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Anal Fistula: An Overview

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An anal fistula is an abnormal channel that develops between the anal canal and the skin near the anus. It may look like a tiny hole in the area of skin surrounding the anus. This article will cover a basic overview of anal fistulas, including the causes, symptoms, types, surgery, recovery and possible complications.


Anal fistula is commonly caused by an anal abscess that has not been adequately treated. This accounts for up to 80% of all cases. This occurs when one of the glands surrounding the anus become blocked and infected, forming an abscess. If the abscess bursts, an anal fistula is formed. About half of all anal abscesses result in the formation of anal fistulas.

Other causes may include:

  • inflammation of the intestine associated with Crohn’s disease or diverticulitis
  • sexually transmitted infections such as HIV, chlamydia or syphilis
  • trauma
  • abnormal growth
  • tuberculosis
  • cancer


The symptoms of an anal fistula may include:

  • Skin irritation around the anus
  • Pain and swelling in the anal region
  • Constant deep throbbing pain in the anal region
  • Worsening of pain when the patient moves, sits down or has a bowel movement
  • Discharge of blood or pus visible on the surface of passed stool

Patients who have any of these symptoms should seek medical advice from a general practitioner. They will receive a diagnosis and recommendations for appropriate treatment.

Types of Anal Fistula

An anal fistula can be classed as simple or complex, depending on the type of fistula tract. A simple anal fistula has a single fistula tract; a complex anal fistula has multiple interconnected tracts.  

Additionally, an anal fistula may be classified as low or high, according to the location of the fistula and its proximity to the sphincter muscles. The anal sphincters are two bands of circular muscle that are responsible for controlling bowel movements.


Anal fistulas are diagnosed based on the symptoms with which the patient presents, the presence of pus at the opening of the fistula opening, and sometimes the heaped-up tissue around the opening.
If other tests are required, dye injection followed by an ultrasound is usually sufficient to outline the fistula tract. In some patients, an MRI or CT scan may be  required to show the full extent of a complex fistula, the presence of an abscess in the anal region, or when other conditions may show the same type of symptoms.


Anal fistulas rarely heal without treatment. In most cases, surgery is required to remove the fistula. Several techniques may be used, depending on the type of anal fistula (simple or complex) and the positioning. These include fistulotomy, seton, an endoanal advancement flap and a bioprosthetic plug. A newer technique is the LIFT (ligation of the intersphincteric fistula tract) procedure.

Most operations can be done in the day surgery unit and patients can return home the same day after surgery. However, they will need to rest for at least several days following the procedure to assist in the recovery process.


Following the surgical removal of the fistula, patients should take care to rest while the area heals. During this time, they need to avoid sitting or moving around too much. They may be more comfortable if they lie down with pillows propped up around them to keep their weight off the anal region. They may plan to return to work as well as other activities when they feel ready.

Some medications can be beneficial during the recovery process, including:

  • analgesic medication to manage pain
  • antibiotics to prevent or treat infection
  • laxatives to reduce stool impaction and ensure the regular passage of soft stools

There will usually be a dressing over the wound when the patient leaves the hospital. Patients should be instructed how to change the dressing themselves, as this will need to be done frequently. Additionally, follow-up appointments are usually needed to check the progress of the wound healing in the weeks following surgery.


In some cases, there can be complications associated with the surgery to remove an anal fistula. These may include infection, bowel incontinence and recurrence of the anal fistula. The risk of these complications depends on the type of fistula and surgical technique that was used, but is usually small.

If patients note heavy bleeding from the wound or the anal region, increasing pain or discharge, constipation or fever shortly after the surgery, they should know that these are abnormal and should seek medical advice to manage these symptoms.


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