Toxic megacolon in patients with severe acute colitis: computed tomographic features.

OBJECTIVE: The objective of the study was to evaluate computed tomography (CT) in the differential diagnosis of patients with toxic megacolon (TM) complicating severe acute colitis (SAC) and patients with SAC but no TM.

MATERIALS AND METHODS: We identified 16 patients who presented clinically complicated SAC and CT examination before surgery. The CT scans of these patients were retrospectively evaluated in consensus by two abdominal radiologists blinded to the clinical and pathological results for CT findings of SAC, i.e., diffuse colonic wall thickening, submucosal edema, pericolonic fat stranding and ascites, and CT findings of TM reported in the literature, i.e., segmental colonic wall thinning, air-filled colonic distension over 6 cm with abnormal haustral pattern, nodular pseudopolyps and associated small bowel distension. Fisher's Exact Test was used for all statistical analyses.

RESULTS: Segmental colonic wall thinning with abnormal haustral pattern was noted in TM only (P=.001). As compared to patients with SAC but no TM as a complication, patients with TM showed statistically more frequent air-filled colonic distension over 6 cm (P=.001) and nodular pseudopolyps (P=.001). Diffuse colonic wall thickening (P=.036) and submucosal edema (P=.036) were more present in cases of uncomplicated SAC. Pericolonic fat stranding (P=.12), ascites (P=.6), and small bowel and gastric distension (P=1) were not distinctive criteria.

CONCLUSION: Computed tomography is useful in distinguishing patients with TM from patients with SAC but no TM as a complication. The association of air-filled colonic distension >6 cm, abnormal haustral pattern and segmental colonic parietal thinning seems pathognomonic of TM and should lead to rapid surgery.