Evaluation of perianal fistulas in patients with Crohn's disease.

Crohn's disease is a chronic inflammatory disorder that can affect any part of the gastrointestinal tract from the mouth to the anus. The disease is characterized by transmural inflammation that can be complicated by the development of fibrotic strictures, perforation, abscess formation, and fistulization. Perianal fistulas may arise from inflamed or infected anal glands (fistula-in-ano) and/or penetration of fissures or ulcers of the rectum or anal canal.[1] Classification of fistulas in Crohn's disease is based on the origin and terminus of the fistulous tract. Fistulas may develop between 2 segments of bowel (enteroenteric fistula), a segment of bowel and an adjacent organ (eg, enterovesicular), or between a segment of bowel and the skin (enterocutaneous).[2,3] Fistulas that communicate with the skin are known as external fistulas; those that communicate with adjacent structures within the abdomen and pelvis are known as internal fistulas.[2] Population-based estimates of the lifetime risk of fistula development in Crohn's disease range from 14% to 38%.[4-6] The development of fistulas may precede or coincide with the diagnosis of Crohn's disease. One cohort study estimated the rate of fistula formation preceding the diagnosis of Crohn's disease to be 45%.[4,5,7] Rates of spontaneous fistula closure are low, with estimates ranging from as low as 6% to 13% in placebo-treated patients in randomized controlled trials of 6-mercaptopurine (6-MP) and infliximab.[8,9] Spontaneous remission rates of simple fistulas-in-ano have been reported to be as high as 50%.[7,10]