This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genitourinary radiology, Subject name: Radiology
Rim Sign on Contrast Studies of kidney is seen in? 
Select and explain. 
A. Chronic Hydronephrosis, B. Renal Coical Necrosis, C. Renal Papillary Necrosis, D. RCC
A: Chronic Hydronephrosis
Answer: A: Chronic Hydronephrosis 
Explanation: RIM SIGN-Chronic Hydronephrosis REVERSE RIM SIGN-Renal Coical Necrosis * RIM sign indicates the markedly thinned out atrophic renal parenchyma surrounding the dilated pelvicalyceal system in Chronic Hydronephrosis