Communication with biliary tree well visualized on MRCP
Central dot sign visible on T1WI C+
Hepatolithiasis: Signal voids within dilated ducts
• ERCP: Dilatation (usually saccular) of large intrahepatic ducts with alternating biliary strictures
PATHOLOGY
• Pathogenesis not completely understood but likely due to arrest or derangement in remodeling of ductal plate
Considered to be variant of fibropolycystic liver disease
Typically autosomal recessive inheritance
• Frequently associated with polycystic hepatorenal syndrome (usually autosomal recessive), hepatic fibrosis, and medullary sponge kidney
• Presentation in childhood or young adulthood often due to cholangitis, cholestasis, or progressive hepatic fibrosis
CLINICAL ISSUES
• Supportive therapy (antibiotics, sphincterotomy, stone removal) for cholangitis and stone disease
• Surgery, including partial hepatectomy or liver transplant, may be option depending on distribution of involvement
(Left) Gross photograph of the liver shows clusters of dilated and cystic intrahepatic bile ducts in a patient with Caroli disease. (Courtesy J. Misdraji, MD.)
(Right) Frontal ERCP shows saccular dilatation of the large intrahepatic ducts as well as multiple ductal filling defects, representing biliary calculi , a characteristic constellation of findings in Caroli disease.
(Left) Axial T2WI MR shows gross, irregular dilation of the intrahepatic bile ducts .
(Right) Coronal MRCP in the same patient makes it easier to recognize the continuity of the cystic intrahepatic lesions with the biliary tree, compatible with Caroli disease. The gallbladder is also seen . This patient was treated with liver transplantation.
TERMINOLOGY
Synonyms
• Communicating cavernous biliary ectasia
Definitions
• Originally divided into 2 variants
Caroli disease (“pure” form): Congenital multifocal saccular dilation of large intrahepatic bile ducts (IHBDs) in absence of other hepatic abnormalities
Caroli syndrome (“complex” form) : More common variant characterized by cystic dilatation of large intrahepatic ducts, hepatic fibrosis, and portal hypertension
IMAGING
General Features
• Best diagnostic clue
Multiple intrahepatic cysts of varying size that communicate with biliary tree
Central dot sign: Enhancing tiny dots (portal radicles) within dilated intrahepatic bile ducts on CECT
• Location
Saccular dilatation of intrahepatic ducts can be diffuse, lobar, or segmental
– Caroli syndrome usually involves entire liver diffusely
– Caroli disease occasionally can be lobar (usually left lobe) but usually predominates in 1 segment
Number of cysts usually < 10 in cases with lobar distribution
• Size
Cysts can be of variable size (mm to cm)
• Morphology
Segmental saccular dilatation of large intrahepatic bile ducts separated by normal or dilated bile ducts
– Individual cysts are contiguous with biliary tree
Size of common bile duct (CBD) is classically thought to be normal
– Extrahepatic duct may be dilated in up to 50%, possibly due to prior cholangitis, passage of stones, or concurrent choledochal cyst
Caroli syndrome (more common variant) frequently associated with autosomal recessive polycystic kidney disease (ARPKD), medullary sponge kidney, medullary cystic disease
• Considered to be a variant of fibropolycystic liver disease
Other variants include congenital hepatic fibrosis, autosomal dominant (ADPKD) and recessive (ARPKD) polycystic liver and kidney disease, biliary hamartomas, and choledochal cyst
• Todani classification of choledochal cysts
Caroli disease is classified as type V choledochal cyst: Cystic dilation of intrahepatic bile ducts
Dilatation (saccular more often than fusiform) of large intrahepatic ducts (either diffuse, lobar, or segmental) with alternating sites of bile duct strictures/narrowing
Hepatolithiasis and sludge are common and appear as filling defects
In cases with cholangitis, ERCP may demonstrate communication of biliary tree with biliary abscesses
CT Findings
• Nonenhancing cysts of varying size that communicate with biliary tree
Variably distributed (diffuse, lobar, or segmental)
• Enhancing portal radicles surrounded by saccular dilated ducts yields central dot sign on CECT
Enhancing “dot” can be either at center or periphery of dilated duct
• Hyperdense hepatolithiasis may be easier to perceive on NECT
• Other findings related to concurrent hepatic fibrosis
Hypertrophic lateral segment, atrophic right lobe (similar to other causes of cirrhosis)
Normal or hypertrophied medial segment (distinct feature not usually seen in other causes of cirrhosis)
• Other findings related to frequently associated renal abnormalities
Findings of ARPKD, ADPKD, medullary sponge kidney, medullary cystic disease
Communication with biliary tree most evident on MRCP
Due to communication with biliary tree, cysts fill with contrast in hepatobiliary phase when using hepatobiliary contrast agent (e.g., gadoxetate [Eovist])
Central dot sign visible on T1WI C+: Enhancement of portal radicles within dilated IHBD
– Portal radicles may appear as signal void at center of dilated ducts on T2W or MRCP images
Hepatolithiasis appears as nonenhancing signal voids within dilated ducts
• Other findings related to concurrent hepatic fibrosis, with involved areas appearing T1 and T2 hypointense with volume loss
• Other findings related to frequently associated renal abnormalities, including polycystic disease, medullary sponge kidney, or fibrotic small kidneys
Ultrasonographic Findings
• Dilated intrahepatic bile ducts: Communication between cysts and biliary tree may be difficult to demonstrate on US
• Echogenic septa may completely or incompletely traverse dilated lumen of bile ducts (intraductal bridging sign)
• Small portal venous branches may be partially or completely surrounded by dilated IHBD (US correlate of central dot sign
Visible as focus on color Doppler vascularity within (center or periphery) dilated bile duct
• Intraductal calculi common and appear as echogenic nodules with dense posterior acoustic shadowing
• Areas of hepatic fibrosis associated with areas of heterogeneous echotexture (and variable echogenicity)
Nuclear Medicine Findings
• Hepatobiliary scan: Unusual pattern of retained radiotracer activity throughout liver within dilated ducts
Imaging Recommendations
• Best imaging tool
MRCP
• Protocol advice
DIFFERENTIAL DIAGNOSIS
AD Polycystic Hepatic Disease
• Numerous (> 10 but usually hundreds) hepatic cysts
• No biliary dilatation or communication between cysts and biliary tree
Cysts do not opacify on cholangiography
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Enhancing “dot” (portal radicles) at either center or periphery of dilated duct: Central dot sign on CECT
in a patient with Caroli disease. (Courtesy J. Misdraji, MD.)
, a characteristic constellation of findings in Caroli disease.
.
with the biliary tree, compatible with Caroli disease. The gallbladder is also seen 
. This patient was treated with liver transplantation.
Segmental saccular dilatation of large intrahepatic bile ducts separated by normal or dilated bile ducts
Due to communication with biliary tree, cysts fill with contrast in hepatobiliary phase when using hepatobiliary contrast agent (e.g., gadoxetate [Eovist])
