Caroli Disease: Comprehensive Imaging Guide and Clinical Overview
Overview
Caroli disease is a rare congenital disorder characterized by segmental, nonobstructive saccular or fusiform dilatation of the intrahepatic bile ducts. It was first described by Jacques Caroli and represents a subtype of fibropolycystic liver disease. Clinically, patients present with recurrent cholangitis, biliary lithiasis, and in some cases, portal hypertension. The disease follows an autosomal recessive inheritance pattern when associated with congenital hepatic fibrosis, often termed Caroli syndrome, and isolated forms may show different genetic associations. The hallmark clinical symptoms include abdominal pain, fever, and jaundice reflecting episodes of biliary stasis and infection.
Key Imaging Features
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Ultrasound and cross-sectional imaging reveal saccular or fusiform dilatation of the intrahepatic bile ducts, typically sparing the extrahepatic biliary tree.
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The classic “central dot sign” is seen as a punctate hyperintensity or enhancement representing intraluminal fibrovascular bundles (portal vein branches) within dilated bile ducts, best appreciated on MR cholangiopancreatography (MRCP) and contrast-enhanced MR imaging.
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MRCP demonstrates communication of cystic ducts with the biliary tree, differentiating Caroli disease from simple cystic lesions.
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CT imaging shows hypoattenuating intrahepatic ductal dilations with no extrahepatic bile duct involvement, sometimes revealing intrahepatic stones or biliary sludge.
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Mild hepatic fibrosis and portal hypertension signs (e.g., splenomegaly, varices) may be detected in associated Caroli syndrome.
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Complications identifiable on imaging include cholangitis-related findings, biliary strictures, and the presence of cholangiocarcinoma, which may appear as focal masses or intraluminal filling defects.
Pathophysiology
Caroli disease arises from abnormal embryologic remodeling of the ductal plate during bile duct development, resulting in segmental dilatation of the large intrahepatic bile ducts. The dilatations are lined by bile duct epithelium and contain intraductal fibrovascular bundles responsible for the “central dot sign.” This dilatation leads to bile stasis, a predisposition to recurrent bacterial cholangitis, bile duct stone formation, and progressive inflammation causing periductal fibrosis. In the syndromic form (Caroli syndrome), congenital hepatic fibrosis occurs due to simultaneous ductal plate malformation affecting smaller interlobular bile ducts, explaining portal hypertension and hepatic fibrosis findings. Chronic biliary stasis and inflammation increase the risk of cholangiocarcinoma in these patients.
Differential Diagnosis
| Condition | Distinguishing Imaging Features |
|---|---|
| Autosomal Dominant Polycystic Liver Disease (ADPLD) |
Numerous uniformly sized cysts scattered throughout the liver parenchyma with no communication with bile ducts; no “central dot sign.” |
| Choledochal Cysts |
Fusiform or cystic dilation primarily involving the extrahepatic bile duct with possible intrahepatic ductal dilatation; key is extrahepatic involvement. |
| Biliary Hamartomas (Von Meyenburg Complexes) |
Multiple small, uniformly sized cystic lesions without biliary communication; no dilated bile ducts; typically hypointense on T1 and hyperintense on T2 MRI. |
| Primary Sclerosing Cholangitis (PSC) |
Beading and strictures of intra- and extrahepatic bile ducts; no saccular cystic dilatation; irregular, narrowed bile ducts without “central dot sign.” |
| Intrahepatic Cystic Neoplasms |
Usually do not communicate with biliary tree on MRCP; may show solid enhancing components and mass effect. |
Imaging Protocols and Techniques
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Magnetic Resonance Cholangiopancreatography (MRCP) is the imaging modality of choice to noninvasively visualize the biliary tree, demonstrating intrahepatic ductal dilatations and confirming communication with the biliary system.
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Contrast-enhanced MRI with T2-weighted sequences is critical to identify the “central dot sign,” evaluate ductal morphology, and detect complications like cholangiocarcinoma.
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High-resolution T2-weighted MR sequences help in identifying bile duct dilatation and intraductal contents such as stones or sludge.
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CT imaging with intravenous contrast provides complementary information regarding liver parenchyma, bile duct anatomy, presence of stones, and portal hypertension signs.
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Ultrasound is useful for initial screening showing cystic bile duct dilatation and internal echoes suggesting stones but limited by operator dependency and lower specificity.
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Direct cholangiography (ERCP or percutaneous) is reserved for cases where noninvasive imaging is inconclusive or when interventional management is planned.
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Follow-up imaging is essential for monitoring disease progression, evaluating evolution of fibrosis, detecting new strictures, or early neoplastic transformation.
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