An anal fistula — also called fistula-in-ano — is a tunnel that develops between the inside of the anus and the outside skin around the anus. The anus is the muscular opening at the end of the digestive tract where stool exits the body.

Most anal fistulas are the result of an infection that starts in an anal gland. The infection causes an abscess that drains on its own or is drained surgically through the skin next to the anus. This drainage tunnel remains open and connects the infected anal gland or the anal canal to a hole in the outside skin around the anus.

Causes

Most anal fistulas are caused by an infection that starts in an anal gland. The infection results in an abscess that drains on its own or is drained surgically through the skin next to the anus. A fistula is the tunnel that forms under the skin along this drainage tract. The tunnel connects the anal gland or anal canal to a hole in the outside skin around the anus.

Rings of sphincter muscle at the opening of the anus allow you to control the release of stool. Fistulas are classified by their involvement of these sphincter muscles. This classification helps the surgeon determine treatment options.

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