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An anal fistula is when a small, tunnel like structure (tract) develops between the back passage (anal canal) and the opening to the outer skin surrounding the anus. On the surface of the skin around the anus, one or more of the fistula ends may be seen as holes, which tunnel down into the back passage.

There are many different types of fistula, ranging from a simple, singular tract to more complicated fistulas which can be made up of several tracts which branch out. Some fistulas can be connected to the muscles responsible for controlling your bowels.

An anal fistula usually develops after an anal abscess (a collection of pus) bursts. It can also form when an abscess has not been completely treated.

They can also be caused by a condition which affects the intestines, such as irritable bowel syndrome or Crohn's disease.

Most anal fistulas require surgery, as they rarely heal if left untreated. However, complications are rare, and in most cases a fistula will not develop for a second time.



The symptoms of an anal fistula may include:

Pain tends to worsen when you sit, move around, pass stools or cough

If a fistula has been caused by a condition which causes inflammation of the intestines, such as irritable bowel syndrome (IBS), ulcerative colitis, diverticulitis or Crohn's disease, you may experience other symptoms such as:



Anal abscess

Anal fistulas most commonly develop as a result of an anal abscess. An abscess is a collection of pus and infected fluid. An anal abscess normally develops after a small gland, just inside the anus, becomes infected with bacteria or foreign matter. Abscesses are usually treated with a course of antibiotics. In most cases, you will also need to have the infected fluid drained away from the abscess.

If an anal abscess bursts before it has been treated, then it can sometimes lead to an anal fistula. A fistula may also occur if an abscess has not completely healed, or if the infected fluid has not been entirely drained away.

An abscess does not always develop into a fistula. Approximately half of all people who experience an anal abscess will go on to develop a fistula. There is no way of predicting when a fistula will develop.

Anal fistulas are also a common complication of conditions that result in inflammation of the intestines. Some of these conditions include:



To make a diagnosis, your GP will look at your medical history and carry out a physical examination. Your GP will pay particular attention to any history of anal abscesses or conditions which affect your bowels, such as Crohn's disease, as these conditions can sometimes lead to an anal fistula.

When conducting a physical examination, your GP will look closely at your anal region to see if there are physical signs of a fistula. The opening of a fistula normally appears as a red, inflamed spot, which is often oozing pus. If your GP is able to locate the opening of the fistula, they may be able to make a more accurate judgement as to where the path of the fistula lies. Sometimes the path of the fistula can be felt as a hard, cord-like structure beneath the skin.

In many cases, you may have to have further testing carried out so that a more detailed look at the fistula can take place. Your doctor may use the following instruments to carry out further investigation:

If your fistula is in a complicated or unusual position, your doctor may also have to carry out further tests, which may include:



The main aim of treatment for an anal fistula is to heal the fistula with as little effect on the anal sphincter muscles (the ring of muscles that open and close the anus) as possible. Damage to the sphincter muscles could cause incontinence problems in the future.

Very few anal fistulas are able to heal by themselves, so surgery is usually necessary.