Accuracy of Magnetic Resonance Imaging in Predicting TNM Staging and Circumferential Resection Margin Compared with Pathologic Assessment on Whole-mount Section in Rectal Cancer

ABSTRACT

PURPOSE: Recently, magnetic resonance imaging (MRI) has become the preferred diagnostic tool for preoperative assessment of TNM staging and circumferential resection margin (CRM) in patients with rectal cancer. The aim of this study is to evaluate the accuracy of preoperative MR imaging in the prediction of T, N stage and CRM compared with pathologic results on whole- mount sections. METHODS: Thirty-five consecutive patients with rectal cancer were enrolled between Dec. 2005 and Apr. 2006. 1.5-T MR imaging, was performed, and pathologic results were investigated on whole-mount sections. The agreement between MR imaging and pathologic examination for the assessment of T, N stage and status of CRM were analyzed using kappa statistics. RESULTS: The accuracy of MR imaging compared with pathologic assessment of T stage was 82.9% (kappa=0.56), and that of N stage was 74.3% (kappa= 0.31). Of the MR imaging planes, the oblique axial plane showed the most accurate prediction of CRM, regardless of tumor position within the circumference of the rectum. The accuracy of MR imaging in the oblique axial plane for predicting the CRM was 81.0% (kappa=0.62) in anterior and posterior rectal tumors and 71.4% (kappa=0.43) in laterally located rectal tumors. With a different CRM criteria for the measured distance in MR imaging, the accuracy of the 2-mm CRM criterion was 77.1% (kappa=0.53). CONCLUSIONS: MR imaging in predicting T stage showed fair agreement according to kappa statistics. Of the MR imaging planes, the oblique axial plane provided the most accurate CRM information compared with pathologic examination. The actual measured distance of the CRM in MR imaging can be applied to the pathologic CRM.