Wiktionary
pyonephrosis
n. An infection of the renal collecting system, in which pus collects in the renal pelvis and causes distension of the kidney.
Wikipedia
Pyonephrosis
Pyonephrosis ( Greek pyon "pus" + nephros "kidney") is an infection of the kidneys' collecting system. Pus collects in the renal pelvis and causes distension of the kidney.
It can cause kidney failure.