An anal fistula is an abnormal tunnel under the skin that connects the anal canal in the colon to the skin of the buttocks. Most anal fistulas form in reaction to an anal gland that has developed a pus-filled infection (abscess).
The symptoms of an anal abscess and an anal fistula can be similar and may include:
Pain and swelling around the anal area
Fever and chills
Feeling tired and sick
Redness, soreness, or itching of the skin around the anal opening
Pus drainage near the anal opening
Who's at risk
If you develop an anal abscess, you have about a 50% chance of developing an anal fistula. Even if your abscess drains on its own, you have about the same risk for a fistula.
Certain conditions that affect your lower digestive tract or anal area may also increase your risk. These include:
Radiation treatment for rectal cancer
If you have symptoms that suggest an anal fistula, your healthcare provider may refer you to a specialist who specializes in colon and rectal diseases. The specialist will ask about your symptoms and your medical history. During your physical exam, the doctor will look for a fistula opening near your anal opening. He or she may press on the area to see if it is sore and if pus comes out. Different methods may be used to help with the diagnosis, such as:
Fistula probe. A long, thin probe is guided through the outer opening of the fistula. A special dye may be injected to find out where the fistula opens up on the inside.
Anoscope. This is a special scope used to look inside your anal canal.
Imaging studies. These may include an ultrasound, which creates an image of the anal area using sound waves. Or they may include an MRI, which makes images of the area by using special magnets and a computer.
Once you have an anal fistula, antibiotics alone will not cure it. You will need to have surgery to cure the fistula. Surgical treatment options include:
Fistulotomy. This procedure opens up the fistula in a way that allows it to heal from the inside out. It is usually an outpatient procedure. This means you go home the same day.
Filling the fistula with a special glue or plug. This is a newer type of treatment that closes the inner opening of the fistula. The doctor then fills the fistula tunnel with a material that your body will absorb over time.
Reconstructive surgery or surgery that is done in stages. This may be an option in some cases.
Seton placement. This procedure involves placing a suture or rubber band (seton) in the fistula that is progressively tightened. It lets the fistula heal behind the seton and reduces the risk of incontinence.
Note: Anal fistulas are very common in people with Crohn’s disease. For those with both Crohn's disease and a fistula, medical therapy is often tried before surgery.
Complications include a fistula that recurs after treatment and an inability to control bowel movements (fecal incontinence). This is most likely if some of the muscle around the anal opening, called the anal sphincter, is removed.
When to call the healthcare provider
Call your healthcare provider if you have symptoms of an anal fistula, especially if you have a history of a previous anal abscess. If you have been treated for an abscess or fistula, let your provider know right away if you have any of the following:
Trouble controlling your bowel movements
Managing anal fistula
When recovering from anal fistula treatment, make sure to take pain medicine as directed by your surgeon. Finish all of your antibiotics. Don’t take any over-the-counter medicines without first talking to your provider.
Other important instructions may include:
Soaking in a warm bath 3 or 4 times a day
Wearing a pad over your anal area until healing is complete
Resuming normal activities only when you are cleared by your surgeon
Eating a diet high in fiber and drinking plenty of fluids
Using a stool softener or bulk laxative as needed