97. Meyer CG, Penn I, James L. Liver transplantation for cholangiocarcinoma: results in 207 patients.

Transplantation 2000;69(8):1633–1637.

98. Robles R, Figueras J, Turrion VS, et al. Spanish experience in liver transplantation for hilar and

peripheral cholangiocarcinoma. Ann Surg 2004; 239(2):265–271.

99. Rea DJ, Munoz-Juarez M, Farnell MB, et al. Major hepatic resection for hilar cholangiocarcinoma:

analysis of 46 patients. Arch Surg 2004;139(5):514–523; discussion 523–525.

100. Sudan D, DeRoover A, Chinnakotla S, et al. Radiochemotherapy and transplantation allow longterm survival for nonresectable hilar cholangiocarcinoma. Am J Transplant 2002;2(8):774–779.

101. Kipp BR, Stadheim LM, Halling SA, et al. A comparison of routine cytology and fluorescence in situ

hybridization for the detection of malignant bile duct strictures. Am J Gastroenterol

2004;99(9):1675–1681.

102. McMasters KM, Tuttle TM, Leach SD, et al. Neoadjuvant chemoradiation for extrahepatic

cholangiocarcinoma. Am J Surg 1997;174(6):605–608.

103. Klempnauer J, Ridder GJ, von Wasielewski R, et al. Resectional surgery of hilar

cholangiocarcinoma: a multivariate analysis of prognostic factors. J Clin Oncol 1997;15(3):947–954.

104. Nagino M, Nimura Y, Kamiya J, et al. Segmental liver resections for hilar cholangiocarcinoma.

Hepatogastroenterology 1998;45(19):7–13.

105. Nakeeb A, Tran KQ, Black MJ, et al. Improved survival in resected biliary malignancies. Surgery

2002;132(4):555–563.

106. Jarnagin WR, Fong Y, DeMatteo RP, et al. Staging, resectability, and outcome in 225 patients with

hilar cholangiocarcinoma. Ann Surg 2000; 234(4):507–517.

107. Jang JY, Kim SW, Park DJ, et al. Actual long-term outcome of extrahepatic bile duct cancer after

surgical resection. Ann Surg 2005;241(1):77–84.

108. Konstadoulakis MM, Roayaie S, Gomatos IP, et al. Aggressive surgical resection for hilar

cholangiocarcinoma: is it justified? Audit of a single center’s experience. Am J Surg

2008;196(2):160–169.

109. Yubin L, Chihua F, Zhixiang J, et al. Surgical management and prognostic factors of hilar

cholangiocarcinoma: experience with 115 cases in China. Ann Surg Oncol 2008;15(8):2113–2119.

110. Blumgart LH, Hadjis NS, Benjamin IS, et al. Surgical approaches to cholangiocarcinoma at

confluence of hepatic ducts. Lancet 1984;1(8368):66–70.

111. Reding R, Buard JL, Lebeau G, et al. Surgical management of 552 carcinomas of the extrahepatic

bile ducts (gallbladder and periampullary tumors excluded). Results of the French Surgical

Association Survey. Ann Surg 1991;213(3):236–241.

112. Lieser MJ, Barry MK, Rowland C, et al. Surgical management of intrahepatic cholangiocarcinoma: a

31-year experience. J Hepatobiliary Pancreat Surg 1998;5(1):41–47.

113. Berdah SV, Delpero JR, Garcia S, et al. A western surgical experience of peripheral

cholangiocarcinoma. Br J Surg 1996;83(11):1517–1521.

114. Fong Y, Blumgart LH, Lin E, et al. Outcome of treatment for distal bile duct cancer. Br J Surg

1996;83(12):1712–1715.

115. Nakeeb A, Pitt HA, Sohn TA, et al. Cholangiocarcinoma. A spectrum of intrahepatic, perihilar, and

distal tumors. Ann Surg 1996;224(4):463–473; discussion 473–475.

116. Jarnagin WR, Burke E, Powers C, et al. Intrahepatic biliary enteric bypass provides effective

palliation in selected patients with malignant obstruction at the hepatic duct confluence. Am J Surg

1998;175(6):453–460.

117. Glattli A, Stain SC, Baer HU, et al. Unresectable malignant biliary obstruction: treatment by selfexpandable biliary endoprostheses. HPB Surg 1993;6(3):175–184.

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118. Kuvshinoff BW, Armstrong JG, Fong Y, et al. Palliation of irresectable hilar cholangiocarcinoma

with biliary drainage and radiotherapy. Br J Surg 1995;82(11):1522–1525.

119. Lee BH, Choe DH, Lee JH, et al. Metallic stents in malignant biliary obstruction: prospective longterm clinical results. AJR Am J Roentgenol 1997;168(3):741–745.

120. Rumalla A, Baron TH, Wang KK, et al. Endoscopic application of photodynamic therapy for

cholangiocarcinoma. Gastrointest Endosc 2001;53(4):500–504.

121. Yee K, Sheppard BC, Domreis J, et al. Cancers of the gallbladder and biliary ducts. Oncology

(Williston Park) 2002;16(7):939–946, 949; discussion 949–950, 952–953, 956–957.

122. Stemmler J, Heinemann V, Schalhorn A. Capecitabine as second-line treatment for metastatic

cholangiocarcinoma: a report of two cases. Onkologie 2002;25(2):182–184.

123. Meyerhardt JA, Zhu AX, Stuart K, et al. Phase-II study of gemcitabine and cisplatin in patients with

metastatic biliary and gallbladder cancer. Dig Dis Sci 2008;53(2):564–570.

124. Thongprasert S, Napapan S, Charoentum C, et al. Phase II study of gemcitabine and cisplatin as

first-line chemotherapy in inoperable biliary tract carcinoma. Ann Oncol 2005;16(2):279–281.

125. Oberfield RA, Rossi RL. The role of chemotherapy in the treatment of bile duct cancer. World J Surg

1988;12(1):105–108.

126. Borghero Y, Crane CH, Szklaruk J, et al. Extrahepatic bile duct adenocarcinoma: patients at high

risk for local recurrence treated with surgery and adjuvant chemoradiation have an equivalent

overall survival to patients with standard-risk treated with surgery alone. Ann Surg Oncol

2008;15(11):3147–3156.

127. Fletcher MS, Brinkley D, Dawson JL, et al. Treatment of high bileduct carcinoma by internal

radiotherapy with iridium-192 wire. Lancet 1981; 2(8239):172–174.

128. Iwasaki Y, Ohto M, Todoroki T, et al. Treatment of carcinoma of the biliary system. Surg Gynecol

Obstet 1977;144(2):219–224.

129. Kopelson G, Gunderson LL. Primary and adjuvant radiation therapy in gallbladder and extrahepatic

biliary tract carcinoma. J Clin Gastroenterol 1983;5(1):43–50.

130. Ikeda H, Kuroda C, Uchida H, et al. [Intraluminal irradiation with iridium-192 wires for

extrahepatic bile duct carcinoma–a preliminary report (author’s transl)]. Nihon Igaku Hoshasen

Gakkai Zasshi 1979; 39(12):1356–1358.

131. Todoroki T, Iwasaki Y, Okamura T, et al. Intraoperative radiotherapy for advanced carcinoma of

the biliary system. Cancer 1980;46(10):2179–2184.

132. Shiina T, Mikuriya S, Uno T, et al. Radiotherapy of cholangiocarcinoma: the roles for primary and

adjuvant therapies. Cancer Chemother Pharmacol 1992;31(suppl):S115–S118.

133. Koga A, Watanabe K, Fukuyama T, et al. Diagnosis and operative indications for polypoid lesions of

the gallbladder. Arch Surg 1988;123(1):26–29.

134. Furukawa H, Kosuge T, Shimada K, et al. Small polypoid lesions of the gallbladder: differential

diagnosis and surgical indications by helical computed tomography. Arch Surg 1998;133(7):735–

739.

135. Akiyama T, Sahara H, Seto K, et al. Gallbladder cancer associated with cholesterosis. J Gastroenterol

1996;31(3):470–474.

136. Kozuka S, Tsubone N, Yasui A, et al. Relation of adenoma to carcinoma in the gallbladder. Cancer

1982;50(10):2226–2234.

137. Aldridge MC, Gruffaz F, Castaing D, et al. Adenomyomatosis of the gallbladder. A premalignant

lesion? Surgery 1991;109(1):107–110.

138. Kurihara K, Mizuseki K, Ninomiya T, et al. Carcinoma of the gall-bladder arising in

adenomyomatosis. Acta Pathol Jpn 1993;43(1–2):82–85.

139. Aldridge MC, Bismuth H. Gallbladder cancer: the polyp-cancer sequence. Br J Surg 1990;77(4):363–

364.

140. Csendes A, Burgos AM, Csendes P, et al. Late follow-up of polypoid lesions of the gallbladder

smaller than 10 mm. Ann Surg 2001;234(5):657–660.

141. Farris KB, Faust BF. Granular cell tumors of biliary ducts. Report of two cases and review of the

literature. Arch Pathol Lab Med 1979;103(10):510–512.

142. Hadjis NS, Collier NA, Blumgart LH. Malignant masquerade at the hilum of the liver. Br J Surg

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1985;72(8):659–661.

143. Standfield NJ, Salisbury JR, Howard ER. Benign nontraumatic inflammatory strictures of the

extrahepatic biliary system. Br J Surg 1989;76(8):849–852.

144. Verbeek PC, van Leeuwen DJ, de Wit LT, et al. Benign fibrosing disease at the hepatic confluence

mimicking Klatskin tumors. Surgery 1992;112(5):866–871.

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SECTION I: COLON AND RECTUM

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Chapter 64

Colon and Rectal Anatomy and Physiology

Sandy H. Fang and Elizabeth C. Wick

Key Points

1 The mesorectum is invested by the fascia propria of the rectum.

2 The ileocolic branch of the superior mesenteric artery supplies the right colon and part of the

transverse colon.

3 The inferior mesenteric artery supplies part of the transverse colon, sigmoid colon, and rectum.

4 The inguinal lymph nodes drain the lymphatics from the anal canal below the dentate line.

5 The colon has 1013 bacteria, which promote mucosal immunity, help digest complex nutrients, and

protect against pathogenic organisms.

6 Alterations in the colonic flora have been associated with inflammatory bowel disease and colorectal

cancer.

7 Constipation is one of the most common conditions treated by physicians, but only rarely is it due to

colonic inertia.

8 During postoperative ileus, the stomach recovers after 1 to 2 days, the small bowel after 1 day, and

the colon after 3 days.

9 Thoracic epidural use after colorectal surgery can shorten postoperative ileus.

10 Sacral nerve stimulation is a newer and effective treatment for fecal incontinence.

INTRODUCTION

While the complex coordination of stool through the colon, rectum, and anus is the main function of the

colon, it also plays a role in the complex digestion and absorption of carbohydrate and protein residue,

creates a balanced environment for bacteria, and lubricates stool for transit. Understanding the anatomy

and physiology of the colon, rectum, and anus is important to treating the pathology associated with it.

EMBRYOLOGY OF THE COLON AND RECTUM

The primitive gut is derived from endoderm and begins to form during the third to fourth week of

gestation. It is divided into three segments: foregut, midgut, and hindgut. Embryologically, the colon is

derived from the midgut, which is supplied by the superior mesenteric artery, and the hindgut, which is

supplied by the inferior mesenteric artery.1 The midgut gives rise to the small intestine distal to the

ampulla of Vater, the cecum and appendix, the ascending colon, and the right half to two-thirds of the

transverse colon. During the sixth gestational week, the midgut herniates from the abdominal cavity

into the extraembryonic coelom, undergoes a 270-degree counterclockwise rotation around the superior

mesenteric artery, and then returns to the abdominal cavity at 10 weeks’ gestation. The hindgut gives

rise to the distal one-third of the transverse colon, descending and sigmoid colon, rectum, and upper

portion of the anal canal. The terminal end of the hindgut is the endoderm-lined pouch termed the

cloaca. During development, the cloaca is partitioned by the urorectal septum into the rectum and upper

anal canal and urogenital sinus. Ultimately, the distal anal canal arises from canalization of the

ectoderm. The pectineal or dentate line marks the junction between tissue derived from endoderm and

ectoderm in the anal canal.

ANATOMY OF THE COLON AND RECTUM

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The colon begins in the right lower quadrant of the abdomen as the cecum. The ileum enters the colon

at the posteromedial aspect at the ileocecal valve.1 Characteristics unique to the colon are (a) taeniae

coli, (b) haustra, and (c) appendices epiploicae, located on the antimesenteric surface of the colon.

There are three taeniae (anterior, posterior medial, and posterior lateral), which are condensations of

the outer longitudinal muscle layer in the colon. They are named according to their attachments: taenia

mesocolica (attached to the mesocolon), taenia omentalis (attached to the greater omentum), taenia

libera (no attachments). The taeniae originate at the base of the appendix, course along the length of

the colon, and then converge at the rectosigmoid junction.

On average, the colon is 150 cm long. The taenia are one-sixth shorter than the colon and are

believed to be responsible for pockets of the colon wall called sacculations or haustra.1 The epiploicae

appendices are fat appendages seen on the colonic serosa.

The colon consists of five layers: mucosa, submucosa, circular muscle layer, longitudinal muscle layer,

and serosa (Fig. 64-1). Microscopically, the colonic mucosa is a columnar epithelium marked by crypts

and goblet cells. Unlike the small intestine, the columnar epithelium of the colon and rectum does not

have villi. The submucosa is the strongest layer of bowel and contains Meissner plexus. The myenteric

plexus of Auerbach is on the external surface of the circular muscle layer. The outer longitudinal

muscles form the taeniae coli. Finally the serosa is not present in the lower portions of the rectum.

The colon begins in the right lower quadrant with the cecum. The cecum extends approximately 6 to

8 cm below the ileocecal valve (where the terminal ileum enters the posteromedial aspect of the cecum)

(Fig. 64-2). The angulation between the ileum and cecum via the superior and inferior ileocecal

ligaments is important in maintaining competence against reflux at the ileocecal junction.2 The cecum is

the widest portion of the colon (7.5 to 8.5 cm in diameter), has the thinnest wall, and is entirely

enveloped by peritoneum. The appendix originates from the lowest portion of the cecum and can be

readily identified by following the converging taeniae. In 85% to 95% of people, the appendix lies

posterior to the cecum, lateral and in line to the terminal ileum, but the position can vary, with the

most frequent variants being retrocecal (toward the psoas muscle), pelvic, and retroileal.3 During

colonoscopy, visualization of the appendiceal orifice and ileocecal valve are the landmarks required in a

complete colonic examination. From the cecum, the right colon ascends to the hepatic flexure

(approximately 15 cm). The hepatic flexure is anterior to the inferior pole of the right kidney and

overlies the second portion of the duodenum. The hepatic flexure is marked by medial, anterior, and

downward angulation of the colon. When the right colon and mesentery are mobilized during a

colectomy, care must be taken to avoid injury to the underlying duodenum. Only the anterior surface of

the right colon is invested with peritoneum; laterally, the white line of Toldt marks the extent of the

peritoneal covering and serves as an important landmark during surgical mobilization of the colon.

Figure 64-1. Layers of the colonic wall.

The transverse colon stretches from the hepatic flexure to the splenic flexure and is the longest

segment of colon (between 30 cm and 60 cm). The transverse colon is suspended by the transverse

mesocolon and is completely intraperitoneal. It is the most mobile portion of the colon and may descend

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to the level of the iliac crests or deep into the pelvis. The greater omentum descends from the greater

curve of the stomach in front of the transverse colon and then ascends to attach to the transverse colon

on its anterosuperior edge. To mobilize the transverse colon or enter the lesser sac, the fusion plane of

the omentum to the transverse colon must be dissected. The splenic flexure is situated high in the left

upper quadrant, more cephalad than the hepatic flexure, and lies anterior to the mid-left kidney and

abuts the lower pole of the spleen. There are attachments from the colon to the diaphragm at the level

of the 10th and 11th ribs and spleen (phrenocolic and splenocolic ligaments), and these must be

carefully divided during mobilization of the splenic flexure to avoid splenic injury.

The descending colon is approximately 25 cm long and courses from the splenic flexure to its junction

with the sigmoid colon at the pelvic brim. It lies anterior to the left kidney and, like the right colon, the

anterior, lateral, and medial portions of the descending colon are covered by peritoneum.

The sigmoid colon extends from the pelvic brim to the sacral promontory, where it continues as the

rectum and generally measures 15 to 50 cm in length. It is completely invested by peritoneum. The

rectosigmoid junction is marked by the convergence of the colonic taenia. The sigmoid colon is

extremely mobile and has a generous mesentery that extends along the pelvic brim from the iliac fossa

across the sacroiliac joint to the second or third sacral segment. Because of its mobile mesentery, the

sigmoid colon can twist and cause an obstruction, termed sigmoid volvulus. The left ureter runs in the

intersigmoid fossa, which is at the base of the mesosigmoid. When a high ligation of the inferior

mesenteric artery is performed during a cancer operation or the sigmoid colon is being mobilized along

the white line of Toldt, the left ureter should be identified to avoid inadvertent injury. Preoperative

placement of urinary stents can be useful for locating the ureter intraoperatively in complex,

reoperative pelvic surgery.

1 At the sacral promontory, the colon becomes the rectum. The outer layer of the rectal wall is

composed of the longitudinal muscle, where the three teniae splay. The rectum measures 12 to 15 cm in

length. It proceeds posterior and caudal along the curvature of the sacrum and coccyx, passing through

the levator ani muscles, at which point it turns abruptly caudal and posteriorly at the anorectal ring,

becoming the anal canal. Anterior to the rectum are the uterine cervix and posterior vaginal wall in

women, and the bladder and prostate in men. Posteriorly, the rectum occupies the sacral concavity

where the median sacral vessels, presacral veins, and sacral nerves run, all of which are invested in the

presacral fascia. The rectum is marked by three curves. The upper and lower curves are convex and to

the right, while the middle is convex and to the left. Within the lumen, these correspond to the valves

of Houston, which separate the lower third, middle third, and upper third of the rectum – important

landmarks when the location of a rectal abnormality is established endoscopically (the lower rectal

valve is at 7 to 8 cm from the anal verge, middle rectal valve at 9 to 11 cm, and upper rectal valve at

12 to 13 cm).4 The valves do not contain all layers of the bowel wall and thus biopsy at this location

carries minimal risk of perforation. The middle valve of Houston is the internal landmark corresponding

to the anterior peritoneal reflection. The anterior and lateral surfaces of the upper third of the rectum

are intraperitoneal, whereas only the anterior surface of the middle third of the rectum is

intraperitoneal in location. The lower third of the rectum is entirely extraperitoneal. The mesorectum is

the term used to describe the areolar tissue surrounding the rectum that contains nerves, lymphatics,

and terminal branches of the superior hemorrhoidal branch of the inferior mesenteric artery. Although it

invests the rectum circumferentially, the mesorectum is most prominent posterior to the rectum. It is

invested by the fascia propria of the rectum, a continuation of the parietal endopelvic fascia (Fig. 64-3).

The fascia propria (investing fascia) includes the distal two-thirds of the posterior rectum and the distal

one-third of the anterior rectum, where it is no longer intraperitoneal. A total mesorectal excision

entails removal of the entire rectum without violating the fascia propria of the rectum. This is

accomplished by mobilizing the rectum using the plane between the fascia propria of the rectum and the

presacral fascia. Anterior to the investing fascia (fascia propria) is a delicate layer of connective tissue

known as Denonvilliers fascia, which separates the rectum from its anterior structures. Waldeyer fascia

(rectosacral fascia) is the presacral fascia that is an extension of the parietal pelvic fascia from the

periosteum of sacral segment four to the posterior wall of the rectum. It contains branches of the sacral

splanchnic nerves. Below Waldeyer fascia is the supralevator or retrorectal space.

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Figure 64-2. General anatomic components of the colon.

Figure 64-3. Fascial relationships of the pelvis.

The surgical anal canal begins at the anorectal ring or levator ani muscles and extends to the anal

verge. It measures 2 to 4 cm and is usually longer in men than in women. The internal anal sphincter

(continuation of the circular smooth muscle of the rectum) and the external anal sphincter (continuation

of the puborectalis muscle) encircle the anal canal and control fecal continence. The internal anal

sphincter relies on autonomic innervation, while the external anal sphincter uses somatic innervation.

The median length and thickness of the female anterior external sphincter is 11 and 13 mm and thus a

small tear sustained during vaginal delivery may cause fecal incontinence.5 There are three layers of the

external sphincter – subcutaneous (traversed by the conjoined longitudinal muscle with some fiber

attachments to the skin), superficial (connective tissue attaches posteriorly, forming the anococcygeal

ligament), and deep (continues with the puborectalis muscle). Between the internal and external anal

sphincters, the longitudinal muscle of the rectum joins fibers of the levator ani and puborectalis muscles

to form the conjoined longitudinal muscle. The dentate line marks the transition between the columnar

epithelium of the intestine and the squamous epithelium of the anal canal. The transition between these

two epithelia is called the anal transitional zone. The Columns of Morgagni are the 6 to 14 longitudinal

folds located at the dentate line. Small pockets between these columns called anal crypts contain anal

glands, which may become obstructed with foreign material to cause an infection. Below the dentate

line is the anoderm, which extends to the anal verge and does not contain accessory skin structures,

such as hair, sebaceous and sweat glands. The autonomic nervous system innervates proximal to the

dentate line and the somatic nervous system supplies the anoderm and distally.

Pelvic Floor

The perineal body is the tendinous insertion of the external anal sphincter, bulbocavernosus, and

superficial and deep transverse perineal muscles. It supports the perineum and separates the vagina

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from the anus.

Three striated muscles that attach to the pubic bone make up the pelvic floor or levator ani muscles:

iliococcygeus, pubococcygeus, and puborectalis. The pelvic floor muscles are supplied by branches from

the third sacral nerve, while the external anal sphincter is supplied by nerve fibers traveling with the

pudendal nerve on the levators undersurface.

The puborectalis originates from the back of the symphysis pubis and forms a U-shaped sling as it

joins the opposite muscle posteriorly. The iliococygeus muscle arises from the ischial spine and posterior

part of the obturator fascia and travels inferiorly, posteriorly, and medially to insert into the last two

segments for the sacrum and coccyx. The pubococcygeus muscle arises from the anterior half of the

obturator fascia and the posterior pubis. Its fibers are directed backward, downward, and medially,

where they decussate with fibers of the opposite side. The decussation is called the anococcygeal raphe.

Anorectal Spaces

The perianal space surrounds the anal canal superficially and contains the external hemorrhoidal plexus.

The ischioanal space extends laterally and goes superiorly to the levator ani from the skin on the

perineum. The levator ani and external sphincter muscles form the medial boundary, while the lateral

wall is formed by the obturator fascia. The superficial postanal space connects the perianal spaces with

each other posteriorly below the anococcygeal ligament, while the deep postanal space lies above the

anococcygeal ligament. The ischioanal and perianal spaces make the ischioanal fossa. The deep postanal

and ischiorectal spaces form a horseshoe configuration that may be involved in a horseshoe abscess.

Below the perianal space between the sphincter muscles is the intersphincteric space. The submucosal

space contains the internal hemorrhoidal plexus and lies between the internal anal sphincter and the

mucosa distal to the dentate line. Proximally, it becomes the submucosa of the rectum. Above the

levator complex is the supralevator space, which extends superiorly to the peritoneum at the rectosacral

fascia. The retrorectal space extends above the rectosacral fascia and lies between the upper two-thirds

of the rectum and sacrum.

Arterial Blood Supply

2 3 The arterial blood supply to the colon, rectum, and anus is highly variable. The following

summarizes the general courses of the arterial blood supply. The superior mesenteric artery arises from

the aorta, runs posterior to the pancreas, and passes anterior to the third portion of the duodenum (Fig.

64-4). In addition to supplying the small bowel through jejunal and ileal branches, the superior

mesenteric artery gives rise to the ileocolic, right colic, and middle colic branches that supply the

cecum, ascending colon, and proximal transverse colon. The right colic arterial anatomy is particularly

variable and can be absent or arise from the ileocolic or the superior mesenteric artery. The middle colic

artery has a right branch that supplies the hepatic flexure and the right portion of the transverse colon,

while the left branch supplies the left portion of the transverse colon. The inferior mesenteric artery

arises from the anterior surface of the aorta, typically 3 to 4 cm above the aortic bifurcation, and

supplies the distal transverse colon, descending colon, sigmoid colon, and upper rectum. The inferior

mesenteric artery gives rise to the left colic artery and sigmoidal branches, then continues in the

sigmoid mesentery, and after crossing the left iliac vessels, is renamed the superior rectal/hemorrhoidal

artery. The inferior mesenteric artery may also function as an important collateral vessel to the lower

extremities during instances of distal aortic occlusion. The superior hemorrhoidal artery descends

behind the rectum and splits into right and left branches in the mesorectum. It is the main blood supply

of the rectum. The middle and inferior rectal/hemorrhoidal arteries arise from either the internal

pudendal arteries or the hypogastric arteries and supply the distal two-thirds of the rectum. The

presence of the middle rectal artery, in particular, can be variable. A series of arterial arcades along the

mesenteric border of the entire colon, known as the marginal artery of Drummond, connect the superior

mesenteric and inferior mesenteric arterial systems. The marginal artery may be attenuated or absent at

the distal transverse colon/splenic flexure, the delineation between the midgut and hindgut, and thus

ischemic colitis most commonly affects this region. The arc of Riolan (“meandering mesenteric artery”)

is a short loop connecting the left branch of the middle colic artery and the trunk of the inferior

mesenteric artery. The inferior rectal/hemorrhoidal arteries traverse the ischioanal fossa and supply the

anal canal and external anal sphincter muscles.

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Figure 64-4. Arterial blood supply of the colon.

Figure 64-5. Venous drainage of the colon by the portal vein.

VENOUS DRAINAGE

The veins that drain the large intestine bear the same terminology and follow a course similar to that of

their corresponding arteries (Fig. 64-5). The veins from the right colon and transverse colon, along with

the veins draining the small intestine, drain into the superior mesenteric vein. The superior mesenteric

vein runs slightly anterior to and to the right of the superior mesenteric artery. The superior mesenteric

vein courses beneath the neck of the pancreas, where it joins with the splenic vein to form the portal

vein. The inferior mesenteric vein is a continuation of the superior rectal vein and drains blood from the

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