The sigmoid vein, also called the vena sigmoideus, refers to one group of sigmoid veins. These veins are tributaries of the inferior mesenteric vein, which is a tributary of the hepatic portal vein.

Each sigmoid vein is curved or crescent-shaped, like the uncial sigma (a variation of the Greek letter “sigma”), which resembles the letter “c.”

These veins travel through the colon's curved part into the rectum. The function of each sigmoid vein is to drain the sigmoid colon, the portion of the large intestine closest to the anus and rectum. The sigmoid colon, part of the digestive system, must be drained in order to properly extract salt and water from solid wastes before the body eliminates them.

The inferior mesenteric vein receives each sigmoid vein from the iliac and sigmoid colons. The sigmoid vein empties into the superior rectal vein, which later turns into the inferior mesenteric vein.