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
[{'content': 'Following is true of pyonephrosis except: \nSelect and explain. \nA. Commonly associated with renal calculi, B. Always unilateral, C. Is a complication of hydronephrosis, D. Follows acute pyelonephritis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 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.', 'role': 'assistant'}]