A fistula occurs when two organs or vessels form an abnormal connection. Anal fistulas occur when the skin around the opening of the anus forms an abnormal connection with the surface of the anal canal. An anal abscess is a major cause of fistula.
 
Cause of Fistula
A fistula can occur when the mucus gland within the anus becomes chronically inflamed, causing an abnormal connection between the anal canal and the opening of the anus that does not heal. This can cause continuous or occasional discharge of pus, blood, and/or mucus.
 
Surgery of Fistula

• A fistulotomy involves the insertion of a probe into the fistula and using a scalpel or cautery to open up the abnormal connection. The wound must then be cared for until it heals from the inside out and tissue grows into the open wound.
• A fistulectomy involves the removal of the fistula. Then some tissue from the rectum is used to close and repair the sphincter muscle.
• LIFT (ligation of the intersphincteric fistula tract) is the technique to close the fistula without injury to the anal sphincter.