This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Rim sign in IVP is seen in – 
Select and explain. 
A. Polycystic kidney, B. Hydronephrosis, C. Chronic pyelonephritis, D. Hypemephroma
B: Hydronephrosis
Answer: B: Hydronephrosis 
Explanation: Two most important causes of rim sign on nephrogram are -
	(i) Hydronephrosis (chronic obstruction), and
	(ii) Renal artery occulusion.