Current techniques in imaging of fistula in ano: three-dimensional endoanal ultrasound and magnetic resonance imaging.

Perianal fistula is an abnormal communication between the anal canal and perianal skin. The majority of perianal fistulous disease results from either cryptoglandular inflammation or Crohn's disease. These groups differ in pathophysiology, prognosis, and strategies for imaging and treatment. Endoanal ultrasound and magnetic resonance imaging represent current imaging strategies for evaluating perianal fistulas and may be used alone or in combination. The use of three-dimensional technique and peroxide fistulography optimize the ultrasound evaluation of perianal fistula. The use of multiple imaging planes and sequences including fat suppression and contrast enhancement optimize the magnetic resonance imaging protocol. Examples of the imaging appearance of perianal fistulas and a proposed flowchart for imaging modality selection are provided.