Corpus: Inferior mesentric vein

The inferior mesenteric vein is a tributary of the splenic vein that drains venous blood from the descending colon, sigmoid colon, and rectum via the left colic, sigmoid, and superior rectal veins.

The inferior mesenteric vein runs retroperitoneally within the paraduodenal fold, distinct from the similarly named inferior mesenteric artery. Starting from the rectum, the vein ascends along the descending colon, crossing beneath the transverse colon and the duodenojejunal flexure. It ultimately drains into the splenic vein beneath the pancreatic neck, contributing venous blood from the left side of the large intestine to the portal vein.

In cases of portal hypertension, the inferior mesenteric vein participates in the formation of compensatory portocaval shunts. Blood backs up into the inferior mesenteric vein and flows through the inferior rectal veins into the internal pudendal veins and further into the inferior vena cava via the internal iliac veins. This increased pressure in the rectal veins may lead to the formation of haemorrhoids.