Teratoid hepatoblastoma: multidirectional differentiation of stem cell of the liver.

Hepatoblastoma is the most common malignant hepatic neoplasm of childhood, showing a wide spectrum of epithelial and mesenchymal components. Teratoid hepatoblastoma, which reveals multiple lines of tissue differentiation such as mucinous epithelium, melanin pigment, endocrine differentiation, glial and mesenchymal components, has rarely been observed. We report a case of teratoid hepatoblastoma in a 22-month-old girl. She had been diagnosed with hepatoblastoma through percutaneous needle biopsy of the liver and treated with 10 chemotherapy cycles of epirubicin, VP-16 and cisplatin and with hepatic artery embolization. After 10 months, an extended left lobectomy was performed. Grossly, a multinodular, partly well-demarcated, solid mass (7 x 5 cm) with dense fibrosis and focal cystic change occupied almost the entire specimen. There was extensive necrosis due to preoperative treatment. Microscopically, the tumor showed multiple lines of differentiation, which was composed of embryonal, fetal hepatocytes and mesenchymal elements with numerous foci of osteoid. There were also other components showing endodermal, neural, melanocytic and endocrine differentiation. These teratoid components were considered relatively resistant to preoperative chemotherapy, in contrast to extensive necrosis of both embryonal and fetal hepatocytes. These teratoid features of hepatoblastoma are considered to be a multidirectional differentiation of the small epithelial cells or stem cells of the tumor.