of spleen in children. Surg Radiol Anat 32:25–30. Petroianu A 1996 Subtotal splenectomy in Gaucher’s disease. Eur J Surg 162:511–13. Cortés JA, Pellico LG 1988 Arterial segmentation in the spleen. Surg Radiol Anat 10:323–32. Petroianu A 2003 Subtotal splenectomy for treatment of retarded growth and sexual development associated with splenomegaly. Minerva Chir Dawson DL, Molina ME, Conner CES 1986 Venous segmentation of the 58:413–14. human spleen. Am Surg 52:253–6. Petroianu A 2011 The Spleen. London: Bentham Science. DeLand FH 1970 Normal spleen size. Radiology 97:589–92. Petroianu A, Ferreira VL, Barbosa AJA 1989 Morphology and viability of the Faller A 1985 Splenic architecture reflected in the connective tissue structure spleen after subtotal splenectomy. Braz J Med Biol Res 22:491–5. of the human spleen. Experientia 41:164–7. Petroianu A, Petroianu S 1994 Anatomy of gastrosplenic vessels in patients García-Porrero JA, Lemes A 1988 Arterial segmentation and subsegmenta- with schistosomal portal hypertension. Clin Anat 7:80–3. tion in the human spleen. Acta Anat 131:276–83. A detailed description of the relation between the arterial distribution and Petroianu A, Simal CJR, Barbosa AJA 1992 Impairment of phagocytosis by spleen segmentation. mammalian splenic macrophages by 99mTc sulphur colloid. Med Sci Res 20:847–9. Gupta CD, Gupta SC, Arora AK et al 1976 Vascular segments in the human Poulin EC, Thibaut C 1993 The anatomical basis for laparoscopic splenec- spleen. J Anat 121:613–16. tomy. Can J Surg 36:484–8. Gupta SB, Gupta SC, Gupta CD 1980 Venous segments in the human spleen. Re G, Casali A, Cavalli D et al 1985 Morphological bases of splenic circula- Indian J Med Res 72:465–9. tion in congestive splenomegaly. Haematologica 70:283–90. Gürleyik E, Gürleyik G, Bingöl K et al 2000 Perfusion and functional Scothorne RJ 1985 The spleen. Histopathology 9:663–9. anatomy of the splenic remnant supplied by short gastric vessels. Excerpta Med 179:490–3. Skandalakis PN, Colborn GL, Skandalakis LJ et al 1993 The surgical anatomy of the spleen. Surg Clin North Am 73:747–68. Hermann HJ, Winkel K 1977 Scintigraphy of the spleen. Lymphology One of the most complete descriptions of splenic anatomy. 10:115–19. Jakobsen SS, Jakobsen US 1997 The weight of normal spleen. Forensic Sci Sow ML, Dia A, Ouedraogo T 1991 Anatomic basis for conservative surgery Int 88:215–23. of the spleen. Surg Radiol Anat 13:81–7. Krieken JH, Velde J 1988 Normal histology of the human spleen. Am J Surg Sylvester PA, Stewart R, Ellis H 1995 Tortuosity of the human splenic artery. Pathol 12:777–85. Clin Anat 8:214–18. A description of the tortuosity of the splenic artery, demonstrating its Kudoh G, Hoshi K, Murakami T 1979 Fluorescence microscopic and enzyme importance in anatomical and surgical approaches. histochemical studies of the innervation of the human spleen. Arch Histol Jpn 42:169–80. Tarantino G, Scalera A, Finelli C 2013 Liver-spleen axis: intersection between Liu DL, Xia S, Xu W et al 1996 Anatomy of vasculature of 850 spleen speci- immunity, infections and metabolism. World J Gastroenterol 19: mens and its application in partial splenectomy. Surgery 119:27–33. 3534–42. A detailed description of the vascular anatomy of the spleen and its role in Torres RR 1998 The true splenic blood supply and its surgical applications. surgical procedures on the spleen. Hepato-Gastroent 45:885–8. McFee RB, Musacchio T, Gorgescu D et al 1995 Wandering spleen with Trubel W, Turkof, E, Rokitansky A et al 1985 Incidence, anatomy and ter- torsion in a geriatric patient. Dig Dis Sci 40:2656–9. ritories supplied by the posterior gastric artery. Acta Anat 124:26–30. Merchea A, Dozois EJ, Wang JK et al 2012 Anatomic mechanisms for splenic Trubel W, Rokitansky A, Turkof, E et al 1988 Correlations between posterior injury during colorectal surgery. Clin Anat 25:212–17. gastric artery and superior polar artery in human anatomy. Anat Anz 167:219–23. Merran S, Cohen PK, Servois V 2007 Scanographie de la rate: anatomie normale, variantes et pièges. J Radiol 88:549–58. Üngör B, Malas MA, Sulak O et al 2007 Development of spleen during fetal period. Surg Radiol Anat 29:543–50. Mikhail Y, Kamel R, Nawar NN et al 1979 Observations on the mode of termination and parenchymal distribution of the splenic artery with Weiss L 1983 The red pulp of the spleen. Clin Haematol 12:375–93. evidence of splenic lobation and segmentation. J Anat 128:253–8. Xu WL, Li SL, Wang Y et al 2009 Role of color Doppler flow imaging Mirjalili SA, McFadden SL, Buckenham T et al 2012 A reappraisal of adult in applicable anatomy of spleen vessels. World J Gastroenterol 15: abdominal surface anatomy. Clin Anat 25:844–50. 607–11.

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CHAPTER 71 Suprarenal (adrenal) gland The suprarenal (adrenal) glands lie immediately superior and slightly shape, flattened in the anteroposterior plane and marginally larger than anterior to the upper pole of each kidney (see Figs 74.5, 62.8). Golden the right. The bulk of the right suprarenal sits on the apex of the right yellow in colour, each gland possesses two functionally and structurally kidney and usually lies slightly higher than the left gland, which lies distinct areas: an outer cortex and an inner medulla. The glands are on the anteromedial aspect of the upper pole of the left kidney. surrounded by perinephric fat enclosed within the renal fascia, and At birth, the glands are proportionately larger and are approximately separated from the kidneys by a small amount of fibrous tissue. one-third the size of the ipsilateral kidney. The cortex of each gland is The dimensions of the suprarenal glands in adults in vivo have been expanded by a well-developed ‘fetal zone’, responsible for producing measured from axial computed tomography (CT) scans (Vincent et al dehydroepiandrosterone (DHEA), the substrate for placental oestrogen, 1994). The mean maximum width of the body of the suprarenal gland in the fetus. The suprarenal cortex (specifically the fetal zone) reduces is 61 mm (right) and 79 mm (left), and the mean width of each limb in size immediately after birth and the medulla grows comparatively of the gland (medial and lateral) is approximately 30 mm. No indi- little. By the end of the second postnatal month, the weight of the vidual suprarenal limb should measure more than 5 mm in transverse suprarenal has reduced by more than 50%. The glands begin to grow section. In adults, each suprarenal gland weighs approximately 5 g (the again by the end of the second year and regain their weight at birth by medulla contributes about one-tenth of the total weight) and has a puberty. There is little further weight increase in adult life. volume of approximately 3–6 cm3 (Wang et al 2013). Small accessory suprarenal nodules, composed mainly of cortical The glands are macroscopically slightly different in external appear- tissue (also known as ‘adrenal rests’), may occur in the areolar tissue ance (Fig. 71.1). The right is pyramidal in shape and has two well- near the suprarenal glands. They are also occasionally found in the developed lower projections (limbs), giving a cross-sectional appearance spermatic cord, epididymis or testis in boys (Altin et al 1992), and similar to a three-pointed star. The left gland is more semilunar in ovary or broad ligament of the uterus in girls. Ectopic suprarenal tissue may cause diagnostic confusion and is rarely the site of neoplastic change. A Area related to stomach RIGHT SUPRARENAL GLAND The right suprarenal gland lies posterior to the inferior vena cava, sepa- rated from it by only a thin layer of fascia and connective tissue. It also Suprarenal vein lies posterior to the right lobe of the liver and anterior to the right crus Hepatic area of the diaphragm and superior pole of the right kidney (Fig. 71.2). Its inferior surface or base overlaps the anterosuperior aspect of the upper pole of the right kidney, with the two lower projections (limbs) of the gland straddling the renal tissue. The anterior surface has two distinct facets: a narrow medial facet that lies posterior to the inferior vena cava, and a triangular lateral facet that lies in contact with the bare area of Area the liver. The lowest part of the anterior surface may be covered by the related to pancreas peritoneal reflection of the inferior layer of the coronary ligament, Area related to which also represents the upper recess of the hepatorenal pouch (see inferior vena cava Fig. 63.2). Here, the gland lies posterior to the lateral border of the Suprarenal vein second part of the duodenum. Below the apex, near the anterior border of the gland, the right suprarenal vein emerges from the hilum to join the inferior vena cava. This vein is short, which makes surgical resection Right Left of the gland or mobilization of the inferior vena cava potentially haz- ardous. It may be inadvertently avulsed from the inferior vena cava B during surgery or, occasionally, by high-energy deceleration injuries. The posterior surface of the gland is divided into upper and lower areas by a curved transverse ridge. The large upper area is slightly convex and abuts the diaphragm, whereas the small lower area is concave and lies in contact with the superior aspect of the upper pole of the right kidney. Area The medial border of the gland is thin and lies lateral to the right coeliac related to ganglion and the right inferior phrenic artery where the artery runs over diaphragm the right crus of the diaphragm. LEFT SUPRARENAL GLAND The left suprarenal gland is closely applied to the left crus of the dia- phragm, separated from it by a thin layer of fascia (see Fig. 71.2). The medial aspect is convex longitudinally, whereas the lateral aspect is concave because it is moulded by the medial surface of the upper pole Area related to Area related Suprarenal vein of the left kidney. The superior border is sharply defined while the right kidney to left kidney inferior surface is more rounded. The upper part of the anterior surface is covered by the peritoneum of the posterior wall of the lesser sac, Right Left which separates it from the stomach and sometimes from the postero- 1194 Fig. 71.1 The suprarenal glands. A, Anterior aspect. B, Posterior aspect. inferior border of the spleen. A small lower part of the anterior surface

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Suprarenal (adrenal) gland 1195 17 RETPAHC Right lobe of liver Inferior vena Left crus of Pancreas Inferior phrenic arteries cava diaphragm Superior suprarenal arteries Right suprarenal gland Left suprarenal gland A Left kidney Right suprarenal Right crus of Left suprarenal Left kidney gland diaphragm gland Inferior vena cava Inferior suprarenal artery Right kidney Middle suprarenal artery Abdominal aorta Liver Right kidney Right suprarenal Left suprarenal Left kidney gland gland Fig. 71.3 The arterial supply and venous drainage of the suprarenal glands. (With permission from Drake RL, Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd ed, Elsevier, Churchill Livingstone. Copyright 2010.) the capsule before penetrating the gland to form a subcapsular arterial plexus, from which fenestrated sinusoids pass around clustered glomer- ulosa cells and between the columns in the zona fasciculata to a deep plexus in the zona reticularis. Venules from this plexus pass between medullary chromaffin cells to medullary veins, which they enter between prominent bundles of smooth muscle fibres. Some relatively large arteries bypass this indirect route and pass directly to the medulla (Fig. 71.4). The arterial supply of the suprarenal gland is prone to considerable variation (Manso and DiDio 2000, Dutta 2010); only the main variants will be described here. Superior suprarenal arteries The superior suprarenal artery usually arises from the ipsilateral inferior phrenic artery and passes to the gland as four or five small branches; it may occasionally arise from the abdominal aorta. Middle suprarenal arteries The middle suprarenal artery is usually single, but may be multiple or absent. It often arises from the lateral aspect of the abdominal aorta at around the level of the superior mesenteric artery and ascends slightly over the crura of the diaphragm to anastomose with the other suprar- enal arteries on the surface of the gland. The right middle suprarenal B artery passes behind the inferior vena cava close to the right coeliac ganglion, whereas the left middle suprarenal artery passes close to the Fig. 71.2 Magnetic resonance imaging (MRI) of the suprarenal glands. A, left coeliac ganglion, splenic artery and the superior border of the pan- Axial T1 weighted MRI. B, Coronal T2 weighted MRI. (Courtesy of Dr creas. The middle suprarenal artery may originate from either the ipsi- Louise Moore, Chelsea & Westminster Hospital.) lateral inferior phrenic or renal artery. Inferior suprarenal arteries is not covered by peritoneum and lies adjacent to the pancreas and The inferior suprarenal arteries often contribute most of the arterial splenic artery. The hilum faces inferiorly from the lower part of the supply to the gland. One or two arteries usually arise from the ipsilateral medial aspect. The left suprarenal vein emerges from the hilum and renal artery, but the inferior suprarenal arteries may originate from runs inferomedially to join the left renal vein. The posterior surface of either the abdominal aorta or the ipsilateral gonadal artery. the gland is divided by a ridge into a lateral area adjoining the kidney and a smaller medial area that lies in contact with the left crus of the Veins diaphragm. The medial border lies lateral to the left coeliac ganglion Medullary veins emerge from the hilum to form a suprarenal vein, and the left inferior phrenic and left gastric arteries, which ascend on which is usually single. The right vein is very short, and passes directly the left crus of the diaphragm. and horizontally into the posterior aspect of the inferior vena cava. An accessory right suprarenal vein is occasionally present and runs from the hilum superomedially to join the inferior vena cava above the right VASCULAR SUPPLY AND LYMPHATIC DRAINAGE suprarenal vein. The short course renders the right suprarenal vein(s) vulnerable to injury or even avulsion from the inferior vena cava during Arteries surgery if undue traction is applied. The left suprarenal vein is longer The suprarenal glands have one of the highest arterial flow rates per and descends medially, anterolateral to the left coeliac ganglion, then gram of tissue (up to 5 ml/g/min) (Williams and Leggett 1989). Each passes posterior to the pancreatic body and usually drains into the left gland is supplied by superior, middle and inferior suprarenal arteries, renal vein; it may receive the left inferior phrenic vein (Loukas et al whose main branches may be multiple (Fig. 71.3). They ramify over 2005). Since the venous drainage from each gland is usually via a single

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SuPRAREnAl (AdREnAl) glAnd 1196 8 nOITCES Capsule Zona glomerulosa Zona Cortex Secretes: fasciculata Mineralo- Zona corticoids reticularis (including aldosterone) Medulla Capsular artery Capsule Secrete: Zona glomerulosa Glucocorticoids (including cortisone) Sex hormones (including dehydroepi- androsterone) Cortical sinusoid Zona fasciculata Preganglionic sympathetic terminal Zona Medullary reticularis arteriole Secretes: Adrenaline Medullary capillary Medulla Medullary Preganglionic sympathetic terminal vein Secretes: Noradrenaline Fig. 71.4 The gross sectional appearance, microstructure, vasculature and ultrastructure of the suprarenal gland. Brief functional summaries are included.

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Suprarenal (adrenal) gland 1197 17 RETPAHC C ZG Cx M ZF ZR Fig. 71.5 A cross-section through an adult suprarenal gland showing the cortex (Cx) and highly vascular medulla (M). The cortex is shown at higher magnification to demonstrate the outer capsule (C), the zona glomerulosa (ZG), zona fasciculata (ZF) and zona reticularis (ZR). The boundaries between zones are indistinct and variable. (Courtesy of Mr Peter Helliwell and the late Dr Joseph Mathew, Department of Histopathology, Royal Cornwall Hospitals Trust, UK.) vein, infarction of the gland is more likely to be caused by damage to sympathetic neurones). A smaller proportion of postganglionic sympa- a suprarenal vein than to one of the suprarenal arteries. thetic nerve fibres innervate cortical blood vessels. Other nerve fibres Understanding variant suprarenal venous anatomy is important to containing a variety of neurotransmitters have been identified within avoid bleeding during minimally invasive adrenalectomy, particularly the suprarenal cortex and may be involved in modulating steroid in patients with large tumours and phaeochromocytomas. Cadaver hormone secretion. The cell bodies of afferent nerve fibres arising in studies have shown little variation in suprarenal venous anatomy but the suprarenal medulla are almost all located in dorsal root ganglia, suggest that variants are more commonly found on the right (Cesme- although some lie in vagal ganglia; their precise function is unknown basi et al 2014). However, a small clinical series showed that there may (Mravec 2005). be a higher rate of suprarenal vein variants in patients with phaeochro- mocytoma (Parnaby et al 2008). Anticipating variant suprarenal venous anatomy is key to minimiz- MICROSTRUCTURE ing bleeding during laparoscopic adrenalectomy, particularly in patients with large tumours or phaeochromocytomas. Sholten et al (2013) In section, the suprarenal gland has an outer cortex, which is yellowish reported variant suprarenal veins in 13% of individuals undergoing in colour and forms the main mass, and a thin medulla, forming about laparoscopic adrenalectomy, more often on the right (17%) than the one-tenth of the gland, which is dark red or greyish, depending on its left (9%). Common variants included an absent main suprarenal vein; content of blood (see Fig. 71.4; Fig. 71.5). The medulla is completely two or more suprarenal veins draining one side; and veins draining to enclosed by cortex, except at the hilum. The gland has a thick collagen- the inferior phrenic vein or, on the left, to the inferior vena cava. ous capsule from which trabeculae extend deep into the cortex. The capsule contains a rich arterial plexus (see above) that supplies branches Lymphatic drainage to the gland. Lymphatic channels within the capsule of the suprarenal gland com- municate with subserous lymphatics that drain medially to para-aortic Suprarenal cortex and paracaval nodes (Merklin 1966). A few capsular lymphatics com- municate with lymph vessels that pass through the diaphragm. The suprarenal cortex is composed of a zona glomerulosa, a zona fasci- culata and a zona reticularis (see Fig. 71.5). The outer, subcapsular, zona INNERVATION glomerulosa consists of a narrow region of small polyhedral cells arranged in rounded clusters. The cells have deeply staining nuclei and The suprarenal gland, relative to its size, has a greater autonomic supply a basophilic cytoplasm containing a few lipid droplets. Ultrastructur- than any other organ. The nerves are distributed throughout the gland: ally, their cytoplasm displays an abundant smooth endoplasmic reticu- around blood vessels (regulating blood flow), in the medulla (stimulat- lum that is typical of steroid-synthesizing cells. The broader, intermediate, ing the release of catecholamines from chromaffin cells), and in the zona fasciculata consists of large polyhedral basophilic cells arranged cortex (where they may influence steroid hormone production; Tóth in straight columns, two cells wide, separated by parallel fenestrated et al (1997)). A suprarenal plexus lies between the medial aspect of venous sinusoids. The cells contain many lipid droplets and large each gland and the coeliac and aorticorenal ganglia. It contains pre- amounts of smooth endoplasmic reticulum. The innermost part of the dominantly preganglionic sympathetic fibres that originate in the lower cortex, the zona reticularis, consists of branching interconnected thoracic spinal segments, reach the plexus via branches of the greater columns of rounded cells with cytoplasm containing smooth endoplas- splanchnic nerves, and synapse on clusters of large medullary chromaf- mic reticulum, numerous lysosomes and aggregates of brown lipofuscin fin cells (which can be regarded as homologous with postganglionic pigment that accumulate with age.

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SuPRAREnAl (AdREnAl) glAnd 1198 8 nOITCES Cortical cells produce several hormones, and the cells of the zonae tumour. For other tumours and disorders of the suprarenal gland fasciculata and reticularis are also rich in ascorbic acid. Cells in the zona requiring surgery, minimally invasive techniques are now generally pre- glomerulosa produce mineralocorticoids, e.g. aldosterone, which regu- ferred. The original laparoscopic approaches were described in 1992 lates electrolyte and water balance; cells in the zona fasciculata produce (transabdominal; Gagner et al 1992) and 1995 (posterior retroperito- hormones maintaining carbohydrate balance (glucocorticoids), e.g. cor- neal; Mercan et al 1995). The posterior approach is considered superior tisol (hydrocortisone); and cells in the zona reticularis produce sex on account of its safety, rapidity, avoidance of the peritoneal cavity, and hormones (progesterone, oestrogens and androgens). The suprarenal the ability to operate on both sides without repositioning the patient cortex is essential to life and its complete removal is lethal without (Morris and Perrier 2012). This has been confirmed in several large replacement therapy. It exerts considerable control over lymphocytes cohort studies (Walz et al 2006, Dickson et al 2011). and lymphoid tissue; an increased secretion of corticosteroids can result Nevertheless, conventional laparoscopy has certain disadvantages, in a marked reduction in lymphocyte numbers. such as a two-dimensional view, unstable camera platform, and rigid The deeper part of the zona fasciculata widens in pregnancy. Cortical instrumentation. Robotic surgery is a new and emerging technique now atrophy in elderly males is greatest in the same region. performed in many centres and offers the advantages of a three- dimensional stable platform, seven degrees of freedom, and enhanced Suprarenal medulla vision (Taskin and Berber 2013). During the last decade, experience with robotic adrenalectomy has highlighted several facets, including a steep learning curve, no significant reduction in the need to convert to The suprarenal medulla is composed of groups and columns of chro- an open procedure, operative complications or blood loss compared to maffin cells (phaeochromocytes), separated by wide venous sinusoids conventional laparoscopy, and longer operative times (although this and supported by a network of reticular fibres. Chromaffin cells, so decreases with experience). Robotic surgery is also more expensive. called from their colour reaction to dichromate fixatives, form part of However, with appropriate patient selection, robotic adrenalectomy can the neuroendocrine system and are functionally equivalent to postgan- be advantageous. For example, patients with familial suprarenal disor- glionic sympathetic neurones. They synthesize, store (as granules) and ders, who are more likely to have bilateral pathology, require cortical release the catecholamines noradrenaline (norepinephrine) and adren- sparing, or have glands that may be difficult to access posteriorly, are aline (epinephrine) into the venous sinusoids. Release is under pregan- particularly good candidates for robotic surgery. glionic sympathetic control, mediated by the sympathetic neurones that In the posterior retroperitoneal approach, the patient is placed in occur either singly or in small groups in the medulla. the prone jack-knife position to open up the interval between the costal The majority of chromaffin cells synthesize adrenaline and store it margin and iliac crest posteriorly. A small incision is made 2 cm inferior in small granules with a dense core. Less numerous noradrenaline- and parallel to the twelfth rib, and the perinephric fascia is entered secreting cells have larger granules with a dense eccentric core. Some using blunt dissection or with the aid of laparoscopic visualization. A cells synthesize both hormones. Chromogranin proteins package cate- dissecting balloon is then inserted and inflated under laparoscopic cholamines within the granules, which also contain enkephalins, control, after which a 12 mm trocar is inserted into the cavity and CO opiate-like proteins that may have endogenous analgesic effects in some 2 is insufflated up to a pressure of 20–25 mmHg. The 0° laparoscope is circumstances. All of the cells are large, with large nuclei and basophilic, replaced by a 45° telescope, and two additional 5- or 10 mm ports are faintly granular cytoplasm. They form single rows along the venous inserted medial and lateral to the initial port. Dissection is initiated at sinusoids. Sympathetic axon terminals synapse with the chromaffin the superior aspect of the suprarenal gland and proceeds laterally and cells on the surfaces that face away from the sinusoids. then inferiorly. The medial surface of the gland is dissected last and the The sinusoids are lined by fenestrated endothelium and drain to the adrenal vessels isolated and divided either with clips or a harmonic central medullary vein and hilar suprarenal vein. Under normal circum- scalpel (Lal and Clark 2010). stances, little adrenaline or noradrenaline is released; secretion is Similar steps are taken in the robotic approach. The robot is docked increased in response to fear, anger or stress. Unlike the cortex, the after insertion of the 5- and 10 mm secondary ports; the robotic grasper suprarenal medulla is not essential to life. is placed in the lateral port and the harmonic scalpel in the medial before proceeding with the dissection. In obese (or Cushingoid) patients, identification of a relatively SUPRARENAL GLAND EXCISION normal-sized suprarenal gland can be extremely difficult and time- consuming. The suprarenal vein emerges from the lower medial border Removal of one or both of the suprarenal glands may be performed of the gland and is often a very substantial structure. In contrast, the using ‘open surgery’, which remains the standard of care for patients supplying arteries tend to be small and named arteries are often difficult with adrenocortical carcinoma who require en bloc resection of the to identify during surgery. KEY REFERENCES Cesmebasi A, Du Plessis M, Iannatuono M et al 2014 A review of the Manso JC, DiDio LJ 2000 Anatomical variations of the human suprarenal anatomy and clinical significance of adrenal veins. Clin Anat 27: arteries. Ann Anat 182:483–8. 1253–63. A study of vascular corrosion casts, demonstrating anatomical variations of Reviews the surgical anatomy of the suprarenal veins, including their the arterial supply to the suprarenal gland. development.

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Suprarenal (adrenal) gland 1198.e1 17 RETPAHC REFERENCES Altin MA, Gündo H, Aksoy F 1992 Adrenal rests in the inguinal region in Merklin RJ 1966 Suprarenal gland lymphatic drainage. Am J Anat 119: children. Pediatr Surg Int 7:446–8. 359–74. Cesmebasi A, Du Plessis M, Iannatuono M et al 2014 A review of the Morris L, Perrier N 2012 Advances in robotic adrenalectomy. Curr Opin in anatomy and clinical significance of adrenal veins. Clin Anat 27: Onc 24:1–6. 1253–63. Mravec B 2005 A new focus on interoceptive properties of adrenal medulla. Reviews the surgical anatomy of the suprarenal veins, including their Auton Neurosci 120:10–7. development. Parnaby CN, Galbraith N, O’Dwyer PJ 2008 Experience in identifying the Dickson PV, Jimenez C, Chisholm GB et al 2011 Posterior retroperitoneo- venous drainage of the adrenal gland during laparoscopic adrenalec- scopic adrenalectomy: a contemporary American experience. J Am Coll tomy. Clin Anat 21:660–5. Surg 212:659–65. Sholten A, Cisco R, Vriens M et al 2013 Variant adrenal venous anatomy in Dutta S 2010 Suprarenal gland – arterial supply: an embryological basis and 546 laparoscopic adrenalectomies. JAMA Surg 148:378–83. applied importance. Rom J Morphol Embryol 51:137–40. Taskin HE, Berber E 2013 Robotic adrenalectomy. Cancer J 19:162–6. Gagner M, Lacroix A, Bolte E 1992 Laparascopic adrenalectomy in Cushing’s Tóth IE, Vizi ES, Hinson JP et al 1997 Innervation of the adrenal cortex, its syndrome and pheochromocytomas. New Engl J Med 327:1033. physiological relevance, with primary focus on the noradrenergic trans- Lal G, Clark OH 2010 Thyroid, parathyroid, and adrenal. In: Brunicardi FC, mission. Microsc Res Tech 36:534–45. Andersen DK, Billiar TR et al (eds) Schwartz’s Principles of Surgery, 9th Vincent JM, Morrison ID, Armstrong P et al 1994 The size of normal adrenal ed. New York: McGraw-Hill; Ch. 38. glands on computed tomography. Clin Radiol 49:453–5. Loukas M, Louis RG Jr, Hullett J et al 2005 An anatomical classification Walz M, Alesina P, Wegner F et al 2006 Posterior retroperitoneoscopic of the variations of the inferior phrenic vein. Surg Radiol Anat 27: adrenalectomy – results of 560 procedures in 520 patients. Surgery 566–74. 140:843–8. Manso JC, DiDio LJ 2000 Anatomical variations of the human suprarenal Wang X, Jin ZY, Xue HD et al 2013 Evaluation of normal adrenal gland arteries. Ann Anat 182:483–8. volume by 64-slice CT. Chin Med Sci J 27:220–4. A study of vascular corrosion casts, demonstrating anatomical variations of Williams LR, Leggett RW 1989 Reference values for resting blood flow to the arterial supply to the suprarenal gland. organs of man. Clin Phys Physiol Meas 10:187–217. Mercan S, Seven R, Ozarmagan S et al 1995 Endoscopic retroperitoneal adrenalectomy. Surgery 118:1071–5.

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SUBSECTION: Urogenital system CHAPTER 72 Development of the urogenital system A pronephros is present in human embryos only as clusters of cells in URINARY SYSTEM the most cranial portions of the nephrogenic cord (see Figs 72.1–72.2). More caudally, similar groups of cells appear and become vesicular. The The urinary and reproductive systems develop from intermediate mes­ dorsal ends of the most caudal of the vesicles join the primary excretory enchyme and are intimately associated with one another, especially in duct. Their central ends are connected with the coelomic epithelium by the earlier stages of their development. The urinary system develops cellular strands, which probably represent rudimentary peritoneal ahead of the reproductive or genital systems. funnels. Glomeruli do not develop in association with these cranially Intermediate mesenchyme is disposed longitudinally in the trunk, situated nephric tubules, which ultimately disappear. It is doubtful subjacent to the somites (in the folded embryo), at the junction between whether external glomeruli develop in human embryos. the splanchnopleuric mesenchyme (adjacent to the gut medially) and the somatopleuric mesenchyme (subjacent to the ectoderm laterally) Primary excretory duct (Fig. 72.1). In lower vertebrates, intermediate mesenchyme typically In stage 11 embryos of approximately 14 somites, the primary excretory develops serial, segmental, epithelial diverticula termed nephrotomes. duct can be seen as a solid rod of cells in the dorsal part of the neph­ Each nephrotome encloses a cavity, the nephrocele, which communi­ rogenic cord. Its cranial end is about the level of the ninth somite and cates with the coelom through a peritoneal funnel, the nephrostome its caudal tip merges with the undifferentiated mesenchyme of the cord. (Fig. 72.2). The dorsal wall of a nephrotome evaginates as a nephric It differentiates before any nephric tubules and, when the latter appear, tubule. The dorsal tips of the cranial nephric tubules bend caudally and it is at first unconnected with them. In older embryos, the duct has fuse to form a longitudinal primary excretory duct, which grows cau­ lengthened and its caudal end becomes detached from the nephrogenic dally and curves ventrally to open into the cloaca. The more caudally cord to lie immediately beneath the ectoderm. From this level, it grows placed, and therefore chronologically later, tubules open secondarily caudally, independent of the nephrogenic mesenchyme, and then into this duct or into tubular outgrowths from it. Glomeruli, specific curves ventrally to reach the wall of the cloaca. It becomes canalized arrangements of capillaries and overlying coelomic epithelium, arise progressively from its caudal end to form a true duct, which opens into from the ventral wall of the nephrocele (internal glomeruli) or the roof the cloaca in embryos at stage 12. Clearly, up to this stage, the name of the coelom adjacent to the peritoneal funnels (coelomic or external ‘duct’ is scarcely appropriate. glomeruli), or in both situations (see Fig. 72.2). Mesonephros It has been customary to regard the renal excretory system as three organs – the pronephros, mesonephros and metanephros – succeeding From stage 12, mesonephric tubules, which develop from the interme­ each other in time and space, such that the last to develop is retained diate mesenchyme between somite levels 8–20, begin to connect to the as the permanent kidney (see Figs 72.1–72.2). However, it is difficult primary excretory duct, which is now renamed the mesonephric duct. to provide reliable criteria by which to distinguish these stages or to More caudally, a continuous ridge of nephrogenic mesenchyme extends define their precise limits in embryos. to the level of somite 24. The mesonephric tubules (nephrons) are not metameric; there may be two or more mesonephric tubules opposite Pronephros each somite. The intermediate mesenchyme becomes visible in stage 10 embryos and Within the mesonephros, each tubule first appears as a condensation can be distinguished as a nephrogenic cord when 10 somites are present. of mesenchyme cells, which epithelialize and form a vesicle. One end A B C Fig. 72.1 A, The major epithelial populations within a stage 11 Neural tube embryo, viewed from a ventrolateral position. B, The position of pronephros and mesonephros on the posterior Foregut thoracic and abdominal walls. C, The position of mesonephros Pericardial and metanephros. cavity Peritoneal Pronephros funnels Pericardio- peritoneal canals Intraembryonic coelom Mesonephros Mesonephros Peritoneal cavity Mesonephric Metanephros duct Allantois Cloaca Ureteric bud Mesenchyme around Mesenchyme around connecting stalk connecting stalk 1199

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DeveloPment of the urogenital system 1200 8 noitCes Neural tube Fusion forms primary Primary excretory Somite cavity Nephric tubules excretory duct duct grows caudally Ectoderm evaginate and to reach cloaca turn caudally Lateral splanchnic arteries Coelom Endoderm Single fused aorta Notochord Nephrostome Internal and Right aorta Nephrocele external glomeruli Nephrogenic cord of intermediate mesoderm Aorta Postcardinal vein Pronephros Rudimentary in mammals Primary excretory duct now termed Mesonephric mesonephric duct (Wolffian) duct Gut Genital ridge Mesonephros Mesonephric tubule Mesonephric tubule Metanephros Metanephric cap Collecting ducts Lobulated fetal kidney Renal corpuscle Medullary loop Allantois Ureteric bud branching dichotomously Early bladder Urachus Ureter Urogenital sinus Bladder Vas deferens Genital Seminal vesicle tubercle Trigone of bladder Fig. 72.2 Principal features of the primitive vertebrate nephric system for comparison with the development of the human nephric system. A considerable period of embryonic and fetal life has necessarily been compressed into a single diagram. (Modified with permission from Williams PL, Wendell-Smith CP, Treadgold S 1969 Basic Human Embryology, 2nd edn. London, Pitman Medical & Scientific.)

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urinary system 1201 27 retPahC of the nephric ridge, and, at the caudal end of the ridge, it projects into the cavity of the coelom in the substance of a mesonephric fold (see Fig. 72.3). As the mesonephric ducts from each side approach the uro­ genital sinus, the two mesonephric folds fuse, between the bladder ventrally and the rectum dorsally, forming a transverse partition across the cavity of the pelvis, which is somewhat inappropriately called the genital cord (see Fig. 72.3). In the male, the peritoneal fossa between Tubal fold the bladder and the genital cord becomes obliterated, but it persists in (mesonephric fold) the female as the uterovesical pouch. In the male, the mesonephric duct Aorta itself becomes the canal of the epididymis, vas deferens and ejaculatory duct. Mesonephros urogenital sinus Arterial supply The primitive hindgut ends in a cloacal region. This is connected ven­ Gonad to glomerulus trally with a blind­ending diverticulum, the allantois, which is inti­ mately related to the development of the caudal portion of the urinary Mesonephric system. The enteric and allantoic portions of the hindgut are separated nephron by the proliferation of the urorectal septum, a partition of mesenchyme and endoderm in the angle of the junction of hindgut and allantois Mesonephric duct (Fig. 72.4; see Fig. 72.7). Molecular markers of the urorectal septum Hindgut Paramesonephric mesenchyme, also termed the intercloacal mesenchyme, include Six1 (Müllerian) duct and Six2 (Wang et al 2011, Wang et al 2013). The endodermal epithe­ lium beneath the mesenchyme of the urorectal septum approaches but Genital cord does not fuse with the cloacal membrane; it effectively divides the membrane into anal (dorsal) and urogenital (ventral) membranes, and the cloacal region into dorsal and ventral portions. The dorsal portion Urogenital sinus of the cloacal region is the putative rectum. The ventral portion can be further divided into: a cranial vesico­urethral canal, continuous above with the allantoic duct; a middle, narrow channel, the pelvic portion; and a caudal, deep, phallic section, which is closed externally by the urogenital membrane. The second and third parts together constitute the urogenital sinus. The ventral pericloacal mesenchyme contributes to the genital tubercle (Wang et al 2013) (see Fig. 72.20). Fig. 72.3 The relative positions of the mesonephros and early gonad in Metanephros the abdomen in the ambisexual stage of development. The mesonephric and paramesonephric ducts run within the tubal fold to the urogenital The pronephros and mesonephros are linear structures. They both sinus. contain stacks of tubules distributed along the craniocaudal axis of the embryo, an arrangement that results in the production of hypotonic urine. In marked contrast, the tubules in the metanephric kidney are arranged concentrically, and the loops of Henle are directed towards of the vesicle grows towards and opens into the mesonephric duct, the renal pelvis. This arrangement allows different concentration gradi­ while the other dilates and invaginates. The outer stratum forms the ents to develop within the kidney and results in the production of glomerular capsule, while the inner cells differentiate into mesonephric hypertonic urine. Metanephric nephrons do not join with the existing podocytes, which clothe the invaginating capillaries to form a glomer­ mesonephric duct but with an evagination of that duct, which branches ulus. The capillaries are supplied with blood through lateral branches dichotomously to produce a characteristic pattern of collecting ducts. of the aorta. It has been estimated that 70–80 mesonephric tubules and The metanephric kidney develops from three sources. An evagina­ a corresponding number of glomeruli develop. However, these tubules tion of the mesonephric duct, the ureteric bud, and a local condensa­ are not all present at the same time; it is rare to find more than 30–40 tion of mesenchyme, the metanephric blastema, form the nephric in an individual embryo because the cranial tubules and glomeruli structure (Fig. 72.5). Angiogenic mesenchyme migrates into the develop and atrophy before the development of those situated more metanephric blastema slightly later to produce the glomeruli and vasa caudally. recta. It is possible that an intact nerve supply is also required for By the end of the sixth week, each mesonephros is an elongated, metanephric kidney induction. The actions of a range of intra­ and spindle­shaped organ that projects into the coelomic cavity, one on each extracellular factors involved in metanephric development have been side of the dorsal mesentery, from the level of the septum transversum presented (Kanwar et al 2004). to the third lumbar segment. This whole projection is called the mesone­ An epithelial–mesenchymal interaction between the duct system and phric ridge, mesonephros or Wolffian body (see Fig. 72.1B–C; Fig. 72.3). the surrounding mesenchyme occurs in both mesonephric and meta­ It develops subregions, and a gonad develops on its medial surface. nephric systems. In the mesonephric kidney, development proceeds in There are striking similarities in structure between the mesonephros a craniocaudal progression, and cranial nephrons degenerate before and the permanent kidney or metanephros, but the mesonephric neph­ caudal ones are produced. In the metanephric kidney, a proportion of rons lack a segment that corresponds to the descending limb of the the mesenchyme remains as stem cells that continue to divide and loop of Henle. The mesonephros is believed to produce urine by which enter the nephrogenic pathway later, when the individual col­ stage 17. A detailed comparison of the development and function of lecting ducts lengthen. The temporal development of the metanephric the mesonephros and metanephros in staged human embryos is not kidney is patterned radially, such that the outer cortex is the last part available. to be formed. The following interactions occur in the development of In stage 18 embryos (13–17 mm), the mesonephric ridge extends the metanephric kidney (see Fig. 72.5). The ureteric bud undergoes a cranially to about the level of rib 9. In both sexes, the cranial end of series of bifurcations within the surrounding metanephric mesenchyme, the mesonephros atrophies; in embryos 20–mm in length (stage 19), a and forms smaller ureteric ducts. At the same time, the metanephric mesonephros is found only in the first three lumbar segments, although mesenchyme condenses around the dividing ducts to form S­shaped it may still possess as many as 26 tubules. The most cranial one or clusters, which transform into epithelia and fuse with the ureteric ducts two tubules persist as rostral aberrant ductules (see Fig. 72.13); the at their distal ends. Blood vessels invade the proximal ends of the succeeding five or six tubules develop into either the efferent ductules S­shaped clusters to form vascularized glomeruli. of the testis and lobules of the head of the epididymis (male), or the The ureteric bud bifurcates when it comes into contact with the tubules of the epoophoron (female); the caudal tubules form the caudal metanephric blastema in response to extracellular matrix molecules aberrant ductules and the paradidymis (male), or the paroophoron synthesized by the mesenchyme. Both chondroitin sulphate proteogly­ (female). can synthesis and chondroitin sulphate glycosaminoglycan processing are necessary for the dichotomous branching of the ureteric bud. In mesonephric duct metanephric culture, incubation of fetal kidneys in β­D­xyloside, an Once mesonephric nephrons connect to the primary excretory duct, it inhibitor of chondroitin sulphate synthesis, dramatically inhibits uret­ is renamed the mesonephric duct. This runs caudally in the lateral part eric bud branching.

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DeveloPment of the urogenital system 1202 8 noitCes A B Peritoneal cavity Peritoneal cavity Allantois Midgut Mesonephric ducts entering back of urogenital sinus Mesenchymal proliferation of urorectal septum grows Hindgut towards and fuses with cloacal membrane Cloacal membrane forming: U r ogenital membrane Cloaca Anal membrane Connecting stalk C Rectum Anal membrane Urogenital membrane Urinary bladder Peritoneal Peritoneal cavity cavity Urachus Urinary bladder Amnion Pubic symphysis Urethra Fig. 72.4 The division of the hindgut into urinary and enteric Perineal body parts: left ventrolateral view of the intraembryonic coelom and Anal membrane corresponding midsagittal sections. A, The early cloaca. Urachus B, Proliferation of the urorectal septum. C, Complete separation of Rectum the urethra and anal canal, and position of the perineal body. Subsequent divisions of the ureteric bud and associated mesen­ the angiogenic mesenchyme produce fibronectin and other components chyme define the gross structure of the kidney and the major and minor of the glomerular basement membrane. The isoforms of type­IV colla­ calyces, the distal branches of the ureteric ducts that will form the col­ gen within this layer follow a specific programme of maturation as the lecting ducts of the kidney. The proximal position of the ureteric bud filtration of macromolecules from the plasma becomes restricted. elongates to form the developing ureter (see Fig. 72.6). As the collecting Although the timing of human development is not the same as other ducts elongate, the metanephric mesenchyme condenses around them. mammalian species, similar growth and transcription factors are An adhesion molecule, syndecan, can be detected between the mesen­ thought to underpin kidney development (Chai et al 2013, Batchelder chymal cells in the condensate. The cells switch off expression of neural et al 2010, Davidson 2009, Faa et al 2012). A number of genes involved cell adhesion molecule (N­CAM), fibronectin and collagen I, and start in the development of the renal medulla and vasa recta in the mouse to synthesize liver cell adhesion molecule (L­CAM; also called E cad­ have been identified (Song and Yosypiv 2012). The genetic, epigenetic herin) and the basal lamina constituents, laminin and collagen IV. The and in utero environmental factors in the pathogenesis of non­syndromic mesenchymal clusters are thus converted to small groups of epithelial forms of human congenital anomalies of the kidney and urinary tract cells, which undergo complex morphogenetic changes. Each epithelial (CAKUT) have been considered (Yosypiv 2012). group elongates, and forms first a comma­shaped, then an S­shaped, Platelet­derived growth factor (PDGF) β­chain and the PDGF recep­ body, which continues to elongate and subsequently fuses with a branch tor β­subunit (PDGFR β) have been detected in developing human of the ureteric duct at its distal end, while expanding as a dilated sac at glomeruli between 54 and 109 days’ gestation. PDGF β­chain is local­ its proximal end (see Fig. 72.5). The latter involutes, and cells differenti­ ized in the differentiating epithelium of the glomerular vesicle during ate locally such that the outer cells become the parietal glomerular cells, its comma­ and S­shaped stages, while PDGFR β is expressed in the while the inner ones become visceral epithelial podocytes. The podo­ undifferentiated metanephric blastema, vascular structures and intersti­ cytes develop in close proximity to invading capillaries derived from tial cells. Both PDGF β­chain and PDGFR β are expressed by mesangial angiogenic mesenchyme outside the nephrogenic mesenchyme. This cells, which may promote further mesangial cell proliferation. third source of mesenchyme produces the endothelial and mesangial Metanephric mesenchyme will develop successfully in vitro, which cells within the glomerulus. The (metanephric­derived) podocytes and makes experimental perturbation of kidney development comparatively

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urinary system 1203 27 retPahC A Metanephric mesenchyme Mesonephric duct Expansion of the first six divisions produces the Ureteric bud branches renal pelvis, Ureteric bud dichotomously into the major and metanephric mesenchyme minor calyces B C Metanephric mesenchyme Branching collecting proliferates and separates ducts and proliferating with the branching of the duct metanephric mesenchyme Metanephric mesenchyme locally converts to epithelia at the sides Collecting duct of the duct from ureteric bud Comma- and S-shaped metanephric vesicles Metanephric epithelium forms comma-shaped vesicles Branches from the collecting duct elongate Fully formed metanephric nephrons joined to collecting ducts Fully formed metanephric nephrons join to Metanephric vesicles the collecting duct become S-shaped and elongate Elongated loop of Henle Fig. 72.5 An overview of metanephric kidney development. A, The ureteric bud arises from the mesonephric duct. The metanephric mesenchyme proliferates and separates with each subdivision of the ureteric bud. B, The metanephric mesenchyme converts to epithelia, forming comma- and S-shaped vesicles, which become metanephric nephrons. C, All stages of metanephric development are present concurrently. The most recently formed nephrons are on the outer aspect of the kidney. easy to evaluate. Early experimental studies demonstrated that other greater values for renal volume than female fetuses from the third tri­ mesenchymal populations, and spinal cord, were able to induce ureteric mester onwards. Kidney weight is lower in infants with a birth weight bud division and metanephric development. Nerves enter the develop­ less than −2 SDs for gestational age, reflecting a decreased number of ing kidney very early, travelling along the developing ureter. If develop­ nephrons. This relative smaller kidney size continues into early child­ ing kidney rudiments are incubated with antisense oligonucleotides, hood and may be a factor in adult kidney pathology (Geelhoed et al which neutralize nerve growth factor receptor (NGF­R) mRNA, neph­ 2009). rogenesis is completely blocked, suggesting that metanephric mesen­ chyme induction is a response to innervation. The powerful inductive endocrine development of the kidney effect of the spinal cord on metanephric mesenchyme may be a further The kidney functions not only as an excretory organ, but also as an expression of this phenomenon. All stages of nephron differentiation endocrine organ, secreting hormones that are concerned with renal are present concurrently in the developing metanephric kidney (see Fig. haemodynamics. Before birth, homeostasis is controlled by the pla­ 72.5). Antigens for the brush border of the renal tubule appear when centa. The fetal kidney produces amniotic fluid. The kidneys of pre­ the S­shaped body has formed. They appear first in the inner cortical mature babies of less than 36 weeks are immature. They contain area. The metanephric kidney is lobulated throughout fetal life, but incompletely differentiated cortical nephrons, which compromise their this condition usually disappears during the first year after birth (see ability to maintain homeostasis. Problems of immaturity are further Fig. 72.8). Varying degrees of lobulation occasionally persist through­ compounded by the effects of hypoxia and asphyxia, which modify out life. renal hormones. The growth of left and right kidneys is well matched during develop­ Renal hormones include the renin–angiotensin system, renal pros­ ment. Fetal kidney volume increases most during the second trimester taglandins, the kallikrein–kinin system and renal dopamine. Renin is in both sexes. For reasons that are not understood, male fetuses show found in the smooth muscle cells of arterioles, interlobular arteries and

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DeveloPment of the urogenital system 1204 8 noitCes A B C Allantois Mesonephric duct Urogenital sinus Ureteric bud Early ureter The mesonephric ducts and ureters The ureters open directly and separately into the urogenital enlarge as they enter the urogenital sinus above the mesonephric ducts. The openings of the sinus. They become absorbed into mesonephric ducts descend; their walls are incorporated the posterior wall of the sinus into the urogenital sinus, forming the trigone of the bladder D E Urachus Urinary bladder Ureter Ureteric opening Region of trigone Region of trigone Uterovaginal duct from fused Mesonephric duct paramesonephric duct Urethra In the female the fused paramesonephric In the male the mesonephric ducts ducts form the uterovaginal duct. form the vasa deferentia and ejaculatory ducts, The mesonephric ducts degenerate which enter the urethra through the prostate gland Fig. 72.6 The development of the urinary part of the urogenital sinus and formation of the trigone of the bladder. A–C, E, Posterior views. D, Male and female, median sagittal sections. (Based on Tuchmann-Duplessis H, Haegel P 1972 Illustrated Human Embryology, Vol 2 Organogenesis. London: Chapman and Hall. With kind permission of Springer Science+Business Media.) branches of the renal artery, and has also been described in the distal ureter convoluted tubule cells. Kallikrein has been demonstrated in rat fetal The wall of the early ureter is initially highly permeable. Its lumen later kidney, and prostaglandins have been demonstrated in the renal becomes obliterated and is subsequently recanalized. Both of these medulla and renal tubule. Renal dopamine is produced (mainly) by the processes begin in intermediate portions of the ureter and proceed enzymatic conversion of L­dopa to dopamine in the early segments of cranially and caudally. Recanalization is not associated with metane­ the proximal convoluted tubule, and is also sourced locally from phric function, but perhaps reflects the rapid elongation of the ureter dopaminergic nerves. Other renal hormones include an antihyperten­ as the embryo grows. Two fusiform enlargements appear at the lumbar sive lipid, which is produced in the interstitial cells of the renal medulla, and pelvic levels of the ureter at 5 and 9 months, respectively (the pelvic and, possibly, histamine and serotonin. Growth factors produced by enlargement is inconstant). As a result, the ureter shows a constriction human embryonic kidney cells include erythropoietin and interleukin at its proximal end (pelviureteric region) and another as it crosses the β (which stimulate megakaryocyte maturation) and transforming pelvic brim. A third narrowing is always present at its distal end and is growth factor­β. related to the growth of the bladder wall. At first, the distal end of the ureter is connected to the dorsomedial ascent of the kidney aspect of the mesonephric duct but, as a result of differential growth, The metanephric kidney is initially sacral. As the ureteric outgrowth this connection comes to lie lateral to the duct. lengthens, it becomes positioned more and more cranially. The metanephric pelvis lies on a level with the second lumbar vertebra urinary bladder when the embryo reaches a length of about 13 mm. During this period The urinary bladder develops from the cranial vesico­urethral canal, the ascending kidney receives its blood supply sequentially from arter­ which is continuous above with the allantoic duct (see Fig. 72.4; Figs ies in its immediate neighbourhood, i.e. the middle sacral and 72.6, 72.7). The mesonephric ducts open into the urogenital sinus early common iliac arteries. The definitive renal artery is not recognizable in development. The ureters develop as branches of the mesonephric until the beginning of the third month. It arises from the most caudal ducts, which attain their own access to the developing bladder, and their of the three suprarenal arteries, all of which represent persistent meso­ orifices open separately into the bladder on the lateral side of the nephric or lateral splanchnic arteries. Additional renal arteries are opening of the mesonephric ducts. Later, the two orifices become sepa­ relatively common, and may enter at the hilum or at the upper or rated still further and, although the ureter retains its point of entry into lower pole of the gland – they also represent persistent mesonephric the bladder, the mesonephric duct opens into that part of the urogenital arteries. sinus that subsequently becomes the prostatic urethra (see Fig. 72.6E).

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urinary system 1205 27 retPahC A Urorectal septum B Allantoic duct Mesonephric duct Umbilical artery Metanephric Hindgut Allantoic duct (ureteric) Bladder diverticulum Notochord Enteric hindgut Spinal cord Cloaca, showing Cloacal membrane ridge produced by urorectal septum Endodermal cloaca Postanal gut Postanal gut C Allantoic duct Mesonephric ducts D Metanephric diverticulum (ureteric bud) Umbilical vessels Enteric hindgut Mesonephric duct Urorectal septum Ureter Peritoneum Pelvis of ureter Allantoic duct Bladder Genital tubercle Endodermal cloaca Cloacal membrane Umbilical cord Postanal gut Notochord Tail Future rectum Notochord Endodermal cloaca Spinal cord Spinal cord E Fused paramesonephric ducts Colon F Mesonephric duct Ureter Centrum of vertebra Allantoic duct Pubic symphysis Urinary bladder Bladder Mesonephric ducts Lower limb Ureter Fused paramesonephric ducts Glans clitoridis Phallic portion of urogenital sinus Spinal cord Proctodeum Pelvic portion of Notochord urogenital sinus Sinus tubercle Rectum Fig. 72.7 A, The caudal end of a human embryo, 4 weeks, showing the left lateral aspects of the spinal cord, notochord and endodermal cloaca. B, The endodermal cloaca of a human embryo, near the end of the fifth week. Part of the left wall of the cloaca, including the left mesonephric duct, has been removed, together with the adjoining portions of the walls of the developing bladder and rectum. A piece of the ectoderm around the cloacal membrane has been left in situ. A wire is shown passing along the right mesonephric duct into the cloaca. C, The caudal end of a human embryo, 5 weeks, showing the endodermal cloaca. D, The caudal end of a human embryo, 6 weeks. The cloaca is becoming divided by the urorectal septum. E, The caudal end of a female human fetus, 81–9 weeks, from the left-hand side, showing structures in and near the median plane. The cloaca is now completely divided into 2 urogenital and intestinal segments. F, Part of the vesico-urethral portion of the endodermal cloaca of a female human fetus, 81–9 weeks. The sinus 2 tubercle is the elevation on the posterior wall of the urogenital sinus, caused by the fusion with the paramesonephric ducts.

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DeveloPment of the urogenital system 1206 8 noitCes The remainder of the vesico­urethral canal forms the body of the Right inferior phrenic Inferior vena cava bladder and urethra, and its apex is prolonged to the umbilicus as a vein and artery narrow canal, the urachus. For many years, it was believed that the absorption of the mesone­ phric ducts into the urogenital sinus contributed a mesodermal epithe­ Left suprarenal lium into the endodermal bladder, limited to the trigone and the dorsal Right suprarenal gland gland wall of the proximal half of the prostatic urethra to the opening of the Coeliac trunk prostatic utricle and ejaculatory ducts, or its female homologue, the Superior mesenteric whole female urethral dorsal wall. Antibody labelling and studies on Right kidney artery transgenic mice have now demonstrated that the region of the com­ bined ducts close to the urogenital sinus, referred to as the common Right renal vein Left renal vein and artery nephric duct, undergoes local apoptosis as a part of the normal develop­ Left kidney ment of the trigone region of the bladder and the establishment of Inferior mesenteric separate entry points for the ureters and mesonephric ducts (Mendel­ artery Right ureter sohn 2009). Retinoic acid is required for ureter insertion into the uro­ Abdominal aorta genital sinus (Batourina et al 2005). There is no mesodermal epithelial Left ureter contribution to the bladder at the trigone. This is further supported by Right gonadal artery the observations that tissue combination of fetal urogenital sinus mes­ and vein enchyme with epithelial mesoderm or endoderm produces different outcomes. Tissue recombinant with endoderm gives rise to prostatic epithelium, whereas the same mesenchyme combined with epithelial Rectum mesoderm forms seminal vesicle epithelium. Trigone epithelium dif­ ferentiates into prostatic epithelium, confirming an endoderm lineage Bladder deflected Right umbilical artery downwards (Tanaka et al 2010). The previous mechanism for trigone development also suggested Fig. 72.8 The posterior abdominal wall of a full-term neonate. Note the that the muscle in that region derived from the ureter and contributed lobulated kidneys and relatively wide calibre of the ureters. to the valve­like entry point that prevents urinary reflux. Studies have now shown that the ureter passes through a tunnel in the bladder wall in parallel with blood vessels. Such a tunnel forms even in the absence of ureters (Viana et al 2007). Study of smooth muscle progenitors present at birth (Fig. 72.8; see Fig. 14.6C). Addition of new cortical shows that the bulk of the trigone derives from bladder muscle (detru­ nephrons continues in the first few months of postnatal life, after which sor), with a limited contribution from ureteral longitudinal smooth general growth of the glomeruli and tubules results in the disappear­ muscle fibres at the lateral edges. Eponymous muscle such as Mercier’s ance of lobulation. The renal blood flow is lower in the neonate; adult bar and Bell’s muscle, which were thought to arise from the ureter, are values are attained by the end of the first year. The glomerular filtration derived from bladder muscle (Viana et al 2007). rate at birth is approximately 30% of the adult value, which is attained Bladder filling and emptying cycles are required for normal bladder by 3–5 months of age. remodelling during fetal development; in this process, detrusor smooth The neonatal urinary bladder is egg­shaped and the larger end is muscle cells undergo cyclical apoptosis and proliferation. Mechanical directed downwards and backwards (Figs 72.9–72.10; see Figs 14.6B– stretching promotes proliferation. Bladders in which the fluid is 14.7). Although described as an abdominal organ, nearly one­half of diverted do not show this cycle, and do not enlarge or undergo normal the neonatal bladder lies below a line drawn from the promontory of remodelling; the detrusor stops growing, producing a low­volume, low­ the sacrum to the upper edge of the pubic symphysis, i.e. within the compliance bladder, although the serosal connective tissues continue cavity of the true pelvis. From the bladder neck, the bladder extends to expand (Wei et al 2012). As yet, there is little information on the anteriorly and slightly upwards in close contact with the pubis, until it development of bladder interstitial cells of Cajal, which are present reaches the anterior abdominal wall. The apex of the contracted bladder within detrusor, bladder microvessels and the mucosal lamina propria lies at a point midway between the pubis and the umbilicus. When the (Johnston et al 2010). bladder is filled with urine, the apex may extend up to the level of the umbilicus. It is therefore possible to obtain urine by inserting a needle, Ultrasound antenatal imaging of the connected to a syringe, into the bladder through the abdominal wall urinary system about 2 cm above the pubic symphysis, and then aspirating the con­ The fetal bladder may be identified by ultrasound examination at 9–11 tents into the sterile syringe. The success rate of the procedure is variable weeks’ gestation in transverse and sagittal section. Filling and emptying and depends on the bladder being full; a much higher success rate has over a 30–45 minute cycle can be demonstrated. The absence of a been reported by using an ultrasound scanner to locate the bladder and bladder image at 13 weeks or later is considered abnormal. At 20 weeks, confirm that it contains urine prior to insertion of the needle. the kidneys are best visualized in a section of the abdomen caudal to There is no true fundus in the fetal bladder as there is in the adult. that used for abdominal circumference estimation. The diameter of the Although the anterior surface is not covered with peritoneum, perito­ renal pelvis is reported in the anterior posterior view; 7 mm or less is neum extends posteriorly as low as the level of the urethral orifice. considered normal at mid­gestation (To and Periera 2015). Because the apex of the bladder is relatively high, pressure on the lower The routine use of ultrasound as an aid to in utero diagnosis of abdominal wall will express urine from an infant bladder. Moreover, abnormalities has revealed a prevalence of 1–2 abnormal fetuses per because the bladder remains connected to the umbilicus by the obliter­ 1000 ultrasound procedures, of which 20–30% are anomalies of the ated remains of the urachus (see Fig. 14.7), stimulation of the umbilicus genitourinary tract, detectable as early as 12–15 weeks’ gestation. The can initiate micturition in babies. The elongated shape of the bladder decision to be made after such a finding is by no means clear. Urinary in neonates means that the ureters are correspondingly reduced in obstruction is considered an abnormality, yet transient modest obstruc­ length and they lack a pelvic portion. The bladder does not gain its tion is considered normal during canalization of the urinary tract, and adult, pelvic, position until about the sixth year. A distinct interureteric has been reported in 10–20% of fetuses in the third trimester. A delay fold is present in the contracted neonatal bladder. in canalization, or in the rupture of the cloacal membrane, can produce Anomalies of the urinary system a dilation. Similarly, the closure of the urachus at 32 weeks may be associated with high­resistance outflow for the system, which again Congenital anomalies of the kidney and urinary tract are relatively produces transient obstruction. Distension of the fetal bladder, which common (3–6% of live births) (Yosypiv 2012). Renal agenesis is the may indicate lower urinary tract obstruction, affects 2.2/10,000 births, absence of one or both kidneys. In unilateral renal agenesis, the remain­ more commonly in males (Hodges et al 2009, Dias et al 2014). Over ing kidney exhibits compensatory hypertrophy and produces a nearly half of such cases are caused by the development of posterior urethral normal functional mass of renal tissue. Atresia of the ureter during valves (a congenitally obstructing posterior urethral membrane); there development causes a non­functional multicystic dysplastic kidney, may also be a dilated posterior urethra and thickened bladder wall. thought to be secondary to urinary obstruction being present while the tubules are still forming. Problems with kidney ascent can result in a Neonatal urinary system pelvic kidney. Alternatively, the kidneys may fuse together at their At full­term parturition, the two kidneys weigh approximately 23 g. caudal poles, producing a horseshoe kidney, which cannot ascend out They function early in development and produce the amniotic fluid that of the pelvic cavity because the inferior mesenteric artery prevents surrounds the fetus. The lobulated appearance of fetal kidneys is still further migration. A duplex kidney arises when two ureteric buds meet

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urinary system 1207 27 retPahC Fimbriated end of uterine tube Suspensory ligament of ovary Inferior epigastric artery and vein Mass of meconium Median umbilical ligament Round ligament of uterus Sacrum Urinary bladder Fundus of uterus Left ovary Vesico-uterine pouch Body of uterus Vaginal fornices Pubic symphysis Suspensory ligament of clitoris Recto-uterine pouch Body and glans of clitoris Coccyx Sphincter urethrae Levator ani Urethra External anal sphincter Longitudinal vaginal columns Deep transverse perineal muscle Anus Anal columns External anal of anal canal sphincter Fig. 72.9 A midsagittal section through the pelvis of a full-term female neonate. Note the abdominal position of the urinary bladder and uterus. (After Crelin ES 1969 Anatomy of the Newborn. Philadelphia: Lea and Febiger.) Ossification centre of Superior rectal artery Left hypogastric nerve first vertebral segment of sacrum Left ureter Rectovesical pouch Ileum Sacral canal Median umbilical ligament Dorsal sacral Apex of urinary bladder foramina Body of bladder Fundus of bladder Pelvic sacral foramina Ampulla of vas deferens Ejaculatory duct Retropubic space Prostate gland Prostatic part of urethra Suspensory ligament of penis Rectovesical septum Corpus cavernosum Coccyx Glans Levator ani External anal sphincter Internal anal sphincter Corpus spongiosum and spongiose part of urethra Bulbospongiosus Anal column of anal canal External spermatic fascia Anal valve enclosing left testis Dartos tunic of scrotum Membranous part Bulb Remains of gubernaculum testis and tail of urethra of epididymis within external spermatic fascia Fig. 72.10 A midsagittal section through the pelvis of a full-term male neonate. Note the abdominal position of the urinary bladder. (After Crelin ES 1969 Anatomy of the Newborn. Philadelphia: Lea and Febiger.)

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DeveloPment of the urogenital system 1208 8 noitCes Umbilical cord Genital tubercle Urogenital membrane Urogenital swellings Urogenital Anal membrane membrane Genital tubercle Anal membrane Normal Exstrophy of the bladder and epispadias Fig. 72.11 Bladder exstrophy. Misalignment of the genital tubercle and urogenital swellings with the urogenital membrane during early development results in subsequent malposition of the bladder, urethra and associated sphincters. The disappearance of the urogenital membrane exposes the posterior wall of the bladder, and the urethral opening is on the superior side of the penis or clitoris. (Redrawn from Tuchmann-Duplessis H, Haegel P 1972 Illustrated Human Embryology, Vol 2 Organogenesis. London: Chapman and Hall. With kind permission of Springer Science+Business Media.) the metanephros; it is characterized by two pelvicalyceal systems and is germ cells are delineated very early in development, they are seques­ associated with ureterocele, ectopic insertion of the ureter, and vesico­ tered in the extraembryonic tissues until the gonadal ridge is ready to ureteric reflux. receive them. It was thought that development to one or other sexual It was thought that renal cysts arose from clumps of vesicular cells, phenotype occurred after migration of the primordial germ cells to the which persisted when the tips of branches from the ureteric diverticu­ indifferent gonads. However, it is now recognized that the development lum failed to fuse with metanephrogenic cap tissue. It is now believed of male or female gonads, genital ducts and external genitalia is far that they are wide dilations of a part of otherwise continuous nephrons. more complicated, and is the result of a complex interplay between In most cases, autosomal dominant polycystic kidney disease results genetic expression, timing of development and the influence of sex from mutations of PKD1 or PKD2 genes, which are expressed in human hormones. As development proceeds, a significant proportion of early embryos from 5–6 weeks of development within the mesonephros embryonic urinary tissue is incorporated into the reproductive tracts, and later the metanephros (Chauvet et al 2002). In this condition, especially in the male. The earliest stage of reproductive development, the cystic dilation may affect any part of the nephron, from Bowman’s prior to the arrival of the primordial germ cells into the gonad, is termed capsule to collecting tubules. Less common is infantile cystic renal the indifferent or ambisexual stage. disease, inherited as a recessive trait, in which the proximal and distal Early gonadal development (ambisexual or tubules are dilated to some degree but the collecting ducts are grossly affected. indifferent stage) There is evidence that infants born small for gestational date retain Essentially, four different cell lineages contribute to the gonads. Cells smaller kidneys throughout childhood. A causal relationship between are derived from: proliferating coelomic epithelium on the medial side low birth weight and later chronic kidney disease is speculated, as well of the mesonephros; underlying mesonephric mesenchyme; invading as susceptibility to hypertension in adult life (White et al 2009). angiogenic mesenchyme already present in the mesonephros; and Anomalies of the ventral body wall caudal to the umbilicus, espe­ primordial germ cells that arise from the epiblast very early in develop­ cially with inappropriate siting of the genital tubercle, can result in ment and later migrate from the allantoic wall. exstrophy of the bladder (Fig. 72.11) (Suzuki et al 2009, Williams The formation of the gonads is first indicated by the appearance of 2013). In this condition, the urorectal septum (internal) is associated an area of thickened coelomic epithelium on the medial side of the with the genital tubercle (external), which means that the urogenital mesonephric ridge in the fifth week, stage 16 (Figs 72.12–72.13; see and anal membranes are widely separated. When the urogenital mem­ Fig. 72.16). Elsewhere on the surface of the ridge, the coelomic epithe­ brane involutes, the posterior surface of the bladder is exposed to the lium is one or two cells thick, but over this gonadal area it becomes anterior abdominal wall. The lower part of the abdominal wall is, multilayered. Thickening rapidly extends in a longitudinal direction therefore, occupied by an irregularly oval area, covered with mucous until it covers nearly the whole of the medial surface of the ridge. The membrane, on which the two ureters open. The periphery of this extro­ thickened epithelium continues to proliferate, displacing the renal cor­ verted area, which is covered by urothelium, becomes continuous with puscles of the mesonephros in a dorsolateral direction, and forms a the skin. projection into the coelomic cavity: the gonadal ridge. Surface depres­ The volume of amniotic fluid is used as an indicator of renal func­ sions form along the limits of the ridge, which is, thus, connected to tion but, because other sources produce amniotic fluid in early gesta­ the mesonephros by a broad mesentery, the mesogenitale. In this way, tion, amniotic volume does not reflect fetal urinary output until the the mesonephric ridge becomes subdivided into a lateral part – the second trimester (see p. 179). Too little amniotic fluid is termed oligo­ tubal fold, containing the mesonephric and paramesonephric ducts, hydramnios; too much, polyhydramnios. Although variation in the and a medial part – the gonadal fold. The tubal fold also contains the amount of amniotic fluid may suggest anomalies of either the gut or nephric tubules and glomeruli at its base (see Fig. 72.3). the kidneys, it is not always possible to correlate even severe oligohy­ Up to the seventh week, the ambisexual gonad possesses no sexually dramnios with renal dysfunction. There is an important relationship differentiating feature. From stage 16, the proliferating coelomic epithe­ between the volume of amniotic fluid, lung development and maturity, lium forms a number of cellular epithelial cords (sometimes called and oligohydramnios has been shown to be associated with pulmonary primary sex cords), separated by mesenchyme. The cords remain at hypoplasia (Ch. 52). the periphery of the primordium and form a cortex. Proliferation and labyrinthine cellular condensation of the mesonephric mesenchyme, including angiogenic mesenchyme, produce a central medulla. REPRODUCTIVE SYSTEM Reproductive ducts Development of the reproductive organs from the intermediate mesen­ The paramesonephric, Müllerian, ducts develop in embryos of both chyme starts from stage 14, about 10 days later than the urinary system. sexes, but become dominant in the development of the female repro­ Bilateral paramesonephric (Müllerian) ducts develop alongside the ductive system. They are not detectable until the embryo reaches a mesonephric ducts, and the midportion of each mesonephros under­ length of 10–12 mm (early sixth week). Each begins as a linear invagi­ goes thickening to form the gonadal ridge. Although the primordial nation of the coelomic epithelium, the paramesonephric groove, on the

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reproductive system 1209 27 retPahC A B Amniotic cavity Amnion Neural tube Somite Notochord Mesonephros Mesonephric duct Gonad X Y Gonad Paramesonephric (Müllerian) duct Mesonephros Midgut Midgut Mesonephric duct Intraembryonic Metanephros coelom Allantois Yolk sac Fig. 72.12 A, The position of the gonads on the posterior abdominal wall, anteromedial to the mesonephros. B, A transverse section of figure A, through the line X–Y. A Mesonephros Mesonephric nephrons Proliferating coelom epithelium Paramesonephric (Müllerian) duct Mesonephric duct B Appendix epididymis C Gubernaculum Tunica albuginea Appendix testis Efferent ductules Testis Urogenital sinus Ovary Epididymis Uterine tube Epoophoron Vas deferens Gubernaculum ovarii Uterus Seminal vesicle Gartner’s duct Gubernaculum testis Utricle of prostate Cervix Fig. 72.13 A, The indifferent or ambisexual stage of development. B, Male. The mesonephric ducts are retained (left) and the paramesonephric ducts involute (right). C, Female. The paramesonephric (Müllerian) ducts are retained (right) and the mesonephric ducts involute (left). lateral aspect of the mesonephric ridge near its cranial end. The blind caudal end of the mesonephros in the eighth week. It turns medially caudal end continues to grow caudally into the substance of the ridge and crosses ventral to the mesonephric duct to enter the genital cord, as a solid rod of cells, which becomes canalized as it lengthens. Through­ where it bends caudally in close apposition with its fellow from the out the extent of the mesonephros, it is lateral to the mesonephric duct, opposite side (see Fig. 72.13). The two ducts reach the dorsal wall of which acts as a guide for it. The paramesonephric duct reaches the the urogenital sinus during the third month, and their blind ends

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DeveloPment of the urogenital system 1210 8 noitCes produce an elevation called the Müllerian or sinus tubercle (see Figs defined as the cranial end of the mesonephros degenerates. The caudal 72.7F, 72.19). vertical parts of the two ducts fuse with each other to form the utero­ At the end of the indifferent stage, each paramesonephric duct con­ vaginal primordium (Fig. 72.14). This gives rise to the lower part of the sists of vertical cranial and caudal parts and an intermediate horizontal uterus, and, as it enlarges, it takes in the horizontal parts to form the region. The mesonephric ducts course caudally, medial to the parameso­ fundus and most of the body of the adult uterus. A constriction between nephric ducts, and both duct systems open into the urogenital sinus. the body of the uterus and the cervix can be found at 9 weeks. The The genital ducts possess an external serosa on some surfaces, derived stroma of the endometrium and the uterine musculature develop from from coelomic epithelium; a smooth muscle muscularis, derived from the surrounding mesenchyme of the genital cord. underlying mesenchyme; and an internal mucosa, derived either from Failure of fusion of the two paramesonephric ducts can lead to a the mesonephric duct or from the invaginated tube of coelomic epithe­ range of anomalies summarized in Figure 72.15. These fusions can also lium that forms the paramesonephic duct. The layers are invaded by contribute to anomalies of vaginal development. angiogenic mesenchyme and by nerves. At birth, the uterus is 2.5–5 cm long (average 3.5 cm), 2 cm wide between the uterine tubes, and a little over 1 cm thick (see Figs 72.9, uterus and uterine tubes 14.6C–14.7). The body of the uterus is smaller than the uterine cervix, In the female, the mesonephric duct is vestigial. Cranially, it becomes which forms two­thirds or more of the length. The isthmus between the the longitudinal duct of the epoophoron, while, caudally, it is referred body and the cervix is absent. The fetal female reproductive tract is to as Gartner’s duct (Table 72.1). The cranial part of the paramesone­ affected by maternal hormones and undergoes some enlargement in phric ducts forms the uterine tubes, and the original coelomic invagina­ the fetus. The endocervical glands are active before birth and the cervical tion remains as the pelvic opening of the tube. The fimbriae become canal is usually filled with mucus. The uterus is relatively large at birth and, subsequently, involutes to about one­third of its length and more than half of its weight; it does not regain its neonatal size and weight Table 72.1 Homologies of the parts of the urogenital system in male and female until puberty. The uterine tubes are relatively short and wide. The position of the uterus in the pelvic cavity depends, to a great Gonad Testis Ovary extent, on the state of the bladder anteriorly and the rectum posteriorly. Gubernacular cord Gubernaculum testis Ovarian and round ligaments If the bladder contains only a small amount of urine, the uterus may Mesonephros Appendix epididymis (?) Appendices vesiculosae (?) be anteverted but it is often in a direct line with the vagina (see Figs (Wolffian body) Efferent ductules Epoophoron 72.9, 72.19). Lobules of epididymis Paradidymis Paroophoron vagina Aberrant ductules At approximately 60 mm crown–rump (CR) length, an epithelial pro­ Mesonephric duct Duct of epididymis Duct of epoophoron (Gartner’s duct) (Wolffian duct) Vas deferens liferation, the sinuvaginal bulb, arises from the dorsal wall of the uro­ Ejaculatory duct genital sinus in the region of the sinus tubercle (see Figs 72.7F, 72.14B). Part of bladder and prostatic Part of bladder and urethra Its origin marks the site of the future hymen. The proliferation gradually urethra extends cranially as a solid, anteroposteriorly flattened plate inside the Paramesonephric Appendix testis Uterine tube tubular condensation of the uterovaginal primordium, which will, (Müllerian) duct Uterus eventually, become the fibromuscular vaginal wall. The caudal tip of Prostatic utricle Vagina (?) the paramesonephric duct epithelium recedes until, at about 140 mm Allantoic duct Urachus Urachus (CR), its junction with the epithelial proliferation lies in the cervical Cloaca: canal. Dorsal part Rectum and upper part of anal Rectum and upper part of anal canal canal Starting from its caudal end and gradually extending cranially Ventral part Most of bladder Most of bladder and urethra through its whole extent, the solid plate formed by the sinus prolifera­ Part of prostatic urethra tion enlarges into a cylindrical structure. After this, the central cells Urogenital sinus Prostatic urethra distal to desquamate to establish the vaginal lumen. As the upper end of the utricle vaginal plate enlarges, it grows up to embrace the cervix, and then is Bulbourethral glands Greater vestibular glands excavated to produce the vaginal fornices. The boundary of origin of Rest of urethra to glans Vestibule the vaginal mucosa, between the epithelial contribution of the para­ Genital folds Ventral penis Labia minora mesonephric ducts and the sinuvaginal bulb, has been defined in the Genital tubercle Penis Clitoris mouse (Kurita 2010, Kurita 2011). Anomalies of paramesonephric duct Urethra in glans fusion can produce related vaginal anomalies (see Fig. 72.15). The A B Urachus Uterine tube Broad ligament Mesonephric kidney Uterovaginal canal and gonad descend Bladder Ureter Sinuvaginal tubercle Allantois Recto-uterine Metanephric pouch (of Douglas) Rectum Urogenital sinus kidney ascends Gubernaculum Fig. 72.14 Relative movements of the gonads and associated tubes. A, Gonads and mesonephros move caudally, and the metanephros ascends. B, A posterior view of the mesonephric ducts (ureters) and the fused paramesonephric ducts (uterovaginal canal) in the female. For earlier development, see Figure 72.3. (Based on Tuchmann-Duplessis H, Haegel P 1972 Illustrated Human Embryology, Vol 2 Organogenesis. London: Chapman and Hall. With kind permission of Springer Science+Business Media.)

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reproductive system 1211 27 retPahC Partial or total failure of fusion of the terminal portion of the paramesonephric (Müllerian) ducts and also that, once the epithelial cells no longer secrete a basal lamina, the remaining ductal epithelial cells transform into mesenchyme that remains in the vicinity of the involuting duct (Allard et al 2000). Ves­ tigial remnants of the paramesonephric ducts are most likely to persist cranially and/or caudally, at the limits of the local exocrine effects of AMH. A vestige of the cranial end of the duct persists as the appendix testis (see Figs 72.13, 72.19; see Table 72.1). The fused caudal ends of the two ducts are connected to the wall of the urogenital sinus by a solid utricular cord of cells, which soon merges with a proliferation of sinus epithelium, the sinu­utricular cord. The latter is similar to, but less extensive than, the sinus proliferation in the female. The proliferat­ ing epithelium is claimed to be an intermingling of the endoderm of Uterus didelphyd Bicervical uterus Unicervical uterus with double vagina bicornis bicornis the urogenital sinus with the lining epithelia of the mesonephric and paramesonephric ducts, which have extended on to the surface of the Failure of resorption of the uterovaginal septum after fusion of the paramesonephric (Müllerian) ducts sinus tubercle. As the sinu­utricular cord grows, so the utricular cord recedes from the tubercle. In the second half of fetal life, the composite cord acquires a lumen and becomes dilated to form the prostatic utricle, the lining of which consists of hyperplastic stratified squamous epithe­ lium. The sinus tubercle becomes the colliculus seminalis. The main reproductive ducts in the male are derived from the meso­ nephric ducts; the latter persist under the action of androgens that are probably secreted down the ducts themselves, and are subsumed into the male reproductive system as the metanephric kidney develops. The mesonephric duct gives rise to the canal of the epididymis, vas deferens and ejaculatory duct. The seminal vesicle and the ampulla of the vas deferens appear as a common swelling at the end of the mesonephric Completely Bilocular Bilocular duct during the end of the third and into the fourth months. Their bilocular uterus unicervical uterus bicervical uterus appearance coincides with degeneration of the paramesonephric ducts, although no causal relation between the two events has been estab­ Partial or total atresia of the terminal portion of one or both paramesonephric (Müllerian) ducts lished. Separation into two rudiments occurs at about 125 mm crown– heel length. The seminal vesicle elongates, its duct is delineated and hollow diverticula bud from its wall. Around the sixth month (300 mm crown–heel length), the growth rate of both vesicle and ampulla is greatly increased. Figure 72.10 shows the position of the ampulla of the vas deferens in the neonate, possibly in response to increased secretion of prolactin by the fetal or maternal hypophysis, or to the effects of placental hormones. The tubules of the prostate show a similar increase in growth rate at this time. Primordial germ cells Unilateral atresia Partial bilateral atresia: Partial bilateral atresia: The primordial germ cells are formed very early from the epiblast (see uterus bicornis unicollis atresia of cervix atresia of vagina Fig. 10.3). They are larger (12–20 µm in diameter) than most somatic Fig. 72.15 Uterovaginal anomalies. (Based on Tuchmann-Duplessis H, cells, and are characterized by vesicular nuclei with well­defined nuclear Haegel P 1972 Illustrated Human Embryology, Vol 2 Organogenesis. membranes, and by a tendency to retain yolk inclusions long after these London: Chapman and Hall. With kind permission of Springer have disappeared from somatic cells. It is not yet clear whether the Science+Business Media.) primordial germ cells are derived from particular blastomeres during cleavage, if they constitute a clonal line from a single blastomere, or if they are the product of a progressive concentration of the nucleus of the fertilized ovum by unequal partition at successive mitoses. Primor­ urogenital sinus undergoes relative shortening craniocaudally to form dial germ cells spend the early stages of development within the extra­ the vestibule, which opens on the surface through the cleft between the embryonic tissues near the end of the primitive streak and in the genital folds. The lower end of the vaginal plate grows caudally so that, connecting stalk (see Fig. 10.4). In this situation, they are away from in 109 mm embryos, the vaginal rudiment approaches the vestibule. In the inductive influences to which the majority of the somatic cells are fetuses of 162 mm, the vaginal lumen is complete, except at the cephalic subjected during early development. end, where the fornices are still solid; they are hollow by 170 mm. At Primordial germ cells can be identified in human embryos in stage approximately halfway through gestation (180 mm), the genital canal 11, when the number of cells is probably not more than 20–30. When is continuous with the exterior. During the later months of fetal life, the tail fold has formed, they appear within the endoderm and the the vaginal epithelium is greatly hypertrophied, apparently under the splanchnopleuric mesenchyme and epithelium of the hindgut, as well influence of maternal hormones, but, after birth, it assumes the inactive as in the adjoining region of the wall of the yolk sac. They migrate form of childhood. dorsocranially in the mesentery, by amoeboid movements and by In the neonate, the vagina is 2.5–3.5 cm long and 1.5 cm wide at growth displacement, and pass around the dorsal angles of the coelom the fornices, and the uterine cervix extends into the vagina for about (medial coelomic bays) to reach the genital ridges from stage 15 (see 1 cm. The posterior vaginal wall is longer than the anterior wall, giving Fig. 72.16). It is believed that the genital ridges exert long­range effects the vagina a distinct curve (see Figs 72.9, 72.19, 14.7). The cavity is on the migrating primordial germ cells, in terms of controlling their filled with longitudinal columns covered with a thick layer of cornified, direction of migration and supporting the primordial germ­cell popula­ stratified, squamous epithelium. These cells slough off after birth, when tion. Primordial germ cells contact each other via long processes and the effect exerted by maternal hormones is removed. retain cytoplasmic bridges when they divide. They are usually in close The orifice of the vagina is surrounded by a thick, elliptical ring of proximity to somatic cells, which may modify the local environment, connective tissue: the hymen. During childhood, the hymen becomes forming junctional complexes with them. The surface of primordial a membranous fold along the posterior margin of the vaginal lumen. germ cells displays binding sites for extracellular matrix macromole­ Should the fold form a complete diaphragm across the vaginal lumen, cules. A range of molecular markers associated with the migration and it is termed an imperforate hymenal membrane. proliferation of primordial germ cells has been described (Soto­Suazo and Zorn 2005, Runyan et al 2006, De Felici 2013). reproductive ducts in the male Primordial germ cells proliferate both during and after migration to In the male, most of the paramesonephric ducts atrophy (see Fig. 72.13) the mesonephric ridges. Cells that do not complete this migration under the influence of anti­Müllerian hormone (AMH; also called mainly degenerate, but if they survive, they can give rise to germ cell Müllerian inhibiting substance, or MIS), which is released into the tumours, usually in the midline (Runyan et al 2006). After segregation, mesonephric duct by the Sertoli cells of the testis. It is thought that the when they are often termed primary gonocytes, they divide to form epithelial cells of the paramesonephric duct initially undergo apoptosis secondary gonocytes.

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DeveloPment of the urogenital system 1212 8 noitCes Indifferent stage Aorta Primordial germ cells Lateral coelomic bay Medial coelomic bay Mesonephric (Wolffian) duct Invaginating paramesonephric Median dorsal mesentery (Müllerian) duct Mesonephric tubule Gut tube Genital ridge Paramesonephric (Müllerian) duct Primordial germ cells associate with sex cords Mesonephric glomerulus Sex cord Female Male Mesonephric duct and tubules begin to degenerate Some mesonephric Primordial germ cells tubules fuse with enclosed with cord cells medullary ends Rete ovarii of sex cords Retrogression Uterine tube Mesovarium Vestigial duct and tubule of epoophoron Seminiferous tubules Mesorchium Rete ovarii Efferent ductules Tunica albuginea Broad ligament Ductus deferens Interstitial cells Uterine tube Rete testis Degenerating Interlobular septum Stromal cells paramesonephric duct Primordial ovarian follicles Fig. 72.16 The development of the gonads and associated ducts, as seen in transverse section, to show the fate of the primordial germ cells, mesonephric duct and tubules, and paramesonephric duct in males and females. (Modified with permission from Williams PL, Wendell-Smith CP, Treadgold S 1969 Basic Human Embryology, 2nd edn, London, Pitman Medical & Scientific.)

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reproductive system 1213 27 retPahC Development of the gonads medulla. The majority remain in the cortex, where they may be joined by a second proliferation from the coelomic epithelium overlying the The factors that lead to formation of either testis or ovary are described gonad. In histological sections of ovaries from the third and subsequent below and in Figure 72.16. The morphological events that occur in each months, the epithelial cords appear as clusters of cells, which may type of gonadal development are presented first. contain primitive germ cells, separated by fine septa of undifferentiated mesenchyme. An ovarian rete condenses in the medullary mesenchyme testis and some of its cords may join mesonephric glomeruli. The medulla Most studies support the hypothesis that the seminiferous tubules are subsequently regresses, and connective tissue and blood vessels from formed from cords of epithelial cells derived from the proliferating this region invade the cortex to form the ovarian stroma. During this coelomic epithelium (see Figs 72.13, 72.16). The cords lengthen, partly invasion, the clusters of epithelial cortical cells break into individual by addition from the coelomic epithelium, and encroach on the groups of supporting cells (now identified as granulosa cells), which medulla, where they unite with a network of cells derived from the surround the primordial germ cells (now identified as primary oocytes) mesonephric mesenchyme destined to become the rete testis. Primor­ that have entered the prophase of the first meiotic division. Primary dial germ cells are incorporated into the cords, which later become oocytes are derived from a mitotic division of the primordial germ cells enlarged and canalized to form the seminiferous tubules. The cells (naked oogonia). Their epithelial capsules consist of flattened pregranu­ derived from the surface of the early gonad form the supporting Sertoli losa cells derived from proliferations of coelomic epithelium. The ovary cells. The latter proliferate throughout fetal and early postnatal life (less now has its full complement of primary oocytes. The majority undergo than 6 months) and perhaps again at puberty initiation (Sharpe et al atresia, a hormonally controlled apoptotic process, but the remainder 2003); when they stop dividing, they mature and cannot be reactivated. resume development after puberty, when they complete the first meiotic Each Sertoli cell can only support a fixed number of germ cells during division shortly before ovulation. The granulosa cells at this time their development into spermatozoa, i.e. the number of Sertoli cells enlarge and multiply to form the stratum granulosum; as they do so, produced at this time determines the maximal limit of sperm output they become surrounded by thecal cells, which differentiate from the (Sharpe et al 2003). Because the germ cells make up the bulk of the stroma. adult testis, the number of Sertoli cells is a major determinant of the There are temporospatial changes within the developing ovary. Neu­ size to which the testes will grow (factors that impair the process of rotropins and their receptors have been shown to be expressed within spermatogenesis, resulting in the loss of germ cells, will also affect the fetal ovary between 13 and 21 weeks. NT4 is localized initially in testicular size). Variation in Sertoli cell number is probably the most epithelioid cells mingled with oogonia, then within oogonial mRNA, important factor in accounting for the enormous variation in sperm and finally in granulosa cells of the primordial follicles, with lesser counts between individual men, whether fertile or infertile. Indeed, the expression in the enclosed oocytes (Anderson et al 2002). available data for adult men indicate that Sertoli cell numbers vary Expression of p450c17, a steroidogenic enzyme involved in the pro­ across a fifty­fold range (Sharpe et al 2003). Although some of this duction of androgens, has been shown in the human fetal ovary during variation may result from attrition of Sertoli cell numbers because of the second and third trimesters (Cole et al 2006). Its temporospatial ageing, the major differences in Sertoli cell numbers will have been expression showed a movement from the cortex to the medulla, with determined by events in fetal and/or childhood life. its presence in primary interstitial cells in the cortex from 14 weeks to The interstitial cells of the testis are derived from mesenchyme and, 23 weeks, but not in hilus interstitial cells; between 27 and 33 weeks, possibly, also from coelomic epithelial cells that do not become incor­ few cells stained for p450c17, but there was an increase after 33 weeks porated into the tubules. Among other cell lines, they form the embry­ in theca interstitial cells associated with preantral follicles. Positive­ onic and fetal cells of Leydig, which secrete testosterone and insulin­like staining hilus interstitial cells were rarely seen before 33 weeks. The factor 3 (Insl3). A later migration of mesenchyme beneath the coelomic temporospatial expression was similar in anencephalic fetuses of the epithelium forms the tunica albuginea of the testis. same age, indicating that anterior pituitary function is not regulating The cords of the rete testis become connected to the glomerular this maturation. The authors suggest a possible role for insulin in regu­ capsules in the persisting part of the mesonephros. Ultimately, they lating fetal ovary androgen production. It is noted that overexpression become connected to the mesonephric duct by the 5–12 most cranial of interstitial androgen production is a component in the pathophysiol­ persisting mesonephric tubules. These become exceedingly convoluted ogy of polycystic ovary syndrome (Cole et al 2006). and form the lobules of the head of the epididymis. The mesonephric duct, which was the primitive ‘ureter’ of the mesonephros, becomes the sex determination in the embryo canal of the epididymis and the vas deferens of the testis. The seminifer­ It was believed that the gonads were indifferent or ambisexual until the ous tubules do not acquire lumina until the seventh month; the tubules arrival of the primordial germ cells in the gonadal ridge, at which point of the testicular rete become canalized somewhat earlier. the sex of the embryo was ‘turned on’ by the presence of the male or Disorders of development of the testis and reproductive tract in the female germ cells. It is now clear that the germ cells may be essentially male fetus seem to be increasing in incidence. Testicular maldescent irrelevant to testis determination; embryos in which the genital ridges (cryptorchidism) and hypospadias appear to have doubled or trebled are devoid of germ cells may still undergo otherwise normal testis in incidence in the last 30–50 years, while testicular cancer has increased development. It is not clear if the germ cells are necessary for ovarian by an even greater margin and is now the most common cancer of determination. They are required for the proper organization and dif­ young men. Although testicular cancer is primarily a disease of young ferentiation of the ovary, and their absence results in the development men (95% of cases affect 15­ to 45­year­old males), it is now established of ‘streak gonads’, where only lines of follicular cells can be seen, as in that this age incidence reflects activation of premalignant carcinoma-in- Turner’s syndrome. situ (CIS) cells, which are present at birth and which almost certainly The processes of sex determination and differentiation involve inter­ arise during fetal life. It is now accepted that CIS cells are primordial acting pathways of gene activity, which lead to the total patterning of germ cells/gonocytes that have failed to complete differentiation into the embryo as either male or female. spermatogenic germ cells (Rajpert­De Meyts 2006). Anomalies of devel­ In the current, generally accepted, model of sex determination in opment of the testis and reproductive tract (e.g. gonadal dysgenesis, humans, the female pathway is considered to be the ‘set­up’ programme; cryptorchidism, small testes) are important risk factors for the develop­ in other words, this is the course of events that will occur, unless there ment of testicular germ cell cancer. However, the most dramatic change is modification via differentiation of Sertoli cells, which leads to testis that appears to have occurred in the relatively recent past is a fall in formation. The trigger for the latter is the presence of a Y chromosome, sperm counts of around 40–50% (1% per year over the last 50 years). which diverts development into the testicular pathway. The resulting Although this dramatic decrease is obviously manifest only in adult­ cellular changes convert the indifferent gonad into a testis, which then hood, as is the case with testicular cancer there is growing evidence that produces three key hormones (AMH, Insl3 and testosterone), which it may reflect impaired testicular development during fetal or childhood collectively induce masculinization of the fetus and, thus, acquisition life (Dean and Sharpe 2013). of male secondary sexual characteristics. The possession of a Y chromosome is usually associated with a male ovary developmental pathway. Deletion mapping of the Y chromosome in a The ovary develops from the middle part of the gonadal ridge only. The class of XX males arising from abnormal X : Y interchange at meiosis cranial part of the gonadal ridge becomes the suspensory ligament of showed that the male­determining region of the chromosome was a the ovary (infundibulopelvic fold of peritoneum), and its caudal region conserved sequence located near its tip, termed the testis­determining is incorporated into the ovarian ligament. factor (TDF). This sequence contains a gene that is established to be the The ovary closely resembles the testis early in development, except ‘master switch’ that programmes the direction of sexual development, that its characteristically female features are slower to differentiate (see the so­called SRY gene (sex­determining region on the Y chromosome). Figs 72.13, 72.16). Few, if any, of the epithelial cords invade the It is believed to be genetically and functionally equivalent to the TDF.

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DeveloPment of the urogenital system 1214 8 noitCes The SRY gene acts initially within the epithelial cords of cells derived involves two phases – transabdominal and inguinoscrotal – which are from the coelomic epithelium of the ambisexual gonad. These cells can regulated by distinct morphological and endocrine factors (Barteczko potentially differentiate into either Sertoli or granulosa cells (the sup­ and Jacob 2000). porting cells for the germ cells in the testis and ovary, respectively). Studies indicate that SRY initiates testis formation from the indifferent Transabdominal phase gonad by directing the development of supporting­cell precursors as Each testis initially lies on the dorsal abdominal wall. As it enlarges, its Sertoli rather than granulosa cells (Albrecht and Eicher 2001). Gene cranial end degenerates and the remaining organ therefore occupies a expression is seen first in cells designated as pre­Sertoli, located cen­ more caudal position. It is attached to the mesonephric fold by the trally in the developing gonad, and then later in the cranial and caudal mesorchium (the mesogenitale of the undifferentiated gonad), a peri­ poles. Once the developmental pathway of Sertoli cells is directed, this toneal fold that contains the testicular vessels and nerves, and a quantity influences the differentiation of the other cell types in the testicular of undifferentiated mesenchyme. It also acquires a secondary attach­ pathway, so that Leydig cells appear later, and the connective tissue ment to the ventral abdominal wall, which has a considerable influence becomes organized into a male pattern. The germ cells are also affected on its subsequent movements. At the point where the mesonephric fold by this environment. When they arrive, they become enclosed within bends medially to form the genital cord (see Fig. 72.3), it becomes the Sertoli cells and do not enter meiosis; they continue to proliferate connected to the lower part of the ventral abdominal wall by an inguinal (which is characteristic of spermatogenesis), instead of ceasing prolif­ fold of peritoneum covering a mesenchymal cord, termed the guber­ eration and entering meiosis and meiotic arrest, as occurs in the ovary. naculum or genito­inguinal ligament (see Figs 72.3, 72.13; Fig. 72.17). Thus, the development of male characteristics follows the expression of The distal end of this cord seems to align to the inguinal part of the SRY, and female characteristics develop in its absence. milk line which extends from the axilla to the femoral region (see Fig. Studies of XY individuals with sex reversal (i.e. XY females) and cor­ 53.28). It has been suggested that this line corresponds to the original responding gene knockout studies in mice have established that SRY lateral edge of the embryo, which expresses the apical ectodermal ridges initiates testis development by inducing the expression of another gene, and mesenchymal progress zones of the upper and lower limbs (Hutson SOX9 (SRY­like HMG­box protein 9), and expression of the latter in the 2013, Hutson et al 2014). absence of SRY is sufficient for male determination. It is now known Up to about 10 weeks, the gubernaculum in male and female that there is a multi­step cascade of gene expression changes that essen­ embryos is the same, but then production of Insl3 from the Leydig cells tially works to reinforce SOX9 expression and, thus, to consolidate stimulates enlargement (known as the ‘swelling reaction’) of the guber­ development down the male pathway; these genes include WT1 naculum in males. This serves to anchor the fetal testis near the future (Wilm’s tumour gene), GATA4 (GATA­binding protein 4), FGF9 (fibrob­ inguinal canal as the abdominal cavity enlarges between 10 and last growth factor 9) and DAX-1 (orphan nuclear receptor DAX­1) 15 weeks. By comparison, the gubernaculum in females remains thin (Biason­Lauber 2010, Munger et al 2013). This cascade also actively and subsequently develops into the round ligament (see below). The represses expression of genes that promote development along the cranial attachment of the urogenital ridge, known as the cranial suspen­ female pathway; these include RSPO1 (R­spondin 1), WNT4 (Wingless­ sory ligament, regresses in males under the action of androgens. type MMTV integration site family member 4) and FOXL2 (Forkhead After the midgut loop returns to the abdomen, the anterior abdomi­ box L2). In turn, activation of the female cascade of gene expression nal wall inferior to the umbilical cord lengthens. As each umbilical actively suppresses expression of SOX9 and/or other genes in the ‘male artery runs ventrally from the dorsal to the ventral wall, it pulls up a cascade’. Therefore, development of either a testis or an ovary results falciform peritoneal fold, which forms the medial boundary of a peri­ from a reinforcing programme of gene expression changes, and inacti­ toneal fossa, the saccus vaginalis of lateral inguinal fossa, into which vating mutations in any one of these genes, or their aberrant expression each testis projects. in the wrong sex fetus, has the potential to interfere, partially or com­ pletely, with normal gonad formation and, thus, with downstream Inguinoscrotal phase sexual development (Biason­Lauber 2010, Munger et al 2013). However, The caudal end of the gubernaculum is initially associated with a spe­ fewer than 50% of disorders of sex development (DSD) in humans can cific portion of the milk line of the abdominal wall around which the be explained by alterations in the expression of known genes, such as future inguinal canal is formed by differentiating abdominal wall those listed; this means that more genes and new pathways remain to muscles. An interaction with the mammary line ectoderm and underly­ be discovered, and these may involve completely new mechanisms. ing mesenchyme may trigger gubenacular meristematic growth similar Very recently, the first example of sex reversal (in mice) due to an epi­ to that seen in the progress zone of the limb bud. Between 25 and 35 genetic change was reported, which resulted from the inactivating weeks, the male gubernaculum begins to bulge out from the abdominal mutation of a gene (JMJD1A) involved in histone demethylation of muscles and elongate across the pubis and into the scrotum (see Fig. genes, thus allowing their expression (Kuroki et al 2013). Absence of 72.17). An outpocketing of peritoneum, the processus vaginalis, extends this demethylase prevented normal demethylation of the Sry gene and, into the gubernaculum, hollowing it out so that the proximal part is thus, failure of its expression in an otherwise normal XY mouse with a divided into a crescentic parietal layer within which the cremaster normal Sry gene. muscle develops, and a central column attached to the epididymis. Subsequent development of the male phenotype requires fetal secre­ Elongation of the soft, gelatinous end of the gubernaculum, which, in tion of testosterone, AMH and Insl3. Of these, testosterone is the most the early stage, is formed mainly of hyaluronic acid, is controlled by important, as it has body­wide effects, both on the developing repro­ androgens. The exact mechanism mediating elongation in humans is ductive system/genitalia and on numerous other organs/tissues, includ­ uncertain. In rodent models, there is good evidence that androgens ing the brain. Also important is the development of the appropriate cause sexual dimorphism of the sensory branches of the genitofemoral cytoplasmic testosterone­binding receptor protein (the androgen recep­ nerve, which supplies the gubernaculum, the developing cremaster tor). Sertoli cells synthesize AMH, which causes the regression of the muscle within it, and part of the scrotum. The genital branch of the Müllerian ducts, and Leydig cells produce testosterone, which promotes nerve releases calcitonin gene­related peptide (CGRP), which stimulates the development of the mesonephric ducts, sets into process the devel­ growth of the gubernacular tip along a chemotactic gradient to the opment of male external genitalia, and sensitizes other tissues to testos­ scrotum. terone. Absence of a functional androgen receptor, as occurs in the The testis remains in apposition with the deep inguinal ring, held complete androgen insensitivity syndrome (CAIS), results in XY indi­ by the gubernaculum during the fourth to sixth months (Barteczko and viduals who have testes and degenerated Müllerian ducts, but cannot Jacob 2000). From 35 weeks the extracellular matrix of the gubernacu­ respond to the circulating testosterone produced by their testes; they lum is resorbed and it forms a fibrous attachment to the inside of the therefore develop female secondary sexual characteristics. scrotum. Testis descent during the inguinoscrotal phase occurs relatively rapidly about the seventh month, the left testis usually descending Descent of the gonads ahead of the right. It is thought that intra­abdominal pressure acting The gonads develop on the posterior abdominal wall bilaterally along through the patent processus vaginalis contributes to this migration the central portion of the mesonephros. This region receives a rich (Hutson 2012). In full­term male neonates, over 95% have descended blood supply, which is directed to the gonads as the mesonephros testes, although, in premature babies, descent may not be complete. involutes. Both gonads descend, the testis to lie outside the abdominal After descent, the distal processus vaginalis persists as a ‘tiny satellite cavity, and the ovary to the pelvis; however, they both retain their early peritoneal cavity’ around the testis as the tunica vaginalis, which blood supply from the dorsal aorta. becomes firmly attached to the surrounding scrotum within a few weeks. The proximal part of the processus vaginalis then obliterates, Descent of the testis and there is evidence that this also is controlled by androgens indirectly The mechanism of testicular descent is not completely understood and, via CGRP released from the genitofemoral nerve. Both exogenous CGRP to some extent, remains controversial. Recent evidence suggests that it and hepatocyte growth factor can cause obliteration in vitro of the

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reproductive system 1215 27 retPahC A B Metanephric kidney Ureter Testis External oblique muscle Epididymis Transversalis Epididymis Testis fascia Abdominal gubernaculum Internal Vas deferens oblique muscle External oblique aponeurosis Abdominal Interstitial gubernaculum gubernaculum Subcutaneous gubernaculum Interstitial Superficial gubernaculum inguinal ring Subcutaneous C Deep inguinal ring Epididymis gubernaculum Gubernaculum Transversalis fascia = internal spermatic fascia Vas deferens Processus vaginalis Internal oblique muscle = Seminiferous Transversalis cremaster muscle tubules fascia External oblique muscle = Tunica Internal external spermatic fascia albuginea oblique muscle Processus vaginalis Fig. 72.17 The descent of the testis. The testis is retroperitoneal throughout development. It becomes obliquely orientated during abdominal descent. A, The gubernaculum attached to the lower part of the testis has an abdominal part covered with developing peritoneum, an interstitial part and a distal end embedded in the anterior abdominal wall at the site of the future inguinal canal. B, The gubernaculum swells, becoming similar in width to the testis. The distal-most portion of the gubernaculum bulges into abdominal wall muscles and grows 3–5 cm over the superior pubic ramus and into the scrotum. A crescentic column of peritoneum, the processus vaginalis, develops in the expanding gubernaculum. C, The testis gains a crescentic covering of visceral and parietal peritoneum (which forms the tunica vaginalis) and muscle and connective tissue layers as it passes through the deep and superficial inguinal rings. The coverings remain around the ductus deferens, whereas the proximal processus vaginalis normally becomes obliterated by 3 weeks after birth. (Based on Tuchmann-Duplessis H, Haegel P 1972 Illustrated Human Embryology, Vol 2 Organogenesis. London: Chapman and Hall. With kind permission of Springer Science+Business Media.) pro cessus vaginalis in hernial sacs excised from babies with indirect (15% affected). It is also seen in myelomeningocoele affecting the inguinal hernia. upper lumbar spinal cord (>30% affected), although in these latter cases At birth, the processus vaginalis is narrowed and collapsed, but not it is not clear whether low abdominal pressure or genitofemoral nucleus necessarily completely obliterated. It remains patent for 2 weeks in dysplasia is the cause (Hutson 2012). Cryptorchidism used to be con­ nearly 70% of male infants but, by 3 weeks after birth, it is at least sidered a relatively minor birth defect that was corrected surgically partially obliterated in 80% of male infants, the left side before the sometime during childhood. It is now considered to be a symptom of right. testicular dysgenesis syndrome, a spectrum that includes hypospadias, Persistent patency of the processus vaginalis leads to indirect inguinal impaired semen quality and testicular germ cell cancer (Toppari et al hernia (widely patent and allowing prolapse of bowel), or hydrocele 2014). Since germ cell numbers decrease rapidly in undescended testes, (narrow patency permitting only intraperitoneal fluid to trickle down orchipexy is now undertaken between 6–9 months of postnatal life. into the tunica vaginalis). During obliteration, fluid may trickle only Further delay results in impaired testicular catch­up growth in boys: part of the way down the processus vaginalis to produce an encysted even with early orchipexy, men with bilateral undescended testes are hydrocele of the cord. This is a relatively common but transient state six times more likely to be infertile (Lee and Shortliffe 2014). and usually resolves completely within a few weeks by further oblitera­ tion. Because of perinatal androgen exposure, the spermatic cord and Descent of the ovary scrotum are relatively large in the neonate, as are the seminal vesicles The relative movements of the ovary are less extensive than those of the and adjacent ampullae of the vas deferens. testis and are not hormonally regulated. Like the testis, the ovary ulti­ In aberrant testicular descent, the testis may remain in the abdomen, mately reaches a lower level than it occupies in the early months of fetal although this is thought to be uncommon because the hormonal and life, but it does not leave the pelvis to enter the inguinal canal, except morphological features of the transabdominal phase are relatively in certain anomalies. The ovary is connected to the medial aspect of the simple. By contrast, the indirect endocrine regulation and complex mesonephric fold by the mesovarium (homologous with the mesor­ migratory process of the gubernaculum during the inguinoscrotal phase chium), and to the ventral abdominal wall by the inguinal fold (see is frequently abnormal, leading to the testis lying in the inguinal or Fig. 72.13; Fig. 72.18). A mesenchymatous gubernaculum develops in pubic region in 2–5% of neonates. Rarely, the testis may lie in the this fold but, as it traverses the mesonephric fold, it acquires an addi­ perineum, in the upper part of the thigh or at the root of the penis. The tional attachment to the lateral margin of the uterus near the entrance cause for these aberrant locations is unknown but is most likely to be of the uterine tube. Its lower part, caudal to this uterine attachment, secondary to aberrant migration of the gubernaculum, perhaps caused becomes the round ligament of the uterus, and the part cranial to this by a mislocated genitofemoral nerve. becomes the ovarian ligament. Collectively, these structures are homo­ Testes that have descended may not remain within the scrotum if logous with the gubernaculum testis in the male (Fig. 72.19). This new the spermatic cord does not double its length between birth and puberty uterine attachment may be correlated with the restricted ovarian (Hutson 2013). It is thought that the aetiology of such acquired unde­ descent. At first, the ovary is attached to the medial side of the mesone­ scended testes is also linked to that of hydrocele and hernia. Causes phric fold but, in accordance with the manner in which the two mes­ may be deficient prenatal and postnatal androgens and inadequate onephric folds form the genital cord, it is finally connected to the CGRP from the genitofemoral nerve. posterior layer of the broad ligament of the uterus. The gubernacula Cryptorchidism is common in infants with abdominal wall defects thus develop in the female, unlike the male, as bilateral fibrous bands such as bladder exstrophy, exomphalos (30% affected) and gastroschisis or ligaments in the absence of Insl3. They do not extend into the labia

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DeveloPment of the urogenital system 1216 8 noitCes A B Ovary Degenerating mesonephros Ovarian ligament Mesovarium Mesosalpinx Uterine tube Uterine tube Uterus Broad ligament of uterus Gubernaculum ovarii Uterus C D Uterine tube Mesosalpinx Ovarian ligament Mesovarium Mesovarium Broad ligament Mesosalpinx Round ligament Broad ligament Round ligament Fig. 72.18 The descent of the ovary. A, An early developing left ovary and uterine tube. B, The start of posterior movement of the ovary. C, The left ovary in its definitive posterior position. D, A sagittal section of the ligaments associated with the ovary, viewed from a left lateral position. (Based on Tuchmann-Duplessis H, Haegel P 1972 Illustrated Human Embryology, Vol 2 Organogenesis. London: Chapman and Hall. With kind permission of Springer Science+Business Media.) majora, but end in the connective tissue just external to the external the enteric hindgut, and ventrocaudally is in contact with overlying ring of the inguinal canal because, in the absence of androgens, there ectoderm at the cloacal membrane. Proliferation of mesenchyme at the is no migratory phase analogous to inguinoscrotal migration in the angle of the junction of the hindgut and allantois produces a urorectal male. The saccus vaginalis is present in the female. Its prolongation into septum (intercloacal mesenchyme), which grows caudally, promoting the inguinal canal (sometimes termed the canal of Nuck) is normally the movement, but not the fusion, of the endodermal epithelium completely obliterated, but may remain patent and form the sac of a towards the cloacal membrane (Fig. 72.20). The cloaca becomes sepa­ potential indirect inguinal hernia. rated into a presumptive rectum and anal canal dorsally, and a pre­ In the neonate, the ovaries lie in the lower part of the iliac fossae. sumptive urinary bladder and urogenital sinus ventrally; the cloacal The long axis of the ovary is almost vertical. It becomes temporarily membrane is divided into anal and urogenital parts, respectively. horizontal during descent, but regains the vertical when it reaches The nodal centre of division is the site of the future perineal body. the ovarian fossa. The ovaries complete their descent into the ovarian The urogenital sinus receives the mesonephric and paramesonephric fossae in early childhood. Thus, at birth, the ovary and the lateral ducts. end of the corresponding uterine tube lie above the pelvic brim. They Anomalies of cloacal development may result in a range of defects. do not sink into the lesser pelvis until the latter enlarges sufficiently In extroversion of the cloaca (ectopia cloacae), the urorectal septum to contain both of them and the other pelvic viscera, including the does not develop and there is failure of mesenchymal migration around bladder. Neonatal ovaries are 1–3.6 mm long (Stranzinger and Strouse the ventral body wall to support the umbilical cord; this results in a 2008) and their combined weight at birth is 0.3 g, which is relatively large abdominal defect with a central colonic portion and bilateral large, and much larger than the combined weight of the testes (see bladder components. With only partial development of the urorectal Figs 72.9, 14.6C). The ovaries double in weight during the first 6 septum, the urogenital sinus may remain with a high confluence of postnatal weeks. They bear surface furrows, which disappear during bladder, vagina and rectum. The cloacal membrane may be abnormally the second and third postnatal months. All of the primary oocytes for elongated and prematurely ruptured throughout its whole extent, prior the reproductive life of a female are present in her ovaries by the end to the formation of the urorectal septum, or, in some cases, there may of the first trimester of pregnancy. Of the 7 million primary oocytes be only a small sinus opening externally at the skin. The anal muscu­ estimated to be present at the fifth month of gestation, 1 million lature is often present but not associated with the anal canal. remain at birth and 40,000 by puberty; only 400 are ovulated during reproductive life. Pelvic floor The pelvic floor consists of the ligamentous supports of the cervix, and Cloaca and external genitalia the pelvic and urogenital diaphragms, and constitutes another partition The cloaca is that region at the end of the primitive hindgut that is that traverses the body cavity. Little is known about pelvic floor devel­ continuous with the allantois (see Figs 72.4, 72.7). The allantois, a opment in the human. The striated muscle is derived from the dermo­ ventral diverticulum, passes into the connecting stalk of the early myotomes in a similar manner to the muscles of the ventrolateral body embryo prior to tail­folding and is then drawn into the body cavity after wall. Puborectalis appears in 20–30 mm embryos, following opening stage 10. It retains an extension into the connecting stalk, and later into of the anal membrane, and striated muscle fibres can be seen at the umbilicus, throughout embryonic life. The cloaca is a slightly 15 weeks. The smooth muscle of the urethral sphincter is also present dilated cavity lined with endoderm. It is initially connected cranially to at this time.

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reproductive system 1217 27 retPahC Indifferent stage Mesonephric (Wolffian) duct Mesonephric tubules Paramesonephric (Müllerian) duct Gonad Mesonephros Urachus Gubernaculum Metanephros Primitive bladder Trigone Sinus (Müllerian) tubercle Ureter Rectum Anal canal Female Male Urachus Paroophoron Vas deferens Seminal vesicle Trigone Ovary Ureter Fimbriae Epoophoron Ligament of ovary Uterine tube Round ligament of uterus Ureter Urachus Prostatic utricle Prostate Bulbourethral gland Superior aberrant ductules Paradidymis Appendix epididymis Appendix testis Efferent ductules Epididymis Line of degenerate Müllerian duct Line of Gartner’s duct Testis Inferior aberrant ductule Vagina Fossa terminalis Gubernaculum Fig. 72.19 The development of the urogenital system from the indifferent stage to the definitive male and female states. (Modified with permission from Williams PL, Wendell-Smith CP, Treadgold S 1969 Basic Human Embryology, 2nd edn. London, Pitman Medical & Scientific.) urethra believed that these regions are invaded by ectoderm because they are The urethra is derived from endoderm, as are the prostate gland and innervated by somatic nerves. vagina (both outgrowths of the lower urogenital sinus), and the other Urethral defects caused by anomalous development are not uncom­ small glandular structures that develop around the caudal body mon in the male. In epispadias, the urethra opens on the dorsal aspect orifices. of the penis at its junction with the anterior abdominal wall. This In the male, the prostatic urethra proximal to the orifice of the pro­ anomaly is considered to be a less severe form of exstrophy of the static utricle is derived from the vesico­urethral part of the cloaca and bladder. In the simplest form of hypospadias, related to incomplete the incorporated caudal ends of the mesonephric ducts. The remainder canalization of the urethral plate, the urethra may open on the ventral of the prostatic part, the membranous part, and probably the part (perineal) aspect of the penis at the base of the glans, and the part of within the bulb, are all derived from the urogenital sinus. The anterior the urethra that is normally within the glans is absent. In more severe urethra, as far as the glans, is formed by canalization of the urethral cases, the genital folds fail to fuse, and the urethra opens on the ventral plate (see below). Secondary ingrowth of mesenchyme fuses the genital aspect of a malformed penis just in front of the scrotum. A still greater folds over the urethra (see Fig. 72.20). The short section within the glans degree of this anomaly is accompanied by failure of the genital swell­ may be formed from ectoderm, which invaginates into the glans. ings to unite with each other. In these cases, the scrotum is divided and, In the female, the urethra is derived entirely from the vesico­urethral since the testes are also frequently undescended, the resemblance to the region of the cloaca, including the dorsal region derived from the meso­ labia majora is very striking, leading to genital ambiguity. In such cases, nephric ducts. It is homologous with the part of the prostatic urethra it is important to determine at the earliest time not only the chromo­ proximal to the orifices of the prostatic utricle and the ejaculatory ducts. somal status of the infant but also the internal anatomy and state of The region of the early urethra remains open to form the vestibule, into development of the internal genital tract. Sex assignment and rearing which the definitive urethra and vagina open (see Fig. 72.20). It is will depend on these factors.

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DeveloPment of the urogenital system 1218 8 noitCes The urethral sphincter first forms as a mesenchymal condensation Umbilical cord around the urethra in 12–15 mm (stage 18) embryos, after division of Early bladder Allantoic duct the cloaca. The mesenchyme proliferates and becomes defined at the bladder neck in 31 mm embryos, and along the anterior part of the urethra by 69 mm. The muscle fibres differentiate after 15 weeks’ devel­ opment, at which time both smooth and striated fibres are present. In females, there is continuity between the smooth muscle of the urethral Genital tubercle Endodermal cloaca wall and of the bladder. In males, the muscle fibres are less abundant Cloacal because of the local development of the prostate. Striated muscle fibres membrane form around the smooth muscle, initially in the anterior wall of the urethra, and later encircle the smooth muscle layer. The origin of the striated muscle is not known; it could be derived from the myogenic cells that give rise to puborectalis. The smooth and striated components of the urethral sphincter are closely related, but there is no mixing of fibres as occurs in the anorectal sphincter. Prostate gland The prostate gland arises during the third month from interactions Urogenital sinus Hindgut between the urogenital sinus mesenchyme – mesenchyme that was associated with the mesonephric and paramesonephric ducts and the endoderm of the proximal part of the urethra. This region has been Genital tubercle termed the Müllerian duct–urogenital sinus junction (Cai 2008). Early Genital fold outgrowths, some 14–20 in number, arise from the endoderm around Urogenital orifice the whole circumference of the tube, but mainly on its lateral aspects and excluding the dorsal wall above the utricular plate. They give rise Anal orifice to the outer glandular zone of the prostate. Later outgrowths from and tubercles the dorsal wall above the mesonephric ducts arise from the epithelium of mixed urogenital, mesonephric and, possibly, paramesonephric origin that covers the cranial end of the sinus tubercle. They produce the internal zone of glandular tissue that appears to be patterned by the mesenchyme that surrounded the lower end of the mesonephric Labioscrotal and paramesonephric ducts. The developing gland is affected by the swelling local hormonal environment, as, in response to increased androgens, recombination of female vaginal mesenchyme can direct endodermal epithelium to form prostate gland (Cai 2008). The outgrowths, which are at first solid, branch, become tubular and invade the surrounding Male Female mesenchyme. The latter differentiates into smooth muscle, associated blood and lymphatic vessels and connective tissue, and is invaded by autonomic nerves. An early surge in androgens at 8–10 weeks is associated with endodermal growth, with mesenchymal proliferation occurring later at 12 weeks, when maternal oestrogen levels increase Glans penis Glans clitoridis (Cai 2008). Urethral groove Similar outgrowths occur in the female but remain rudimentary in the absence of androgenic stimulation. The urethral glands correspond Urethral orifice to the mucosal glands around the upper part of the prostatic urethra, and the para­urethral glands correspond to the true prostatic glands of Genital fold the external zone. Vagina The bulbourethral glands in the male, and the greater vestibular glands in the female, arise as diverticula from the epithelial lining of the urogenital sinus. Scrotal Labial swelling swelling external genitalia Patterning of the external genitalia may be achieved by mechanisms Anus similar to those that pattern the face and limb. In the cranial region, neural crest mesenchyme makes an important contribution to the organization of the pharyngeal arches and the regions around the upper sphincters. Neural crest also arises from the tail­bud region, specifically from a population of cells termed the caudoneural hinge, which share the same molecular markers as the primitive node. The neural tube at Glans penis this level is derived from a mesenchymal–epithelial transformation of Glans clitoridis caudoneural hinge cells, which form a cylinder. Neural crest cells de­ laminate from the dorsal surface of the cylinder in a rostrocaudal direc­ Urethral orifice tion. It is not known whether neuronal neural crest arising from Fused genital folds secondary neurulation processes contributes to the caudal interface between endoderm and ectoderm. Many of the genes controlling exter­ nal genital development have been identified (Kojima et al 2010, Blas­ Vestibule chko et al 2012). Labium majus The external genitalia, like the gonads, pass through an indifferent Labium minus state before distinguishing sexual characters appear (see Fig. 72.20). Scrotum From stage 13, primordia of the external genitalia, composed of under­ lying proliferating mesenchyme covered with ectoderm, arise around Median raphe the cloacal membrane, between the primitive umbilical cord and the caudal limit of the embryo. During stage 15, the cloacal membrane is Anus divided by the urorectal septum into a cranial urogenital membrane and a caudal anal membrane (see Fig. 72.4). Local ectodermal– Fig. 72.20 The development of the external genitalia from the indifferent mesenchymal interactions give rise to the anal sphincter, which will stage to the definitive male and female states. develop even without the presence of the anal canal. A surface elevation, produced by underlying pericloacal mesenchyme, the genital tubercle, appears at the cranial end of the urogenital membrane and two lateral

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reproductive system 1219 27 retPahC A B C Fig. 72.21 Scanning electron micrographs of early human external genitalia. A, The indifferent stage in a human embryo, estimated as 42 postovulatory days. B, A human female embryo at 12 weeks’ development. The genital folds are not fused. C, A human male embryo at 12 weeks. Fusion of the genital folds has occurred. (Photographs by P Collins.) ridges, the genital or urethral folds, form each side of the membrane wards to become continuous with the genital folds at the margins of (see Fig. 72.20). The genital tubercle forms a distinct primordium, the urethral orifice. As the urethral folds meet to form the terminal part which will become the glans of either the penis or the clitoris. Elonga­ of the urethra, the ventral horns of the ridge fuse to form the frenulum. tion of the genital folds and urogenital membrane produces a primitive The epithelial lamella breaks down over the dorsum and sides of the phallus. As this structure grows, it is described as having a cranial surface glans to form the preputial sac, and thus free the prepuce from the analogous to the dorsum of the penis, and a caudal surface analogous surface of the glans. Thereafter, the prepuce grows as a free fold of skin, to the perineal surface of both sexes. The urogenital sinus, contiguous which covers the terminal part of the glans. Although the prepuce and with the internal aspect of the urogenital membrane, becomes attenu­ glans begin to separate from the fifth month in utero, they may still be ated within the elongating phallus, forming the primitive urethra. The joined at birth. The preputial sac may not be complete until 6–12 months urogenital membrane breaks down at about stage 19, allowing com­ or more after birth and, even then, the presence of some connecting munication of ectoderm and endoderm at the edges of the disrupted strands may still interfere with the retractability of the prepuce. membrane and continuity of the urogenital sinus with the amniotic The mesenchymal core of the phallus is comparatively undifferenti­ cavity. Urine can escape from the urinary tract from this time. The ated in the first 2 months, but the blastemata of the corpora cavernosa endodermal layer of the attenuated distal portion of the urogenital become defined during the third month. Nerves are present in the dif­ sinus, which is now displayed on the caudal aspect of the phallus, is ferentiating mesenchyme from the seventh week. Despite containing termed the urethral plate. As mesenchyme proliferates within the genital less smooth muscle and elastic tissue than the adult, the neonatal penis folds, the urethral plate sinks into the body of the phallus, forming a is capable of erection. primary urethral groove. The genital folds meet proximally in a trans­ The scrotum is formed by proliferation of the genital swellings. The verse ridge immediately ventral to the anal membrane. genital swellings fuse across the midline covering the base of the penis. While these changes are in progress, two labioscrotal (genital) swell­ The testes descend into the scrotum prior to birth. The gelatinous matrix ings appear, one on each side of the base of the phallus, and extend of the gubernaculum is then resorbed and the tunica vaginalis becomes caudally, separated from the genital folds by distinct grooves (see Fig. adherent to the connective tissue of the scrotum. In the neonate, the 72.20; Fig. 72.21). penis and scrotum are relatively large. The scrotum has a broad base As a general rule, epithelium, which can be touched easily and has that does not narrow until after the first year. Both the septum (i.e. the a somatic innervation, is derived from ectoderm. In the buccal cavity mesenchyme remaining between the tunica vaginalis on each side) and and pharynx, the ectoderm/endoderm zone is towards the posterior the walls of the scrotum are relatively thicker than in adults. third of the tongue; touch here usually elicits the gag reflex. In the anal canal, the outer portion, distal to the anal valves, is derived from ecto­ Female genitalia derm and has a somatic innervation, whereas the epithelium proximal The female phallus, which exceeds the male in length in the early stages, to the valves is derived from endoderm and has an autonomic becomes the clitoris. The genital swellings remain separate as the labia innervation. majora and the genital folds also remain separate, forming the labia Homologies of the parts of the urogenital system are shown in minora (see Fig. 72.20). The perineal orifice of the urogenital sinus is Table 72.1. retained as the cleft between the labia minora, above which the urethra and vagina open. The prepuce of the clitoris develops in the same way Male genitalia as its male homologue. By the fourth month, the female external geni­ The growth of male external characteristics is stimulated by androgens talia can no longer be masculinized by androgens. regardless of the genetic sex. The male phallus enlarges to form the At birth, neonatal females have relatively enlarged labia minora, penis. The genital swellings meet each other ventral to the anus and clitoris and labia majora. The labia majora are united by a posterior unite to form the scrotum (see Fig. 72.20). The genital folds fuse with labial commissure. The distal end of the round ligament of the each other from behind forwards, enclosing the phallic part of the uterus, the gubernaculum ovarii, ends just outside the external inguinal urogenital sinus behind to form the bulb of the urethra, and closing ring. the definitive urethral groove in front to form the greater part of the There is evidence that in certain tissues, e.g. urogenital sinus and spongiose urethra. Fusion of the folds results in the formation of a genital swellings, testosterone is converted into 5α­dihydrotestosterone. median raphe and occurs in such a way that the lining of the postglan­ In XY individuals with a genetic deficiency of the enzyme responsible dular urethra is mainly, perhaps wholly, endodermal in origin, formed for this conversion, not only functioning testes but also female external by canalization of the urethral plate. Thus, as the phallus lengthens, the genitalia, with an enlarged clitoris and a small vaginal pouch, are urogenital orifice is carried onwards until it reaches the base of the glans present, suggesting that external genital development is under the at the apex of the penis. From the tip of the phallus, an ingrowth of control of 5α­dihydrotestosterone (Kang et al 2014). Such individuals surface ectoderm occurs within the glans to meet and fuse with the are often raised as girls; however, at puberty the external genitalia penile urethra. Subsequent canalization of the ectoderm permits a con­ become responsive to testosterone, which causes masculinization at this tinuation of the urethra within the glans. time. The glans and shaft of the penis are recognizable by the third month. Disorders of sex development The prepuce also begins to develop in the third month, when the primary external orifice of the urethra is still at the base of the glans. A The acquisition of appropriate gonads, reproductive ducts, external ridge consisting of a mesenchymal core covered by epithelium appears genital structures and matching gender identity occurs through a myriad proximal to the neck of the penis and extends forwards over the glans. of complex processes, both local and systemic. Anomalous develop­ A solid lamella of epithelium deep to this ridge extends backwards to mental processes, leading to differences in sex chromosomes, gonadal the base of the glans. The ventral extremities of the ridge curve back­ structure and position, retention of ductal homologues, androgen

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DeveloPment of the urogenital system 1220 8 noitCes insensitivity, androgen excess, and ambivalent external genitalia requir­ ing gender assignment, were previously described as intersexual condi­ Average girl tions or hermaphrodism. Such terminology is non­specific, confusing and perceived as potentially pejorative by affected individuals. Advances in the identification of molecular genetic causes of such conditions have Height spurt led to proposed changes to describe them as ‘disorders of sex develop­ 9½–14½ ment’ (DSD): congenital conditions in which development of chromo­ somal, gonadal or anatomical sex is atypical (Lee et al 2006). The range Menarche of anomalous development and its management by multidisciplinary Bud 10–16½ teams, as well as by the affected family, are comprehensively covered Breast 2 3 4 5 by Arboleda and Vilain (2014). 8–13 Pubic hair 2 3 4 5 Maturation of the reproductive organs 8–14 at puberty Until the adolescent growth spurt, the reproductive organs grow very 8 9 10 11 12 13 14 15 16 17 18 slowly. Generally, the changes occur over a time period termed puberty. The sequence of these events is much less variable than the age at which Average boy Apex strength spurt they take place. The sequence of puberty in girls and boys is shown in Figure 72.22. In girls, the appearance of the breast bud is usually the first sign of Height spurt puberty. The uterus and vagina develop simultaneously with the breast. 10½–16 13–17½ Menarche occurs after the peak of the height spurt; onset is more closely related to radiological than to chronological age. It has been suggested Penis that the menarche occurs as a critical weight of 50 kg is attained, and 11–14½ 13½–17 certainly sports and excessive restriction of diet, which may reduce Testis weight below this level, can cause amenorrhoea in women who were 10–13½ 14½–18 previously menstruating normally. Tall girls reach sexual maturity Pubic hair 2 3 4 5 earlier than short ones, but girls with a late adolescent growth spurt and 10–15 14–18 later puberty are ultimately taller on the average than those who pass through the menarche early, for they have longer to grow. A girl who has begun to menstruate can be predicted to grow a further 7.5 cm at 8 9 10 11 12 13 14 15 16 17 18 most. Menarche marks a definitive stage of uterine development but Age (years) does not mean attainment of full reproductive function. Many of the Fig. 72.22 The average ages at which maturation events occur in early menstrual cycles may not involve ovulation. adolescent girls and boys. The figures beneath the bars indicate the The earliest sign of puberty in boys is the growth of the testes and range of ages within which each event may begin and end. Figures within scrotum. The volume of the testes may be estimated: the average adult the bars indicate the developmental stage. The velocity of the strength volume is 20 ml, and a volume of 6 ml indicates that puberty has spurt peaks later than the height spurt in boys, associated with started. Later, the penis, prostate and seminal vesicles begin to enlarge. testosterone and growth hormone levels. It is appreciated that the Increased testosterone levels produced by the Leydig cells of the testes assessment and interpretation of the strength spurt during puberty is promote changes in the larynx, skin and distribution of bodily hair. complex (De Ste Croix 2007). (Adapted with permission from Tanner JM 1962 Growth at Adolescence, 2nd edn. Oxford: Blackwell Publishing.) KEY REFERENCES Arboleda VA, Vilain E 2014 Disorders of sex development. In: Strauss JF, Sharpe RM, McKinnell C, Kivlin C et al 2003 Proliferation and functional Barbieri RL (eds) Yen & Jaffe’s Reproductive Endocrinology, 7th ed. maturation of Sertoli cells, and the relevance to disorders of testis func­ Philadelphia: Elsevier, Saunders; Ch. 17. tion in adulthood. Reproduction 125:769–84. This chapter considers the complexities of disorders of sex development and This paper considers the importance of Sertoli cell development and the their management. future sperm count of adult males. Barteczko KJ, Jacob MI 2000 The testicular descent in human. Origin, devel­ Tanaka ST, Ishii K, Demarco RT et al 2010 Endodermal origin of bladder opment and fate of the gubernaculum Hunteri, processus vaginalis trigone inferred from mesenchymal­epithelial interaction. J Urol 183: peritonei and gonadal ligaments. Adv Anat Embryol Cell Biol 156:III–X, 386–91. 1–98. This paper presents the molecular evidence for the origin of the bladder This paper presents excellent images of early human testis and its descent trigone mucosa. into the scrotum. Wang C, Wang JY, Borer JG et al 2013 Embryonic origin and remodelling of Chai O, Song C, Park S et al 2013 Molecular regulation of kidney develop­ the urinary and digestive outlets. PLoS One 8:e55587. ment. Anat Cell Biol 46:19–31. This paper considers the development of the cloacal region and its separation This paper examines the molecular processes behind some of the into enteric and urogenital parts. epithelial:mesenchymal interactions occurring in the developing kidney. White SL, Perkovic V, Cass A et al 2009 Is low birth weight an antecedent Hutson JM 2013 Undescended testis: the underlying mechanisms and the of CKD in later life? A systematic review of observational studies. Am J effects on germ cells that cause infertility and cancer. J Pediatr Surg Kidney Dis 54:248–61. 48:903–8. This paper considers the evidence that impaired nephrogenesis caused by low This paper considers the relationships between testicular development and birth weight may give rise to chronic kidney disease. final testis maturity. Lee PA, Houk CP, Ahmed SF et al 2006 Consensus statement on manage­ ment of intersex disorders. International Consensus Conference on Intersex. Paediatrics 118:e488–500. This paper presents the recommendations in intersex disorder management.

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Development of the urogenital system 1220.e1 27 retPahC REFERENCES Albrecht KH, Eicher EM 2001 Evidence that SRY is expressed in pre­Sertoli Hutson JM, Baskin LS, Risbridger G et al 2014 The powers and perils of cells and Sertoli and granulosa cells have a common precursor. Dev Biol animal models with urogenital anomalies: handle with care. J Ped Urol 240:92–107. 10:699–705. Allard S, Adin P, Gouédard L et al 2000 Molecular mechanisms of hormone­ Johnston L, Woolsey S, Cunningham RM et al 2010 Morphological expres­ mediated Müllerian duct regression: involvement of β­catenin. Develop­ sion of KIT positive interstitial cells of Cajal in human bladder. J Urol ment 127:3349–60. 184:370–7. Anderson RA, Robinson LLL, Brooks J et al 2002 Neurotropins and their Kang H, Imperato­McGinley J, Zhu Y et al 2014 5a­reductase­2 deficiency’s receptors are expressed in the human fetal ovary. J Clin Endocrinol effect on human fertility. Fertil Steril 101:310–16. Metab 87:800–07. Kanwar YS, Wada J, Lin S et al 2004 Update of extracellular matrix, its recep­ Arboleda VA, Vilain E 2014 Disorders of sex development. In: Strauss JF, tors, and cell adhesion molecules in mammalian nephrogenesis. Am J Barbieri RL (eds) Yen & Jaffe’s Reproductive Endocrinology, 7th ed. Physiol Renal Physiol 286:F202–15. Philadelphia: Elsevier, Saunders; Ch. 17. Kojima K, Kohri K, Hayashi Y 2010 Genetic pathway of external genitalia This chapter considers the complexities of disorders of sex development and formation and molecular etiology of hypospadias. J Pediatr Urol 6: their management. 346–54. Barteczko KJ, Jacob MI 2000 The testicular descent in human. Origin, devel­ Kurita T 2010 Developmental origin of vaginal epithelium. Differentiation opment and fate of the gubernaculum Hunteri, processus vaginalis 80:99–105. peritonei and gonadal ligaments. Adv Anat Embryol Cell Biol 156:III–X, Kurita T 2011 Normal and abnormal epithelial differentiation in the female 1–98. reproductive tract. Differentiation 82:117–126. This paper presents excellent images of early human testis and its descent into the scrotum. Kuroki S, Matoba S, Akiyoshi M et al 2013 Epigenetic regulation of mouse sex determination by the histone demethylase Jmjd1a. Science 341: Batchelder CA, Lee CCI, Martinez ML et al 2010 Ontology of the kidney and 1106–9. renal developmental markers in the Rhesus monkey (Macaca mulatta). Anat Rec 293:1971–83. Lee JJ, Shortliffe LMD 2014 Undescended testes and testicular tumors. In: Holcomb GW, Murphy JP, Ostlie DJ (eds) Ashcraft’s Pediatric Surgery, Batourina E, Tsai S, Lambert S et al 2005 Apoptosis induced by vitamin A 6th ed. Elsevier; Ch. 51, pp. 698–701. signalling is crucial for connecting the ureters to the bladder. Nat Genet 37:1082–9. Lee PA, Houk CP, Ahmed SF et al 2006 Consensus statement on manage­ ment of intersex disorders. International Consensus Conference on Biason Lauber A 2010 Control of sex development. Best Prac Res Clin Endo­ Intersex. Paediatrics 118:e488–500. crinol Metab 24:163–86. This paper presents the recommendations in intersex disorder management. Blaschko SD, Cunha GR, Baskin LS 2012 Molecular mechanisms of external Mendelsohn C 2009 Using mouse models to understand normal and abnor­ genitalia development. Differentiation 84:261–8. mal urogenital tract development. Organogenesis 5:306–14. Cai Y 2008 Participation of caudal Müllerian mesenchyme in prostate devel­ Munger SC, Natarajan A, Looger LL et al 2013 Fine time course expression opment. J Urol 180:1898–903. analysis identifies cascade of activation of repression and maps a puta­ Chai O, Song C, Park S et al 2013 Molecular regulation of kidney develop­ tive regulator of mammalian sex determination. PLoS 9:1–17. ment. Anat Cell Biol 46:19–31. Rajpert­De Meyts E 2006 Developmental model for the pathogenesis of This paper examines the molecular processes behind some of the testicular carcinoma in situ: genetic and environmental aspects. Human epithelial:mesenchymal interactions occurring in the developing kidney. Reprod Update 12:303–23. Chauvet V, Qian F, Boute N et al 2002 Expression of PKD1 and PKD2 tran­ Runyan C, Schaible K, Molyneaux K et al 2006 Steel factor controls midline scripts and proteins in human embryo and during normal kidney devel­ cell death of primordial germ cells and is essential for their normal opment. Am J Pathol 160:973–83. proliferation and migration. Development 133:4861–9. Cole B, Hensinger K, Maciel GAR et al 2006 Human fetal ovary development Sharpe RM, McKinnell C, Kivlin C et al 2003 Proliferation and functional involves the spatiotemporal expression of P450c17 protein. J Clin Endo­ maturation of Sertoli cells, and the relevance to disorders of testis func­ crinol Metab 91:3654–61. tion in adulthood. Reproduction 125:769–84. Davidson AJ 2009 Mouse kidney development. StemBook (ed) The Stem This paper considers the importance of Sertoli cell development and the Cell Research Community: StemBook; doi/10.3824/stembook.1.34.1. future sperm count of adult males. Dean A, Sharpe RM 2013 Clinical review: anogenital distance or digit length Song R, Yosypiv IV 2012 Development of the kidney medulla. Organogene­ as measures of fetal androgen exposure: relationship to male reproduc­ sis 8:10–17. tive development and its disorders. J Clin Endocrinol Metab 98: Soto­Suazo M, Zorn TM 2005 Primordial germ cells migration: morphologi­ 2230–8. cal and molecular aspects. Anim Reprod 2:147–60. De Felici M 2013 Origin, migration, and proliferation of human primordial Stranzinger E, Strouse PJ 2008 Ultrasound of the pediatric female pelvis. germ cells. In: Coticchio G, Albertinit DF, De Santis L (eds) Oogenesis. Semin Ultrasound CT MR 29:98–113. London: Springer; Ch. 2, pp. 19–37. Suzuki K, Economides A, Yanagita M et al 2009 New horizons at the cau­ De Ste Croix M 2007 Advances in paediatric strength assessment: changing dal embryo: coordinated urogenital/reproductive organ formation by our perspective on strength development. J Sports Sci Med 6:292–304. growth factor signalling. Curr Opin Genet Dev 19:491–6. Dias T, Sairam S, Kumarasiri S 2014 Ultrasound diagnosis of fetal renal Tanaka ST, Ishii K, Demarco RT et al 2010 Endodermal origin of bladder abnormalities. Best Pract Res Clin Obstet Gynaecol 28:403–15. trigone inferred from mesenchymal­epithelial interaction. J Urol 183: Faa G, Gerosa C, Fanni D et al 2012 Morphogenesis and molecular mecha­ 386–91. nisms involved in human kidney development. J Cell Physiol 227: This paper presents the molecular evidence for the origin of the bladder 1257–68. trigone mucosa. Geelhoed JJM, Verburg BO, Nauta J et al 2009 Tracking and determinants To M, Pereira S 2015 Routine fetal anomaly scan. In: Coady AM, Sarah B of kidney size from fetal life until the age of 2 years: the Generation R (eds) Twining’s Textbook of Fetal Abnormalities, 3rd ed. Churchill Liv­ Study. Am J Kidney Dis 53:248–58. ingstone; Ch. 3, pp. 60–80. Hodges SJ, Patel B, McLorie G et al 2009 Posterior urethral valves. Scientific Toppari J, Rodprasert W, Virtanen HE 2014 Cryptorchidism – disease or World Journal 14:1119–26. symptom? Annales d’Endocrinologie 75:72–6. Hutson JM 2012 Undescended testis, torsion, and varicocele. In: Coran AG Viana R, Batourina E, Huang H et al 2007 The development of the bladder (ed) Pediatric Surgery, 7th ed. Saunders; Ch. 77, pp. 1003–19. trigone, the center of the anti­reflux mechanism. Development 134: Hutson JM 2013 Undescended testis: the underlying mechanisms and the 3763–9. effects on germ cells that cause infertility and cancer. J Pediatr Surg Wang C, Gargollo P, Guo C et al 2011 Six1 and Eya1 are critical regulators 48:903–8. of peri­cloacal mesenchymal progenitors during genitourinary tract This paper considers the relationships between testicular development and development. Dev Biol 360:186–94. final testis maturity.

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DeveloPment of the urogenital system 1220.e2 8 noitCes Wang C, Wang JY, Borer JG et al 2013 Embryonic origin and remodelling of This paper considers the evidence that impaired nephrogenesis caused by low the urinary and digestive outlets. PLoS One 8:e55587. birth weight may give rise to chronic kidney disease. This paper considers the development of the cloacal region and its separation Williams A 2013 Congenital abnormalities of the lower urinary tract. Surgery into enteric and urogenital parts. 31:371–7. Wei W, Howard PS, Kogan B et al 2012 Urinary diversion results in marked Yosypiv IV 2012 Congenital anomalies of the kidney and urinary tract: decreases in proliferation and apoptosis in fetal bladder. J Urol 188: genetic disorder? Int J Nephrol. doi:10.1155/2012/909083. 1306–12. White SL, Perkovic V, Cass A et al 2009 Is low birth weight an antecedent of CKD in later life? A systematic review of observational studies. Am J Kidney Dis 54:248–61.

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CHAPTER 73 True pelvis, pelvic floor and perineum ischiococcygeus form the pelvic diaphragm and delineate the lower TRUE PELVIS AND PELVIC FLOOR limit of the true pelvis (Fig. 73.2). The fasciae investing the muscles are continuous with visceral pelvic fascia above, perineal fascia below, and The true pelvis is a bowl-shaped structure formed from the sacrum, obturator fascia laterally. pubis, ilium, ischium, the ligaments that interconnect these bones, and the muscles that line their inner surfaces. The true pelvis is considered Piriformis to start at the level of the plane passing through the promontory of the Piriformis forms part of the posterolateral wall of the true pelvis and is sacrum, the arcuate line on the ilium, the iliopectineal line and the attached to the anterior surface of the sacrum, the gluteal surface of the posterior surface of the pubic crest. This plane, or ‘inlet’, lies at an angle ilium near the posterior inferior iliac spine, the capsule of the adjacent of between 35° and 50° up from the horizontal; above this plane, the sacroiliac joint and, sometimes, to the upper part of the pelvic surface bony structures are sometimes referred to as the false pelvis. They form of the sacrotuberous ligament. It passes out of the pelvis through the part of the walls of the lower abdomen. In children, the width of the greater sciatic foramen above the sacrospinous ligament. Within the pelvic inlet is an age-independent predictor of chest width and thoracic pelvis, the posterior surface of the muscle lies against the sacrum, and dimensions (Emans et al 2005). The ‘outlet’ of the true pelvis is formed the anterior surface is related to the rectum (especially on the left), the by the ischiopubic rami, ischial tuberosities, sacrotuberous ligaments sacral plexus of nerves and branches of the internal iliac vessels. Piri- and distal sacrum. The bones surround a central pelvic canal that forms formis is described in more detail in Chapter 80. a ventrally concave curve (the curve of Carus); in the female, it consti- tutes the birth canal. The details of the topography of the bony and Obturator internus ligamentous pelvis are considered fully in Chapter 80. Obturator internus and the fascia over its upper, inner (pelvic), surface form part of the anterolateral wall of the true pelvis. It is attached to the structures surrounding the obturator foramen, ischio-pubic ramus, MUSCLES AND FASCIAE OF THE PELVIS the pelvic surface of the hip bone below and behind the pelvic brim, and the upper part of the greater sciatic foramen. It is also attached to Pelvic muscles the medial part of the pelvic surface of the obturator membrane. The muscle is covered by a fascial layer, and the muscle fibres can be seen The muscles arising within the pelvis form two groups. Piriformis and through this semi-transparent membrane from within the pelvis. Spe- obturator internus form part of the walls of the pelvis, and are consid- cialized portions of the fascia give attachment to some of the fibres of ered primarily as muscles of the lower limb (Fig. 73.1). Levator ani and levator ani (tendinous arch of levator ani), so that only the upper Greater sciatic foramen Sacral promontory Piriformis Ischiococcygeus Ischium Ischial spine Obturator Obturator fascia canal Tendinous arch Superior of levator ani pubic ramus Sacrospinous Anococcygeal ligament ligament Lesser sciatic foramen Iliococcygeus Inferior pubic (ischiopubic) ramus Sacrotuberous ligament Obturator internus Ischial tuberosity Pubococcygeus Pubovaginalis Fig. 73.1 Piriformis, obturator internus and the ligaments of the pelvis. Fig. 73.2 Muscles of the female pelvis. The superior gluteal and obturator Those muscles relating only to the pelvis or perineum have been omitted vessels and nerves, as well as the pelvic viscera, have been omitted for for clarity. (Adapted with permission from Drake RL, Vogl AW, Mitchell A clarity. (Adapted with permission from Drake RL, Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd ed, Elsevier, Churchill (eds), Gray’s Anatomy for Students, 2nd ed, Elsevier, Churchill Livingstone. Copyright 2010.) Livingstone. Copyright 2010.) 1221

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True pelvis, pelvic floor and perineum 1222 8 noiTces Pubic symphysis Fig. 73.3 Muscles of the female pelvis viewed from above. The sacral nerve roots have been Endopelvic fascia lining superior Pubis divided close to the sacral foramina. The anorectal aspect of deep perineal junction, vagina and urethra have been divided at space/pouch the level of the pelvic floor. Urethra Vagina Tendinous arch of levator ani Pubococcygeus Fascia over obturator internus Iliococcygeus Rectum Ischium Ischiococcygeus Third and fourth sacral foramina Piriformis Anococcygeal ligament Iliac wing Sacrum portion of obturator internus can be seen from above. The lower portion Iliococcygeus Iliococcygeus is attached to the inner surface of the forms part of the boundaries of the ischio-anal fossa. In the male, the ischial spine below and anterior to the attachment of ischiococcygeus, upper portion lies lateral to the bladder, the obturator and vesical and also to the tendinous arch as far forwards as the obturator canal vessels, and the obturator nerve. In the female, the attachments of the (see Fig. 73.2). The most posterior fibres are attached to the tip of the broad ligament of the uterus, the ovarian end of the uterine tubes and sacrum and coccyx, but the majority join fibres from the contralateral the uterine vessels also lie medial to obturator internus and its fascia. side to form a raphe that is effectively continuous with the fibroelastic anococcygeal ligament, which is closely applied to its inferior surface; Levator ani (pubococcygeus, iliococcygeus some muscle fibres may attach into the ligament. The raphe provides a and puborectalis) strong attachment for the pelvic floor posteriorly and must be divided Levator ani is a broad muscular sheet of variable thickness attached to to allow wide excisions of the anorectal canal during abdominoperineal the internal surface of the pelvis. It forms a large portion of the pelvic excisions for malignancy. An accessory slip may arise from the most floor (Fig. 73.3) (Lawson 1974a, Roberts et al 1988, Wendell-Smith posterior part and is sometimes referred to as iliosacralis. and Wilson 1991). The muscle is subdivided into named portions according to their attachments and the pelvic viscera to which they are Puborectalis Puborectalis lies lateral to pubococcygeus and cannot related (pubococcygeus, iliococcygeus and puborectalis). These parts been seen from inside the pelvis. It originates from the inner surface of are often referred to as separate muscles but the boundaries between the ischiopubic rami immediately adjacent to, and sometimes arising each part cannot be easily distinguished and, moreover, they perform in part from, the perineal membrane. Its fibres pass lateral to those of many similar physiological functions. Ischiococcygeus (coccygeus) lies iliococcygeus and pubococcygeus to decussate posterior to the rectum immediately cranial to levator ani and is contiguous with it. Pubococcy- at the anorectal junction. The border between puborectalis and some geus is often subdivided into separate parts according to the pelvic fibres of the external anal sphincter is indistinct. viscera to which each part relates (puboperinealis, puboprostaticus or pubovaginalis, puboanalis, puborectalis). Levator ani arises from each Ischiococcygeus Ischiococcygeus may be referred to as a separate side of the walls of the pelvis along the condensation of the obturator muscle, sometimes named coccygeus. It lies as the most posterosuperior fascia (the tendinous arch of levator ani). Fibres from ischiococcygeus portion of levator ani, and arises as a triangular musculotendinous attach to the sacrum and coccyx but the remaining parts of the muscle sheet with its apex attached to the pelvic surface and tip of the ischial converge in the midline. Fibres from iliococcygeus join by a partly spine, and base attached to the lateral margins of the coccyx and the fibrous intersection and form the iliococcygeal raphe posterior to the fifth sacral segment. Ischiococcygeus is rarely absent, but may be almost anorectal junction. Closer to the anorectal junction, and elsewhere completely tendinous rather than muscular. It lies on the pelvic aspect in the pelvic floor, the fibres are more nearly continuous with those of of the sacrospinous ligament and may be fused with it, particularly if the opposite side, such that the muscle forms a sling (iliococcygeus, it is mostly tendinous. The sacrospinous ligament may represent either puborectalis). a degenerate part or an aponeurosis of the muscle, since muscle and ligament are coextensive. Attachments The attachments for pubococcygeus, iliococcygeus and puborectalis are as follows. Relations The superior, pelvic, surface of levator ani is separated only by fascia (superior pelvic diaphragmatic, visceral and extraperitoneal) Pubococcygeus Pubococcygeus originates from the posterior aspect from the urinary bladder, prostate or uterus and vagina, rectum and of the body of the pubis and passes back almost horizontally. The most peritoneum. Its inferior, perineal, surface forms the medial wall of the medial fibres run directly lateral to the urethra and its sphincter as it ischio-anal fossa and the superior wall of the anterior recess of the fossa, passes through the pelvic floor; here, the muscle is correctly called both being covered by inferior pelvic diaphragmatic fascia. The poste- puboperinealis, although, because of its close relationship to the upper rior border is separated from the coccyx by areolar tissue. The medial half of the urethra in both sexes, it is often referred to as pubourethralis; borders of the two levator muscles and the inferior ischiopubic rami despite this, no direct connection with the urethra is present. In males, border the levator hiatus, through which pass the urethra, vagina (in some of these fibres lie lateral and inferior to the prostate and are the female) and anus. In the female, that portion of the hiatus that lies referred to as puboprostaticus (levator prostatae). In females, fibres run anterior to the perineal body is referred to as the urogenital hiatus. further back and attach to the lateral walls of the vagina, where they are referred to as pubovaginalis. In both sexes, fibres from this part of Vascular supply Levator ani is supplied by branches of the inferior pubococcygeus attach to the perineal body; a few elements also attach gluteal, inferior vesical and pudendal arteries. to the anorectal junction. Some fibres, sometimes called puboanalis, decussate and blend with the longitudinal rectal muscle and fascial Innervation The nerves to levator ani originate mainly from the third elements to contribute to the conjoint longitudinal coat of the anal and fourth sacral spinal segments, with lesser contributions from the canal. Behind the rectum, other fibres of pubococcygeus form a tendi- second segment. These nerves enter the pelvis just above, and some- nous intersection as part of the levator raphe. Elements of pubococcy- times pierce, ischiococcygeus to pass along the ventral surface of ischio- geus (puboperineus, pubovaginalis/puboprostaticus and puboanalis) coccygeus and pubococcygeus, supplying these muscles and sending may collectively be referred to as ‘pubovisceralis’. fibres to puborectalis (Sato 1980, Roberts and Krishingner 1967). The

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