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

PURPOSE: To evaluate the value of magnetic resonance (MR) imaging with a fl exible 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 histologica lly proved primary adenocarcincma of the lower or middle third of the rectu m (<12 cm from the pectinate line) were examined at double-contrast-materia l-enhanced MR imaging with a circular polarized flexible surface coil. RESULTS: Assessment of anal sphincteral infiltration at MR imaging was exce llent, with a specificity of 98% and a sensitivity of 100%. In the determin ation 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 (stag e NO at MR imaging), histologic examination showed negative nodes in 27 pat ients and positive nodes in 34. At MR imaging, sensitivity was 68%, and spe cificity was 24%. CONCLUSION: While preoperative staging at MR imaging according to the TNM s ystem still has limited value and accuracy, MR imaging provides the surgeon with valuable information regarding the presence of sphincteral invasion a nd the surrounding structures in patients with cancers in the lower third o f the rectum.