An anal fistula is a passage (tract) from the anal canal to a hole in the skin near the anus. This abnormal condition may occur after rectal surgery, after an abscess in the rectal area, or as a complication of Crohn's disease (a form of inflammatory bowel disease).
Symptoms of an anal fistula include itchy, irritated skin from fluids passing out of the rectum through the hole in the skin. The fluid usually contains mucus and small amounts of blood. An anal fistula may become infected. When infection develops, an anorectal abscess can form.