Small intestine
1135.e1
56
RETPAHC
REFERENCES
Al-Shboul OA 2013 The importance of interstitial cells of Cajal in the gas- Kim HJ, Ko YT, Lim JW et al 2007 Radiologic anatomy of the superior
trointestinal tract. Saudi J Gastroenterol 19:3–15. mesenteric vein and branching patterns of the first jejunal trunk: evalu-
Barker N, van Es JH, Kuipers J et al 2007 Identification of stem cells in small ation using multi-detector row CT venography. Surg Radiol Anat
intestine and colon by marker gene Lgr5. Nature 449:1003–7. 29:67–75.
Barnert J 2007 Motility and transit in the small bowel. In: Current Topics in Kim SK, Cho CD, Wojtowycz AR 2008 The ligament of Treitz (the suspen-
Neurogastroenterology. Proceedings of the 2nd International Sympo- sory ligament of the duodenum): anatomic and radiographic correla-
sium of Neurogastroenterology. Editura Medicală Universitară ‘Iuliu tion. Abdom Imaging 33:395–7.
Haţieganu’: Cluj Napoca, Romania, 4 October. Kocandrle V, Houttuin E, Prohaska JV 1966 Regeneration of the lymphatics
Bertelli E, Di Gregorio F, Bertelli L et al 1995 The arterial blood supply of after autotransplantation and homotransplantation of the entire small
the pancreas: a review. I. The superior pancreaticoduodenal and the intestine. Surg Gynecol Obstet 122:587–92.
anterior superior pancreaticoduodenal arteries. An anatomical and Malik A, Westergaard H 2002 Short bowel syndrome. In: Feldman M,
radiological study. Surg Radiol Anat 17:97–106. Friedman LS, Sleisenger MH (eds) Gastrointestinal and liver disease,
Bertelli E, Di Gregorio F, Bertelli L et al 1996 The arterial blood supply of 7th ed. Philadelphia: Elsevier, Saunders, pp. 1807–16.


the pancreas: a review. II. The posterior superior pancreaticoduodenal Marsh MN, Swift JA 1969 A study of the small intestinal mucosa using the
artery. An anatomical and radiological study. Surg Radiol Anat 18:1–9. scanning electron microscope. Gut 10:940–9.
Bertelli E, Di Gregorio F, Bertelli L et al 1997 The arterial blood supply of Mather Cordiner GR, Calthrop GT 1936 The radiography of the duodenal
the pancreas: a review. IV. The anterior inferior and posterior pancrea- cap. Br J Surg 23:700–15.
ticoduodenal aa., and minor sources of blood supply for the head of Merrett ND, Wilson RB, Cosman P et al 2009 Superior mesenteric artery
the pancreas. An anatomical review and radiologic study. Surg Radiol syndrome: diagnosis and treatment strategies. J Gastrointest Surg
Anat 19:203–12. 13:287–92.
Bianchi A 1984 Intestinal lengthening: an experimental and clinical review. Miller MJ, McDole JR, Newberry RD 2010 Microanatomy of the intestinal
J R Soc Med 77(Suppl 3):35–41. lymphatic system. Ann N Y Acad Sci 1207 Suppl 1:E21–8.
Bianchi HF, Albanèse EF 1989 The supraduodenal artery. Surg Radiol Anat Mostafa RM, Moustafa YM, Hamdy H 2010 Interstitial cells of Cajal, the
11:37–40. maestro in health and disease. World J Gastroenterol 16:3239–48.
Bradley RL 1973 Surgical anatomy of the gastroduodenal artery. Int Surg Murakami G, Hirata K, Takamuro T et al 1999 Vascular anatomy of the
58:393–6. pancreaticoduodenal region: a review. J Hepatobiliary Pancreat Surg
Clevers HC, Bevins CL 2013 Paneth cells: maestros of the small intestinal 6:55–68.
crypts. Annu Rev Physiol 75:289–311. Nightingale J, Spiller R 2001 Normal intestinal anatomy and physiology. In:


Conley D, Hurst PR, Stringer MD 2010 An investigation of human jejunal Nightingale J (ed) Intestinal Failure. London: Greenwich Medical Media,
and ileal arteries. Anat Sci Int 85:23–30. pp. 17–36.
Cornes JS 1965 Number, size, and distribution of Peyer’s patches in the Nightingale J, Woodward JM 2006 Guidelines for management of patients
human small intestine. Part II The effect of age on Peyer’s patches. Gut with a short bowel. Gut 55:1–12.
6:230–3. O’Keefe SJ, Buchman AL, Fishbein TM et al 2006 Short bowel syndrome and
Didierlaurent A, Simonet M, Sirard JC 2005 Innate and acquired plasticity intestinal failure: consensus definitions and overview. Clin Gastroen-
of the intestinal immune system. Cell Mol Life Sci 62:1285–7. terol Hepatol 4:6–10.
Farrell JJ 2002 Digestion and absorption of nutrients and vitamins. In: Ozkurt H, Cenker MM, Bas N et al 2007 Measurement of the distance and
Feldman M, Friedman LS, Sleisenger MH (eds) Gastrointestinal and angle between the aorta and superior mesenteric artery: normal values
liver disease, 7th ed. Philadelphia: Saunders; pp. 1715–50. in different BMI categories. Surg Radiol Anat 29:595–9.
Farrugia G 2008 Interstitial cells of Cajal in health and disease. Neurogas- Rosenblum JD, Boyle CM, Schwartz LB 1997 The mesenteric circulation.
troenterol Motil 20 Suppl 1:54–63. Surg Clin N Am 77:289–306.
Fotiades CI, Kouerinis IA, Papandreou I et al 2005 Current diagnostic and Rountas CH, Fanariotis M, Vlychou M et al 2013 Celiomesenteric trunk
treatment aspects of duodenal diverticula: report of two polar cases and demonstrated by multi-detector computed tomography angiography:
review of the literature. Ann Gastroenterol 18:441–4. two cases of a rare vascular variation. Folia Morphol (Warsz) 72:


Graf O, Boland GW, Kaufman JA et al 1997 Anatomic variants of mesenteric 171–5.
veins: depiction with helical CT venography. AJR Am J Roentgenol Sagar J, Kumar V, Shah DK 2006 Meckel’s diverticulum: a systematic review.
168:1209–13. J R Soc Med 99:501–5.
Gunning KEJ, Friend PJ 1998 Intestinal transplantation. In: Klinck JR, Sanders KM, Ward SM, Koh SD 2014 Interstitial cells: regulators of smooth
Lindop MJ (eds) Anaesthesia and intensive care for organ transplanta- muscle function. Physiol Rev 94:859–907.
tion. London: Chapman & Hall Medical; pp. 297–309. A review of the structural, functional and molecular features of interstitial
Helander HF, Fändriks L 2014 Surface area of the digestive tract – revisited. cells of Cajal and their importance in smooth muscle function.
Scand J Gastroenterol 49:681–9. Straub RH, Wiest R, Strauch UG et al 2006 The role of the sympathetic
Hirai I, Murakami G, Kimura W et al 2001 Long descending lymphatic nervous system in intestinal inflammation. Gut 55:1640–9.
pathway from the pancreaticoduodenal region to the para-aortic nodes: Suda K 2010 Histopathology of the minor duodenal papilla. Dig Surg
its laterality and topographical relationship with the celiac plexus. Oka- 27:137–9.
jimas Folia Anat Jpn 77:189–99 (English abstract). Teitelbaum EN, Vaziri K, Zettervall S et al 2013 Intraoperative small bowel
Horiguchi S, Kamisawa T 2010 Major duodenal papilla and its normal length measurements and analysis of demographic predictors of
anatomy. Dig Surg 27:90–3. increased length. Clin Anat Mar 20. doi: 10.1002/ca.22238.
Horton KM, Fishman EK 2010 CT angiography of the mesenteric circulation. Information on small bowel length in living adults, which varies with sex,
Radiol Clin North Am 48:331–45, viii. height and age.


Husebye E 1999 The patterns of small bowel motility: physiology and Uppal K, Tubbs RS, Matusz P et al 2011 Meckel’s diverticulum: a review. Clin
implications in organic disease and functional disorders. Neurogastro- Anat 24:416–22.
enterol Motil 11:141–61. Van Kruiningen HJ, West AB, Freda BJ et al 2002 Distribution of Peyer’s
Jeppesen PB 2013 Short bowel syndrome – characterisation of an orphan patches in the distal ileum. Inflamm Bowel Dis 8:180–5.
condition with many phenotypes. Expert Opinion Orphan Drugs Walther A, Coots A, Nathan J et al 2013 Physiology of the small intestine
1:515–25. after resection and transplant. Curr Opin Gastroenterol 29:153–8.
Jeppesen PB, Mortensen PB 2002 Enhancing bowel adaptation in short Winston CB, Lee NA, Jarnagin WR et al 2007 CT angiography for delineation
bowel syndrome. Curr Gastroenterol Rep 4:338–47. of celiac and superior mesenteric artery variants in patients undergoing
Johansson ME, Ambort D, Pelaseyed T et al 2011 Composition and func- hepatobiliary and pancreatic surgery. AJR Am J Roentgenol 188:
tional role of the mucus layers in the intestine. Cell Mol Life Sci W13–W19.
68:3635–41. Yamaguchi S, Kuroyanagi H, Milson JW et al 2002 Venous anatomy of the
Kamisawa T, Takuma K, Tabata T et al 2010 Clinical implications of accessory right colon: precise structure of the major veins and gastrocolic trunk
pancreatic duct. World J Gastroenterol 16:4499–503. in 58 cadavers. Dis Colon Rectum 45:1337–40.


CHAPTER
66
Large intestine
absent from the caecum, vermiform appendix and rectum); and the
OVERVIEW
colonic wall is puckered into sacculations (haustrations), visible on
plain radiographs as incomplete septations arising from the bowel wall
The large intestine extends from the ileocaecal junction to the anus. It (see Fig. 66.2; Fig. 66.3). Its calibre is greatest near the caecum, gradu
begins as the caecum and vermiform appendix, which are usually ally diminishes towards the sigmoid colon, and then increases again in
located in the right iliac fossa. The ascending or right colon passes the rectum, where the lower third is dilated to form the rectal ampulla.
upwards in the right flank to the right hypochondrium, where it bends The mean internal diameter of the large intestine is 4.8 cm (Helander
to the left to form the hepatic flexure (right colic flexure) and become and Fändriks 2014).
the transverse colon. This loops across the abdomen with an anteroin During development, the large intestine is temporarily suspended
ferior convexity until it reaches the left hypochondrium, where it curves by a midline dorsal mesentery. However, after rotation of the gut in
inferiorly to form the splenic flexure (left colic flexure). From here, it utero, large portions of it come to lie adherent to the retroperitoneum,
descends in the left flank as the descending or left colon before continu while other segments remain suspended by a mesentery within the
ing as the sigmoid colon in the left iliac region. The sigmoid colon peritoneal cavity. The mesenteries of the colon consist of two layers of
descends into the true pelvis and becomes the rectum anterior to the visceral peritoneum enclosing adipose and connective tissues and sur
third sacral vertebra. The rectum transitions to the anal canal at the level rounding vessels, nerves and lymphatics that run forward from retro
of the pelvic floor (Figs 66.1–66.2). The large intestine thus runs from peritoneal structures. Where colonic mesenteries lie in contact with the


the ileocaecal (ileocolic) junction to the anal verge. It is formed from retroperitoneum, the potential space between the retroperitoneum and
the distal midgut, all of the hindgut, and the proctodeum (Ch. 72 and mesentery, referred to as the ‘subperitoneal space’, forms an avascular
Figs 72.4 and 72.7E). Knowledge of the development of the large intes plane during surgical dissection and allows the tracking of fluid, blood
tine not only helps to explain its anatomy, relations (including perito and disease (Oliphant et al 1996, Coffey 2013) (Ch. 62). The caecum
neal attachments) and neurovascular supply (Ch. 60), but is also may be firmly adherent to the retroperitoneum but is frequently sus
fundamental to understanding congenital large bowel disorders such as pended by a short mesentery, especially in infants. The ascending colon
anorectal malformations and malrotation of the gut. is usually adherent to the retroperitoneum, while the transverse colon
In the adult, the large intestine is approximately 1–1.5 m long in is suspended by a mesocolon and is freely mobile within the upper
vivo, although there is considerable individual variation. The large intes abdomen. The hepatic and splenic flexures may have a short mesentery.
tine differs from the small intestine in several ways: it has a greater The descending colon is adherent to the retroperitoneum, usually down
calibre; for much of its course it is more fixed in position; the outer to the level of the left iliac crest, and the sigmoid colon has a mesentery
longitudinal muscle layer of the colon is concentrated into three longi of variable length. The sigmoid mesentery shortens as it approaches the
tudinal bands, taeniae coli; small fatty projections, appendices epi pelvis and practically disappears at the level of the rectosigmoid junc
ploicae, are scattered over its free surface (although these tend to be tion. The rectum is a retroperitoneal structure.
First part of the duodenum
Spleen
Right lobe of the liver Tail of pancreas
Splenic flexure
Hepatic flexure
Transverse colon


Superior taenia
Third part of the duodenum
Left kidney
Right kidney
Descending colon
Ascending colon
Anterior taenia (libera)
Anterior taenia (libera)
Left iliac crest
Caecum
Sigmoid colon
Vermiform appendix
Rectum
1136 Fig. 66.1 An overview of the abdominal colon and its relations.


Overview
1137
66
RETPAHC
Splenic flexure
Hepatic flexure Appendices epiploicae
Transverse colon
Taenia libera
Fig. 66.2 The appearance of the colon on double contrast barium enema
examination, demonstrating the transverse colon and hepatic and splenic
flexures.
Taenia mesocolica
The posterior attachments of the small bowel mesentery and trans Taenia omentalis
verse mesocolon result in the peritoneal cavity being divisible into Fig. 66.3 Layers of the colonic wall.
named compartments (Ch. 62). The supracolic and infracolic compart
ments are separated by the attachment of the transverse mesocolon to
the posterior abdominal wall. Anteriorly, the transverse colon and trans
verse mesocolon are adherent to the posterior surface of the greater reflection on to the colonic wall. In the transverse colon, the taeniae
omentum. Lifting the greater omentum upwards exposes the infracolic are rotated as a consequence of the dependent position of this segment
compartment. This is divided by the root of the small bowel mesentery of colon and so anterior becomes inferior, posteromedial becomes
that descends obliquely from left to right; to the right lies the right posterior, and posterolateral becomes superior. The width of the taeniae
infracolic compartment, its apex the ileocaecal junction, and to the left, coli remains fairly constant throughout the colon but they broaden out
the left infracolic compartment, bordered laterally by the descending in the distal part of the sigmoid colon and gradually merge to form a
colon and continuous below with the pelvic cavity. complete longitudinal muscle layer around the rectum, which therefore
The microstructure of the large bowel corresponds to the general has no external sacculations.
pattern of the gut wall, having a mucous membrane consisting of epi
thelium, lamina propria and muscularis mucosa, surrounded by an
inner circular and outer longitudinal layer of muscle and a serosa (see INTERNAL APPEARANCE
Figs 66.3, 66.51). The mucosa also contains scattered neuroendocrine
cells derived from the amine precursor uptake and decarboxylation Colonic haustrations represent sites where the mucosa and submucosa


(APUD) cell lineage; these cells produce amines and/or peptides, which of the colonic wall is infolded; these folds partially span the bowel
act as hormones or neurotransmitters. Unlike the small intestine, the lumen but never form a complete, circumferential ring. The pattern of
mucosa of the large intestine lacks villi and the glands (crypts) contain haustrations and appearance of the colonic mucosa help the clinician
a high proportion of goblet (mucinsecreting) cells. In the appendix, appreciate the level reached during flexible endoscopic examinations of
the glands are sparse and numerous lymphoid follicles are found in the the colon (Silverstein and Tytgat 1991). In the caecum, the three longi
mucosa and submucosa. Although it is not a vital organ, the primary tudinal taeniae coli converge to form a characteristic ‘trefoil’ pattern on
function of the colon is transmission and elimination of intestinal the caecal wall (Fig. 66.4). The lower pole of the caecum is usually
contents, but it also has important absorptive and secretory roles. The devoid of haustrations, although a spiral mucosal pattern is often seen
anal sphincter is responsible for both continence and evacuation. The in the region of the orifice of the appendix (Fig. 66.5). The upper
large intestine has its own intrinsic (enteric) nerve supply, the activity caecum and ascending colon possess shallow but deep haustrations,
of which is modulated by extrinsic innervation. which may extend across onethird of the lumen (Fig. 66.6). In the
transverse colon, the haustrations often confer a triangular appearance
to the crosssection of the lumen when viewed along its axis at colon
EXTERNAL APPEARANCE oscopy (Fig. 66.7). The haustrations of the descending and sigmoid
colon tend to be thicker and shorter, producing a more circular cross
The haustrations of the colon are frequently absent in the caecum and section to the lumen (Figs 66.8–66.9). The wall of the colon is thinnest
often relatively sparse in the ascending and proximal transverse colon. in the region of the caecum and ascending colon, where it is most at


They become more pronounced beyond the middle of the transverse risk of perforation during therapeutic endoscopic procedures. The
colon. The sigmoid colon often has marked sacculation. Appendices overall luminal diameter is often smallest in the descending colon. The
epiploicae are small, fatfilled pouches of peritoneum that project from tortuosity of the sigmoid colon means that shorter lengths of colon are
the external surface of the colon and are supplied by blood vessels that visible during endoscopy than elsewhere in the colon. The haustrations
perforate the bowel wall. There are few, if any, appendices epiploicae of the rectum usually form consistent and recognizable transverse folds
on the serosal surface of the caecum, and only a limited number scat and the submucosal vessels tend to be more pronounced than in the
tered along the ascending colon. They are more common over the distal colon (Fig. 66.10). Distinct veins are usually visible during endoscopy,
colon and particularly numerous on the surface of the sigmoid colon, and are most marked above the anorectal junction.
where they can be large in the obese individual. The rectum has no
appendices epiploicae.
The three taeniae coli are located in fairly constant positions beneath RADIOGRAPHIC APPEARANCES
the serosal surface of the colon, except in the transverse colon. They are
found on the antimesenteric aspect of the colon directly opposite the Crosssectional imaging of the colon can be performed with computed
mesentery (taenia libera), posterolaterally (taenia omentalis) and pos tomography (CT) and magnetic resonance imaging (MRI). On axial
teromedially (taenia mesocolica) midway between the taenia libera and imaging, the colon may be filled with particulate faeces and air (Fig.
the mesentery (see Fig. 66.3). In the ascending and descending colon, 66.11). The wall in normal individuals is thin. The caecum and ascend
the posterolateral taenia is often obscured from view by the peritoneal ing colon often contain faecal residue and are easily identified in the


LARgE inTEsTinE
1138
8
nOiTCEs
Ileocaecal
valve
Fig. 66.4 The endoscopic appearance Fig. 66.5 The endoscopic appearance of the orifice of Fig. 66.6 The endoscopic appearance of
of the caecum. The characteristic trefoil the appendix, seen as a slit-like depression near the the ascending colon.
appearance of the confluence of the three centre of this view of the caecal pole. The orifice varies
taeniae is usually obvious. from a small depression to an obvious luminal structure.
The ileocaecal junction is just visible in the top left
corner. (Courtesy of Dr Michael Schultz.)
Fig. 66.7 The Fig. 66.9 The
endoscopic appearance endoscopic appearance
of the transverse colon. of the sigmoid colon.
Note the characteristic Multiple large mucosal
triangular appearance folds are characteristic.
of the haustrations
when viewed
collectively (see also
Fig. 66.11C).
Fig. 66.8 The Fig. 66.10 The endoscopic
endoscopic appearance appearance of the rectum. Note
of the descending colon. the large transverse folds, with little
The lumen tends to look else in the way of mucosal folds,
rather more featureless characterizing the rectum. Prominent
than the more proximal submucosal vessels are often seen,
colon. particularly in the lower third.
retroperitoneum on the right. The transverse colon may contain faeces and superior rectal arteries, with a small contribution from branches of
or gas and lies in a variable position, suspended by its mesentery. The the internal iliac artery (the middle and inferior rectal arteries).
descending colon lies in the retroperitoneum on the left and often The arteries of the midgut and hindgut contribute to an anastomotic
contains little faecal residue. The volume data sets produced by modern vessel, the marginal artery of Drummond, which runs in the mesentery
multislice CT can now produce virtual colonoscopic mucosal images of along the inner margin of the colon and gives off short terminal
the distended and cleaned colon, and surfacerendered images of the branches to the bowel wall. These divide into vasa brevia, which pass


internal surface of the bowel (Fenlon 2002). directly through the muscularis externa of the colonic wall, and vasa
longa, which travel through the subserosa for a short distance before
running through the circular muscle, giving off branches to the appen
VASCULAR SUPPLY AND LYMPHATIC DRAINAGE
dices epiploicae (Fig. 66.13). The marginal artery is formed by the main
branches and arcades arising from the ileocolic, right colic, middle colic
Arteries
and left colic arteries. It is most apparent in the ascending, transverse
The arterial supply of the large intestine is derived from both the supe and descending colons (Fig. 66.14) and poorly developed in the
rior and the inferior mesenteric arteries (Fig. 66.12) (Jackson 1999). sigmoid colon. The marginal artery in the region of the splenic flexure
The caecum, appendix, ascending colon and proximal twothirds of the may be absent or of insufficient calibre to be of functional significance.
transverse colon (derived from the midgut) are supplied from ileocolic, Nevertheless, it may dilate considerably when one of the main visceral
right colic and middle colic branches of the superior mesenteric artery. arteries is compromised since it then provides a collateral arterial supply
The distal third of the transverse colon, descending and sigmoid colon, to the colon. The most susceptible part of the chain of anastomosing
rectum and upper anal canal (hindgut derivatives) are supplied pre vessels is at the junction of midgut and hindgut in the distal transverse
dominantly from the inferior mesenteric artery via the left colic, sigmoid colon near the splenic flexure. However, the arterial supply to this


Overview
1139
66
RETPAHC
Fig. 66.11 The appearance of the colon on
multislice computed tomographic examination.
A, Axial CT. B, Coronal reformat showing
normal calibre and distribution of the abdominal
colon (ascending, transverse and descending).
C, Volume-rendering of the colonic wall using the
axial data set to produce virtual colonoscopic
views, showing the triangular lumen of the
transverse colon. D, Volume-rendering of the
air-filled colon using the axial data set to give an
image similar to a double contrast barium enema,
demonstrating haustrations. (A–B, By courtesy of
Dr Louise Moore, Chelsea and Westminster
Hospital. C–D, By courtesy of GE Worldwide
Medical Systems.)
A B
Ascending Transverse Descending Ascending Caecum Hepatic Small Descending Splenic
colon colon colon colon flexure bowel colon flexure
C D
Middle colic artery Fig. 66.12 The main branches of the superior and
inferior mesenteric arteries.
Middle branch
Right branch Left branch
Right colic artery
Ascending branch
Ileocolic trunk
Left colic artery
Superior division Descending branch
Inferior division
Inferior mesenteric artery
Anterior
caecal branch
Posterior
Sigmoid arteries
caecal branch
Appendicular artery
region may be augmented by an inner arterial arc (of Riolan), which an abdominal aortic aneurysm, when the descending colon remains
runs a meandering course in the colonic mesentery between the main viable because the marginal artery continues to receive an adequate
trunk of the middle colic artery and the ascending branch of the left blood supply from the left branch of the middle colic artery and the
colic artery (Fisher and Fry 1987, Gourley and Gering 2005). When sigmoid colon gains its supply from the middle and inferior rectal arter
present, this vessel is usually only prominent when there is occlusion ies via the superior rectal and sigmoid arteries. When colonic ischaemia
of the superior or inferior mesenteric artery. does occur, it is usually maximal in the region of the splenic flexure and
proximal descending colon because this segment is furthest from the
Colonic vascular occlusion collateral arterial supplies. Occlusion of the common iliac arteries may


The marginal artery of the colon may become massively dilated when also result in dilation of the marginal and inferior mesenteric arteries,
there is chronic stenosis or occlusion of the superior or inferior which become an important collateral supply to the lower limbs via
mesenteric artery. The latter may occur, for example, in association with dilated middle rectal arteries arising from the internal iliac artery.


LARgE inTEsTinE
1140
8
nOiTCEs
Veins descending colon, sigmoid colon and rectum drain into nodes follow
ing the course of the inferior mesenteric artery (Fig. 66.16). In cases
The venous drainage of the large intestine is primarily into the portal
where the distal transverse colon or splenic flexure is predominantly
vein via the superior mesenteric and inferior mesenteric veins, although
supplied by vessels from the middle colic artery, the lymphatic drainage
some drainage from the rectum occurs via middle rectal veins into the
of this area may be predominantly to superior mesenteric nodes.
internal iliac veins, and inferior rectal veins into the internal pudendal
veins. Those parts of the colon derived from the midgut (caecum,
appendix, ascending colon and proximal twothirds of the transverse
colon) drain into colic branches of the superior mesenteric vein, while Right colic Right colic/middle Superior mesenteric Left colic Marginal
hindgut derivatives (distal third of the transverse colon, descending and artery colic trunk artery artery artery
sigmoid colon, rectum and upper anal canal) drain into the inferior
mesenteric vein (Fig. 66.15).
Lymphatic drainage
Lymph drainage from the large intestine follows the course of the arter
ies. Thus, lymphatic vessels of the caecum, ascending and proximal
transverse colon drain ultimately into lymph nodes related to the supe
rior mesenteric artery, while those of the distal transverse colon,
Feeding vessel
Mesentery
(e.g. marginal artery)
Terminal branch
Vasa brevia
Circular muscle
Vasa longa
Serosa
Taenia omentalis
Taenia mesocolica
Ascending Ileocolic Inferior Superior rectal Sigmoid Descending Ascending
Submucosal plexus
colic artery artery mesenteric artery artery branch branch
artery
Submucosa Appendicular vessel Fig. 66.14 The marginal artery running parallel to the colon and providing
an anastomosis between the branches of the superior mesenteric artery
Taenia libera Appendix epiploicae supplying the right side of the colon and the branches of the inferior
mesenteric artery supplying the left side of the colon (digital subtraction


Fig. 66.13 The typical pericolic arrangement of the arterial vasculature. arteriogram). (Courtesy of Dr J Jackson, Hammersmith Hospital, London.)
Middle colic vein Fig. 66.15 The main branches of the superior and
inferior mesenteric veins.
Right branch Left branch
Inferior mesenteric
vein
Ileocolic vein Ascending branch
Left colic vein
Superior branch
Descending branch
Inferior branch
Anterior caecal
branch
Posterior caecal
branch Sigmoid veins
Appendicular vein
Superior rectal vein


Midgut region of large intestine
1141
66
RETPAHC
Middle colic nodes
Fig. 66.16 The lymph vessels and nodes draining
Superior mesenteric the large intestine.
Paracolic nodes nodes
Inferior mesenteric
Upper ileocolic
nodes
nodes
Ascending left
Right colic colic nodes
nodes
Left colic nodes
Paracolic nodes
Paracolic nodes
Lower ileocolic
nodes Descending left
colic nodes
Anterior caecal
nodes
Sigmoid nodes
Posterior caecal
nodes
Appendicular
nodes
Superior rectal Perirectal nodes
nodes
Colic nodes
Lymph nodes related to the colon form four groups: epicolic, paracolic,
intermediate colic and preterminal colic nodes. Epicolic nodes are
minute whitish nodules on the serosal surface of the colon, sometimes
within the appendices epiploicae. Paracolic nodes lie along the medial
borders of the ascending and descending colon and along the mesenteric Ileocaecal valve
borders of the transverse and sigmoid colon. Intermediate colic nodes
lie along the named colic vessels (the ileocolic, right colic, middle colic,
left colic, sigmoid and superior rectal arteries). Preterminal colic nodes
lie along the main trunks of the superior and inferior mesenteric arteries
and drain into preaortic nodes at the origin of these vessels.
Ascending mesocolic lymph nodes are significantly larger than
sigmoid mesocolic lymph nodes; this is relevant to lymph node retrieval
and examination after resection for colonic cancer (Ahmadi et al 2015).
Radical lymphadenectomy during resection of colorectal cancer
Terminal ileum
requires removal of the highest possible lymph nodes draining the
region of colon in which the tumour is located. In cases of cancer
of the rectum or sigmoid colon, this usually involves excision of the
preterminal colic nodes along the inferior mesenteric artery with liga
tion of the artery at its root or just below the origin of the left colic
Vermiform appendix
artery.
MIDGUT REGION OF LARGE INTESTINE
CAECUM
This blind pouch, measuring approximately 6 cm in length, lies below
Fig. 66.17 The caecum and ileocolic junction, double contrast barium
enema appearance.


the level of the ileocolic junction, anterior to the fascia covering the
right iliacus and psoas major, with the lateral cutaneous nerve of the
thigh interposed. The caecum usually lies adjacent to the anterior
tively large diameter of the caecum makes it liable to distension with
abdominal wall unless the greater omentum or loops of small bowel
increased intracolonic pressure and it is the region of the large intestine
are interposed. The caecum is often completely covered by peritoneum,
at greatest risk of perforation secondary to colonic distension (from
which is reflected posteriorly and inferiorly to the floor of the right iliac
obstruction or other pathology).
fossa. Peritoneal folds from the posterior caecal wall may create a variety
of peritoneal recesses around the caecum that have the potential to
Ileocolic junction
become sites of internal herniation; a superior and inferior ileocaecal
recess, a retrocaecal recess and a paracolic recess have been described
(Rivkind et al 1986). The retrocaecal recess frequently contains the The terminal ileum joins the posteromedial aspect of the large intestine
vermiform appendix. The three taeniae coli lie anteriorly, posteromedi at the junction of the caecum and colon, where it projects into the
ally and posterolaterally, and converge on the base of the appendix. lumen of the large intestine as the ileal papilla (Fig. 66.18A). It consists
During childhood, the lateral caecal wall outgrows the medial wall such of two labial folds; its precise shape and form varies from slitlike to an
that the orifice of the appendix, which is originally at the apex of the oval mucosal rosette, depending, in part, on the state of contraction or
caecum (Fig. 66.17), usually comes to lie slightly posteromedially. distension of the caecum. The upper labial fold is approximately hori
Fluid and electrolyte reabsorption by the large intestine begins in zontal and is at the junction between the ileum and colon; the lower
the caecum but occurs mostly in the ascending and transverse colon. lip is longer and more concave, and is at the junction between the ileum


The distensible ‘saclike’ morphology of the caecum allows storage of and caecum. At their bases, the labia fuse and continue as narrow
large volumes of semiliquid chyme from the small intestine. The rela mucosal ridges or frenula.


LARgE inTEsTinE
1142
8
nOiTCEs
A B
5mm
Fig. 66.18 A, The endoscopic appearance of the ileocolic junction (‘ileocaecal valve’), which appears as a bilabial structure on the left of this view of the
caecal pole. B, A photomicrograph showing a longitudinal section through the inferior labium of the ileal papilla (haematoxylin and eosin); the ileal
mucosa is visible superiorly. (A, Courtesy of Dr Michael Schultz. B, Courtesy of Drs. Matthew Pollard and Mark Stringer.)
The ileal papilla is formed by the mucosa, submucosa and external
muscle layers of the ileum, continuing through the wall of the colon Preileal
and combining with corresponding layers from the caecum inferiorly Taenia coli
and the colon superiorly (Fig. 66.18B). The internal surface of the
papilla is lined by small intestinal mucosa and its colonic surface is Postileal
covered by large bowel mucosa; these epithelial surfaces meet near the
tip of the papilla. A localized thickening of the muscle at the base of
the ileal papilla is consistent with physiological data that suggest the Caecum
presence of an intrinsic anatomical sphincter (Pollard et al 2012). In Ileum
addition, the bilabial configuration of the papilla may confer a valvular
function. The ileocolic junction performs several roles: it provides Retrocaecal
partial mechanical and functional separation of the luminal environ Promonteric
ments of the small and large intestine, which differ in their composi
tion, pH and bacterial content; it impedes reflux from the colon; and
it helps to regulate antegrade small bowel transit.
Caecal volvulus Paracolic/precaecal
Pelvic
If the caecum and ascending colon are attached to the posterior
abdominal wall by a narrow mesentery, the ileocolic region is at risk
of twisting about its mesenteric pedicle, creating a caecal volvulus. In Subcaecal
such cases, the caecum becomes markedly distended as a consequence
of the strangulating closed loop bowel obstruction that develops. Non


anatomical factors such as caecal distension may also contribute to the
pathogenesis of caecal volvulus (Madiba and Thomson 2002). Fig. 66.19 The major positions of the appendix encountered at surgery or
postmortem.
APPENDIX artery) (see Fig. 63.10). The luminal orifice is sometimes partially
covered by a mucosal fold forming an asymmetrical ‘valve’ (see Fig.
The vermiform (wormlike) appendix is a narrow, blindending tube, 66.5). The lumen may be widely patent in early childhood but is often
usually between 6 and 10 cm long in the adult. It joins the postero partially or wholly obliterated in the elderly. Agenesis or duplication of
medial wall of the caecum below the ileocolic junction. The appendix the appendix are exceptionally rare (Barlow et al 2013).
grows in length and diameter during early childhood, reaching almost
Microstructure
mature dimensions by about 3 years of age (Searle et al 2013). The
appendix usually lies in the right iliac fossa but its tip may occupy one
of several positions (Fig. 66.19) (Buschard and Kjaeldgaard 1973). In The layers of the wall of the appendix are similar to those of the large
clinical practice, the tip is most commonly retrocaecal or retrocolic intestine in general but with some notable differences. The serosa forms
(behind the caecum or lower ascending colon, respectively, anterior to a complete covering, except along the mesenteric attachment. The outer
iliacus and psoas major), or pelvic (when the appendix descends over longitudinal muscle is a complete layer of uniform thickness, except in
the pelvic brim, in close relation to the right uterine tube and ovary in a few small areas where the muscularis externa is deficient, allowing the
females). Other positions include subcaecal, and pre or postileal serosa to come into contact with the submucosa.
(anterior or posterior to the terminal ileum, respectively), especially The submucosa typically contains large lymphoid aggregates that
when a long appendicular mesentery allows greater mobility. The may extend into the mucosa and disrupt the integrity of the muscularis


surface marking for the base of the appendix has traditionally been mucosae (Fig. 66.20). The mucosa is covered by a columnar epithe
described by McBurney’s point (twothirds of the way along a line lium, which contains M cells where it overlies the mucosal lymphoid
between the umbilicus and right anterior superior iliac spine) but its tissue. Glands (crypts) (see Fig. 4.5) are similar to those of the colon
position is variable and affected by posture, caecal distension and other but are fewer in number and less densely packed. They penetrate deep
factors (Hale et al 2010). into the lamina propria. The submucosal lymphoid tissue frequently
The appendix has a continuous outer layer of longitudinal muscle exhibits germinal centres within its follicles (see Fig. 4.10), indicative
formed by the coalescence of the three taeniae coli. Its lumen is irregu of Bcell activation. Lymphoid follicles are absent at birth but accumu
larly narrowed by submucosal lymphoid tissue. The mesoappendix is a late during the first 10 years of life to become prominent. In adults, the
triangular mesentery running between the terminal ileum and appen lymphoid follicles gradually atrophy; in the elderly, the lumen of the
dix; it contains a variable amount of fat and frequently ends short of appendix may be partially obliterated by fibrous tissue.
the tip of the appendix. A small fold of peritoneum runs between the
terminal ileum and the anterior layer of the mesoappendix (the socalled Acute appendicitis
‘bloodless fold of Treves’), and another fold of peritoneum containing
the anterior caecal vessels extends from the terminal ileal mesentery
Available with the Gray’s Anatomy e-book to the anterior wall of the caecum (and contains the anterior caecal


Large intestine
1142.e1
66
RETPAHC
Acute appendicitis may develop as a consequence of obstruction of the
lumen from inspissated material, a faecolith (appendicolith) or lym
phoid swelling. This can lead to suppuration, infarction and necrosis.
Appendicoliths are more common in children than adults but their
prevalence is variable, reflecting differences between populations, defi
nitions and methods of detection. In one radiographic study of normal
appendices removed incidentally at surgery or at autopsy, calcified fae
coliths were identified in 2.7% (Felson 1949). The increased size of the
appendicular orifice in early childhood and the decreased lumen in the
elderly may be reasons why acute appendicitis is less common in these
age groups. Although the appendix is well supplied by arterial anasto
moses at its base, the appendicular artery is an end artery; its close
proximity to the wall of the appendix makes it susceptible to thrombo
sis during acute appendicitis, which explains the high frequency of
gangrenous perforation seen in the disease.
Visceral afferent nerves are responsible for the initial symptoms of
acute appendicitis arising from distension and inflammation of the
organ: namely, colicky pain with or without vomiting. These afferent
nerves enter the spinal cord at around the level of the tenth thoracic
spinal segment. Abdominal pain from appendicitis is poorly localized
initially and referred to the central (periumbilical) region of the
abdomen, consistent with the midgut origin of the appendix. It is not
until parietal tissues adjacent to the appendix become involved in the
inflammatory process that somatic nociceptors are stimulated, resulting
in localization of pain to the right iliac fossa. Removal of the appendix
is not by itself associated with any discernible longterm sequelae but
this does not mean that it is an entirely vestigial organ. There is some
evidence that the appendix acts as a reservoir for normal gut flora,
enabling the large bowel flora to recover more rapidly after severe gas
troenteritis (Randal Bollinger et al 2007).


Midgut region of large intestine
1143
66
RETPAHC
Ascending Right Transverse Third part of Inferior vena Small
colon kidney colon duodenum cava bowel
A
Fig. 66.20 A low-power micrograph of the appendix in transverse section,
showing part of its circumference and a faecal pellet lodged in its lumen.
Lymphoid tissue (basophilic staining) occupies much of the mucosa
between crypts, and part of the submucosa. The muscularis externa and
outermost serosal layer are seen at the right of the field.
Right kidney B
Transversus Second part Liver Right Hepatic Gallbladder Duodenum, third Transverse
abdominis of duodenum kidney flexure part colon
Iliohypogastric
Fig. 66.22 Axial CT images of the ascending colon obtained (A) at the
level of the mid ascending colon and (B) at the level of the hepatic
nerve
flexure, showing the relationship of the ascending colon and hepatic
flexure to the right lobe of the liver, the right kidney, the second part of
the duodenum, and the gallbladder. (Courtesy of Dr Louise Moore,
Chelsea and Westminster Hospital, London.)
Ilioinguinal
nerve
Gonadal vein
of the ascending colon are covered by peritoneum, which runs laterally
Iliac crest Gonadal artery into the right paracolic gutter and medially into the right infracolic
compartment. The ascending mesocolon is composed of two layers
Psoas major of mesothelium containing fat embedded within a connective tissue
Iliacus lattice, vessels and nerves; it is attached to the retroperitoneum of the
posterior abdominal wall via a layer of connective tissue (Coffey 2013,
Culligan et al 2014), known as Toldt’s fascia, which forms the plane of
Lateral femoral dissection when performing a right hemicolectomy.
cutaneous nerve
Hepatic flexure
The hepatic flexure, forming the junction between the ascending
Femoral nerve Genitofemoral nerve
and transverse colon, is variable in position, and has a less acute
angle than the splenic flexure. It overlies the anterior surface of the
lower pole of the right kidney, abutting the inferior surface of the right


lobe of the liver above (see Fig. 66.21; Fig. 66.22B), the second part of
the duodenum medially, and the fundus of the gallbladder anteromedi
Fig. 66.21 Posterior relations of the ascending colon. ally. The posterior aspect of the hepatic flexure is not covered by peri
toneum and is in direct contact with renal fascia. The greater omentum
often extends from its attachment to the transverse colon on to the
ASCENDING COLON hepatic flexure.
The ascending colon is 15–20 cm long and passes upwards from the
ileocolic junction to the right colic (hepatic) flexure, separated TRANSVERSE COLON
posteriorly by loose connective tissue from the iliac fascia, iliolumbar
ligament, quadratus lumborum, transversus abdominis, and the renal The transverse colon is intraperitoneal. It is highly variable both in
fascia anterior and inferolateral to the right kidney. The lateral femoral length (approximately 50 cm long on average) and the extent to which
cutaneous nerve, usually the fourth lumbar artery, and sometimes the it hangs down anterior to the small bowel between sites of attachment
ilioinguinal and iliohypogastric nerves lie posteriorly as they cross at the right (hepatic) and left (splenic) colic flexures. The greater curva
quadratus lumborum (Fig. 66.21). Both the lateral and anterior surfaces ture of the stomach and the gastrocolic omentum, which fuses with the


Large intestine
1143.e1
66
RETPAHC
Occasionally, the ascending mesocolon is reflected forwards from
the posterior abdominal wall, conferring greater mobility on this
usually retroperitoneal part of the large bowel (Saunders et al 1995).


LARgE inTEsTinE
1144
8
nOiTCEs
transverse colon anteriorly and continues inferiorly as the greater ileal artery (Ouattara et al 2007) (see Fig. 66.12). Accessory appendicu
omentum, are superior. The transverse colon is suspended by the trans lar arteries are common; two or more arteries may supply the
verse mesocolon, which is attached from the lower pole of the right appendix.
kidney, across the second part of the duodenum and pancreas, to the
upper pole of the left kidney (see Fig. 63.2). The splenic flexure lies at Right colic artery
a higher level than the hepatic flexure, often abutting the spleen under The right colic artery is relatively small and variable in its anatomy
the left lower ribs. The disposition of the transverse colon and more (Batra et al 2013). It usually arises as a common trunk with the middle
posteriorly sited flexures results in the anterior taenia of the ascending colic artery, but may originate directly from the superior mesenteric
(and descending) colon lying inferiorly (see above). The transverse artery, or from the ileocolic artery (when it is referred to as an accessory
mesocolon affords considerable mobility to the transverse colon. Occa right colic artery) (Fig. 66.24). It passes to the right, across the right
sionally, the colon may be interposed between the liver and the dia psoas major and quadratus lumborum, crossing the right gonadal
phragm, when it may be mistaken for free intraperitoneal gas on vessels and ureter, just posterior to the peritoneal floor of the right
imaging; when associated with gastrointestinal symptoms it is referred infracolic compartment. Near the left side of the ascending colon, it
to as Chilaiditi’s syndrome (Murphy et al 2000). divides into a descending branch, which runs down to anastomose with
the superior branch of the ileocolic artery, and an ascending branch,
which passes up across the lower pole of the right kidney to the hepatic
VASCULAR SUPPLY AND LYMPHATIC DRAINAGE flexure, where it anastomoses with a branch of the middle colic artery.


OF THE MIDGUT Together, these anastomoses form the marginal artery at the hepatic
flexure.
Arteries
superior mesenteric artery Middle colic artery
The middle colic artery arises from the right side of the superior
The artery of the midgut is the superior mesenteric artery, which arises
mesenteric artery, either separately or in common with the right colic
from the anterior surface of the aorta at the level of the lower border
artery, just inferior to the neck of the pancreas, and passes anteriorly
of the body of the first lumbar vertebra. It runs steeply downwards,
and superiorly within the transverse mesocolon, just to the right of
posterior to the splenic vein and body of the pancreas, with the superior
the midline. As it approaches the colon, it usually divides into right and
mesenteric vein on its right, and directly anterior to the left renal vein,
left branches. The right branch anastomoses with the ascending branch
the uncinate process of the pancreas and the third part of the duode
of the right colic artery. The left branch supplies the terminal part of
num. It then enters the root of the mesentery of the small intestine and
the midgut and anastomoses with a branch of the left colic artery near
passes obliquely downwards and to the right, giving off several branches
the splenic flexure. The marginal artery thus formed lies a few centime
to the large intestine.
tres from the mesenteric edge of the transverse colon. Sometimes,
Ileocolic artery the middle colic artery divides into three or more branches within the
The ileocolic artery arises from the superior mesenteric artery near
the root of the mesentery of the small intestine, descending within the
mesentery to the right towards the caecum, and crossing anterior to the
right ureter, gonadal vessels and psoas major. It usually divides into Ascending branch Posterior caecal artery
superior and inferior branches, the superior branch running up along
Anterior caecal artery
the left side of the ascending colon to anastomose with the right colic
Inferior division of
artery (or right branch of the middle colic artery) (Veeresh et al 2012).
ileocolic artery


The inferior branch runs to the ileocolic junction and divides into
Colic branch
anterior and posterior caecal arteries, the appendicular artery, and an
ileal branch that passes to the left in the ileal mesentery to anastomose Ileal branch
with a terminal ileal branch of the superior mesenteric artery (Fig.
66.23). The latter therefore provides a collateral arterial supply to the Termination
caecum. The ileocolic artery provides the major arterial supply to the of superior
caecum; traction on the caecum in the direction of the anterior superior mesenteric artery
iliac spine will cause the artery to tent up the mesentery, allowing easy Mesenteric-terminal
identification of the vessel. ileal anastomosis
The appendicular artery usually arises directly from the ileocolic
Terminal ileal artery
artery and descends posterior to the terminal ileum to enter the meso
appendix a short distance from the base of the appendix (see Fig.
66.23). Here, it gives off a recurrent branch, which anastomoses at the Anastomosing
base of the appendix with a branch of the posterior caecal artery. The arcades
appendicular artery approaches the tip of the organ, at first near to, and
then in the edge of, the mesoappendix. The terminal part of the artery Recurrent branch
lies on the wall of the appendix and may become thrombosed in appen Appendicular artery
dicitis, resulting in distal gangrene or necrosis. Less commonly, the Fig. 66.23 The arteries of the caecum, vermiform appendix and
appendicular artery may arise from the posterior caecal artery or an ascending colon.
Middle colic artery Superior mesenteric artery Fig. 66.24 Anatomical variants of
the right colic artery.
Absent right colic artery: <5%
Separate right colic artery: 35%
Ileocolic artery
Accessory right colic artery: 10%


Hindgut region of large intestine
1145
66
RETPAHC
A B C Fig. 66.25 Variants in the origin
of the middle colic artery; only
Middle colic artery
replaced arteries have been
Dorsal pancreatic artery Hepatic artery illustrated for simplicity.
Accessory arteries are more
common than completely
replaced arteries. A, The left
colic artery or inferior mesenteric
Middle colic artery artery. B, The dorsal pancreatic
artery. C, The hepatic artery. Each
Superior mesenteric
variant accounts for fewer than
artery
Middle colic artery 5% of cases.
Inferior mesenteric
artery Superior mesenteric Superior mesenteric
artery artery
Left colic artery
transverse mesocolon, in which case the most lateral branches form the
arterial anastomoses. An accessory, or rarely a replaced, middle colic
artery may arise directly from the aorta (Yoshida et al 1993), dorsal
pancreatic, hepatic, inferior mesenteric or left colic arteries (Fig. 66.25). Hilum of spleen
In addition, an accessory middle colic artery is occasionally found
arising from the superior mesenteric artery proximal to the origin of the
Tail of pancreas
actual middle colic artery (Turmezei and Cockburn 2009).
Veins Left renal vein
All the branches of the superior mesenteric artery are accompanied by
correspondingly named veins. These tributaries drain into the superior
mesenteric vein, which ascends to the right of the artery, crossing the
third part of the duodenum and uncinate process of the pancreas.
Behind the neck of the pancreas, at the level of the transpyloric plane
(the lower border of the body of the first lumbar vertebra), it joins the
splenic vein to form the portal vein, which ascends behind the first part
of the duodenum to reach the liver. The right colic vein is highly vari
able: it may drain either directly into the superior mesenteric vein, or
into the right gastroepiploic or inferior pancreaticoduodenal veins to
form a ‘gastrocolic trunk’ that drains into the superior mesenteric vein,
or it may be entirely absent (Yamaguchi et al 2002). Several tributaries


draining into one or more middle colic veins are highly variable in
extent and position. The middle colic veins drain either into the supe Left renal pelvis
rior mesenteric vein, just before its junction with the splenic vein, or
directly into the hepatic portal vein. The appendicular vein usually joins Left ureter
the caecal vein to become the ileocolic vein; infection from the appen
dix can therefore be carried directly to the liver via the portal vein. Inferior mesenteric
vein
Lymphatic drainage
Lymphatic vessels originate from both anterior and posterior aspects of
the colon. Lymph drainage from the midgut follows the course of the
superior mesenteric artery. Thus, lymph from the caecum and appendix
drains to nodes associated with the ileocolic artery, and from the distal
ascending colon and hepatic flexure to nodes along the right colic artery
(see Fig. 66.16). When the distal transverse colon and splenic flexure Fig. 66.26 Relations of the splenic flexure.
are predominantly supplied by the middle colic artery, lymph drainage
of this segment is also largely to superior mesenteric nodes. Lymphatic
vessels in the appendix are numerous and combine to form vessels that be peritoneal and omental adhesions between the two structures. It lies
ascend in the mesoappendix, occasionally interrupted by one or more more superiorly and posteriorly than the hepatic flexure.
nodes. They unite to form three or four larger vessels that anastomose
with lymphatic vessels draining the ascending colon into ileocolic
DESCENDING COLON
nodes.
The descending colon is 25–30 cm long and descends from the splenic
HINDGUT REGION OF LARGE INTESTINE flexure in the left hypochondrium to the level of the iliac crest, where
it curves medially anterior to iliacus to become the sigmoid colon. In
most adults it is retroperitoneal, covered anteriorly and on both sides
Splenic flexure
by peritoneum, but occasionally the descending colon is more mobile,
being suspended from the posterior abdominal wall by a short meso
The splenic flexure marks the junction between the transverse and colon (Saunders et al 1995). Its lateral peritoneal reflection in the left


descending colon, and lies in the left hypochondrium, anterior to the paracolic gutter is marked by a white line (of Toldt). The posterior
tail of the pancreas and the left kidney (Fig. 66.26). Its position with surface of the descending colon is separated by a layer of loose con
respect to the spleen is variable: it usually lies inferomedial to the lower nective tissue from the anterior renal fascia inferolateral to the left
pole, forming the colic impression, but it may lie anterior to the splenic kidney, transversus abdominis, quadratus lumborum, iliacus and the
hilum, or even a little above. The splenic flexure is often attached to the lateral margin of psoas major (Fig. 66.27). The subcostal vessels and
splenic capsule by a peritoneal ligament and inadvertent downward nerves, iliohypogastric, ilioinguinal, lateral femoral cutaneous, femoral
traction on the flexure during surgery may tear the splenic capsule. The and genitofemoral nerves, and, usually, the fourth lumbar artery also
phrenicocolic ligament attaches the flexure to the diaphragm below the lie posteriorly, and loops of jejunum are anterior. The descending
inferior pole of the spleen at about the level of the tenth rib. The splenic colon is smaller in calibre and more deeply placed than the ascending
flexure often adopts a very acute angle such that the end of the trans colon. Appendices epiploicae are more common in this part of the
verse colon overlaps the beginning of the descending colon; there may colon.


LARgE inTEsTinE
1146
8
nOiTCEs
Left gonadal
Left ureter
vessels
Spleen
Left kidney
Psoas major
Genitofemoral
Subcostal
nerve
nerve
Internal iliac
Iliohypogastric artery
nerve
Quadratus Transversus
lumborum abdominis Upper roots
of the
sacral plexus
Ilioinguinal
Gonadal vein nerve Sigmoid colon
Gonadal artery Iliac crest
Psoas major
Iliacus Piriformis
Obturator
Genitofemoral nerve
nerve Lateral femoral External iliac artery and vein
cutaneous nerve
Fig. 66.28 Posterior relations of the sigmoid colon.
Femoral nerve
Diverticular disease
Available with the Gray’s Anatomy e-book
Fig. 66.27 Posterior relations of the descending colon.
MESOCOLON
The mesocolon extends along the entire length of the colon and is
SIGMOID COLON continuous with the small bowel mesentery proximally and the meso
rectum distally. The mesocolon consists of fat embedded within a con
nective tissue lattice and sandwiched between two layers of mesothelium;
The sigmoid colon runs from the lesser pelvis to the beginning of the
it also contains nerves, blood and lymphatic vessels, and lymph nodes.
rectum at the level of the third sacral vertebra. It is usually suspended
A layer of loose connective tissue, known as Toldt’s fascia, lies immedi
from the posterior abdominal and pelvic walls by a fanshaped sigmoid
ately posterior to the mesocolon, where it is adherent to the retroperi
mesocolon, but may be tethered by congenital adhesions to the parietal
toneum of the posterior abdominal wall (Culligan et al 2014). Complete
peritoneum over iliacus. Consequently, its length and position are
excision of the relevant segment of mesocolon by dissecting within or
highly variable. It usually lies within the pelvic cavity anterior to the
behind the plane of Toldt’s fascia has been shown to improve survival
rectum on the peritoneal surface of the bladder (and uterus in the
in colon cancer (Søndenaa et al 2014).


female). It is usually completely invested in peritoneum. The root of
the sigmoid mesocolon has an inverted Vshaped attachment; the right
limb of this inverted ‘V’ ascends from a point anterior to the third sacral RECTUM
vertebra to the bifurcation of the left common iliac vessels (crossed by
the left ureter) and descends from this point along the external iliac
The rectum is continuous with the sigmoid colon at the level of the
vessels.
third sacral vertebra and ends as it passes through the pelvic floor (the
Between the fixed junctions with the descending colon and rectum,
puborectalis part of levator ani), where it is continuous with the anal
the relations of the sigmoid colon are quite variable (Fig. 66.28). Later
canal. It descends within the sacrococcygeal concavity, at first running
ally are the left external iliac vessels, the obturator nerve, ovary or vas
posteriorly and then curving anteriorly. The junction between the ante
deferens, and the lateral pelvic wall; posteriorly lie the left external and
riorly directed distal rectum and the posteriorly directed anal canal is
internal iliac and gonadal vessels, ureter, piriformis and the sacral
the anorectal angle, which is maintained by puborectalis. This is 2–3 cm
plexus; anteroinferiorly lie the bladder in males, or the uterus and
anterior to and slightly below the tip of the coccyx, level with the apex
bladder in females; superiorly and to the right, the sigmoid colon is in
of the prostate in males. The rectum also deviates in three lateral curves:
contact with loops of the ileum. The gonadal vessels and ureter lie in a
upper, convex to the right; middle (the most prominent), convex to the
distinct fascial plane, which is the inferior extension of the retroperito
left; and lower, convex to the right. Both ends of the rectum are in the
neal perirenal fascia and is separate from the sigmoid mesocolon. This
median plane (Fig. 66.30).
plane can be recognized and separated during surgical resection of the
Although variable in absolute length, the rectum is often defined in


sigmoid mesocolon. The taeniae coli of the sigmoid colon are wider
clinical practice as extending approximately 15 cm above the external
than elsewhere in the colon, and coalesce at its distal end to form a
anal margin. Its upper diameter is similar to that of the sigmoid colon,
complete circumferential longitudinal muscle layer. Appendices epi
but more inferiorly it becomes dilated as the rectal ampulla. Unlike the
ploicae are particularly prominent in the sigmoid colon.
sigmoid colon, the rectum has no sacculations, appendices epiploicae
The position and shape of the sigmoid colon depend on its length
or taeniae coli. The taeniae merge a few centimetres above the recto
(which increases with age) and mobility; the length of the sigmoid
sigmoid junction, initially forming wide anterior and posterior muscu
mesocolon (usually longer in males); and the degree of distension of
lar bands that then fuse to form a continuous outer layer of longitudinal
the colon, rectum, bladder and uterus. The length of the sigmoid colon
muscle investing the entire length of the rectum. At the rectal ampulla,
and its mesentery vary between ethnic groups (Alatise et al 2013).
a few longitudinal muscle fibres pass forwards from the anterior rectal
wall to the perineal body and urethra (rectourethralis).
Sigmoid volvulus
The upper third of the rectum is covered by peritoneum on its ante
rior and lateral aspects, and the middle third by peritoneum on its
Available with the Gray’s Anatomy e-book anterior aspect only; the lower third is below the peritoneum. The


Large intestine
1146.e1
66
RETPAHC
Rotation or volvulus of the sigmoid colon may occur around its
mesenteric attachment. Volvulus is more likely when the length of the
sigmoid colon and the length and width of its mesentery are greater
(Akinkuotu et al 2011). Volvulus does not occur when the sigmoid
colon and its mesocolon are short. The anatomical features predispos
ing to sigmoid volvulus are most commonly found in subSaharan
Africans and chronically institutionalized patients.
Acquired diverticula commonly occur in the sigmoid colon, particu
larly in Western populations. These diverticula frequently develop in
parallel rows between the mesenteric taenia coli and the two anti
mesenteric taeniae where the colonic wall is weaker; at this site, the
outer longitudinal muscle is deficient and the circular muscle is tra
versed by arteries supplying the submucosal vascular plexus (Slack
1962). However, the predilection of diverticula in the sigmoid colon
probably relates to causative factors rather than intrinsic differences in
the structure of this segment of the colon. In contrast, congenital diver
ticula may occur at any site in the colon (Fig. 66.29) and are often
found along the mesenteric border.
Fig. 66.29 A CT scan (coronal reformat) showing both right colonic and
sigmoid diverticulosis. (Courtesy of Dr Kamini Patel, Homerton Hospital,
London.)


Hindgut region of large intestine
1147
66
RETPAHC
A B Sacrum
Sacral nerve root
Fibres of piriformis
Rectum
Posterior mesorectal
fascia
Obturator internus Mesorectal fat
Mesorectal vessel
Iliococcygeus part
of levator ani Mesorectal
(pararectal) lymph
Puborectalis part node
of levator ani
Ischio-anal fossa
External anal
sphincter
Fig. 66.30 A, A coronal T2-weighted MRI of the rectum. B, A line diagram illustrating the main features in A.
peritoneum is reflected anteriorly on to the urinary bladder in males to by mesorectal fascia, a distinct layer of connective tissue that is also
form the rectovesical pouch, or on to the posterior vaginal fornix in called the fascia propria of the rectum. This fascia limits the mesorec
females to form the rectouterine pouch (of Douglas). The level of this tum posteriorly and lies anterior to the presacral fascia (of Waldeyer),
reflection is higher in males; the rectovesical pouch is approximately separated by a socalled retrorectal ‘space’. The rectum and mesorectal
7.5 cm above the anorectal junction in males, while the rectouterine fascia are connected to the parietal fascia of the pelvis by two ‘lateral
pouch is approximately 5.5 cm above the anorectal junction in females. ligaments’ (see below) and one posterior ligament, the rectosacral fascia
In neonatal boys, the peritoneum extends on the anterior rectal wall as (Gaudio et al 2010). The latter is a thin layer of connective tissue that
far as the lower limit of the prostate. Superiorly, the peritoneum is passes obliquely downwards from the presacral fascia to fuse with the
firmly attached to the muscle layer of the sigmoid colon by fibrous mesorectal fascia posterior to the rectum 3–5 cm above the anorectal
connective tissue, but as it descends on to the rectum, it is more loosely junction (GarcíaArmengol et al 2008). The mesorectal fascia is sur


attached by fatty connective tissue, which allows considerable expan rounded by a thin and relatively avascular layer of loose areolar tissue,
sion of the upper half of the rectum. which separates it from the posterior and lateral walls of the true pelvis.
When the rectum is empty, the mucosa has several longitudinal folds Superiorly, the mesorectal fascia blends with the connective tissue
in its lower part, which become effaced during distension. The rectum bounding the sigmoid mesentery. Laterally, it extends around the
commonly has three permanent semilunar transverse or horizontal rectum and mesorectum, and becomes contiguous anteriorly with a
folds (although the number can vary), which are most marked in rectal denser condensation of fascia, conveniently described eponymously as
distension (see Fig. 66.10). Two types of horizontal fold have been Denonvilliers’ fascia. This fascia is sometimes confusingly known as
recognized. One consists of the mucosa, the circular muscle layer and rectovesical fascia in males but it extends caudal to the bladder and is
part of the longitudinal muscle, and is marked externally by an indenta particularly dense posterior to the prostate and seminal vesicles; it lies
tion. The other is devoid of longitudinal muscle and has no external immediately anterior to the mesorectal fascia, to which it may be fused
marking. The most superior fold at the beginning of the rectum may (Lindsey et al 2000). In females, Denonvilliers’ fascia combines with
be on either the left or the right and occasionally encircles the rectal the anterior mesorectal fascia to form the rectovaginal septum (Zhai
lumen. The middle fold is largest and most constant, and lies immedi et al 2009).
ately above the rectal ampulla, projecting from the anterior and right Mesorectal fascia is visible by CT, MRI and dissection (Bissett et al
wall just below the level of the anterior peritoneal reflection; the circular 2001). On MRI scans, the mesorectum appears as a fatfilled envelope
muscle is particularly prominent in this fold. The inferior fold is on the containing blood vessels and lymph nodes; small nerves are not visible
left and the most variable. but interlacing connective tissue strands can be seen. The mesorectal


fascia is recognizable on axial MRI images as a lowsignal layer sur
Relations Posterior to the rectum and mesorectum, separated by the rounding the mesorectum, corresponding to a distinct condensation of
presacral fascia, are the lower three sacral vertebrae, coccyx, median and fascia seen on histological sections (Brown et al 1999). Identification
lateral sacral vessels, and the lowest portion of the sacral sympathetic of this layer in patients with a malignant rectal tumour can help predict
chain. Laterally, the upper rectum is related to the sigmoid colon and/ the success of surgical resection. Branches of the inferior hypogastric
or small bowel, while below the peritoneal reflection lie levator ani, plexus and middle rectal vessels enter the mesorectum anterolaterally.
obturator internus, the obturator nerve and vessels, ureters, the inferior They are ensheathed by fascia and are sometimes collectively referred
hypogastric plexus, internal iliac vessels, piriformis and the sacral to as the ‘lateral rectal ligaments’. The number and calibre of the middle
plexus. Anteriorly, the rectum is related to the sigmoid colon and/or rectal vessels are highly variable; they may be very small or even absent
small bowel in both sexes, and the base of the bladder, seminal vesicles, (Sato and Sato 1991). The ‘lateral ligaments’ are not clearly seen on MRI
vas deferens, terminal parts of the ureters, and the prostate in males or CT scanning, and only appear as an identifiable structure with surgi
(see Figs 66.34, 76.17). In females, the cervix/body of the uterus and cal traction on the rectum. The fascia of the ‘ligaments’ is flimsy and
vagina are anterior, the latter separated from the rectum by a rectovagi probably plays little role in support of the rectum. Parietal fascia covers
nal septum. In postmenopausal females, and after childbirth, the con levator ani and the muscles of the side wall of the pelvis, and is continu
nective tissue of the rectovaginal septum may atrophy or become ous posteriorly with the presacral fascia (see Fig. 66.36).


thinned, reducing the support of the anterior rectal and posterior
vaginal walls. Rectal prolapse
Available with the Gray’s Anatomy e-book
MESORECTUM AND RECTAL FASCIAE
Rectocele
Although the rectum has no mesentery, its surrounding fat is enclosed
within a fascial envelope known as the mesorectum. This constitutes a Available with the Gray’s Anatomy e-book
distinct compartment that is intimately related to the rectum down to
the level of levator ani (Figs 66.31–66.36). It contains the superior
Rectal cancer
rectal artery and its branches, the superior rectal vein and its tributaries,
lymphatic vessels and nodes, and adipose connective tissue. The meso
Available with the Gray’s Anatomy e-book rectum is much bulkier posteriorly (see Figs 66.31, 66.32). It is enclosed


Large intestine
1147.e1
66
RETPAHC
In prolapse of the rectum involving all layers of the rectal wall, the mid tumour recurrence (Heald et al 1982). In total mesorectal excision, the
and upper rectum descend towards the pelvic floor on straining. Descent posterolateral plane of dissection is outside the mesorectal fascia but
occurs within the lumen of the rectum as a form of intussusception, anterior to the presacral fascia and its underlying venous plexus. Later
and may be a consequence of the large diameter of the rectal ampulla ally, the plane is interrupted only by small branches of the middle rectal
and relative fixation of the anal canal. The loose adipose tissue of the vessels; anteriorly, it merges with the rectovesical or rectovaginal fascia.
upper mesorectum and the ‘lateral ligaments’ offer only limited resist The inferior hypogastric plexus is closely related to the plane of dissec
ance against rectal descent. Chronic enlargement of the anorectal space tion laterally; these nerves must be preserved to retain bladder and
bound by levator ani commonly occurs in patients suffering from recur sexual function. Total mesorectal excision involves complete excision
rent rectal prolapse, but is probably a consequence rather than a cause of the rectum down to the level of the pelvic floor, where the puborec
of the prolapse. In females, the rectouterine pouch also descends with talis component of levator ani merges with the deep component of the
the anterior rectal wall. external anal sphincter. Superiorly, the inferior mesenteric artery is
When the rectovaginal septum is grossly effaced, especially in post ligated near its origin.
menopausal females, the pressure of defecation can cause bulging of In abdominoperineal excision of the rectum, it should be noted that
the rectal wall into the posterior vagina and, in extreme cases, through the mesorectum becomes extremely thin at the point where the rectum
the vaginal introitus. Weakness of the pelvic floor muscles contributes passes through levator ani. To achieve adequate surgical margins, the


to the prolapse by allowing descent of the perineum during straining. plane of dissection is through the ischioanal fossa and levator ani
An important concept in the surgical treatment of adenocarcinoma outside the puborectalis sling and into the mesorectal plane well above
of the rectum is the necessity of excising the rectum in continuity with the pelvic floor.
the mesorectum and its contained lymph nodes in order to avoid local


LARgE inTEsTinE
1148
8
nOiTCEs
A B
Sacrum
Posterior mesorectum
Mesorectal vessel
Peritoneal
reflection
Posterior mesorectal
fascia
Bladder
Presacral vessel
Rectoprostatic
space
Presacral fat
Prostate
Rectum
Anterior
mesorectum
Anococcygeal raphe
Anterior
mesorectal Levator ani
fascia
Posterior external
Anterior external anal sphincter
anal sphincter
Anal canal
Fig. 66.31 A, A sagittal T2-weighted MRI of the rectum in a male. B, A line diagram illustrating the main features in A.
A B
Sacrum
Posterior mesorectum
Presacral vessel
Pelvic peritoneal
reflection
Posterior mesorectal
Uterus fascia
Mesorectal vessel
Bladder
Presacral space
Vagina
Rectovaginal
Rectum
septum
Levator ani
Anterior
mesorectum Anococcygeal
ligament
Anterior
mesorectal Puborectalis
fascia
External
anal sphincter
Anal canal
Fig. 66.32 A, A sagittal T2-weighted MRI of the rectum in a female. B, A line diagram illustrating the main features in A.


Hindgut region of large intestine
1149
66
RETPAHC
B
A
Base of broad Uterine cervix
ligament
Anterior mesorectal
Obturator internus fascia
Internal iliac vessel Rectum
Posterior mesorectum
Piriformis
Presacral fascia Mesorectal vessel
Posterior
Sacrum
mesorectal
fascia
Fig. 66.33 A, An axial T2-weighted MRI of the upper rectum in a female. B, A line diagram illustrating the main features in A.
A B Prostatic fascia
Anterior mesorectal
Prostate fascia
Prostatic venous
Obturator internus
plexus
Branches of inferior
hypogastric plexus Obturator fascia
Levator fascia Ischium
Levator ani Rectum
Ischio-anal fossa Mesorectal fascia
Gluteus maximus
Coccyx
Fig. 66.34 A, An axial T2-weighted MRI of the mid rectum below the peritoneal reflection in a male. B, A line diagram illustrating the main features in A.
A B
Bladder
Obturator internus
Vagina
Obturator fascia
Levator ani Anterior
(puborectalis) mesorectal fascia
Ischio-anal fossa Mesorectal fascia
Rectum above
Top of anorectal junction
anococcygeal
ligament
Tip of coccyx
Fig. 66.35 A, An axial T2-weighted MRI of the low rectum below the peritoneal reflection in a female. B, A line diagram illustrating the main features in A.


LARgE inTEsTinE
1150
8
nOiTCEs
A B
Anterior mesorectal
Prostate fascia
Obturator internus Prostatic vessels
Obturator fascia Branches of inferior
hypogastric plexus
Mesorectum
Piriformis Piriformis
Mesorectal fascia Mesorectal vessels
Presacral
(piriformis) fascia
Sacrum
Fig. 66.36 A, A light microscope transverse section of the mid rectum (male, cadaveric specimen). B, A line diagram illustrating the main features in A.
Left colic
Inferior
artery
mesenteric
vein
Catheter Inferior mesenteric artery
Marginal
artery (of
Inferior Drummond) Ascending branch
mesenteric
Left colic artery
artery
Descending branch
Superior
rectal
Sigmoidal
artery
arteries
Sigmoid arteries
Fig. 66.37 A digital subtraction arteriogram showing the inferior Superior rectal artery
mesenteric artery and its branches.
VASCULAR SUPPLY AND LYMPHATIC DRAINAGE
OF THE HINDGUT
Arteries
inferior mesenteric artery
The artery of the hindgut is the inferior mesenteric artery (Figs 66.37–
66.39), which arises from the anterior or left anterolateral aspect of the
Fig. 66.38 The inferior mesenteric artery.
aorta behind the inferior border of the third part of the duodenum
3–4 cm above the aortic bifurcation, at the level of the third lumbar
vertebra. It runs obliquely down to the pelvic brim, beneath the peri thus formed supply the distal third of the transverse and the descending
toneal floor of the left infracolic compartment, initially anterior and colon. The left colic artery may originate from or in common with a
then to the left of the aorta. It gives off the left colic and sigmoid arter sigmoid artery (Murono et al 2015). Occasionally, an accessory, or
ies, and crosses the origin of the left common iliac artery medial to rarely a replaced, left colic artery may originate from the trunk of the


the ureter, with the inferior mesenteric vein lying between. Beyond the superior mesenteric artery or its middle colic or first jejunal branch
pelvic brim, it continues in the root of the sigmoid mesocolon as the (Fig. 66.40). When present, it runs laterally in the upper left colic
superior rectal artery. mesentery just inferior to the duodenojejunal flexure to supply the
upper descending colon, and forms part or all of the marginal artery in
Left colic artery the region of the distal transverse colon. The left colic artery may itself
The left colic artery usually arises from the inferior mesenteric artery give rise to an accessory left middle colic artery. Occasionally, the left
shortly after its origin, ascends within the left colic mesentery and colic artery gives rise to a branch shortly after its origin, which ascends
divides into an ascending and a descending branch (see Figs 66.38– in the mesentery and anastomoses directly with a similar descending
66.39). The ascending branch passes upwards across the left psoas branch of the left branch of the middle colic artery (the socalled arc of
major, gonadal vessels, ureter and left kidney, and is crossed by the Riolan; van Gulik and Schoots 2005).
inferior mesenteric vein; its terminal branches anastomose with those The dominant arterial supply of the splenic flexure is usually from
of the left branch of the middle colic artery within the transverse meso the left colic artery but may be from the left branch of the middle colic
colon. The descending branch passes laterally and downwards, and artery. The marginal artery in this region may be absent or small, but it
anastomoses with branches from the ascending branch and the highest may enlarge considerably if the inferior mesenteric artery is stenosed or
sigmoid artery to form part of the marginal artery. The arterial arcades occluded (see p. 1100).


Hindgut region of large intestine
1151
66
RETPAHC
Posterior aspect of rectum
Superior rectal
artery Right branch
Inferior mesenteric artery
Main descending
branch
Left colic artery,
ascending branch
Left colic artery,
descending branch
Descending colon Middle rectal artery
Marginal artery
Levator ani
Terminal descending
branches
Inferior rectal
branch of internal Ascending branches
pudendal artery
Anal canal
Fig. 66.41 The arterial supply of the rectum.
Fig. 66.39 The vascular supply of the descending colon from the inferior
mesenteric artery via the ascending and descending branches of the left
Vascular ligation in left colonic resections
colic artery, coronal reformat CT. (Courtesy of Dr Louise Moore, Chelsea
and Westminster Hospital, London.) During resection of the distal descending and sigmoid colon, ligation
of the inferior mesenteric artery close to its origin preserves the bifurca
tion of the left colic artery and helps to maintain the arterial supply to
the proximal descending colon via the anastomosis between the left
branch of the middle colic artery and the ascending branch of the left
colic artery. Ligation of the left colic artery close to its bifurcation may
interfere with this supply and render the proximal descending colon
more likely to become ischaemic. Similarly, if the inferior mesenteric
vein is ligated, then the bifurcation of the left colic vein forms the route
of venous drainage from the proximal descending colon to the middle
colic vein.
Superior rectal artery
The principal arterial supply to the upper twothirds of the rectum is
Middle colic via the artery of the hindgut – specifically, its pelvic continuation, the
artery
superior rectal artery (Fig. 66.41). The inferior mesenteric artery crosses
the left common iliac vessels medial to the ureter and descends in
the medial limb of the sigmoid mesocolon, straddled by the inferior
Superior mesenteric artery hypogastric nerves on either side. As it crosses the pelvic brim, it
becomes the superior rectal artery. At the level of the third sacral verte
Left colic artery bra, where the rectum begins, the artery enters the upper mesorectum


in the midline and divides into two branches that descend, initially
posterolaterally, and then on each side of the rectum. Terminal branches
Inferior mesenteric artery
pierce the rectal wall and anastomose with branches of the middle and
inferior rectal arteries within the rectal submucosa.
Middle and inferior rectal arteries
The middle rectal arteries arise either directly from the anterior division
Sigmoid artery of the internal iliac artery or from the inferior vesical artery (vaginal
artery in females). When present, they enter the mesorectum antero
laterally in the ‘lateral ligaments’ and provide some additional supply
to the middle third of the rectum. The inferior rectal arteries are termi
nal branches of the internal pudendal arteries. They cross the ischio
anal fossa to enter the upper anal canal laterally and supply the internal
and external anal sphincters, the anal canal and perianal skin. Ascend
ing branches supply the distal third of the rectum, anastomosing with
Fig. 66.40 A replaced left colic artery arising from the middle colic branch
terminal branches of the superior rectal artery in the rectal submucosa.
of the superior mesenteric artery.
The rectum also receives a small arterial supply from the median sacral
artery via a branch that enters posteriorly at the level of the anorectal
Sigmoid arteries junction.
The inferior mesenteric artery gives rise to between two and five sigmoid
Veins
arteries, which descend obliquely in the sigmoid mesocolon anterior to
the left psoas major, ureter and gonadal vessels. They supply the distal inferior mesenteric vein
descending colon and sigmoid colon, and anastomose superiorly with The inferior mesenteric vein drains the rectum, sigmoid, descending
the left colic artery and inferiorly with the superior rectal artery. Unlike and distal transverse colon (see Fig. 66.15; Fig. 66.42). It begins as the
the arrangement in the small intestine, arterial arcades do not form continuation of the superior rectal vein from the rectal plexus, through
until the arteries are close to the wall of the colon, when small branches which it connects with the middle and inferior rectal veins. The inferior


arise that supply the sigmoid colon directly. A true marginal artery is mesenteric vein lies to the left of the inferior mesenteric artery in the
less obvious in the sigmoid colon. A significant interval often exists in retroperitoneum and ascends anterior to the left psoas major and left
the mesentery between the highest sigmoid artery and the descending ureter; it may cross the gonadal vessels or ascend medial to them. It lies
branch of the left colic artery; this forms a useful guide to the arterial just lateral or occasionally posterior to the duodenojejunal flexure,
territories during surgical dissection. where it can be located intraoperatively. The inferior mesenteric vein


LARgE inTEsTinE
1152
8
nOiTCEs
Inferior mesenteric node
Inferior mesenteric
artery
Left colic vein
Preterminal node
Inferior mesenteric
vein
Intermediate nodes
Superior rectal Internal iliac nodes
Catheter in inferior
artery
mesenteric artery
Marginal vein
Pararectal nodes
Middle rectal
artery
Epirectal nodes
Inferior rectal artery
Fig. 66.42 The inferior mesenteric vein and its tributaries, digital
subtraction arteriogram. (Courtesy of Dr Adam Mitchell, Charing Cross Fig. 66.43 Lymph nodes of the rectum and upper anal canal (viewed from
Hospital, London.) behind).
receives the superior rectal vein, several sigmoid veins, and the left colic paracolic to intermediate nodes in the sigmoid mesocolon. Intramural
vein. It usually passes posterior to the lower border of the body of the lymph from the rectum and anal canal above the dentate line drains
pancreas and anterior to the left renal vein to drain into the splenic predominantly to pararectal nodes in the adipose tissue of the mesorec
vein, but it may drain into the confluence of the splenic and superior tum and then along lymphatics accompanying the superior rectal artery
mesenteric veins or directly into the superior mesenteric vein (Graf et al (Fig. 66.43). These intermediate nodes then drain to lymph nodes
1997). along the inferior mesenteric artery and, from there, to preaortic nodes.
Some lymphatics from the lower rectum travel with the middle and
Rectal venous plexus inferior rectal arteries to internal iliac nodes, and along the median
A rectal venous plexus surrounds the rectum and connects anteriorly sacral artery to presacral nodes. The clinical significance of such drain
with the vesical plexus in males or the uterovaginal plexus in females. age in relation to the spread of malignancy from the lower rectum is
It consists of internal veins beneath the mucosa of the rectum and upper debated (Bell et al 2009).
anal canal, and external veins lying outside the muscular wall. The
upper twothirds of the rectum and the internal part of the rectal venous


INNERVATION OF THE LARGE INTESTINE
plexus drain mainly to the superior rectal vein and, from there, to the
inferior mesenteric vein; the middle third of the rectum drains by one
or more middle rectal veins into the internal iliac vein; and the lower The innervation of the large intestine is complex, and includes the
third of the rectum and anal canal drains via inferior rectal veins into enteric nervous system (made up of motor neurones, intrinsic sensory
the internal pudendal veins. The rectal venous plexus is therefore a site neurones, and interneurones lying within the wall of the gut); the
of communication between the portal and systemic venous systems. autonomic nervous system (sympathetic and parasympathetic innerva
tion); and extrinsic sensory innervation (visceral afferents) (Brookes
Superior rectal vein et al 2009) (Ch. 59).
Venous tributaries from the rectal venous plexus ascend in the rectal The enteric nervous system consists of ganglionated nerve plexuses
submucosa and pierce the rectal wall to form the superior rectal vein. lying in the submucosa (Meissner’s plexus) and between the longitudi
This runs in the upper mesorectum and root of the sigmoid mesocolon nal and circular smooth muscle layers (Auerbach’s myenteric plexus).
to the left of the superior rectal artery, crossing the pelvic brim and left Collectively, these nerves are concerned with control of mucosal func
common iliac vessels to form the inferior mesenteric vein (see Figs tions (secretion, blood flow) and the propulsion of luminal contents
66.15, 66.44). by rhythmic and synchronized contractions. Motor neurones may be
inhibitory or excitatory. Intrinsic sensory neurones are activated by
Left colic vein mechanical stimuli such as stretch and muscle tension, and by chemical
The left colic vein is formed from several tributaries, including ascend stimuli released by neuroendocrine cells in the wall of the gut (see Fig.
ing and descending branches that correspond to similarly named arter 3.26). Sensory neurones project locally on to myenteric interneurones


ies. The left colic vein usually lies superior to its corresponding artery, and motor neurones, allowing the spread of reflex activity along the
and has a shorter course because the inferior mesenteric vein lies lateral gut. Interstitial cells of Cajal are present within the submucosal and
to the inferior mesenteric artery (see Fig. 66.42). Occasionally, there are myenteric nerve plexuses. In summary, they act as a link between
two left colic veins that both drain into the inferior mesenteric vein. smooth muscle cells and extrinsic neurones, and are responsible for the
intrinsic pacemaker activity of the gut; their activity is modulated by
Lymphatic drainage
autonomic nerves.
Small lymphoid aggregates measuring no more than a few millimetres The large intestine is richly innervated by sympathetic neurones that
are occasionally visible on the surface of the large bowel (epicolic and originate either directly from the sympathetic chain or indirectly via the
epirectal nodes). Lymph from the descending colon drains to paracolic aortic plexus; the former are mostly involved in the control of blood
nodes in the mesentery adjacent to the bowel and, from there, to inter flow (vasoconstriction), while the latter also influence the secretory
mediate nodes along the left colic artery (Jamieson and Dobson 1909). activity and motility of the gut. The cell bodies of preganglionic sym
Lymphatics from the sigmoid colon follow a similar pathway from pathetic fibres supplying the midgut are found in the intermediolateral


Anal canal
1153
66
RETPAHC
columns of the fifth to the twelfth thoracic spinal segments and those create the anorectal angle. The anal canal lies 2–3 cm anterior and
of the hindgut in the intermediolateral columns of the first and second slightly inferior to the tip of the coccyx, opposite the apex of the prostate
lumbar spinal segments. Postganglionic sympathetic neurones from in males. At the anal verge, the squamous epithelium lining the lower
both sources release noradrenaline (norepinephrine), causing presyn anal canal becomes continuous with the skin of the perineum. The area
aptic inhibition within enteric circuits, slowing gut motility and driving of pigmentation of skin around the anal verge corresponds approxi
contraction of the ileocaecal and internal anal sphincters. Sympathetic mately to the extent of the external anal sphincter. Identification of the
supply to the midgut is conveyed to the coeliac and superior mesenteric anal verge may be difficult, particularly in males in whom the perineum
plexuses via the greater and lesser splanchnic nerves; postganglionic may ‘funnel’ upwards into the lower anal canal, but the characteristic
axons are distributed with branches of the superior mesenteric artery. puckering of the skin formed by the penetrating fibres of the conjoint
Sympathetic supply of the hindgut is conveyed via the lumbar splanch longitudinal muscle of the anal canal provides a useful landmark.
nic nerves that synapse in the abdominal aortic and inferior mesenteric The anal canal consists of an inner epithelial lining, a vascular
plexuses, and via sacral splanchnic nerves that synapse in the superior subepithelium, the internal and external anal sphincters, and fibro
and inferior hypogastric plexuses; postganglionic fibres are distributed muscular supporting tissue, as well as dense neuronal networks of
with branches of the inferior mesenteric artery and are inhibitory to autonomic and somatic origin. Functionally, it represents a zone of
colonic muscle. high pressure. It is between 2 and 5 cm long in adults; the anterior
The midgut receives its parasympathetic innervation from the vagus, wall is slightly shorter than the posterior. It is usually shorter in


via the coeliac and superior mesenteric plexuses, whereas the hindgut females. At rest, it forms an oval or triradiate slit in the anteroposte
receives its parasympathetic innervation from the pelvic splanchnic rior plane rather than a truly circular canal. The arrangement of the
nerves. The cell bodies of the pelvic splanchnic nerves are located in the external anal sphincter and its attachments to the perineal body and
second to fourth sacral spinal segments, the sacral parasympathetic coccyx create sites of maximum pressure in the anterior and posterior
nucleus. These parasympathetic fibres enter the inferior hypogastric midline of the canal.
plexus, where some synapse. From here, some pass directly to the Anteriorly, the middle third of the anal canal is attached by dense
rectum and other pelvic viscera while others ascend by one of two connective tissue to the perineal body, which separates it from the
routes: either within the hypogastric nerves to the superior hypogastric membranous urethra in males and from the lower vagina in females.
plexus to be distributed along branches of the inferior mesenteric artery, Laterally and posteriorly, the anal canal is surrounded by the loose
or by passing directly through the retroperitoneal tissues to reach the adipose tissue of the ischioanal fossae; this arrangement allows expan
splenic flexure and descending and sigmoid colon. Most preganglionic sion of the canal but offers a potential pathway for the spread of peri
parasympathetic neurones synapse in intramural plexuses in the gut anal sepsis. Posteriorly, the anal canal is attached to the coccyx via the
wall; from here, postganglionic neurones innervate the glands (secreto anococcygeal ligament, a midline fibroelastic structure that runs
motor) and muscle (motor) of the large intestine. Parasympathetic between the posterior aspect of the middle region of the external anal
stimulation is integral to colonic propulsion and defecation and to sphincter and the coccyx. The anococcygeal ligament is traditionally
relaxation of the internal anal sphincter. regarded as lying just inferior to the midline raphe of levator ani but


Visceral afferent impulses mediating sensations of distension and its relationship to the raphe is more complex (Kinugasa et al 2011).
spasm from the midgut travel with the vagus nerve while the hindgut The ischial spines may be palpated laterally by an examining finger
is innervated by afferent neurones with cell bodies in the lumbar in the upper anal canal. The pudendal nerves pass over the attachment
(mostly L2 and L3) and sacral dorsal root ganglia (mostly S1 and S2) of the sacrospinous ligament at this point and pudendal nerve motor
(Brookes et al 2009). These travel alongside autonomic nerves and are terminal latency may be measured digitally using a modified electrode
often erroneously referred to as ‘sympathetic afferents’ or ‘parasympa worn on the examining glove.
thetic afferents’. Visceral afferent innervation of intramural colonic
blood vessels probably conveys the sensation of colonic distension
(Song et al 2009), while visceral afferents in the rectum convey the LINING OF THE ANAL CANAL
sensation of rectal filling and are involved in reflex propulsive activity.
The upper part of the anal canal is lined by reddish columnar epithe
lium similar to that of the rectum; it contains secretory and absorptive
MOTOR FUNCTION OF THE LARGE INTESTINE cells with numerous tubular glands or crypts. Distally, the epithelium
becomes cuboidal and darker just above the level of the anal valves (Fig.
Healthy colorectal function includes absorption of water and sodium 66.47). The subepithelial tissues are mobile and relatively distensible,
from the bowel lumen, net antegrade propulsion of intestinal contents and contain submucosal arterial and venous plexuses.
at an adequate rate, and temporary faecal storage. Colonic motor activ In the midanal canal, there are 6–10 vertical mucosal folds, the anal
ity is greatest during the day and increases on waking and after meals. columns. These are better defined in children than in adults. The
It is characterized by sustained tonic contractions and brief phasic columns frequently contain a terminal branch of the superior rectal
contractions. Phasic contractions are subdivided according to whether artery and vein, supplemented to a variable degree by middle and infe


or not they propagate along the colon. Nonpropagating contractions rior rectal vessels (Thomson 1975). Dilated submucosal veins in the
are associated with segmental mixing of luminal contents, whereas upper anal canal form an internal haemorrhoidal venous plexus. Tiny
propagated sequences can be retrograde or antegrade. In the normal arteriovenous connections to these dilated submucosal veins give the
colon, antegrade activity occurs more frequently than retrograde blood within them a higher oxygen tension and therefore a redder
sequences, which are seen more in the proximal colon. Highamplitude colour than normal venous blood. The submucosal vessels are most
propagated contractions occur in adults 4–6 times per day, originate prominent in the leftlateral, rightposterior and rightanterior quad
anywhere in the colon (but mostly proximally), and migrate for a vari rants of the wall of the canal (approximately 3, 7 and 9 o’clock when
able distance distally (Narducci et al 1987, Bharucha 2012). They are viewed in the lithotomy position); here, the subepithelial tissues are
often associated with defecation or passing flatus. The sigmoid colon expanded into three ‘anal cushions’. Although variable in number and
exhibits cyclical bursts of motor activity, which may be important in position, the cushions help to seal the anal canal and contribute to the
modulating the delivery of faeces to the rectum. A highpressure zone maintenance of continence to flatus and fluid. The anal cushions are
with unique contractile properties in response to sigmoid and rectal important in the pathogenesis of haemorrhoids. The lower ends of the
distension or contraction has been demonstrated in the distal sigmoid columns form small crescentic folds, called anal valves, between which
(the socalled rectosigmoid sphincter; Shafik et al 2003). Rectal motor lie small recesses known as anal sinuses. The anal valves and sinuses
activity is characterized by motor complexes that can be triggered by together form the scalloped dentate (or pectinate) line, which is firmly
propagating contractions from the proximal colon and by the delivery anchored to submucosal connective tissue. Anal glands open into small


of stool or gas from the sigmoid colon. However, since these frequently depressions, anal crypts, in the anal valves. The glands are branched and
propagate retrogradely, it has been suggested that they help to keep the lined by stratified columnar epithelium. Cystic dilations in the glands
rectum empty, thereby preventing the untimely delivery of colonic may extend through the internal anal sphincter and even into the exter
contents. nal sphincter (SeowCheon and Ho 1994).
The epithelium below the dentate line is smooth and typically shows
an abrupt transition to parchmentcoloured, nonkeratinized, stratified
ANAL CANAL
squamous epithelium, which lacks sweat and sebaceous glands and hair
follicles but contains numerous somatic sensory nerve endings convey
The anal canal begins at the anorectal junction and ends at the anal ing sensations of touch, pain and temperature. It extends down to the
verge (Figs 66.44–66.46). It is directed posteriorly because the slinglike intersphincteric groove, a palpable depression at the lower border of
puborectalis component of levator ani pulls the rectum forwards to the internal sphincter. Below the intersphincteric groove, the anal canal