A long, mobile loop on a narrow mesenteric base
Expansion
The sigmoid colon is vulnerable because of the mismatch between:
- A long, mobile loop of bowel
- A narrow sigmoid mesocolon base
The greater the length and the narrower the base, the easier it is for the loop to rotate about its mesenteric axis. Chronic constipation, a high-fibre diet, institutional care and increasing age all predispose by elongating the loop.
Rotation produces a closed loop obstruction and, if it exceeds about 180 degrees, occludes the mesenteric vessels and causes ischaemia.
Initial management is endoscopic decompression with a flatus tube, which is possible precisely because the twist is accessible from below, but recurrence is common, so elective sigmoid colectomy is often required.
Caecal volvulus is the rarer counterpart and requires an abnormally mobile caecum from incomplete embryological fixation.