An anal fistula is a small tunnel that connects an infected gland inside the anus to an opening on the skin around the anus. Symptoms include pain and swelling around the anus.

Surgery is almost always necessary to cure an anal fistula. The goal of the surgery is a balance between getting rid of the fistula while protecting the anal sphincter muscles, which could cause incontinence if damaged.

Fistulas in which there is no or little sphincter muscle involved are treated with a fistulotomy. In this procedure, the skin and muscle over the tunnel are cut open to convert it from a tunnel to an open groove. This allows the fistula tract to heal from the bottom up.