Imaging in perianal fistulising Crohn's disease: A practical guide for the gastroenterologist

Perianal fistulising Crohn's disease is a challenging complication that can affect up to 20% of patients with Crohn's disease and is associated with significant morbidity. Despite advances in medical therapies, particularly anti-tumor necrosis factor agents, the majority of patients still require surgical intervention. Accurate diagnosis and monitoring are essential to optimise outcomes and guide multidisciplinary management. Although clinical scoring systems such as the perianal disease activity index are widely used, their subjective application limits their reproducibility and reliability, underscoring the need for more objective methods of evaluating perianal fistulising Crohn's disease activity. Imaging has thus become central to the objective assessment of perianal fistulising Crohn's disease, with magnetic resonance imaging (MRI) recognised as the gold standard in view of its ability to provide clear, detailed images of the perianal region in a radiation-free manner. Guidelines also endorse the use of imaging modalities such as endoanal ultrasound and transperineal ultrasound as viable alternatives to MRI for the assessment of perianal fistulising Crohn's disease in centres with appropriate expertise. This article aims to evaluate and compare the diagnostic accuracy and clinical utility of MRI, endoanal ultrasound, and transperineal ultrasound in the assessment of perianal fistulising Crohn's disease, highlighting their respective strengths, limitations, and roles in clinical practice.