A patient I saw last week had a history of a rectal fistula. I'd never heard of this condition, even as I spent months reading about recto-vaginal and vesico-vaginal fistulas last spring in preparation for research in Sierra Leone that never happened. At any rate, I searched and ended up at eMedicine:

For reasons of intrinsic anatomy, rectovaginal fistulas are found only in women.

That sentence right there is why, as a physician in training, Google is no longer the friend it once was.