The Inferior Mesenteric Artery (IMA) is a major branch of the abdominal aorta that supplies arterial blood to the organs of the hindgut – the distal 1/3 of the transverse colon, splenic flexure, descending colon, sigmoid colon, and rectum. This article discusses the anatomy of the inferior mesenteric artery, including its anatomical position, major branches, and clinical correlations.
The inferior mesenteric artery is the last of the three major anterior branches of the abdominal aorta (the other two being the coeliac trunk and superior mesenteric artery). It arises at the third lumbar vertebra (L3), near the inferior border of the duodenum, 3-4 cm above where the aorta bifurcates into the common iliac arteries. As the artery arises from the aorta, it descends anteriorly to its parent vessel, before moving to the left side. It is a retroperitoneal structure - situated behind the peritoneum.
The branches of the inferior mesenteric artery supply the structures of the embryonic hindgut, which include the distal 1/3 of the transverse colon, splenic flexure, descending colon, sigmoid colon, and rectum. These are supplied by three major branches of the IMA - the left colic artery, sigmoid artery, and superior rectal artery.
The left colic artery is the first branch of the IMA, supplying the distal 1/3 of the transverse colon and the descending colon. After arising from its parent artery, it travels anteriorly to the psoas major muscle, left ureter, and left internal spermatic vessels, before dividing into two branches - ascending and descending.
The sigmoid arteries supply the descending colon and the sigmoid colon, and are typically composed of two to four branches. The uppermost branch is termed the superior sigmoid artery. These branches run inferiorly, obliquely and to the left, crossing over the psoas major, left ureter, and left internal spermatic vessels in the process.
The superior rectal artery is a continuation of the inferior mesenteric artery, supplying the rectum. It descends into the pelvis, crossing the left common iliac artery and vein. At the S3 vertebral level, the artery divides into two terminal branches – one supplying each side of the rectum. Within the walls of the rectum, smaller divisions of these branches eventually communicate with the middle and inferior rectal arteries.
A left hemicolectomy is the surgical resection (removal) of the descending colon. It can be performed for a variety of reasons, such as removal of colon cancer, treatment of diverticulitis, inflammatory bowel disease, or trauma. During the procedure, the surgeon must identify and ligate the branches of the inferior mesenteric artery. This is done by shining a light through the mesentery to identify the IMA and inferior mesenteric vein (note that the course of the IMV is different than that of the IMA). The IMA is then traced back to the aorta, and divided proximally.
There are two major anastomoses of the IMA, both involving a union with branches of the superior mesenteric artery. The first is the marginal artery (of Drummond), which forms a continuous arterial circle along the inner border of the colon. Straight vessels (vasa recta) arise from the artery to supply the colon. It is formed by the union of several branches, namely the ileocolic, right colic, middle colic, left colic, and sigmoid branches of the SMA and IMA, respectively.
The Inferior Mesenteric Artery (IMA) is an arterial branch of the abdominal aorta. It arises at L3, near the inferior border of the duodenum, approximately 3-4 cm above the point where the aorta bifurcates into the common iliac arteries. As the artery arises from the aorta, it descends anteriorly to its parent vessel before shifting to the left side. It is a retroperitoneal structure, meaning that it is situated behind the peritoneum.
The branches of the IMA supply the structures of the embryonic hindgut. These include the distal 1/3 of the transverse colon, the splenic flexure, the descending colon, the sigmoid colon, and the rectum. The IMA has three major branches: the left colic artery, sigmoid artery, and superior rectal artery.
The left colic artery is the first branch of the IMA and supplies the distal 1/3 of the transverse colon and the descending colon. After arising from the IMA, the left colic artery travels anteriorly to the psoas major muscle, the left ureter, and the left internal spermatic vessels before dividing into its ascending and descending branches:
The sigmoid arteries supply the descending colon and the sigmoid colon. There are typically two to four branches, with the uppermost branch referred to as the superior sigmoid artery. These arteries run inferiorly, obliquely, and to the left, crossing over the psoas major, the left ureter, and the left internal spermatic vessels.
The superior rectal artery is a continuation of the IMA and supplies the rectum. It descends into the pelvis, crossing the left common iliac artery and vein. At the S3 vertebral level, the artery divides into two terminal branches, each supplying one side of the rectum. Within the walls of the rectum, smaller divisions of these branches eventually communicate with the middle and inferior rectal arteries.
A left hemicolectomy is a surgical resection of the descending colon. It can be performed to treat a variety of conditions, such as to remove colon cancer, to treat diverticulitis, to treat inflammatory bowel disease, or to treat trauma. During this procedure, the surgeon must dissect the branches of the IMA. They can identify the IMA and the inferior mesenteric vein (IMV) by shining a light through the mesentery, remembering that the IMV follows a different path than the IMA. Once they have located the artery, they trace it back to the aorta and divide it proximally.
The IMA has two major anastomoses with branches of the superior mesenteric artery (SMA): the marginal artery (of Drummond) and the arc of Riolan.
The splenic flexure can be considered to be a watershed area because it is supplied by the most distal branches of two major arteries. This has the advantage of making the area more resistant to ischaemia if one of the arteries becomes occluded, while at the same time making it more sensitive to systemic hypoperfusion.
Horseshoe kidney is a congenital disorder where the kidneys are fused together, forming a horseshoe shape. This condition affects 1/400 people, and is more common in males. During embryonic development, the kidneys ascend from the pelvis to the abdomen. In a person with horseshoe kidney, the fused kidney becomes hooked underneath the IMA, and is located in the lower abdomen. Horseshoe kidney does not typically require any treatment, and is usually asymptomatic. However, complications can occur due to poor drainage of the kidney, such as hydronephrosis, renal stones, and infection.
