This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nuclear medicine, Subject name: Radiology
Hot rim sign on hepatobiliary scintigraphy (Tc99m-HIDA ) is seen in ? 
Select and explain. 
A. Chronic cholecystitis, B. Biliary Atresia, C. Gangrenous Cholecystitis, D. Porcelain GallBladder
C: Gangrenous Cholecystitis
Answer: C: Gangrenous Cholecystitis 
Explanation: * Increased Pericholecystic hepatic band of radio tracer activity called Rim sign. * A rim of increased hepatic activity directly adjacent to the gallbladder fossa in association with non visualization of the gall bladder is a specific sign of acute cholecystitis paicularly associated with gangrene and perforation . Below CT Image Shows Emphysematous Cholecystitis with Necrosis and Air within the wal of GB.It is surgical Emergency with high risk of GB perforation and moality.