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MAGNETIC RESONANCE IMAGING OVERSTAGES RECTAL POLYPS UNDERGOING ENDOSCOPIC RESECTION: A US ACADEMIC CANCER CENTER EXPERIENCE
Phillip S. Ge
*, Victoria G. Terrazas Morales, Emmanuel Coronel, Gene Liaw, Raju S. Gottumukkala, Brian K. Bednarski, George J. Chang, Tsuyoshi Konishi, Craig A. Messick, Y. Nancy You, Montserrat Guraieb Trueba
Gastroenterology, Hepatology and Nutrition, The University of Texas MD Anderson Cancer Center, Houston, TX
BACKGROUND: Pelvic magnetic resonance imaging (MRI) is recommended by National Comprehensive Cancer Network guidelines in the initial staging of rectal cancer, intended to provide accurate assessment of tumor depth (T-staging) and presence of lymph node metastasis. However, it is unclear whether this accuracy is maintained among large rectal polyps referred for endoscopic resection. Here we aimed to evaluate the accuracy of pre-resection pelvic MRI among rectal polyps being referred for endoscopic resection.
METHODS: We analyzed consecutive patients who underwent pelvic MRI prior to referral for endoscopic resection for rectal neoplasia over a 6-year period from 2018-2024, as part of a larger prospective endoscopic resection database. Demographics, initial MRI findings, procedural characteristics, resection outcomes, histopathologic diagnosis, and adverse events were recorded.
RESULTS: A total of 44 patients with large rectal polyps underwent MRI prior to endoscopic resection. Mean lesion size was 5.8 cm (SD, 3.2 cm).
En bloc, complete (R0), and curative resection were respectively achieved in 88.6%, 75.0%, and 72.7% cases. Patients were followed up for mean 14.5 months (SD, 29.6 months), demonstrating no local or metastatic recurrences. A total of 7 patients (21.3%) underwent surgical resection, of which 2 were due to aborted endoscopic resection and 5 were due to high-risk histopathological features. Of these, 2 were found to have invasive adenocarcinoma (both with lymph node metastasis), 2 had residual adenoma, and 3 were negative resections.
Correlation of Pelvic MRI with Histopathology: Pre-resection MRI findings categorized 24 (54.5%) lesions as T0/T1, 16 (36.4%) as T2, and 4 (9.1%) as T3, and 4 (9.1%) as either NX/N1. Direct internal sphincter involvement was reported on MRI in 2 (4.5%) patients. Final histopathologic diagnosis included 5 (11.4%) adenomas, 21 (47.7%) with high grade dysplasia, 5 (11.4%) with intramucosal adenocarcinoma, 9 (20.5%) pT1 adenocarcinoma, and 4 (9.1%) pT2 adenocarcinoma. No patients were noted to have direct sphincter involvement. When compared to MRI, findings were discordant in 21 (47.7%) patients (
p < 0.01 on Wilcoxon signed-rank test), in which MRI over-staged lesions in 18 (40.9%) and under-staged lesions in 3 (6.8%) patients.
CONCLUSIONS: Given that endoscopic resection has become increasingly common as an organ-sparing alternative to rectal surgery, pre-resection MRI staging information may directly impact decisions of whether or not to proceed with endoscopic resection. Our findings demonstrate that MRI over-stages rectal polyps in over a third of cases. These findings are potentially clinically impactful and warrant additional larger prospective study for further validation.
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