Preoperative assessment of local tumor extent in advanced rectal cancer: CT or high-resolution MRI?

Background: We compared high-resolution magnetic resonance imaging (MRI) wi th computed tomography (CT) in the assessment of tumor infiltration in surr ounding structures for locally advanced primary and recurrent rectal cancer . Methods: Twenty-six patients with operable, locally advanced rectal cancer (15 recurrent and 11 primary) were evaluated with conventional pelvic CT an d 1.5-T high-resolution MRI with a quadrature phased-array coil. The images were scored for invasion of nine neighboring pelvic structures, and the re sults were compared with surgical and histologic findings. Results: A total of 234 structures in 26 patients was evaluated for tumor i nvasion. For MRI the, sensitivity was 97% and the specificity 98%; for CT, the sensitivity was 70% and the specificity was 85%. The difference in perf ormance was statistically significant (p < 0.001). The failure most frequen tly made on CT was the false-positive prediction of pelvic floor and pirifo rm muscle invasion (14), whereas MRI showed only four false-positive predic tions. MRI correctly predicted all four cases of sacral bone invasion, thre e of which were missed by CT. MRI was accurate in 20 patients (80%) and CT in only five patients (19%). Conclusion: High-resolution MRI using a quadrature phased-array coil is hig hly accurate and superior to CT in predicting tumor infiltration in surroun ding structures for locally advanced primary or recurrent rectal cancer and is recommended in the preoperative work-up of these tumors.