What differentiates a type 1 choledochal cyst to a type 4A
Type 1 have dilation of the extrahepatic bile duct (either focal or the entire length), while type 4A have fusiform dilation of the entire extrahepatic bile duct with the extension of dilation of the intrahepatic bile ducts.
Why is CT cholangiogram rarely performed in developed countries?
MRCP is safer as it doesn't require the administration of contrast agent and provide images equivocal to ERCP. The contrast for CT cholangiogram, Meglumine iotroxate (Biliscopin), is an iodine-containing contrast and has a small but not negligible risk of reaction at ~2% (range 0.8-3.4%), though anaphylaxis is rare. MRCP is safer as it doesn't require the administration of contrast agent and provide images equivocal to ERCP.
CT cholangiogram (post-Biliscopin)
The common hepatic and common bile duct show fusiform dilatation, involving almost its entire length. Maximum diameter measures approximately 3.7x3.4cm on the axial plane. There are few small focal outpouchings seen along the left wall of this dilated CBD. Overall findings are in keeping with a type 4A choledochal cyst by Todani classification.
No obvious residual calculi identified. No leakage was seen.