Cystic biliary pathologies

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Cystic diseases of the biliary tree are congenital or acquired cystic dilatations involving the intrahepatic and/or extrahepatic bile ducts.

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They encompass a spectrum of ductal plate malformations ranging from isolated extrahepatic cysts to diffuse intrahepatic ductal ectasia.

These lesions may occur singly or diffusely and vary from simple cystic dilatations to complex intrahepatic cystic disorders.

Classification

Category	Examples	Key Features
Extrahepatic biliary cysts (Choledochal cysts)	Todani types I, II, III	Fusiform or saccular dilatation of CBD or CHD
Intrahepatic biliary cystic diseases	Caroli disease / Caroli syndrome	Saccular intrahepatic ductal dilatation
Combined intra- & extrahepatic cystic diseases	Type IV (a/b) choledochal cysts	Both intra- and extrahepatic involvement
Cystic neoplastic lesions	Biliary cystadenoma / cystadenocarcinoma	Multiloculated cystic neoplasms
Secondary / acquired cysts	Post-traumatic, post-obstructive, parasitic (hydatid)	Secondary etiologies

Imaging Features by Modality

1. Ultrasound (First-line)

Detects anechoic cystic structures communicating with biliary tree.
Choledochal cyst: Cystic mass separate from gallbladder, continuous with CBD.
Caroli disease: Multiple cystic spaces in liver communicating with bile ducts; possible central dot sign (portal vein branch within cyst).

2. CT

Demonstrates size, site, and communication with biliary system.
Choledochal cyst: Well-defined cystic lesion at porta hepatis / CBD.
Caroli disease: Multiple cystic intrahepatic dilatations; may show enhancing portal radicles within cysts (central dot sign).
Associated findings: Intrahepatic calculi, cholangitis, hepatic fibrosis.

Classification

Imaging Features by Modality

1. Ultrasound (First-line)

2. CT

3. MRCP (Gold Standard for Classification)