An anal fistula is a communication or tunnel between the internal lining of the anal canal and the skin outside the anus.

What is a fistula?

A fistula is an abnormal track or tunnel between the inner and outer lining of the anus that may develop after spontaneous or surgical drainage of an abscess.  Discharge of pus may be constant or intermittent as the external opening on the skin may only heal temporarily.

Anal fistula is more common in males than females.  There is a maximal incidence between the third and the fifth decades.  Fistulas are usually simple and due to an infected anal gland.  Uncommonly, fistulas that are more complex may be secondary to other pathology such as Crohn’s disease.

The presence of a symptomatic anal fistula is an indication for operation because spontaneous healing is very rare.  If fistulas are not treated, they can lead to recurrent abscesses and persistent discharge.  The aim of fistula surgery is to cure the fistula with the lowest possible recurrence rate and minimal changes in continence.  This requires knowledge of the primary track, the site of the internal opening, the amount of sphincter muscles involved and any secondary extensions.  For the majority of fistulas, the above factors can be determined easily with clinical assessment.  However, radiological investigations are required for complex fistulas prior to operation.


Surgery is always required to cure a fistula.  The track between the skin and anus needs to be identified and exposed.  This can be treated by one of four methods:

  • a fistulotomy: laying open the track; always done this way if the fistula is low, involving minimal sphincter;
  • a seton: essentially as a temporary drain or to slowly divide the track to better preserve sphincter if higher;
  • a fistula division: suitable for special circumstances;
  • an advancement flap: to cover the internal opening (and used for more complex tracks).

It may also be necessary to have an initial examination under anaesthesia.  Most fistulae operations are performed in hospital.

Sphincter control after surgery

There may be some weakness of the muscle after fistulotomy.  The degree will depend on the anatomy of the fistula and the amount of sphincter remaining after treatment.  An anorectal physiology review may be necessary.

Common myths

Fistulas are NOT related to cancer.

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