What is an Anal Abscess or Fistula?

An abscess is a collection of pus, infected fluid. In the anus, abscesses usually start from an infected gland which sits between the two rings of muscle that surround the anus, the internal and external anal sphincters. If you imagine two cylinders of muscle, an inner and outer like two flowerpots slotted inside each other, the abscess is between these two layers. The abscess can then extend towards the skin round the anus and normally forms a lump there, which is painful and may discharge, a “perianal abscess” Sometimes the abscess pushes through the outer ring of muscle, the external sphincter into the fat of the buttock and forms a bigger abscess further away from the anus, an “ischiorectal abscess”

A fistula is an abnormal track or communication between two areas of the body, in this case between the inside skin of the anus and the skin around the anus. An anal fistula usually develops as a result of an anal abscess that is drained or bursts. Up to half of those who develop an anal abscess will go onto develop an anal fistula. As the original infected gland had an opening into the middle of the anus there is now the potential for a track to be formed from that point to the skin round the anus, a fistula.


An abscess is a painful lump and as the area is very sensitive, it can be very painful. It might discharge spontaneously which will produce some improvement in symptoms and resolution of the lump.

The history of a fistula is that it starts with an abscess, which settles (with or without surgery) but then intermittently the same area flares up again with a painful lump that discharges, appears to resolve, only to recur from time to time. In some cases there is a persistent spot near the anus which continually discharges a little pus and blood.


Many patients need no special tests before treatment but in some more complex cases an MRI scan or other tests are helpful in showing where the track goes. Sometimes other conditions cause infections round the anus such as Crohn’s disease and if this is suspected then your surgeon will arrange tests to hopefully exclude it.


An abscess is usually easily treated by surgical drainage (incision of the skin over the abscess) under a general anaesthetic. In the very early stage there may be a role for antibiotics but not often.

The surgical wound then needs dressing maybe several times a day, after a bath or shower to clean the area. As a rule just an external dressing is applied, putting a dressing into the depths of the wound (packing) is not often needed. The procedure is done as a day case but you may need support of the GP and community nurse for the dressings.

Fistula treatment can be simple or if complex, can be difficult to treat. You may require a number of procedures to reach a satisfactory outcome depending on the complexity of the fistula track. Surgery is performed as a day-case. For a simple fistula not involving any anal muscle the track can be ‘laid open’ by passing a probe along the track and cutting the skin and fat overlying it. Where there is muscle encompassed by the fistula it is important to preserve the muscle to maintain continence. Here the aim of surgery is to seal the track without cutting muscle. If your fistula is complex then your Surgeon will have a full discussion about the benefits and risks of the various treatments available.