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Simple liver cysts are rarely complicated by intracystic hemorrhage. We encountered a case of simple liver cyst that was morphologically similar to biliary cystadenocarcinoma, which was complicated by asymptomatic intracystic hemorrhage and successfully treated by right lobectomy. A large cystic lesion of the liver was detected in a 57-year-old woman during a mass screening health check. Abdominal ultrasonography (US) revealed that the cystic lesion, containing many hyperechoic papillary structures, occupied almost the entire region of the right hepatic lobe. In addition, a round mural nodule, measuring approximately 5 cm in diameter, was detected in the cystic wall. Abdominal computed tomography (CT) revealed that the inner part of the cystic lesion showed homogeneous low density, but CT did not show the round nodule detected by US. On T1-weighted sequence of magnetic resonance imaging (MRI), the lesion showed homogeneous high signals, together with a low-signal tumorous lesion in the cystic wall. T2-weighted sequence of MRI showed unhomogeneous high signals, together with high signals in the tumorous part. These findings did not exclude the possibility of a malignant cystic tumor, such as biliary cystadenocarcinoma. Therefore, right lobectomy was performed. Histological examinations of resected tissue specimens revealed that the lesion was a liver cyst containing a large amount of blood clot, and that the tumorous lesion detected by US and MRI was a large mass of blood clot which was partly liquefied. This case indicates the diagnostic importance of the morphological discordance between CT and US or MRI findings for liver cyst containing a large amount of blood clot.

A 37-year-old man presented complaining of epigastralgia. Abdominal ultrasonography revealed the presence of a papillary tumor (9 mm in diameter) in the cystic lesion (18 mm in diameter) in hepatic segment 4, which was accompanied by mild intrahepatic bile duct dilatation. Although abdominal computed tomography also showed the cystic lesion, it did not show papillary tumors inside the lesion. Endoscopic retrograde cholangiography showed the communication between the cystic lesion and the left hepatic duct. In addition, mucus was observed in the common bile duct. When transpapillary intraductal ultrasonography was performed through the left hepatic duct using a fine ultrasonic probe, a hyperechoic papillary and lobulated tumor was clearly shown in the cystic lesion. The wall of the cyst was smooth and there was no sign of tumor infiltration. Based on these findings, biliary cystadenoma was diagnosed and an extended left lobectomy was carried out. However, pathological findings postoperatively revealed that the lesion was a localized biliary papilloma, developing and extending to the intrahepatic duct. This case is rare and there have been no published reports describing a biliary papilloma morphologically similar to biliary cystadenoma.

The results of this study suggest that, when encountering a case of AIP with elevated levels of gamma-globulins, IgG, and IgG4, an effort should be made to detect other systemic extrapancreatic abnormalities and initiate steroid administration.