Comparative study of MRI and x-ray computed tomography in the preoperative evaluation of rectal carcinoma

Twenty-one patients with middle and low rectal carcinomas have been operated by abdominoperineal resection (APR) in 11 patients, and low anterior resection (LAR) with coloanal anastomosis in 7 and colorectal anastomosis in 3. The distance of the lower margin of the tumor to insertion of the levator ani on the rectal wall was correctly evaluated by CT in 15 of 21 cases (71%) and by MR in 14 of 21 (67%) while digital examination correctly assessed the distance in 17 of 21 (81%). CT and MR were unable to assess extension through the rectal wall. No significant discordance was observed between CT and MR in assessing extension to the perivesical fat, adjacent organs, pelvic side wall or lymphnodes. According to the TNM classification, MR correctly staged 76% (16 of 21) of patients while CT correctly staged 71% (15 of 21).