Volumetric Changes in Perianal Fistulizing Crohn's Disease Measured by Magnetic Resonance Is Feasible and Could Be a Potential Biomarker to Predict Clinical Outcomes.

Background and aim: Changes in 3D volumetry of perianal fistulas in patients with Crohn's disease (CD) measured by MRI could be an imaging biomarker of interest. The objective of the study was to determine the value of volumetric changes in CD perianal fistulas after medical treatment to predict outcomes.

Methods: This is a retrospective single-center pilot study evaluating CD patients with active perianal fistulas who started biological therapy between 2012 and 2021. Eligible patients were those who had both pre- and post-treatment pelvic MRI and clinical follow-up of 2-5 years. Patients were categorized as clinically active or in remission based on fistula drainage. Using specific software, we calculated the 3D volume of the fistulas, and their active and fibrotic components. We evaluated MRI volumetric changes between assessments and analyzed their predictive value for clinical remission.

Results: We included 24 patients (83.3% with complex fistulas), of which 13 were in clinical remission at the last follow-up. Logistic regression analysis identified the percentage of relative change in the volumetric active component as an independent predictor of clinical remission (OR 0.92 [0.86-0.98] p = 0.013). The area under receiver operating characteristic (ROC) curve was 85.3% (p < 0.0001). A reduction of ≥ 16% in the volumetric percentage of the active component has a sensitivity of 84.6 and specificity of 81% in predicting clinical remission during follow-up.

Conclusion: Changes in the 3D MRI volumetry of perianal fistulas might have value in predicting clinical remission. Specifically, the reduction in the volumetry of the active component emerges as a promising biomarker for assessing therapeutic response.