MRI for Rectal Cancer Primary Staging and Restaging After Neoadjuvant Chemoradiation Therapy: How to Do It During Daily Clinical Practice

Purpose: To provide a practical overview regarding the state-of-the-art of the magnetic resonance imaging (MRI) protocol for rectal cancer imaging and interpretation during primary staging and restaging after neoadjuvant chemoradiation therapy (CRT), pointing out technical skills and findings that radiologists should consider for their reports during everyday clinical activity.Method: Both 1.5T and 3.0T scanners can be used for rectal cancer evaluation, using pelvic phased array external coils. The standard MR protocol includes T2-weighted imaging of the pelvis, high-resolution T2-weighted sequences focused on the tumor and diffusion-weighted imaging (DWI). The mnemonic DISTANCE is helpful for the interpretation of MR images: DIS, for distance from the inferior part of the tumor to the anorectal-junction; T, for T staging; A, for anal sphincter complex status; N, for nodal staging; C, for circumferential resection margin status; and E, for extramural venous invasion.Results: Primary staging with MRI is a cornerstone in the preoperative workup of patients with rectal cancer, because it provides clue information for decisions on the administration of CRT and surgical treatment. Restaging after CRT is crucial for treatment planning, and findings on post-CRT MRI correlate with the patient's prognosis and survival. It may be useful to remember the mnemonic word "DISTANCE" to check and describe all the relevant MRI findings necessary for an accurate radiological definition of tumor stage and response to CRT.Conclusions: "DISTANCE" assessment for rectal cancer staging and treatment response estimation after CRT may be helpful as a checklist for a structured reporting.