MR Imaging for the Preoperative Planning of Sphincter-saving Surgery for Tumors of the Lower Third of the Rectum: Use of Intravenous and Endorectal Contrast Materials

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Abstract
PURPOSE: To evaluate the value of magnetic resonance (MR) imaging with a flexible surface coil in predicting the resectability of tumors in the lower rectum and the feasibility of sphincteral salvage. MATERIALS AND METHODS: In a prospective study, 61 patients with histologically proved primary adenocarcinoma of the lower or middle third of the rectum (<12 cm from the pectinate line) were examined at double-contrast-material–enhanced MR imaging with a circular polarized flexible surface coil. RESULTS: Assessment of anal sphincteral infiltration at MR imaging was excellent, with a specificity of 98% and a sensitivity of 100%. In the determination of tumor infiltration into adjacent organs (T4), the specificity was 100%, and the sensitivity was 90%, with surgical and histologic findings as the standards. While MR imaging showed negative nodes in 40 patients (stage N0 at MR imaging), histologic examination showed negative nodes in 27 patients and positive nodes in 34. At MR imaging, sensitivity was 68%, and specificity was 24%. CONCLUSION: While preoperative staging at MR imaging according to the TNM system still has limited value and accuracy, MR imaging provides the surgeon with valuable information regarding the presence of sphincteral invasion and the surrounding structures in patients with cancers in the lower third of the rectum.