MRI to guide clinical management of rectal cancer: updated consensus recommendations from the European Society of Gastrointestinal and Abdominal Radiology (ESGAR): PART II—Restaging and response evaluation

Objectives: To provide up-to-date consensus recommendations on the acquisition, interpretation and reporting of MRI for restaging and response evaluation of rectal cancer after neoadjuvant treatment. Materials and methods: A panel of twenty-six abdominal imaging experts from the European Society of Gastrointestinal and Abdominal Radiology (ESGAR) participated in an online consensus process, led by three independent non-voting chairs. The process adhered to an adapted version of the RAND-UCLA Appropriateness Method. A total of 126 items were scored (22 general, 55 on primary staging, and 49 on restaging after neoadjuvant treatment), and classified using a cut-off of ≥ 80% to establish consensus. Results: Consensus was reached for 121 items (96%), from which recommendations regarding hardware, patient preparation, image acquisition protocols, criteria for image interpretation, and MRI reporting were constructed. The current manuscript addresses the results related to restaging after neoadjuvant treatment. Only 1/49 restaging items did not reach consensus. Compared to the previous guideline editions, updated and more detailed recommendations were established on how to assess fibrosis after neoadjuvant therapy, how to restage in the setting of organ preservation, the use of tumour regression grading systems, response assessment in mucinous tumours, evaluation of mesorectal fascia (MRF) involvement and presence of extramural venous invasion (EMVI) after neoadjuvant treatment, and how to deal with nodal response for defining the ycN-category after treatment. Conclusions: These updated expert consensus recommendations serve as clinical guidelines for the restaging of rectal cancer after neoadjuvant treatment using MRI. Recommendations for primary staging are addressed in a separate publication. Key Points: Question Since the last ESGAR rectal imaging guideline update, the rectal cancer treatment landscape has further evolved, necessitating updates to the existing guidelines. Findings An online consensus process involving 26 panellists led to 96% consensus across 121 items discussed, including 49 items related to restaging after neoadjuvant treatment. Clinical relevance Key updates included in these updated guidelines for MRI restaging of rectal cancer include new recommendations for assessing fibrosis, identifying patients for organ preservation, use of tumour regression grading systems, assessing mucinous tumours, ycEMVI, ycMRF, and ycN assessment.