(Warning: some blood and tissue here.)
A staghorn calculus is not a deer doing advanced mathematics. Rather, it is a stone (or stones) thats form inside the kidney and over the years, takes on the shape of the renal calyces of the kidney, hence the name.
This x-ray (copied from the Diagnostic Radiology of Houston, Texas) shows a staghorn calculus on the left kidney. Notice the stone's resemblance to the antlers of a stag or deer.
This here below is the surgeon removing part of the staghorn (golden brown, center) from the now open kidney, which was markedly enlarged and filled with pus.
We tried to save the kidney and just remove all the stones but in the end we opted to do a nephrectomy instead as leaving it in would probably do more harm than good as it was infected and already severely deformed structurally and most probably functionally as well.