Performance of Magnetic Resonance Imaging in the Staging of Rectal Polyps Undergoing Endoscopic Resection: A US Academic Cancer Center Experience.

BACKGROUND AND AIMS: Magnetic resonance imaging (MRI) is the preferred staging modality in the evaluation of rectal cancer. We aimed to evaluate the accuracy of MRI among large rectal polyps referred for endoscopic resection. METHODS: We analyzed consecutive patients who underwent MRI prior to endoscopic resection for rectal neoplasia. RESULTS: 44 patients with large rectal polyps (mean size 5.8 cm) underwent MRI prior to endoscopic resection. MRI categorized 24 (54.5%) lesions as T0/T1, 16 (36.4%) T2, and 4 (9.1%) T3. Final pathology demonstrated 5 (11.4%) adenomas, 21 (47.7%) high grade dysplasia, 5 (11.4%) intramucosal adenocarcinoma, 9 (20.5%) pT1 adenocarcinoma, and 4 (9.1%) pT2 adenocarcinoma. Findings were discordant in 21 (47.7%) patients (p < 0.01), where MRI over-staged 18 (40.9%) and under-staged 3 (6.8%) patients. CONCLUSIONS: We demonstrate that MRI over-stages over 40% (18/44) of large rectal polyps. MRI staging should be interpreted cautiously when considering endoscopic resection for large rectal polyps.