3 yrs ago I had one that covered the entire kidney. no empty space at all in there. it never once hurt me. they did think though I would lose the kidney since we had no idea how long it had been in there. if there had been deminished kidney function they would have taken it. it was called a staghorn and I guess they latch on and don't move and that is why it never hurt.
I am praying for your father in law. it's gotta be rough!