Studies on the fine structure of osteoblastoma with notes on the localization of nonspecific acid and alkaline phosphatase.

Electron microscopy of two osteoblastomas revealed the existence of three distinct types of cells in this tumor: osteoblast like, macrophage like, and multinucleated giant cells. In addition to the lysosomes, most Golgi cisternae and vesicles in the osteoblast like cells showed evidence of acid phosphatase activity. Deposits of lead phosphate indicating the site of this enzyme in the macrophage like cells were confined to the large and abundant lysosomes. Wide spread deposition of final product was noted in the cytoplasm of the multinucleated giant cells, both in conventional lysosomes, Golgi regions and special organelles probably corresponding to GERL. With regard to nonspecific alkaline phosphatase, final product indicating the location of enzyme activity was confined to the plasma membranes and associated vesicular and vacuolar structures in the osteoblast like cells. The findings suggest that the giant cells in osteoblastomas participate in lytic bone destructive and resorptive processes while osteoblast like cells appear to be osteoid and bone forming carriers of the neoplastic properties of the tumor.