Fistula in Ano

A fistula-in-ano is an abnormal hollow tract or cavity that is lined with granulation tissue and that connects a primary opening inside the anal canal to a secondary opening in the perianal skin; secondary tracts may be multiple and can extend from the same primary opening. 

What causes fistula-in-ano?

An anal fistula is a small tunnel that develops between the end of the bowel and the skin near the opening of the bottom (anus). It's usually caused by an infection near the anus, which results in a collection of pus (abscess) in the nearby tissue. When the pus drains away, it can leave a small channel behind.

An anal fistula is an infected tunnel between the skin and the anus, the muscular opening at the end of the digestive tract. Most anal fistulas are the result of an infection in an anal gland that spreads to the skin.

Symptoms include pain, swelling and discharge of blood or pus from the anus.