An anal fistula — also called fistula-in-ano — is a tunnel that develops between the inside of the anus and the outside skin around the anus. The anus is the muscular opening at the end of the digestive tract where stool exits the body.
Most anal fistulas are the result of an infection that starts in an anal gland. The infection causes an abscess that drains on its own or is drained surgically through the skin next to the anus. This drainage tunnel remains open and connects the infected anal gland or the anal canal to a hole in the outside skin around the anus.
Surgery is usually needed to treat an anal fistula. Sometimes nonsurgical treatments may be an option.
Symptoms of an anal fistula can include:
- An opening on the skin around the anus
- A red, inflamed area around the tunnel opening
- Oozing of pus, blood or stool from the tunnel opening
- Pain in the rectum and anus, especially when sitting or passing stool
Most anal fistulas are caused by an infection that starts in an anal gland. The infection results in an abscess that drains on its own or is drained surgically through the skin next to the anus. A fistula is the tunnel that forms under the skin along this drainage tract. The tunnel connects the anal gland or anal canal to a hole in the outside skin around the anus.
Rings of sphincter muscle at the opening of the anus allow you to control the release of stool. Fistulas are classified by their involvement of these sphincter muscles. This classification helps the surgeon determine treatment options.
Risk factors for an anal fistula include:
- Previously drained anal abscess
- Crohn's disease or other inflammatory bowel disease
- Trauma to the anal area
- Infections of the anal area
- Surgery or radiation for treatment of anal cancer
Anal fistulas occur most often in adults around the age of 40 but may occur in younger people, especially if there is a history of Crohn's disease. Anal fistulas occur more often in males than in females.
Even with effective treatment of an anal fistula, recurrence of an abscess and an anal fistula is possible. Surgical treatment may result in the inability to hold in stool (fecal incontinence).