Which type involves dilation of both intrahepatic and extrahepatic ducts?

Which type involves dilation of both intrahepatic and extrahepatic ducts?

• A. Type I
• B. Type II
• C. Type IV
• D. Type V

Answer: (C)

The idea here is the Todani classification of choledochal cysts, which describes where the biliary dilation occurs. Type IVa involves dilation of both the intrahepatic ducts and the extrahepatic ducts, meaning the dilations appear inside the liver and outside it. This distinguishes it from the other patterns: dilation limited to the common bile duct is a single extrahepatic pattern, a diverticulum arises off the CBD, and dilation confined to the intrahepatic ducts is Caroli disease (intrahepatic only). So the type that spans both sides of the biliary tree is Type IV (specifically IVa).

The idea here is the Todani classification of choledochal cysts, which describes where the biliary dilation occurs. Type IVa involves dilation of both the intrahepatic ducts and the extrahepatic ducts, meaning the dilations appear inside the liver and outside it. This distinguishes it from the other patterns: dilation limited to the common bile duct is a single extrahepatic pattern, a diverticulum arises off the CBD, and dilation confined to the intrahepatic ducts is Caroli disease (intrahepatic only). So the type that spans both sides of the biliary tree is Type IV (specifically IVa).