Anal fistula

Introduction
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.
The end of the fistula can appear as a hole in the skin around the anus. The anus is the opening where waste leaves the body.
Anal fistulas are usually classed as either:

• simple or complexdepending on whether there is a single fistula tract or interlinking connections
• low or highdepending on its position and how close it is to the sphincter muscles(the rings of muscles that open and close the anus)

What causes an anal fistula?
An anal fistula usually develops after an anal abscess (a collection of pus) bursts, or when an abscess has not been completely treated.
A fistula can also be caused by conditions that affect the intestines, such asinflammatory bowel disease (IBD)or diverticulitis.
An anal fistula affects:

• as many as 50% of people with Crohn’s disease
• up to 30% of people with HIV (a virus that attacks the body’s immune system)
• approximately 30-50% of people with an anal abscess (this isslightly more common in women than men)

Read more information about the causes of an anal fistula here.