Magnetic resonance imaging for assessment of rectal cancer nodes after chemoradiotherapy: A single center experience

Background: Accurate nodal restaging is becoming clinically more important in patients with locally advanced rectal cancer (LARC) with the emergence of organ -preserving treatment after a good response to neoadjuvant chemoradiotherapy (nCRT). Purpose: To evaluate the accuracy of MRI in identifying negative N status (ypN0 patients) in LARC after nCRT. Material and Methods: 191 patients with LARC underwent MRI before and 6-8 weeks after nCRT and subsequent total mesorectal excision. Short -axis diameter of mesorectal lymph nodes was evaluated on the high resolution T2 -weighted images to compare MRI restaging with histopathology.. Results: 146 and 45 patients had a negative N status (ypN0) and positive N status (ypN + ), respectively. On restaging MRI, the 70 % reduction in size of the largest node was associated with an area under the curve (AUC) of 0.818 to predict ypN0 stage, with a sensitivity of 93.3 % and a negative predictive value (NPV) of 95.4 %. No nodes were observed in 38 pts (37 pts ypN0 and 1 patient ypN + ), with sensitivity and NPV of nodes disappearance for ypN0 stage of 93.3 % and 92.5 % respectively. A 2.2 mm cut-off in short -axis diameter was associated with an AUC of 0.83 for the prediction of ypN0 nodal stage, with sensitivity and NPV of 79,5% and 91.1 % respectively. Conclusion: A reduction in size of 70 % of the largest limph-node on MRI at rectal cancer restaging has high sensitivity and NPV for prediction of ypN0 stage after nCRT. The high NPV of node disappearance and of a <= 2.2 mm short -axis diameter is confirmed.