The inferior mesenteric vein drains blood from the rectum, sigmoid colon, descending colon, and splenic flexure (Fig. 4.132). It begins as the superior rectal vein and ascends, receiving tributaries from the sigmoid veins and the left colic vein. All these veins accompany arteries of the same name. Continuing to ascend, the inferior mesenteric vein passes posterior to the body of the pancreas and usually joins the splenic vein. Occasionally, it ends at the junction of the splenic and superior mesenteric veins or joins the superior mesenteric vein.