Corpus: Sigmoid colon

The sigmoid colon, or sigmoid for short, is the part of the colon located in the pelvis.

2.1. Overview

The sigmoid colon starts where the descending colon transitions, roughly at the upper opening of the lesser pelvis. From this point, it travels anterior to the sacrum, curves toward the right side of the pelvis, loops back toward the midline, and finally terminates caudally in the rectum. Its s-shaped structure, approximately 40 cm in length, is the origin of its name.^[1]

The sigmoid colon is completely covered by peritoneum and is attached to the posterior abdominal wall via the sigmoid mesocolon. The mesocolon gradually becomes shorter at both ends of the sigmoid colon, making this section of the bowel highly mobile overall. However, it is firmly anchored at its transition points to the descending colon and the rectum.

2.2. Blood supply

The arterial blood supply to the sigmoid colon comes from the sigmoid arteries, which branch off from the inferior mesenteric artery. Within the mesentery, there are numerous anastomoses connecting the blood vessels of neighboring intestinal sections, ensuring adequate blood flow to the sigmoid colon even if the sigmoid arteries become blocked.

Venous drainage occurs via the inferior mesenteric vein, which flows into the portal circulation via the lienal vein.

2.3. Topography

Posterior to the sigmoid colon lie the external iliac arteries and the left portion of the sacral plexus. Anteriorly, small bowel loops separate the sigmoid colon from the urinary bladder in men and from the uterus in women.

The primary functions of the sigmoid colon are further dehydration of feces and temporary storage before defecation.

The sigmoid colon is a common site for colon carcinomas. After a sigmoid resection, patients initially experience soft or liquid stools. However, the colon’s high functional adaptability typically allows bowel movements to normalize over time.

Inflammation of the sigmoid colon is referred to as sigmoiditis.

An abnormal elongation of the sigmoid colon is known as sigmoid elongatum.