Rectal cancer staging: An up-to-date pictorial review

Colorectal cancer is the third most common malignancy worldwide, and rectal cancer (RC) accounts for 29% of all cases. Local staging of RC is crucial for the purposes of addressing patients appropriately to surgery alone or to preoperative chemoradiotherapy (pCRT) followed by total mesorectal excision (TME). Combined pCRT and TME may negatively affect rectal function, so rectum-sparing approaches such as transanal local excision have been proposed as an alternative to TME for patients showing a major or complete clinical response on restaging after pCRT. Magnetic resonance imaging (MRI) has a fundamental role in the local staging and restaging of RC, with or without positron emission tomography (PET). PET/MRI enables a multiplanar high-resolution morphological study of the pelvis, providing important information on cell density and metabolic activity with diffusion-weighted imaging (DWI) and ¹⁸ F fluorodeoxyglucose uptake respectively. This article offers a pictorial review of the MRI anatomy of the ano-rectal region and an update on local RC staging with a hybrid ¹⁸ F-FDG PET/MRI scan.