Inferior mesenteric artery
Arteria mesenterica inferior
Also known as: IMA
The inferior mesenteric artery (IMA) is the third and smallest unpaired branch from the front of the abdominal aorta, at L3. It supplies the hindgut, from the distal third of the transverse colon to the upper anal canal.
Overview
The IMA arises behind the third and fourth parts of the duodenum, about 3–4 cm above the aortic bifurcation. It runs down and to the left behind the peritoneum. After crossing the left common iliac artery it continues as the superior rectal artery, which enters the sigmoid mesocolon and then the mesorectum.
The hindgut has two classic "watershed" zones, where two arterial territories meet and the blood supply is weakest. One is at the splenic flexure (Griffiths' point), where the SMA and IMA territories meet. The other is at the rectosigmoid junction (Sudeck's point).
Anatomy
- Branches
The left colic artery (with ascending and descending branches), two to four sigmoid arteries, and the superior rectal artery. The superior rectal artery anastomoses with the middle and inferior rectal arteries, which come from the internal iliac system.
Function
- Supplies the hindgut: the distal transverse colon, descending colon, sigmoid colon, rectum and upper anal canal.
Clinical significance
Ischaemic colitis
Ischaemic colitis typically affects the watershed zones, especially the splenic flexure. It occurs in low-flow states and after aortic surgery, when the IMA is often tied off. It causes abdominal pain and bloody diarrhoea.
Colorectal cancer surgery
The level at which the IMA is tied (a "high" tie at its origin or a "low" tie below the left colic artery) determines how many lymph nodes are removed and how well the remaining bowel is supplied in left-sided colon and rectal resections.
Compiled from standard anatomy and physiology references — see the Cardiovascular System sources. For education only; not medical advice.