Rectal MRI for Cancer Staging and Surveillance.

MRI is an integral part of the multidisciplinary treatment of rectal adenocarcinoma. Staging MRI is performed to establish TNM stage and assess for prognostic factors, including circumferential resection margin status and presence of extramural vascular invasion. The results of staging MRI determine which patients will undergo preoperative neoadjuvant chemoradiation before resection. Restaging MRI is performed to evaluate for treatment response and may identify patients with no residual visible tumor who are candidates for a "watch and wait" strategy in lieu of resection. In addition, the results of MRI in conjunction with endoscopy determine the surgical technique used to remove the tumor.