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.

Anal Fistula

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.
  • 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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A seton is a thread or a type of elastic band inserted in the fistula tract or tunnel communicating the anal canal with the skin. The aim is to drain the fistula to prevent build up of pus, that leads to pain, abscess formation and spreading of infection through the tissues.

The seton can be left in place long term if necessary. Often it is placed as the first step towards curing a fistula. If the fistula involves a lot of muscle, or there is complex disease such as Crohns’ disease it is sometimes left there long term, as alternative treatments may not give good outcomes.

While the seton is in place there may be ongoing discharge, as it is acting as a drain. It is unusual to break it, so washing and going to the toilet should be carried out as normal. If there is build up of pain and pus despite it, there may be another fistula or abscesses present, and you may need to see your specialist.

LIFT procedure

LIFT procedure or “Ligation of Intersphincteric Fistula Tract” is an operation used to treat fistulae that are not amenable to laying open. Usually these fistulas involve more muscle, and hence the fistula cannot be layed open or cut safely.

The procedure aims to tie off and close the fistula tract or “tunnel” as it travels between the internal and external sphincter muscle.

The operation is done once the fistula tract is well delineated and there is no other infection. Usually there will be at least one previous operation performed to control the infection or abscess, and inserted a seton to drain it well.

The operation is usually carried out as day surgery. You may be prescribed antibiotics for a week, and simple analgesia.

Sometimes the operation deals with half of the fistula, and the remaining tract can be safely layed open only cutting a small amount of internal sphincter muscle, rather than both the internal and external muscle. There is less chance of faecal incontinence in these cases.


Fistulotomy or “laying open” usually cures the problem. It refers to cutting the tissue over the fistula or ” tunnel”, so there is no longer a tunnel or communication between the anal canal and skin on the outside.

A fistula may be considered “safe” to lay open if it doesn’t involve cutting much muscle. Curing a fistula is the balance between getting rid of it all together, and maintaining adequate continence or control of stool and flatus.

Your surgeon will assess weather a fistula is amenable to this operation. This will be assessed with physical examination (working out how much muscle is above the fistula, and where the internal opening or “hole” is), and sometimes an ultrasound is done to assess the rest of the muscle and how well it is working.

The operation is usually performed under general anaesthetic, and as a day case. Sometimes a flexible sigmoidoscopy or colonoscopy will be performed at the same time or later to rule out other colonic pathology which may be associated with the fistula.

If the amount of skin or tissue cut is significant, sometimes the skin is stitched flat or “marsupialised” to allow faster healing and easier dressings. Some surgeons arrange a community nurse to do dressing, others prefer the patient to digitate or “rub” the wound a few times a day to stimulate growth and clean the wound. The digitation is done with some K-Y jelly or jelly with local anaesthetic in it such as Lignocaine jelly. A gauze can be used on the finger as it has a roughness that can clean the wound.

These wound may take 4-6 weeks to fully heal over.

Advancement flap

An advancement flap is a procedure which aims to cover the internal opening or “hole” of a fistula, so the fistula is able to heal. Healing occurs because tissue covers the entry of ongoing infection, allowing the communication or fistula to close over.

Tissue from the lower rectum (mucosal advancement flap), or from the skin around the anus (anal advancement flap) is used, depending on where the internal opening or “hole” is, and also depending on the surrounding tissue.

This procedure is carried out as a short stay (either day surgery or overnight).

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