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 ⁶. It is more common in the elderly ⁷.

Clinical presentation

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

Pathology

Etiology

There is a wide range of causes; some are geographically-specific ⁵:

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

Associations

• chronic neurological conditions (e.g. Parkinson disease, multiple sclerosis, pseudobulbar palsy)
• medications from chronic psychiatric conditions (e.g. chronic schizophrenia)

Radiographic features

Sigmoid volvulus is differentiated from a cecal 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:

• coffee bean sign ⁵
• Frimann-Dahl sign - three dense lines converge towards the site of obstruction
• absent rectal gas ⁵
• liver overlap sign
• northern exposure sign

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 ^6,7
• whirl sign: twisting of the mesentery and mesenteric vessels
• bird's beak sign: if rectal contrast has been administered ⁶
• 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

Treatment and prognosis

Endoscopic detorsion (e.g. rigid/flexible sigmoidoscopy, colonoscopy) in sigmoid volvulus cases without ischemia or perforation successfully treats ~80% (range 60-95%) of patients and is recommended as the initial treatment ⁸. 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% ⁷. The most serious complication is bowel ischemia.

Differential diagnosis

• large bowel obstruction from other causes
• cecal volvulus: to differentiate between sigmoid volvulus and cecal volvulus please refer to sigmoid volvulus versus cecal volvulus article
• colonic pseudo-obstruction