Fine structure of ossification in craniopharyngiomas

Three cases of adamantinomatous craniopharyngiomas were examined by light and electron microscopy and special attention was paid to the formation of ossified tissue. The tumors were composed of neoplastic epithelial cells with keratinized cell nests and fibrous connective tissue. Keratinized cell masses sometimes directly contacted fibrous connective tissue. In these border areas, multipotential mesenchymal cells in the latter may have differentiated into osteoblasts. Ultrastructurally, these osteoblastic mesenchymal cells were surrounded by amorphous ground matrix and collagen fibrils. Membrane-bound vesicles were occasionally seen among the spaces between the collagen fibrils. These vesicles were presumably derived from osteoblastic mesenchymal cells and were morphologically similar to matrix vesicles. Precipitation of hydroxyapatite crystals in these vesicles was considered to be the initial stage of ossification. Further mineralization of adjacent collagen fibrils resulted in the formation of small bone trabeculae. Then apositional growth of ossified tissue occurred in the surrounding keratinized cell masses.