Pyonephrosis (Greek pyon "pus" + nephros "kidney") is an infection of the renal collecting system. Pus collects in the renal pelvis and causes distension of the kidney.
It can cause kidney failure.
This requires drainage, best performed by ureteral stent placement or nephrostomy.
Pyonephrosis is sometimes a complication of renal stones, which can be a source of persisting infection. It may also occur spontaneously. It can occur as a complication of Hydronephrosis or Pyelonephritis.