[An electron microscopic study on osteoblastoma--ultrastructure and fine localization of alkaline phosphatase]

Three cases of osteoblastoma were studied by electron microscopy. They included two cases of conventional osteoblastoma and one case of aggressive osteoblastoma. In conventional osteoblastoma, ultrastructural features and location of alkaline phosphatase activity of the osteoblast-like cell were similar to those of normal osteoblast. On the other hand, aggressive osteoblastoma cell (case 3) showed different structure from those of a normal osteoblast; the nucleus of the tumor cell showed irregular surface with a small degree of heterochromatin, and poorly developed cytoplasmic organellae. Cytochemically, alkaline phosphatase activity was noted not only on the cytoplasmic membrane, but on the abundant vesicles in the cytoplasm. From these findings we conclude that the aggressive osteoblastoma cells are more immature in morphology and show increased synthesis of alkaline phosphatase.