I don't have any personal experience with fistulas but my mom who had CD had them. Most of them were around the rectum but two burst through her appendectomy scar. As painful as the rectal ones were, I think she felt the ones on her stomach were the worst. She had to tape 4X4 gauze over the area to catch the liquid bm that came out of them and the tape tore her skin apart not to mention what the acids in the bm did to it. As far as I know, they can indeed break out anywhere. This was and is my biggest fear with CD.