An anal fistula is a small channel that develops between the end of the bowel, known as the anal canal, and the skin near the anus (opening where waste leaves the body).
On the surface of the skin around the anus, one or more of the fistula ends may be seen as holes. An anal fistula is painful and can cause bleeding and discharge when passing stools.
There are many different types of fistula, ranging from a simple, single tract, to more complicated fistulae that are made up of several tracts that branch out. Some fistulae can be connected to the sphincter muscles (the rings of muscles that open and close the anus). See symptoms for more information about the different types of fistula.
How common are anal fistulae?
Anal fistulae are more common in men, and occur between 20 and 40 years of age. A study that was published in 2007 and looked at four different European countries, including England, found that there are between one and three cases of anal fistulae for every 10,000 people.
An anal fistula usually develops after an anal abscess (a collection of pus) bursts, or where an abscess has not been completely treated. A fistula can also be caused by a condition that affects the intestines, such as irritable bowel syndrome (IBS) or Crohn's disease.
Among people with Crohn’s disease, the incidence of anal fistulae may be as high as 30-50%. Up to 30% of people with HIV (a virus that attacks the body's immune system) will also develop an anal fistula.
Outlook
Most anal fistulae will require surgery because they rarely heal if they are left untreated. There are several different surgical methods depending on where the fistula is and how complicated it is. New research is also being carried out to investigate non-surgical methods.
Following surgery, there is a risk of the anal fistula reoccurring. For example, after the most common type of surgery for a fistula (known as a fistulotomy) the risk of an anal fistula reoccurring is around 21%. See the treatment section for more information.
