Define Sigmoid Volvulus. Describe its management and pathophysiology.

The Concept

A sigmoid volvulus is a twisting of the sigmoid colon around its mesenteric axis, producing a closed-loop large-bowel obstruction. Because both ends of the loop are occluded, the trapped segment distends massively, and twisting of the mesentery threatens its blood supply — so ischaemia and perforation can follow. It is the commonest type of colonic volvulus and a recognised cause of large-bowel obstruction.

Predisposing Factors

It typically affects the elderly, constipated, and institutionalised (including patients with neurological or psychiatric conditions), in whom a long, redundant sigmoid loop on a narrow mesentery and chronic loading predispose the bowel to twist. A high-fibre diet and chronic constipation contribute to the redundant, loaded colon.

Clinical Features & Diagnosis

There is gross abdominal distension (often dramatic and rapid), colicky lower abdominal pain, and absolute constipation. The plain abdominal X-ray is characteristic, showing a hugely dilated loop arising from the pelvis — the 'coffee-bean' or 'omega' sign — pointing towards the right upper quadrant. CT confirms the diagnosis and assesses for ischaemia (the 'whirl' sign of the twisted mesentery).

Management

If there is no sign of ischaemia or perforation, treatment is endoscopic decompression — passing a sigmoidoscope (or flatus tube) to untwist the loop, which releases a dramatic rush of flatus and stool and deflates the bowel. Because recurrence is common, elective sigmoid colectomy is often considered. Emergency surgery (sigmoid colectomy, e.g. Hartmann's) is required if there is ischaemia, perforation, or failed endoscopic decompression.

Pathophysiology of the Closed Loop

The danger of sigmoid volvulus lies in its closed-loop nature: with both ends of the loop occluded and the mesentery twisted, the segment cannot decompress and its blood supply is progressively cut off, so gangrene and perforation can develop rapidly. This is why any sign of ischaemia (peritonism, systemic upset, blood on the flatus tube, or CT changes) converts an endoscopic problem into an emergency operation.

The Bottom Line

Sigmoid volvulus is a closed-loop obstruction of a redundant sigmoid in the elderly, recognised by the coffee-bean sign, decompressed endoscopically when viable, and resected when ischaemic or recurrent.

A Note on Caecal Volvulus

Sigmoid volvulus should be contrasted with the less common caecal volvulus, which occurs in younger patients with an abnormally mobile caecum, presents as a small-bowel-type obstruction with a dilated caecum displaced to the left upper quadrant, and — unlike sigmoid volvulus — usually requires surgery (right hemicolectomy) rather than endoscopic decompression.

Coffee-bean sign on abdominal radiograph.

• Sigmoid volvulus = twisting of the sigmoid on its mesentery → closed-loop large-bowel obstruction (± ischaemia/perforation).
• Typically elderly, constipated, institutionalised, with a long redundant sigmoid loop.
• Gross distension, colicky pain, absolute constipation; AXR shows a 'coffee-bean'/'omega' loop from the pelvis.
• No ischaemia → endoscopic decompression (sigmoidoscope/flatus tube); recurrence common → elective sigmoid colectomy.
• Ischaemia/perforation/failed decompression → emergency surgery (sigmoid colectomy/Hartmann's).