sigmoid volvulus

Sigmoid volvulus is a cause of large bowel obstruction and occurs when the sigmoid colon twists on its mesentery, the sigmoid mesocolon.

Epidemiology

Large bowel volvulus accounts for ~5% of all large bowel obstructions, with ~60% of intestinal volvulus involving the sigmoid colon . It is more common in the elderly .

Clinical presentation

Symptoms are that of a large bowel obstruction: constipation, abdominal bloating, nausea and/or vomiting. Onset may be acute or chronic.

Pathology

Aetiology

There is a wide range of causes; some are geographically-specific :

  • chronic constipation and/or laxative abuse
  • fibre-rich diet (especially in Africa)
  • Chagas disease (especially in South America)
Associations

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Radiographic features

Sigmoid volvulus is differentiated from a caecal volvulus by its ahaustral wall and the lower end pointing to the pelvis.

Plain radiograph

Abdominal radiographs will show a large, dilated loop of the colon, often with a few gas-fluid levels. Specific signs include:

Fluoroscopy

Although now uncommonly performed, a water-soluble contrast enema exquisitely demonstrates this condition, with the appearances described as the beak sign (or bird beak sign).

CT
  • large gas-filled loop lacking haustra, forming a closed-loop obstruction 
  • whirl sign: twisting of the mesentery and mesenteric vessels
  • bird's beak sign: if rectal contrast has been administered
  • X-marks-the-spot sign: crossing loops of bowel at the site of the transition
  • split wall sign: mesenteric fat seen indenting or invaginating the wall of the bowel

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Treatment and prognosis

Endoscopic detorsion (e.g. rigid/flexible sigmoidoscopy, colonoscopy) in sigmoid volvulus cases without ischaemia or perforation successfully treats ~80% (range 60-95%) of patients and is recommended as the initial treatment . Occasionally patients suffer from recurrent sigmoid volvulus, for which a surgeon may consider sigmoid colopexy (surgical fixation of the sigmoid colon), or in the surgically unfit, a percutaneous endoscopic colostomy (PEC) might be performed.

The mortality rate is 20-25% . The most serious complication is bowel ischaemia.

Differential diagnosis