[A case of early bile duct cancer arising from villous adenoma in choledochal cyst].

Choledochal cyst is an uncommon premalignant anomaly. The morphology and pathogenesis of the premalignant lesion of cholangiocarcinoma arising from the choledochal cyst has not been well described. Herein, we report a rare case of bile duct adenoma arising from choledochal cyst with anomalous union of pancreaticobiliary duct (AUPBD). 50-year-old woman was admitted to our hospital with the complaint of epigastric pain. She had received common bile duct (CBD) exploration and choledocholithotomy and cholecystectomy 3 months earlier under the diagnosis of multiple CBD stones. Intraoperalive cholangiogram was not remarkable except CBD dilatation at that time. Endoscopic retrograde cholangiopancreatography revealed choledochal cyst with AUPBD and round filling defect which disappeared easily on the balloon cholaniogram. On magnetic resonance cholangiopancreatography, the filling defect was confirmed as 2 cm polypoid mass attached to the distal bile duct wall. At laparotomy, a soft whitish mass was palpable on the lower CBD. On histological examination, adenoma with focal carcinoma change arising from choledochal cyst was diagnosed.