A case of early cancer in cystic intrahepatic duct associated with congenital choledochal cyst.

Herein, we report an extremely rare case of early cancer localized in the cystic intrahepatic duct, which is associated with the choledochal cyst including both the intra- and extrahepatic duct (type IV-A cyst). A small polypoid lesion in the cyst was detected by computed tomography. Extensive resection of the choledochal cyst with lobectomy was performed on the tumor in a 23-year-old woman. Tubular adenocarcinoma localized in the wall of the cystic left hepatic duct was histologically confirmed. Awareness of the diagnostic and treatment modalities, with a focus on potential malignancy in the cystic intrahepatic duct, in cases with anomalous arrangement of the pancreatobiliary duct is necessary.