The Common Vein Coyright 2007

Introduction

The superior mesenteric artery (SMA), inferior mesenteric artery (IMA), and internal iliac arteries are the vessels that supply the colon. The SMA is the artery of the midgut while the IMA is the artery of the hindgut.  The distal and terminal portion of the hindgut is supplied by the rectal branches of the internal iliac arteries.

SMA

The SMA, as the midgut artery supplies the right side of the colon from the ileocecal valve to the region of the distal transverse colon and splenic flexure.  The SMA shares the supply of the splenic flexure with the IMA, and therefore does theoretically help supply the proximal hindgut.

The SMA arises from the aorta between T12 and L2.  The usual branches of the SMA to colon include the ileocolic artery, the right colic artery and the middle colic artery, supplying in general the cecum ascending colon and transverse colon respectively.  The ileocolic artery almost always arises directly from the SMA.  The right colic may arise from the SMA, but sometimes arises from one of its branches – the ileocolic or the middle colic artery.  The middle colic artery strangely arises from the SMA from a more proximal position in the SMA than the ileocolic even though it supplies colon that is more distal in location.  Its origin is at the first part of the SMA close to the origins of the jejunal branches.

The branches course in the mesentery and extend to the medial and mesenteric edge of the ascending colon, and then branch so that they course and connect along the inner margin of the colon forming the marginal artery allowing the branches to connect with each other. In the transverse colon the mesenteric edge is posterior and hence the marginal artery is posterior.   The vasa recta (recta = straight) branch from the marginal artery and course over the colon finally penetrating the wall of the colon to form a capillary network in the submucosa.  Once the vessels proceed beyond the marginal artery and into the bowel wall, there are not usually collateral pathways so that any occlusion beyond the marginal artery will result in ischemia.

SMA

The diagram shows the branches of the SMA including the ileocolic (1), right colic (2) and the middle colic (3).  These vessels connect through the marginal artery (4) which runs along the inner or mesenteric border of the colon (4) and gives rise to the vasa recta that run over the colon before branching into the wall of the colon to finally enter the submucosa. Courtesy Ashley Davidoff MD 12005b012

Colonic supply from the SMA

The three major branches to the right colon are demonstrated arising from the SMA (1). The ileocolic (2) right colic (3) and the middle colic (5) arise in usual fashion.  A hepatic flexural artery is an occasionally present, and is shown in this patient (4).  Note that the middle colic (5) arises as the first colic artery even though it supplies a distal portion of the right colon.  It divides in two, with one part of the marginal artery going to the right and the other to the left(6).  The right sided branch will finally connect with the marginal vessels created by the ileocolic and right colic arteries.  The left part of the marginal branch courses to the splenic flexure where it will connect with the marginal component of the left colic artery created by the sigmoid and left colic arteries.  The marginal artery gives rise to the vasa recta (7) which course over the colon before penetrating the wall of the colon. Courtesy Ashley Davidoff MD  12220b01 12220d04

The SMA and celiac axis connect through the pancreaticoduodenal arcade that runs through the head of the pancreas and also connect to some extent through the transverse pancreatic artery that runs through the body and tail of the pancreas.  The arc of Buehler is an embryologic connection between the SMA and celiac axis that is seen uncommonly as a persistent communication.  The SMA also connects to the IMA via the marginal artery on the left side of the colon. Thus the three major arteries and circulations do have important connections that become life saving when one becomes narrowed or blocked.

Coronal CT

CTA of the abdomen can easily identify the proximal portions of the mesenteric vessels and is able to depict the first order of branches reasonably accurately as well.  In this image one is able to see remnants of the  ileocolic, (bright red)  right colic (light maroon) and parts of the middle colic (dark maroon) at 7, 9, and 12 o’clockrespectively. The thinner arteries are seen coursing with slightly plumper veins to the jejunal branches to the left side.  Courtesy Ashley Davidoff MD 45189

Applied Anatomy

Disorders of the SMA arterial circulation are relatively common including bowel ischemia from thrombosis, embolization, dissection, and hypotension.  Disorders that lead to lower GI bleeding include angiodysplasia and diverticular disease.

The following case is from a 71 year old male who presented with brisk rectal bleeding and hemodynamic instability.

Labelled red cell scan

This radionuclide bleeding scan is read from the right upper corner, horizontally across, proceeding to the next rows and reflects progressive accumulation of radionuclide in the left upper quadrant in the splenic flexure in the first few minutes of scanning.  This indicates a rapid bleed in the splenic flexure. Courtesy Ashley Davidoff MD 12220a02

Bleeding artery of the splenic flexure.

The angiogram of the SMA shows a worm like accumulation of contrast (bright red) appearing at the bottom of a puddle of blood (pink blob) noted to be arising from the left side of the middle colic artery.  In the course of the angiogram, one first sees the spillage of contrast as the bright red worm like accumulation and as the contrast continues to spill into the bowel lumen it becomes a puddle of less dense contrast as it mixes wih colonic content and spreads. Courtesy Ashley Davidoff MD  12221 12221b02

Fig 1                                                                                      Fig 2 Embolization

The ability to achieve subselection of the vasa recta allowed us to embolize the bleeding vessel with metallic “coils”.  An X-ray of the specimen shown in figure 2 reveals the metallic coil within the resected splenic flexure.  The cause of the bleed was a hemorrhaging diverticulum. Courtesy Ashley Davidoff MD  12225b01 12225b03

SMA dissection

These magnified views of an aortic dissection (a) show extension of the dissection noted as a fine line in the aorta in a, into the SMA characterized by a linear lucency in the SMA(b).  There is a collar of increased density around the SMA in c and d, representing periadventitial rupture, meaning a contained rupture in the last layer of the blood vessel . Courtesy Ashley Davidoff MD  36940c02

IMA

The IMA originates from the aorta around L3 and is a fairly small vessel arising at an acute angle. One therefore has to choose a catheter that has an acute angle in order to engage this vessel for selective catheterization.

In its proximal portion the vessels parallels the aorta for about 3-4cms.  Its branches include the left colic, sigmoid branches and superior rectal artery.  As stated above it connects with the SMA via the marginal artery with a watershed region created in the splenic flexure.   Since this region is an end arterial circulation for the SMA and IMA it is potentially a weak link in the circulation predisposing it to ischemia.

There are three major branches of the IMA including the left colic artery, sigmoid arteries (usually about 2-3 vessels) and the superior rectal artery (aka superior hemorrhoidal artery).

IMA

Courtesy Ashley Davidoff MD Davidoff art 12005b014

Internal iliac arteries

The iliac supply includes mid to distal rectum and anal regions.  They provide an important collateral pathway between the systemic circulation at large with the mesenteric circulation.  The middle and inferior rectal branches supply the distal rectum and anal regions.

Internal iliac branches to the colon The internal iliac artery (10) supplies the distal part of the rectum and gives rise to the middle rectal artery (11), and inferior rectal (12) arteries.  These are paired arteries arising from the left and right iliacs and they are connected through collaterals with the superior rectal artery. Courtesy Ashley Davidoff MD Davidoff art 12005b016

The single superior rectal artery arises from the terminal portion of the IMA, and divides initially into two main branches, one supplying the left side and one the right of the upper portion of the rectum.  The middle and inferior rectal branches on the other hand, have paired origins, one arising from the left internal iliac and the other from the right internal iliac artery.

Applied Anatomy

Courtesy Ashley Davidoff  45581b05

Courtesy Ashley Davidoff MD  12006 12006b

Courtesy Ashley Davidoff MD  12020 12020b02