The sigmoid colon is an S-shaped loop of colon, very variable in length, running from the pelvic brim to the start of the rectum at about the level of S3. It hangs on its own mesentery, the sigmoid mesocolon, which makes it mobile. It usually lies in the pelvis but can reach into the abdomen.
| Location | From the pelvic brim to the rectosigmoid junction at about S3, mostly in the pelvis and left iliac fossa |
|---|---|
| Parts |
|
| Nerve Supply | Pelvic splanchnic nerves, S2-S4 (parasympathetic); Lumbar splanchnic nerves via the inferior mesenteric plexus (sympathetic) |
| Blood Supply | Sigmoid arteries (from the inferior mesenteric artery) |
| Venous drainage |
|
| Lymphatic drainage |
|
Stores faeces before defecation and continues water absorption.
It is the most common site of diverticular disease in Western populations because high pressures are generated in its narrow lumen. A long loop on a narrow mesenteric base can twist, causing sigmoid volvulus, especially in elderly or constipated patients. It is also a frequent site of colorectal cancer and is inspected by flexible sigmoidoscopy.
Twisting of the sigmoid loop on its mesocolon causing large bowel obstruction with a coffee bean sign on X-ray, often decompressed endoscopically.
Inflammation or perforation of sigmoid diverticula causing left iliac fossa pain, fever and sometimes abscess or fistula to the bladder.
Adenocarcinoma of the sigmoid colon presenting with rectal bleeding, change in bowel habit or obstruction.
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