Anal abscess/ Anal fistula

Anal Abscess

An abscess is a collection of pus in any localised space in the body. An anal abscess is one that occurs in the tissues around the anus.


A number of small glands are normally present between the inner and outer layers of the anal sphincter muscle. Bacteria may lodge in these glands, setting up an infection. An abscess develops from this infective process. This may progress to various areas around the anal canal to involve the anal sphincter muscle and surrounding tissues. The abscess may enlarge and burst through the overlying skin or may require drainage by surgical treatment.


As the amount of pus in an abscess increases, the pressure within it rises. This produces constant throbbing pain which continues until the pus escapes. Other symptoms are fever and sweating.


The pus is drained from the abscess cavity by making an opening through the overlying skin. This may be done under local anaesthesia or general anaesthetic in a hospital or day surgery. A large abscess may require hospital admission, intravenous antibiotics as well as surgical drainage. Antibiotics may be used to control the spread of the infection, but antibiotics alone will not cure an abscess. Pus always needs drainage.


An anal fistula is an abnormal track or tunnel between the internal lining of the anus and the skin. A fistula may develop after drainage of an anal abscess but may occur spontaneously. Discharge of pus and sometimes blood and mucus may be constant or intermittent as the external opening on the skin may heal temporarily.


Surgery is needed to cure a fistula.

The course of the track between the anus and the skin has to be identified and exposed, this is done under anaesthetic.

The track may be treated in one of three ways according to its complexity.

  • Fistulotomy opens the length of the track to the skin's surface allowing the open wound to heal slowly. Some sphincter muscle may be divided. This is the most frequent treatment employed, especially if the tract does not contain too much muscle within its course.
  • A Seton is a loop of flexible material or thread placed along the track to maintain drainage for a period of time.
  • Fistula repair closes the internal opening of the track and preserves anal sphincter muscle. This is a more complex operation. It may involve closing the internal opening with a layer of anal mucosa (mucosal advancement flap), or with some anal skin (anal advancement flap), or tying off the tract between both muscles (LIFT procedure)

Examination under anaesthesia may be necessary to assess the process of healing.

Anal Sphincter Control After Surgery

Fistulotomy divides a varying depth of anal sphincter and this may result in some weakness of the muscle. The effect on continence will depend on the anatomy of the fistula and the amount of intact sphincter remaining after surgical treatment.

Fistulae and other diseases

Most fistulae are the result of infections in an anal gland. However patients suffering from inflammatory bowel disease (colitis and Crohn's disease) are more likely to develop anal abscesses and fistulae.

Fistulae are not related to cancer.


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