An anal fistula is a tunnel that runs between an anal gland and the skin outside the anus. Fistulas usually occur after an anal gland infection, in which the glands fill with fluids and pus, creating an abscess. When an abscess is drained and does not heal completely, the tunnel often remains, creating an anal fistula. Anal fistulas increase the chance of developing another infection in an anal gland, and recurrent abscesses can be painful.
The most common type of anal fistula is an intersphincteric fistula. This type of fistula begins between the inside and outside sphincter muscles and ends next to the anus. A transphincteric fistula can begin between the sphincter muscles or just behind the anus. It ends an inch or two outside the anus and can wrap into a "U" shape, making a horseshoe fistula.
Two uncommon types of fistulas are the suprasphincteric fistula and the extrasphincteric fistula. Suprasphincteric fistulas begin between the sphincter muscles and curve upward to the puborectal muscle. It then dips back down and ends an inch or two outside the anus. An extrasphincteric fistula begins at the rectum and runs down to open just outside the anus.
The abscesses that form prior to anal fistulas typically cause pain and inflammation around the anus. Patients with immune system disorders or conditions, such as AIDS and cancer, are more likely to develop abscesses. People with Crohn's disease, an autoimmune disorder which affects the gastrointestinal tract, are also more likely to develop abscesses and fistulas. Irritation around the anus, fever, and fluid drainage near or around the anus are the most common symptoms of an anal fistula after an abscess has been drained.
Anal fistulas usually require surgery to heal. The surgeon cuts the tunnel open to flush out the contents and then stitches the sides of the tunnel to the surgical incision so that the fistula lays flat. Some patients require more than one surgical procedure if the fistula is complicated, such as a horseshoe fistula.
Some treatment centers offer non-surgical treatment for anal fistulas in the form of fibrin glue or collagen plugs. Fibrin glue is made from plasma protein. Small fistulas that are not severely infected may be sealed with the glue. The internal opening is stitched closed so that the tunnel can heal.