Anal Fistula – Types, Risk Factors, Causes and Treatment


Anal fistula is an abnormal connection or tunnel between two areas in the anorectal region.  The most common cause of anal fistulas is from a blocked mucus gland at the anorectal junction. The gland then becomes inflamed, and in an effort to expel its infected contents, expresses itself, usually as an abscess. As with hemorrhoids, the collection of fluid within a fixed area and the associated inflammation becomes exquisitely tender. You may have systemic signs of illness, including fever. Once the abscess either drains spontaneously or is incised (cut open) and allowed to drain, the pain diminishes. However, a connection between the offending crypt and the outer opening, seen usually in the perianal region, may remain. Occasionally, the outer opening remains in the rectum, and the abscess and the fistula can only be identified by an examination, often under anesthesia. Rarely, the origin of the infection stems from the abdomen or pelvis, as in diverticulitis.


The true prevalence of fistula-in-ano is unknown. The incidence of a fistula-in-ano developing from an anal abscess ranges from 26% to 38%. One study showed that the prevalence of fistula-in-ano is 8.6 cases per 100,000 populations. In men, the prevalence is 12.3 cases per 100,000 population, and in women, it is 5.6 cases per 100,000 population. The male-to-female ratio is 1.8:1. The mean patient age is 38.3 years.

Anal fistula types

Anal fistula can be divided into 2 main types:

A simple anal fistula is one that is relatively shallow and barely passes through the anal sphincter, making treatment fairly simple and uncomplicated.

Complex anal fistulas can take a variety of forms. For example, they may be quite deep, or they may follow a curved course from the inner opening to the outer one, or they may have one internal opening but branch into multiple tracks and external openings, etc. All of these factors make complex anal fistulas more difficult and complicated to treat.

There are three other specific types of anal fistula:

  • Rectovaginal Fistulas
  • Pouch anal and Pouch vaginal fistulas
  • Fistulas in Crohn’s disease

These are more complicated than typical anal fistulas and harder to fix

Rectovaginal fistulas

Fistulas from the anus to the vagina usually follow childbirth and are fixed by repair of the muscles that were damaged. Rectovaginal fistulas due to an infected anal gland can be repaired the same way as anal fistulas but may need reinforcement of the muscles in the area.

Pouch anal and pouch vaginal fistulas

Fistulas from a pouch constructed to replace the rectum in patients with ulcerative colitis and familial polyposis can come from the join up (anastomosis) of the pouch to the anus or from an infected anal gland. These are sometimes difficult to repair and sometimes the pouch needs to be moved down to cover the fistula. Fistulas from the pouch to the vagina happen quite frequently and may need multiple operations to fix.

Fistulas in Crohn’s disease

Patients with Crohn’s disease often develop disease near the anus that includes fistulas. Some of the fistulas are similar to those found in patients without Crohn’s, and these can be repaired in the same way. Other fistulas occur in the setting of Crohn’s disease in the tissues around the anus. These patients need biologic therapy to control the Crohn’s disease before surgery to repair the fistula.

Anal fistula risk factors

Anal fistulas are more common in men. However, women also get them. They are also more common in those 30 to 50 years old. Other things that may raise the risk are:

  • Previous history of anal abscess or fistula
  • Crohn disease
  • Ulcerative colitis
  • Trauma
  • Previous surgery or radiation therapy
  • Cancer
  • Certain infections, including HIV and tuberculosis


The major contributing causes to an anal fistula are clogged anal glands and anal abscesses. Approximately 50% of these abscesses can develop into a fistula, despite abscesses drain spontaneously or are drained surgically. Other conditions that may cause an anal fistula include:

Crohn’s disease (an inflammatory disease of the intestine)

Certain sexually transmitted diseases, e.g. syphilis and chlamydia

Certain infection diseases, e.g. actinomycosis and tuberculosis

Anal cancer or certain type of skin cancer developing around anus area.


Anal fistulas can cause unpleasant symptoms, such as discomfort and skin irritation, and won’t usually get better on their own. The symptoms of an anal fistula can include:

  • Skin irritation around the anus.
  • Constant, throbbing pain. The pain may be worse when you sit down, move around, when you poo or when you cough.
  • Smelly discharge from near your anus.
  • Passing pus or blood when you poo (rectal bleeding).
  • Difficulty controlling bowel movements (bowel incontinence); this is uncommon.

An abscess may form and this causes swelling and redness around your anus, and a high temperature (fever).

Anal fistula complications

A fistula may cause complications such as drainage, sepsis, perforation and peritonitis:

  • Fistula drainage and abscess: Fistulas carry on discharging foul-smelling fluid and cause more painful abscesses.
  • Sepsis: Sepsis is a life-threatening illness that results from an uncontrolled bacterial infection that spreads throughout the body. Symptoms of sepsis include fever, rashes, chills, confusion, disorientation, rapid breathing and heart rate.
  • Perforation
  • Peritonitis: Intestinal fistula may cause inflammation or infection of the peritoneum is commonly seen in fistulas.

Anal fistula diagnosis and test

A diagnosis is initiated by the doctors after going through the medical history and the symptoms of the patient.

Physical Examination

The doctors perform a physical examination to locate the opening of fistula, tenderness and the drain of pus around the anal area. For determining the bloody discharge and tenderness, the doctor resorts to gently pressing around the fistula.

Where finding the external opening of anal fistula can be simple, finding the opening of an internal fistula can be a daunting task. Therefore, a rectal examination is usually recommended for locating the internal opening.

Rectal Examination

Rectal examination is carried out by a doctor to inserting a finger into the anus covered with a glove and lubricated gel for determining the following:

  • Area of infection
  • Sphincter muscles functioning
  • Fistula extension

Other diagnostic tests

Other tests performed for diagnosis to determine the appropriate treatment are as follows:


It involves the use of a specialized telescope fitted with fistula probe used to see inside the rectum. The method of Proctoscopy is usually performed under general anaesthesia.

Anal Endosonography or Anal Ultrasound

This procedure uses high-frequency sound waves used for capturing the images which are beneath the anal canal surface. It is a safe procedure as compared to the other procedures and tests performed.

MRI or Magnetic Resonance Imaging Scan

The method of Magnetic resonance Imaging Scan utilizes powerful magnetic and radio waves that are used for creating detailed images of the organ. This method is generally utilised in case of reoccurring or complex fistulae.

CT or Computerized Tomography Scan

A series of X-Ray and computer is combined in CT or Computerized Tomography Scan method for creating in-depth cross-sectional body images. This method also helps in effectively determining the degree of inflammation.

Treatment and medications

Once you have an anal fistula, antibiotics alone won’t get rid of it. You’ll need to have surgery to treat the fistula. Surgical treatment includes:

  • Fistulotomy: This procedure opens up the fistula in a way that lets it heal from the inside out. It’s 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 provider 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 places a suture or rubber band (seton) in the fistula that is slowly tightened. It lets the fistula drain and heal behind the seton. It lowers the risk for incontinence.

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.

Prevention of Anal fistula

Once you have an anal fissure, you’ll definitely want to avoid getting another one, so follow these simple steps.

Get plenty of fiber. If you’re constipated, passing large, hard, or dry stools can cause an anal fissure. Getting plenty of fiber in your diet especially from fruits and vegetables can help prevent constipation, though.

Get 20 to 35 grams of fiber per day. Foods that are good sources include:

  • Wheat bran
  • Oat bran
  • Whole grains, including brown rice, oatmeal, popcorn, and whole-grain pastas, cereals, and breads
  • Peas and beans
  • Seeds and nuts
  • Citrus fruits
  • Prunes and prune juice

If you can’t get enough fiber through your diet, try fiber supplements.

Whether you eat more fiber-rich foods or take supplements, boost your intake gradually until you notice softer, more-frequent bowel movements. Also, drink plenty of liquids as you take in more fiber. This will help you avoid bloating and gas.

Stay hydrated: That can help you prevent constipation. Drinking plenty of liquids adds fluid to your system, which can make stools softer and easier to pass. Be sure to drink more when the weather gets warmer or as you become more physically active.

Not all drinks are good choices for staying hydrated. Too much alcohol can dehydrate you. Also, although a caffeinated drink may help you go to the bathroom, too much caffeine can dehydrate you as well.

Exercise: One of the most common causes of constipation is a lack of physical activity. Exercise for at least 30 minutes most days to help keep your digestive system moving and in good shape. Work toward 150 minutes or more per week.

Don’t ignore your urge to go: If your body tells you it’s time to have a bowel movement, don’t put it off till later. Waiting too long or too often can weaken the signals that let you know it’s time to go. The longer you hold it in, the dryer and harder it can get, which makes it tougher to pass.

Practice healthy bowel habits: These tips can help lessen constipation and strain on the anal canal. Check these habits regularly to lower your risk of getting a painful anal fissure:

  • When using the bathroom, give yourself enough time to pass bowel movements comfortably. But don’t sit on the toilet too long.
  • Don’t strain while passing stools.
  • Keep the anal area dry.
  • Gently clean yourself after each bowel movement.
  • Use soft, dye-free, and scent-free toilet paper or wipes.
  • Get treatment for ongoing diarrhea.

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