Prediction of tumor stage and lymph node involvement with dynamic contrast-enhanced MRI after chemoradiotherapy for locally advanced rectal cancer

Purpose The usefulness of restaging by magnetic resonance imaging (MRI) after chemoradiotherapy (CTx/RTx) in patients with locally advanced rectal cancer has not yet been established, mostly due to the difficult differentiation between viable tumor and fibrosis. MRI with dynamic contrast-enhanced (DCE) sequences may be of additional value in distinguishing malignant from nonmalignant tissue. The aim of this study was to assess the accuracy of tumor, nodal staging, and circumferential resection margin (CRM) involvement by MRI with DCE sequences after CTx/RTx. Methods The accuracies were assessed by MRI on T2-weighted magnetic resonance (MR) images with DCE sequences in patients with locally advanced rectal cancer after a long course of CTx/RTx. MR images were assessed by two independent radiologists. Results For tumor staging and CRM involvement, MRI with DCE sequences had an accuracy of 45 and 60 %, respectively. The accuracy for nodal staging was 93 %. On MRI, malignant lymph nodes had a median diameter of 8 mm (range, 4–18) and benign lymph nodes a median diameter of 4 mm (range, 3–11). A significant indicator for benign nodes was hypointensity on T2-weighted images (p