A fistula is an abnormal connection between two organs, or between an organ and the outside. For example, a fistula can be a connection between the intestines and the bladder, or the intestines and the vagina or the colon and the outside. If fistulae develop, gas and stools may seep from them. If a fistula is between the intestines and the skin, the patient may experience gas or stool leaking from pores in the skin.