Case of the Month

CLINICAL HISTORY

A 67-year-old man presents with lower abdominal pain five days after undergoing a barium enema that rendered unremarkable results. The patient described abdominal discomfort that started suddenly approximately six hours ago. His medical records revealed a longstanding history of constipation. He had not passed flatus or had a bowel movement in the previous 24 hours. His vital signs were stable.

FINDINGS

Supine radiographs of the abdomen demonstrate a markedly distended loop of sigmoid colon. As shown in Figure 1, it projects into the upper midabdomen (its superior margin being convex), lacks haustral markings, and demonstrates the coffee bean sign.

In Figure 2, the distended sigmoid colon extends left of the midline and superior to the transverse colon, where it demonstrates northern exposure sign (yellow star).

In Figure 3, the ascending colon (yellow arrow), descending colon (orange arrow), and northern exposure sign (blue star) of a dilated sigmoid colon are demonstrated.

DIAGNOSIS

Sigmoid volvulus.

DIFFERENTIAL DIAGNOSES

Pseudovolvulus, ileosigmoid knots, large sigmoid diverticulum, and cecal volvulus.

DISCUSSION

Volvulus can occur at any site of the gastrointestinal tract but most commonly involves the cecum or sigmoid colon. Sigmoid volvulus occurs when the colon twists around its mesentery, causing a partial or complete obstruction. It most commonly occurs in the elderly, especially in those with a history of chronic constipation.

Patients present with various signs and symptoms, including abdominal distention, abdominal pain, and failure to pass stool or flatus. Later in the course of the disease, patients experience vomiting. Additionally, vascular compromise with subsequent cardiac/respiratory failure may ensue.

On physical examination, key findings include a distended abdomen and, occasionally, a palpable mass representing the massively dilated sigmoid colon. Plain films are usually diagnostic, and may demonstrate:

• an inverted U-shape of the sigmoid colon;
• loss of haustral markings;
• coffee bean sign (the mesenteric root of the sigmoid colon seen as a midline density surrounded by distended sigmoid colon);
• bird's beak sign (seen on barium enema, representing contrast within the distal colon adjacent to the site of volvulus);
• bowel loops pointing toward the right upper quadrant (as opposed to the left upper quadrant, as seen with cecal volvulus); and
• northern exposure sign (dilated sigmoid colon superior to the transverse colon).

In cases of cecal volvulus, radiographs demonstrate a markedly distended loop of bowel projecting from the right lower quadrant toward the epigastrium/left upper quadrant. The haustral markings are usually preserved (unlike in sigmoid volvulus), and there is typically dilatation of small bowel loops.

In pseudovolvulus, the transverse colon is dilated, but its inferior margin is convex (opposite of that seen in sigmoid volvulus). A large sigmoid diverticulum is seen as a radiolucent structure on plain films but usually has an airfluid level and should fill with barium. An ileosigmoid knot may be difficult to distinguish from sigmoid volvulus on plain films. Clinically, patients are acutely ill (patient describes severe abdominal pain), with vascular compromise, shock, and resultant colonic gangrene.

Complications include bowel ischemia, sepsis/peritonitis, and perforation.

Submitted by Dr. Shivani Gupta and Dr. Michael Sadler, both at the New York Medical College at St. Vincent's Catholic Medical Center.

BIBLIOGRAPHY

Dahnert W. Radiology review manual, 2nd ed. Baltimore: Williams & Wilkins, 1993:501.
Eisenberg RL. Gastrointestinal radiology: a pattern approach, 2nd ed. Philadelphia: Lippincott, 1990:728-729.
Javors BR, Baker SR, Miller JA. The northern exposure sign: a newly described finding in sigmoid volvulus. AJR 1999;173(3):571-574.
Lee YS, Lee WJ. Coffee-bean sign. CMAJ 2008;178(13):1657.