The northern exposure sign: a newly described finding in sigmoid volvulus.

OBJECTIVE: Previous studies of sigmoid volvulus have focused on the migration and dilatation of the sigmoid with respect to both fixed and mobile landmarks in the abdomen. None has specifically referred to the relationship of this colonic segment to the more proximal large intestine. We analyzed findings on abdominal radiographs, all of which had been obtained with the patient supine, of sigmoid volvulus, with particular attention to the juxtaposition of the sigmoid colon with the transverse colon. MATERIALS AND METHODS: The abdominal radiographs of 30 patients with clinically confirmed sigmoid volvulus were obtained from the teaching files of four hospitals and were retrospectively reviewed. These radiographs were compared with abdominal radiographs of 28 individuals, each of whom had a dilated colon but not sigmoid volvulus. All radiographs had been obtained with the patient in the supine position. RESULTS: The transverse colon was identified in 26 of the 30 patients with sigmoid volvulus. In each of these 26 patients, the sigmoid colon was cephalad to the transverse colon. Of the patients in the control group, the transverse colon was identified in 24 of the 28 patients. In none of these control group patients did the sigmoid colon extend rostral to the transverse colon. Thus, this sign had a sensitivity of 86% and a specificity of 100%. CONCLUSION: A dilated sigmoid colon that ascends cephalad to the transverse colon is a newly described and accurate finding of sigmoid volvulus on abdominal radiographs obtained with the patient supine.