Imaging description

The combination of segmental colonic wall thickening with adjacent pericolonic fat stranding usually indicates acute diverticulitis. Perforated diverticulitis may result in extraluminal air or fluid as additional findings. These signs are highly accurate [1], but occasionally similar findings can be seen in colorectal cancer (Figures 67.1 and 67.2), where the wall thickening is due to the primary tumor and the pericolonic findings of stranding with or without free air or fluid presumably reflect some degree of contained or sealed perforation.

Importance

An incorrect diagnosis of diverticulitis in the setting of a perforated colon cancer may result in a missed chance for diagnosis and potential cure of the malignancy, and create a substantial medicolegal liability. Accordingly, the American Society of Colon and Rectal Surgeons recommends that after resolution of an initial episode of acute diverticulitis, the colon should be adequately evaluated by colonoscopy or contrast enema to exclude other diagnoses, primarily cancer, ischemia, or inflammatory bowel disease [2]. While the recommendation is for colonoscopy or contrast enema, I prefer to recommend follow-up endoscopy since this seems more likely to definitively confirm or refute the diagnosis of colorectal cancer.

Typical clinical scenario

The frequency with which colon cancer mimics diverticulitis at CT is not well established, but in one study of 64 patients with clinically suspected diverticulitis, CT findings suggested diverticulitis in 37 cases [3]. Two (5.4%) of these 37 apparent cases at CT were ultimately found to be due to colorectal carcinoma. Conversely, a reported 1.9 to 3.3% of colorectal cancers present with perforation [4, 5].