[Rational staging and follow-up of colorectal cancer : Do guidelines provide further help?]

CLINICAL/METHODICAL ISSUE: Colorectal cancer is one of the most common malignant tumors. Preoperative imaging is crucial in rectal cancer as patients can only receive optimal treatment when accurate staging is performed. The N‑staging is often difficult with the available options and must be called into question as a staging parameter. STANDARD RADIOLOGICAL
METHODS: Endoscopic ultrasound (EUS) and magnetic resonance imaging (MRI) are particularly suitable for local staging. Multiparametric MRI with diffusion imaging is indispensable for tumor follow-up. METHODICAL INNOVATIONS: The assessment of infiltration of the mesorectal fascia is best accomplished using high-resolution MRI. In addition, extramural vascular infiltration (EMVI) has become established as another important prognostic factor. After neoadjuvant therapy and restaging of locally advanced rectal cancer, the identification and validation of prognostically relevant image parameters are prioritized. Multiparametric MRI of the rectum including diffusion imaging as well as the application of radiological and pathological scores (MR-TRG) are becoming increasingly more important in this context. ASSESSMENT: For the radiologist it is important to become familiar with indicators of the resectability of rectal cancer and to be able to reliably read prognostically relevant imaging parameters in the tumor follow-up. PRACTICAL RECOMMENDATIONS: For the practical application, the establishment of a fixed MRI protocol is essential. In addition to a guideline-compliant TNM classification, the radiologist must provide the clinician with information on infiltration of the mesorectal fascia and extramural vascular infiltration. The MR-TRGs are becoming increasingly more important in tumor follow-up.