Colonic & Anorectal Fistulas

What are colonic and anorectal fistulas?

A fistula is an abnormal passageway, or tunnel, in the body. An internal fistula is an abnormal tunnel between two internal organs. An external fistula is an abnormal tunnel between an internal organ and the outside of the body.

A colonic fistula is an abnormal tunnel from the colon to the surface of the skin or to an internal organ, such as the bladder, small intestine, or vagina.

An anorectal fistula is an abnormal tunnel from the anus or rectum to the surface of the skin around the anus. Women may have rectovaginal fistulas, which are anorectal fistulas between the anus or rectum and the vagina.

How common are colonic and anorectal fistulas?

Colonic fistulas are rare and may occur as a complication of surgery or of a condition such as diverticulitis, Crohn’s disease, or cancer.

Studies conducted in Europe have found that about 1 or 2 in every 10,000 people have anorectal fistulas.13 Anyone can get an anorectal fistula, which usually starts as an infection in a gland inside the anus. Anorectal fistulas are more likely to occur in people who have had an anorectal abscess and in people with Crohn’s disease.

Anorectal fistulas are more common in men than in women. While anorectal fistulas can occur in people of any age, the average age of people with anorectal fistulas is about 40.13,14

What are the complications of colonic and anorectal fistulas?

Colonic fistula

Colonic fistulas can cause complications such as

Anorectal fistula

Anorectal fistulas cause infections and abscesses around the anus, but they rarely cause severe infection. In rare cases, cancer may develop in an anorectal fistula.

What are the symptoms of colonic and anorectal fistulas?

You should see a doctor if you have any symptoms of a colonic or anorectal fistula.

Colonic fistula

Symptoms of colonic fistula vary, depending on the location of the fistula. The contents of the colon may enter the fistula and pass to the other end, which may be in the skin or in an internal organ.

Symptoms of colonic fistula may include fluid, stool, and gas passing

  • through an opening in the skin
  • in the urine
  • through the vagina

A fistula that connects the colon to another part of the intestines may cause symptoms such as

In some cases, colonic fistulas do not cause symptoms.

Anorectal fistula

Symptoms of an anorectal fistula may include

  • drainage of pus from an opening in the skin around the anus
  • swelling and pain near the anus that may come and go, sometimes with redness or fever
  • anal pain

In women, a rectovaginal fistula may cause symptoms such as the passage of stool or gas through the vagina.

What causes colonic and anorectal fistulas?

Most colonic and anorectal fistulas are acquired, meaning that they are not present at birth and develop at some point in a person’s life.

Colonic fistula

The most common cause of colonic fistulas is abdominal surgery. Diseases that cause inflammation of the GI tract, such Crohn’s disease and diverticular disease, can also cause fistulas to form. Other causes include cancer, radiation therapy, and trauma or injury to the abdomen.

Female doctor talking with a patient in bed.
The most common cause of colonic fistulas is abdominal surgery.

Anorectal fistula

Anorectal abscesses, caused by infections of the anal glands, are the most common cause of anorectal fistulas.

Certain health problems may also cause anorectal fistulas, including Crohn’s disease, cancer, and some infections such as tuberculosis and HIV. Damage to the anorectal area due to surgery, childbirth, injury, or radiation therapy may also cause anorectal fistulas.

How do doctors diagnose colonic and anorectal fistulas?

Doctors diagnose colonic and anorectal fistulas based on symptoms and medical history, a physical exam, and imaging tests.

Medical history

Your doctor will ask about your symptoms and history of conditions that may cause fistulas, such as abdominal surgery, Crohn’s disease, diverticular disease, radiation therapy, or injury.

Physical exam

Your doctor will check for tenderness or pain in your abdomen and may listen to sounds inside your abdomen using a stethoscope. Your doctor will examine any opening in your skin to determine if you may have an external colonic fistula.

To check for an anorectal fistula, your doctor will check the skin around your anus for abnormal openings, pain, and signs of inflammation or infection. Your doctor may perform a digital rectal exam and may perform an anoscopy or a proctoscopy to view the inside of the anus and rectum.

Imaging tests

Doctors may use several different imaging tests to diagnose or examine colonic or anorectal fistulas. The type of test depends on the suspected location of the fistula. Tests may include

Doctors may order additional tests to check for complications or to diagnose conditions that can cause fistulas, such as Crohn’s disease or cancer. If a fistula connects to an internal organ, such as the bladder, small intestine, or vagina, doctors may order additional tests to examine these organs.

How do doctors treat colonic and anorectal fistulas?

Colonic fistula

Some colonic fistulas will close on their own without surgery. Your doctor may only treat or prevent any complications to help the fistula heal. Depending on your needs, your doctor may

  • give you fluids and electrolytes
  • give you nutritional support, which may include total parenteral nutrition (TPN), which is intravenous (IV) nutrition, or enteral nutrition, in which you receive liquid food through a tube placed in your nose, stomach, or small intestine
  • prescribe antibiotics and drain any abscesses to treat infection
  • protect your skin from the fluid draining from the fistula if you have an external fistula

If a fistula is not likely to close on its own, doctors perform surgery to close the fistula.

Anorectal fistula

Doctors typically treat anorectal fistulas with surgery. Most anorectal fistulas won’t close on their own without surgery, but some rectovaginal fistulas may close on their own. If you have a rectovaginal fistula, your doctor may recommend delaying surgery to see if the fistula will close.

If you have an anorectal fistula with an abscess, your doctor will drain the abscess to treat the infection. In some cases, doctors may prescribe antibiotics to treat the infection.


Last Reviewed August 2019
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This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. NIDDK translates and disseminates research findings to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by NIDDK is carefully reviewed by NIDDK scientists and other experts.