Sigmoid colon
Colon sigmoideum
Also known as: pelvic colon
The sigmoid colon is a mobile, S-shaped loop of variable length (about 40 cm) that links the descending colon to the rectum at the level of S3. It hangs on the sigmoid mesocolon.
Overview
The sigmoid colon begins at the pelvic brim in the left iliac fossa and ends at the rectosigmoid junction in front of the third sacral vertebra. At that point the taeniae coli spread out to form a continuous longitudinal muscle coat, and the sigmoid mesocolon ends. The sigmoid mesocolon has an inverted-V root. Its apex lies over the bifurcation of the left common iliac artery and the left ureter, which runs in the intersigmoid recess and is at risk during surgery.
The long mesentery makes the sigmoid very mobile, which predisposes it to volvulus. Its narrow lumen and high segmental pressures make it the commonest site of diverticula. The sigmoid colon stores faeces until a mass movement delivers them to the rectum and triggers the urge to defecate.
- Location
Left iliac fossa and pelvis, from the pelvic brim to S3.
Anatomy
- Innervation
Inferior mesenteric plexus (lumbar splanchnics) and pelvic splanchnic nerves (S2–S4).
- Arterial supply
2–4 sigmoid arteries (IMA). The watershed with the superior rectal artery lies at the rectosigmoid (Sudeck point).
- Venous drainage
Sigmoid veins → inferior mesenteric vein.
- Lymphatic drainage
Sigmoid nodes → inferior mesenteric nodes.
- Relations
Anterior and inferior: urinary bladder in males; uterus and upper vagina in females. Posterior: rectum, sacrum, left internal iliac vessels, left ureter and the left sacral plexus.
Function
- Stores faeces.
- Delivers faeces to the rectum by mass movements.
Clinical significance
Diverticulitis
Inflamed sigmoid diverticula cause left iliac fossa pain, fever and leucocytosis ("left-sided appendicitis"). Complications are abscess, perforation with purulent or faecal peritonitis (Hinchey classification), stricture, and colovesical or colovaginal fistula.
Sigmoid volvulus
The sigmoid twists around its mesenteric axis, typically in elderly, constipated, institutionalised or neuropsychiatric patients. Patients have gross distension, and radiographs show a "coffee-bean" sign. Initial treatment is endoscopic decompression, followed by elective resection.
Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.