Fistula

An anal fistula is a small tunnel that connects an abscess, an infected cavity in the anus, to the opening in the skin around the anus. The anus is the external opening through which feces are evacuated from the body. In the anus are several small glands that produce mucus. Sometimes these glands can become blocked and infected, resulting in an abscess. About half of these abscesses can develop into fistulas.