Background. Choledochal cysts are most common in Asian populations. In addition, the incidence of biliary tract malignancies from choledochal cysts is increasing, but the risk of carcinogenesis is still unclear.Material and methods. Clinical data from 214 congenital choledochal cyst cases from 1968 to 2013 were retrospectively analyzed.Results. Todani type I was more common (139, 65.0%) than type IVa (53, 24.8%) or type V (17, 7.9%) in these choledochal cyst patients. Biliary tract malignant tumors occurred in the gallbladder (2, 13.3%), common bile duct (10, 66.7%), and intrahepatic bile duct (3, 20%) in 15 patients (7.0%), including one patient in whom malignant transformation occurred in the intrahepatic bile duct in a type IVa patient 15 years after extrahepatic cyst resection. An age at symptom onset ≥ 60 years was a risk factor (p < 0.001), while an initial complete surgery was a protective factor for carcinogenesis (p = 0.001).Conclusions. Choledochal cysts should be removed once diagnosed because of an increased risk of malignant transformation with increasing age. Complete cyst removal is necessary for the first surgical treatment. Additional hepatectomy should be considered for type IVa choledochal cysts because cholangiocarcinoma can arise from the intrahepatic bile duct years after the extrahepatic cyst excision.
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