A fistula is an abnormal connection between two body parts, such as an organ or blood vessel and another structure. Fistulas can occur in many parts of the body and can form between an artery and vein, bile ducts and the surface of the skin, the cervix and vagina, the neck and throat, the space inside the skull and nasal sinus, the bowel and vagina, the colon and surface of the body, the stomach and surface of the skin, the uterus and peritoneal cavity, an artery and vein in the lungs, and the navel and gut. Fistulas are usually the result of an injury, surgery, infection, or inflammation.

Anal fistula is a specific type of fistula that develops between the inside of the anus and the outside skin around the anus. It is usually a side effect of an anal abscess, an infected wound that drains pus from your anus. The draining abscess can create a tunnel through your anus to the skin outside. Anal fistula can cause symptoms such as an opening on the skin around the anus, a red, inflamed area around the tunnel opening, oozing of pus, blood or stool from the tunnel opening, pain in the rectum and anus, especially when sitting or passing stool, and fever.

Fistulas can be diagnosed by a healthcare provider who specializes in colon and rectal diseases. Different methods may be used to help with the diagnosis, such as physical exam, imaging tests, and endoscopy. Once diagnosed, antibiotics alone will not cure a fistula, and surgery is usually needed to cure it. Surgical treatment options include fistulotomy, filling the fistula with a special glue or plug, reconstructive surgery or surgery that is done in stages, and seton placement.