MR Imaging of Perianal Crohn Disease.

Pelvic magnetic resonance (MR) imaging is currently the standard for imaging perianal Crohn disease. Perianal fistulas are a leading cause of patient morbidity because closure often requires multimodality treatments over a prolonged period of time. This review summarizes clinically relevant anal sphincter anatomy, imaging methods, classification systems, and treatment objectives. In addition, the MR appearance of healing perianal fistulas and fistula complications is described. Difficult imaging tasks including the assessment of rectovaginal fistulas and ileoanal anastomoses are highlighted, along with illustrative cases. Emerging innovative treatments for perianal Crohn disease are now available and have the promise to better control sepsis and maintain fecal continence. Different treatment modalities are selected based on fistula anatomy, patient factors, and management goals (closure versus sepsis control). Radiologists can help maximize patient care by being familiar with MR imaging features of perianal Crohn disease and knowledgeable about what features may influence therapy decisions. © RSNA, 2017 Online supplemental material is available for this article.