Sigmoid volvulus is a cause of large bowel obstruction and occurs when the sigmoid colon twists on its mesentery, the sigmoid mesocolon.
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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.
Associations
chronic neurological conditions (e.g. Parkinson disease, multiple sclerosis, pseudobulbar palsy)
medications from chronic psychiatric conditions (e.g. chronic schizophrenia)
Clinical presentation
Symptoms are that of 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)
Radiographic features
Sigmoid volvulus is differentiated from a cecal volvulus by its ahaustral wall, the lower end pointing to the pelvis and large bowel obstruction.
Plain radiograph
Abdominal radiographs will show a large, dilated loop of the colon, often with a few gas-fluid levels. Specific signs include:
Frimann-Dahl sign - three dense lines converge towards the site of obstruction
absent rectal gas 5
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 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
steel pan sign: a close resemblance to the percussion instrument known as a steelpan 9,10
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.
History and etymology
Von Rokitansky described sigmoid volvulus for the first time in 1836 9.
Differential diagnosis
large bowel obstruction from other causes
cecal volvulus: to differentiate between sigmoid volvulus and cecal volvulus please refer to the sigmoid volvulus versus cecal volvulus article
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