Comparison of transrectal sonography and double-contrast MR imaging when staging rectal cancer

The aim of this study was the prospective comparison of the diagnostic yield of transrectal sonography and double-contrast MR imaging for preoperative staging of rectal cancer. SUBJECTS AND METHODS. Thirty-nine rectal cancer patients (20 men, 19 women) underwent transrectal sonography performed with a 10-MHz endoanal probe and MR imaging (1.0 T or 1.5 T) using a whole-body coil. After rectal application of a superparamagnetic iron oxide MR contrast agent, T1- and T2-weighted images and gadolinium-enhanced double-contrast images were obtained. The results of examinations were compared with the histology of resected specimens.

Histopathology showed four stage T1, 11 stage T2, 18 stage T3, and six stage T4 tumors using the TNM staging system. Nodal metastases were seen in 16 patients. Transrectal sonography could not be performed in 11 patients because of the high location of the tumor. In the remaining 28 patients, the accuracy of transrectal sonography for T stage was 64% overall (patients not receiving radiation, 69%; patients receiving radiation, 60%) and 70% for N stage. In 39 patients, double-contrast MR imaging correctly identified the T stage with an accuracy of 64% overall (patients not receiving radiation, 75%; patients receiving radiation, 53%) and the N stage with an accuracy of 62%. The assessment of rectal wall penetration (Dukes' classification A versus B) revealed a sensitivity, specificity, and accuracy of 93%, 71%, and 82%, respectively, for transrectal sonography and 100%, 60%, and 85% for MR imaging.

If it is technically feasible, transrectal sonography is an accurate method for staging rectal cancer. In proximal or stenotic tumors, double-contrast MR imaging is the method of choice. Diagnostic accuracy of transrectal sonography and MR imaging is high for predicting bowel wall penetration.