Pelvic MRI in children with Crohn disease and suspected perianal involvement.

MRI is an important imaging tool in evaluation of adult and pediatric patients with Crohn disease. Pelvic MRI, in particular, has become the method of choice to evaluate for perianal fistulas and associated complications of Crohn disease. MRI can define the extent and location of perianal fistulas and abscesses, as well as provide critical information for operative management. In this pictorial essay, we describe useful MRI techniques for evaluation of perianal complications in pediatric patients with Crohn disease. We review pertinent anatomy and illustrate typical examples of perianal fistulas with and without abscess. We show one case of clinically suspected perianal fistula that was actually a pilonidal sinus.