This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney & Ureturs, Subject name: Surgery
Following is true of pyonephrosis except: 
Select and explain. 
A. Commonly associated with renal calculi, B. Always unilateral, C. Is a complication of hydronephrosis, D. Follows acute pyelonephritis
B: Always unilateral
Answer: B: Always unilateral 
Explanation: 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.