<prompt> Following is true of pyonephrosis except:Commonly associated with renal calculiAlways unilateralIs a complication of hydronephrosisFollows acute pyelonephritis  <response>: Ans. b Always unilateralRef: Smith 17th Edition, Pages 204-206 In pyonephrosis kidney is a bag of pus. Most common cause is stones followed by Infected hydronephrosis and acute pyelonephritis Mostly unilateral but can be bilateral also Percutaneous nephrostomy is the initial treatment Subcapsular nephrectomy is needed sometimes. 