Imaging of fistula in ano.

Fistula in ano is a common condition that often recurs despite seemingly adequate surgery, usually because of infection that was missed at surgery. It is now increasingly recognized that preoperative imaging can help identify infection that would have otherwise gone unidentified. In particular, magnetic resonance (MR) imaging findings have been shown to influence surgery and markedly diminish the chance of recurrence; thus, preoperative imaging will become increasingly routine in the future. In this article, the authors describe the pathogenesis, classification, and imaging of fistula in ano, with an emphasis on MR imaging. Most important, the authors describe how the radiologist is well placed to answer the surgical riddles that must be solved for treatment to be effective.