A permanent abnormal passageway between two organs in the body, or between an organ and the exterior of the body. Anal and rectalfistulas develop in the wall of the anus or rectum. They connect the interior of the body to one or several openings in the skin. Intestinal fistulas can develop in both the large and small intestine. They are commonly associated with diseases such as inflammatory bowel disease (IBD) and Crohn's disease. (Source)