R.W.
a fistula is an area that no longer has tissue or good tissue. Wethere that be from prolonged infections, poor repairs, repeated damage. The protocol is basically the same. Go in get rid of all the old nasty tissue, possibly transplant new healthy tissue, stitch it up the best they can or do wet to dry dressings and allow the body to fill in the void on it's own.
This is all dependent on exactly where the fistula is of course. I had one under my arm from an ingrown/infected hair follicle. it was cleaned out, bandaged and left to heal on it's own.