An anal fistula is a small channel that can develop between the end of the bowel and the skin near the anus. An anal fistula can cause bleeding and discharge when passing stools - and can be painful.
An anal fistula can occur after surgery to drain an anal abscess. In some cases, an anal fistula causes persistent drainage. In other cases, where the outside of the channel opening closes, the result may be recurrent anal abscesses. The only cure for an anal fistula is surgery.