Corpus: Inferior mesenteric artery

The inferior mesenteric artery, or IMA for short, is an unpaired branch of the abdominal aorta that supplies the intestinal segments from the left colic flexure to the upper part of the rectum.

The inferior mesenteric artery originates from the front of the abdominal aorta, after the renal arteries have branched off, at the level of the third to fourth lumbar vertebrae just before the aortic bifurcation. It is the third unpaired branch of the abdominal aorta.

Unlike the superior mesenteric artery, the IMA runs separately from the inferior mesenteric vein.

Initially, the IMA, like the superior mesenteric artery, runs in the dorsal mesentery during embryonic development. As the gut develops, the descending colon and the artery fuse with the posterior abdominal wall, placing the IMA in a retroperitoneal position. During this phase of development, the inferior mesenteric artery supplies blood to the entire hindgut.

After a brief course caudally and to the left, the IMA divides into three main branches that anastomose with each other:

• Left colic artery: This branch divides into ascending and descending branches, which form vascular arcades around the last third of the transverse colon, the left colic flexure, and the descending colon.
• Sigmoid artery: This branch splits into several vessels that supply the sigmoid colon via vascular arcades.
• Superior rectal artery: The terminal branch, which divides into two or three branches that anastomose and supply the upper rectum, specifically the corpus cavernosum recti.

The IMA supplies the distal third of the transverse colon, the descending colon, the sigmoid colon, and the upper part of the rectum.

Throughout its course, the left colic artery forms important anastomoses with the middle colic artery via the Riolan and Drummond anastomoses, establishing a connection between the inferior mesenteric artery and the superior mesenteric artery.