Giant mesenchymal hamartoma of the liver in an adult.

We report a case of hepatic mesenchymal hamartoma in an adult; this condition is extremely rare, with only 15 cases having been reported in the English-language literature worldwide. The patient was a 36-year-old woman who was seen at her local hospital for upper abdominal distension. A giant multilocular cystic tumor, which had almost entirely replaced the normal parenchyma of the right lobe of the liver, was diagnosed. She was referred to our hospital, where, with a diagnosis of biliary cystadenoma, the tumor was successfully removed by right hemihepatectomy. After an uneventful postoperative course, the patient was discharged from our hospital. On histological examination, the tumor consisted of numerous cystic lesions without epithelial lining cells; hepatocytes, bile duct, and vascular components, without either lobular structure or atypia, were observed in the pseudocyst wall, leading to a diagnosis of hepatic mesenchymal hamartoma. There have been a few previously reported cases of multifocal hepatic mesenchymal hamartoma reappearing in the remaining liver after hepatectomy, although these cases are considered to be extremely rare. Therefore, periodic follow-up will be necessary for the patient.