MR colonography in patients with incomplete conventional colonoscopy

PURPOSE: To assess dark-lumen magnetic resonance (MR) colonography for the evaluation of colonic segments in patients in whom conventional colonoscopy could not be completed. MATERIALS AND METHODS: Institutional review board approval and written informed consent were obtained. Within 24 hours of incomplete conventional colonoscopy, 37 patients (22 women, 15 men; age range, 25-63 years) underwent MR colonography. Contrast material-enhanced T1-weighted three-dimensional images were collected after rectal administration of water for colonic distention. Data from MR colonography were evaluated by two radiologists. With a three-point scale, image quality was characterized in terms of colonic distention (1 = good; 2 = moderate, diagnostic; and 3 = poor, nondiagnostic) and presence of artifacts (1 = none; 2 = moderate, diagnostic; and 3 = extensive, nondiagnostic). Depiction of colorectal disease was assessed according to the following colonic segments: cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum. RESULTS: Four patients had history of colorectal cancer, and each had undergone partial colonic resection of two segments. Hence, 214 segments were evaluated. Conventional colonoscopy failed in assessment of 127 of 214 potentially visible colonic segments in the 37 patients. MR image quality was rated diagnostic in 35 patients and permitted assessment of 206 of 214 potentially visible segments. Nondiagnostic image quality in two patients was attributed to inadequate distention of prestenotic colonic segments owing to high-grade tumor stenosis. All inflammation- and tumor-induced stenoses and all five polyps identified at conventional colonoscopy in poststenotic segments were correctly detected at MR colonography. However, MR-based assessment of prestenotic segments revealed two lesions suspected of being carcinoma, five polyps, and four segments affected by colitis. CONCLUSION: MR colonography proved reliable in evaluating the majority of colonic segments inaccessible with conventional colonoscopy. The identification of additional disease at MR colonography underscores the need for a second diagnostic step in the setting of incomplete conventional colonoscopy.