Hepatic mensenchymal hamartoma of an infant.

An 8-month-old boy was found to have a solitary hepatic mesenchymal hamartoma. Histologically, the lesion appeared as a large island of loose mesenchymal tissue with few cystic bile ducts and liver cells. Electronmicroscopy showed microvilli on the surface of tumor cells and desmosomes between the cells. Immunohistochemical studies showed that alpha-fetoprotein was localized in the proliferating liver cells and bile ductal epithelium of this neoplasm. This case is the 17th case of hepatic mesenchymal hamartoma reported in Japan.