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
• Fever

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).

To diagnose an anal fistula, your health care provider will discuss your symptoms and do a physical exam. The exam includes looking at the area around and inside your anus.

The external opening of an anal fistula is usually easily seen on the skin around the anus. Finding the fistula's internal opening inside the anal canal is more complicated. Knowing the complete path of an anal fistula is important for effective treatment.

One or more of the following imaging tests may be used to identify the fistula tunnel:

• MRI can map the fistula tunnel and provide detailed images of the sphincter muscle and other structures of the pelvic floor.
• Endoscopic ultrasound, which uses high-frequency sound waves, can identify the fistula, the sphincter muscles and surrounding tissues.
• Fistulography is an X-ray of the fistula that uses an injected contrast to identify the anal fistula tunnel.
• Examination under anesthesia. A colon and rectal surgeon may recommend anesthesia during an examination of the fistula. This allows for a thorough look at the fistula tunnel and can identify any possible complications.

Other options to identify the fistula's internal opening include:

• Fistula probe. An instrument specially designed to be inserted through a fistula is used to identify the fistula tunnel.
• Anoscope. A small endoscope is used to view the anal canal.
• Flexible sigmoidoscopy or colonoscopy. These procedures use an endoscope to examine the large intestine (colon). Sigmoidoscopy can evaluate the lower part of the colon (sigmoid colon). Colonoscopy, which examines the full length of the colon, is important to look for other disorders, especially if ulcerative colitis or Crohn's disease is suspected.
• An injected dye solution. This may help locate the fistula opening.

Treatment of an anal fistula depends on the fistula's location and complexity and its cause. The goals are to repair the anal fistula completely to prevent recurrence and to protect the sphincter muscles. Damage to these muscles can lead to fecal incontinence. Although surgery is usually required, sometimes nonsurgical treatments may be an option.

Surgical options include:

• Fistulotomy. The surgeon cuts the fistula's internal opening, scrapes and flushes out the infected tissue, and then flattens the tunnel and stitches it in place. To treat a more complicated fistula, the surgeon may need to remove some of the tunnel. Fistulotomy may be done in two stages if a significant amount of sphincter muscle must be cut or if the entire tunnel can't be found.
• Endorectal advancement flap. The surgeon creates a flap from the rectal wall before removing the fistula's internal opening. The flap is then used to cover the repair. This procedure can reduce the amount of sphincter muscle that is cut.
• Ligation of the intersphincteric fistula tract (LIFT). LIFT is a two-stage treatment for more-complex or deep fistulas. LIFT allows the surgeon to access the fistula between the sphincter muscles and avoid cutting them. A silk or latex string (seton) is first placed into the fistula tunnel, forcing it to widen over time. Several weeks later, the surgeon removes infected tissue and closes the internal fistula opening.

Nonsurgical options include:

• Seton placement. The surgeon places a seton into the fistula to help drain the infection. This allows the tunnel to heal. This procedure may be combined with surgery.
• Fibrin glue and collagen plug. The surgeon clears the tunnel and stitches shut the internal opening. Special glue made from a fibrous protein (fibrin) is then injected through the fistula's external opening. The anal fistula tunnel also can be sealed with a plug of collagen protein and then closed.
• Medication. Medication may be part of treatment if Crohn's disease is the cause of an anal fistula.

In cases of complex anal fistula, more-invasive surgical procedures may be recommended, including:

• Ostomy and stoma. The surgeon creates a temporary opening in the abdomen to divert the intestines away from the anal canal. Waste is collected into a bag on the abdomen. This procedure allows the anal area time to heal.
• Muscle flap. In very complex anal fistulas, the tunnel may be filled with healthy muscle tissue from the thigh, labia or buttock.

Your health care provider may suggest measures to make you more comfortable during healing:

• Use pain medication, as needed
• Soak in a warm sitz bath
• Add fiber to your diet and drink plenty of liquid to prevent constipation
• Avoid straining during bowel movements

If you have an anal fistula, you may be referred to a specialist in digestive diseases (gastroenterologist) or a colon and rectal surgeon.

Here's some information to help you get ready for your appointment.

What you can do

When you make the appointment, ask if there's anything you need to do in advance, such as not eating for a time (fasting) before having a specific test. Make a list of:

• Your symptoms, even if they may seem unrelated to the reason for your appointment
• Key personal information, including major stresses, recent life changes, and personal and family medical history
• All medications, vitamins, herbs or other supplements you take, including the dosages
• Questions to ask your health care provider

Some basic questions to ask include:

• What is likely causing my symptoms?
• Are there any other possible causes for my symptoms?
• Do I need any tests?
• Is my condition likely temporary or ongoing?
• Are there any dietary suggestions I should follow?
• Are there restrictions I need to follow?
• What treatment do you recommend?
• What are the alternatives to the primary approach you're suggesting?
• I have these other health conditions. How can I best manage them together?
• Are there brochures or other printed material I can have? What websites do you recommend?

Don't hesitate to ask other questions during your appointment.

What to expect from your doctor

Your health care provider may ask:

• When did your symptoms begin?
• Have your symptoms been continuous or occasional?
• How severe are your symptoms?
• Where do you feel your symptoms the most?
• Does anything seem to improve your symptoms?
• What, if anything, seems to worsen your symptoms?
• Do you have any other medical conditions, such as Crohn's disease?
• Do you have problems with constipation?