Staging of Rectal Cancer: MRI Protocol, Pelvic Anatomy, and Definitions

Abstract Rectal carcinoma is a prevalent and increasingly diagnosed cancer globally, posing significant mortality and morbidity risks, particularly among younger individuals. Prognosis hinges on several factors, such as site of involvement (upper rectum vs. lower rectum), tumor extension into surrounding tissues, involvement of critical structures like the mesorectal fascia and vessels, and the presence of distant metastases. Treatment approaches are tailored to the tumor's location and extent. Diagnostic tools including digital rectal examination and various imaging modalities like computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography-CT play crucial roles in staging, identifying high-risk patients needing neoadjuvant chemoradiotherapy (CRT), and monitoring treatment response. MRI stands out as the preferred modality for locoregional staging, detecting adverse prognostic indicators, assessing post-CRT changes, and long-term surveillance due to its superior contrast resolution. This review discusses the key concepts in the application of MRI to rectal cancer imaging.