MRI of Perianal Crohn Disease: Technique and Interpretation.

Magnetic resonance imaging (MRI) has emerged as the imaging method of choice for evaluation of perianal fistulizing disease. As treatment of Crohn disease and associated perianal fistulas has evolved to include a combination of systemic treatments and surgical interventions, perianal MRI provides critical information to guide treatment selection and timing. Radiologists need to be familiar with the normal regional anatomy to accurately describe perianal fistulas and any associated complications which can then be used to classify fistulas based on several available classification systems. Following treatment, MRI can provide information that suggests treatment success or failure. We propose a perianal fistula reporting template that includes the necessary information to convey fistula complexity, guide treatment, and evaluate treatment response. This review article will also discuss the postoperative appearance of many treatments currently used for management of perianal fistulizing disease and some associated complications.