Imaging of choledochal cysts

Choledochal cysts are rare cystic dilatations of the intrahepatic and/or extrahepatic biliary tree, which may be mistaken for other cystic lesions if their characteristic features are not recognized. The etiology is unknown, and likely multifactorial, and it is uncertain whether they are congenital or acquired. Multiple imaging modalities can be used to diagnose choledochal cysts, including ultrasound, computed tomography, magnetic resonance (MR) cholangiopancreatography (MRCP), endoscopic retrograde cholangiopancreatography, and percutaneous transhepatic cholangiography. MRCP has replaced the more invasive techniques as the gold standard of diagnosis. In addition, MRCP is helpful in detecting an abnormal pancreaticobiliary junction, which is seen in the majority of choledochal cysts. Reaching a correct diagnosis is essential, given the associated risk of complications, including cholangitis, biliary strictures, stones, and malignancy, and accurately assessing the location and length of involvement is important for surgical planning. This review aims to familiarize radiologists with the different types of choledochal cysts and their imaging features according to the Todani classification.