Anal abscess and fistula

Abscesses can occur anywhere on the body and are due to a collection of bacteria-producing pus. Those that occur around the bottom can also be associated with a connection to the lining of the ano-rectum - this is due to a fistula.

Printable Patient Information Leaflet

Patient Information leaflet (1Mb)

What is an anal abscess?

An anal abscess is a cavity filled with pus found near the back passage (‘anus’). It is a common condition with over 10,000 admissions per year. If you have pain, tenderness, redness and/or a lump in the region of the anus you may be suffering from an abscess. You may also feel ill with a fever.

When the abscess has been treated, it usually heals up and causes no more trouble. Sometimes, it doesn’t fully heal indicating that an anal fistula may have formed.


What is an anal fistula?

An anal fistula nearly always results from a previous abscess. It is a tunnel that connects the lining of the back passage with the skin next to the anus.

Persistent leakage of pus from the opening next to the anus suggests that a fistula has developed.

If this opening partially heals over, pus can build up in the tunnel. This leads to an abscess which discharges itself when the pressure builds up. So a fistula may lead to repeated abscesses occurring at the same site.


What causes an abscess?

An abscess is caused by infection getting in to one of the glands that produces mucus to lubricate the anus.


What causes a fistula?

When an abscess has discharged itself or has been lanced (“drained”), the skin will usually heal over. Sometimes, however, a small hole is left on the outside. This usually means that a tunnel (a “fistula”) has developed between the anal gland and the outside opening.

Only a minority of people who have had an abscess will go on to develop a fistula.


How is an abscess treated?

If the infection is caught very early on, antibiotics may work. However, the majority of abscesses will require to be drained. This usually requires a general anaesthetic (put to sleep) and a short stay in hospital.

It will usually take a few weeks for the abscess cavity (hole) that has been drained to fill up with scar tissue. Sometimes (but often not) the cavity will require “packing” by a district nurse to help the healing process.


How is a fistula treated?

A fistula nearly always requires surgery to cure it.

The majority of fistulae are relatively easy to treat but should preferably be performed by a specialist in colorectal (bowel) surgery.

The surgery usually involves cutting a small part of the anal sphincter muscle away. In this way, the tunnel is opened up (‘deroofed’) to form a trench or groove that heals from the bottom of the trench outwards.

In the same way as for the healing of an abscess cavity, it will usually take a few weeks for the fistula that has been removed to fill up with scar tissue. Once again, the surgery usually requires a general anaesthetic and can be done as a daycase procedure..

It may be necessary for a gauze pad to be worn in the underwear for a week or two after the operation to prevent the drainage from soiling the clothes.

Bowel movements will not affect the healing.

Sometimes the fistula is not the type that can be simply laid open as too much anal sphincter muscle is involved to cut (which may risk incontinence) or there are multiple tracks. In this case a string may be passed through the track (“seton”) and the surgeon will bring you back and discuss further options for your treatment.


What if the problem comes back?

Fistulae can be particularly awkward conditions to treat and can come back. In this case – and for the more complicated fistulae, it may be necessary to do a MRI (magnetic resonance scan) scan of the back passage to check that no other fistulae or “tracks” have been overlooked.

If the fistula is a complicated one, a number of alternative operative approaches are available. Your surgeon will discuss these with you if they are necessary.


How long does it take to recover from this type of surgery?

Discomfort after fistula surgery is moderate for the first week and can be controlled with simple pain killers. The amount of time off work is usually minimal but will depend on the type of job you do.

Bathing or showering two to three times a day helps keep the area clean and comfortable. Laxatives are recommended to minimise the discomfort associated with passing a motion


Further information