Evaluating luminal and post-operative Crohn's disease activity on magnetic resonance enterography: A review of radiological disease activity scores.

Magnetic resonance enterography (MRE) is a non-invasive, radiation-free imaging modality that facilitates the assessment of transmural Crohn's disease activity. It offers advantages over ileo-colonoscopy, which is limited to mucosal-level evaluation, cannot routinely assess small bowel segments proximal to the terminal ileum, and is unable to detect extra-luminal complications. Despite these advantages, the lack of standardised criteria for defining and appraising radiologic disease activity on MRE has contributed to variability in interpretation and clinical application. In response, multiple MRE-based scoring systems have been developed to quantify radiological Crohn's disease activity in both luminal and post-operative settings. Radiological disease activity scores specific to luminal Crohn's disease include the magnetic resonance index of activity (MaRIA), simplified MaRIA, Nancy score, London score, Crohn's disease magnetic resonance imaging (MRI) index, Clermont score, paediatric inflammatory Crohn's MRE index, MRE global score, MRE index, and modified Clermont score. The MR score and the MRI in Crohn's disease to predict postoperative recurrence index have been specifically developed to evaluate post-operative disease recurrence in Crohn's disease. Nevertheless, heterogeneity in scoring parameters, variability in computational complexity, and a lack of consensus regarding optimal score selection, have impeded widespread clinical adoption of radiological disease activity scores. This narrative review aims to summarise the key imaging features of luminal Crohn's disease, explore their integration into existing MRE scoring indices, and critically compare the structure, strengths, and clinical applicability of each. Furthermore, MRI scores specific to post-operative Crohn's disease evaluation, and the assessment of cumulative bowel wall damage using the Lemann index will also be discussed.