This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Radiology
Central dot sign on CT scan is seen in 
Select and explain. 
A. Caroli's disease, B. Primary sclerosing cholangitis, C. Polycystic liver disease, D. Liver hamaoma
A: Caroli's disease
Answer: A: Caroli's disease 
Explanation: Caroli disease is a congenital disorder comprising of multifocal cystic dilatation of segmental intrahepatic bile ductsalso classified as a type V choledochal cyst, according to the Todani classificationPathologically, belongs to the spectrum of fibropolycystic liver disease which results from in utero malformation of the ductal plateTwo types - simple and peripoal fibrosisImaging features:CT/US/ MR:central dot sign = poal vein radicles completely surrounded by dilated bile ductsCholangiography (diagnostic):segmental saccular/fusiform/beaded dilatation of intrahepatic bile ducts extending to the periphery of liver up to 5 cm in diameterbridge formation across dilated luminaintraluminal bulbar protrusionsfrequent ectasia of extrahepatic ducts + CBDComplications:Intraductal stonesCholangitis and AbscessLiver cirrhosisCholangiocarcinomaTodani classification:(Ref: Grainger and Allison&;s diagnostic radiology 6th edition, page 797)