Adenoma mimicking intraductal papillary neoplasm of the bile duct arising in an intrahepatic biliary duplication cyst.

We report a case of a cystic liver tumour in a 47-year-old man with Peutz-Jeghers syndrome (PJS) who had undergone sclerotherapy at another hospital for a cyst in hepatic segment IV (S4) 7 years earlier. Based on the preoperative imaging findings, the patient was diagnosed with an intraductal papillary neoplasm of the bile duct. Percutaneous transhepatic portal vein embolization was performed to increase the residual liver volume, followed by resection of the three right hepatic lobes and the caudate lobe, biliary reconstruction, and portal vein reconstruction. Pathological examination revealed an adenoma arising in an intrahepatic biliary duplication cyst. Retrospectively, the preoperative diagnosis was difficult, but it aligned with previous reports of biliary duplication cysts due to its continuity with the bile duct. Additionally, intrahepatic biliary duplication cysts with tumour lesions or cases in which 18F-fluorodeoxyglucose positron emission tomography was performed have not been previously reported. Therefore, preoperatively listing this disease as a differential diagnosis was difficult. PJS and chronic inflammation associated with cyst sclerotherapy may have contributed to tumour development in the intrahepatic biliary duplication cyst.