Congenital cystic lesions of the biliary tract (CCLBT) are rare congenital biliary pathologies due to an abnormality of the development of ductal plaque during embryogenesis (Congenital Cystic Lesions of the Intrahepatic Bile Ducts,
CCLIBD) or they may be secondary to abnormalities of the pancreaticobiliary junction (Congenital Cystic Lesions of the Extrahepatic Bile Ducts,
CCLEBD) [1].
As regards the CCLIBD,
the caliber of malformed ducts determines the type of ductal plate malformation.
If small interlobular bile ducts are affected,
Von Meyenburg complex or congenital hepatic fibrosis results.
If medium-sized intrahepatic ducts are affected,
autosomal dominant polycystic liver disease results.
Caroli disease is the result of ductal plate malformation of large intra- hepatic bile ducts [2].
Although the cause is unclear,
it is widely accepted that the prototype of CCLED,
choledochal cysts, arises from an anomalous pancreaticobiliary ductal junction,
particularly a long common channel,
which is seen in 50–80% of patients [3,
4,
5].
Clinically,
most of these conditions,
such as biliary hamartomas,
may be asymptomatic and they may be found incidentally on abdominal imaging performed for other indications.
On the other hand,
in a small group of patients,
CCLBT may present in childhood or young adulthood with pain in the right upper quadrant and recurrent attacks of cholangitis with fever and jaundice (in the Caroli disease) or pancreatitis (in choledochal cysts),
which are the most frequent complications [6].
Another known complication is malignancy [6,
7].
The overall risk of cancer in choledochal cysts is 10–15%,
commonly affecting the extrahepatic bile ducts and gallbladder [7].
The different types of fibropolycystic liver disease demonstrate characteristic findings at computed tomography (CT) and magnetic resonance (MR) imaging.
Patients with congenital hepatic fibrosis typically have imaging evidence of liver morphologic abnormalities,
varices,
splenomegaly,
renal lesions,
and other associated ductal plate abnormalities.
Biliary hamartomas usually manifest as multiple cysts that are nearly uniform in size and measure up to 15 mm in diameter.
Autosomal dominant polycystic disease typically manifests as an enlarged and diffusely cystic liver.
In Caroli disease,
cystic or fusiform dilatation of the intrahepatic ducts is seen,
as well as the "central dot sign," which corresponds to a portal vein branch protruding into the lumen of a dilated bile duct.
Choledochal cyst manifests as a fusiform or cystic dilatation of the extrahepatic bile duct [2].
MRI modalities for the analysis of the biliary tree are mainly represented by T2-weighted sequence,
also known as MR cholangiography (MRCP),
and T1-weighted gadolinium-enhanced sequences [8].
In this educational exhibit,
we describe the most common imaging findings of these conditions and provide differential diagnosis on imaging.