A fistula is a connection between the anal lining and the skin. It presents as an opening near the anus from which a small amount of pus or blood may discharge. There is sometimes a small lump that may be uncomfortable. The symptoms are often intermittent. A fistula sometimes develops after drainage of an abscess but it may occur spontaneously. Patients with Crohn’s disease are more likely to develop fistulae but most people with a fistula do not have any other bowel disease. Fistulae rarely heal by themselves and surgery is nearly always required.