Body:
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.