An ultrastructural study of mineralization in craniopharyngiomas.

In eight cases of adamantinomatous craniopharyngioma examined ultrastructurally special attention was paid to the process of mineralization. The tumors were usually composed of neoplastic epithelial cells and fibrous connective tissue stroma. Islands of keratinized cells were frequently observed in the epithelial cell zone. In most of the degenerated keratinized cells cytoplasmic organelles had disappeared except for tonofibrils and membrane-bound round vesicles were seen among the numerous tonofibrils. Needle-shaped crystals were deposited within some vesicles. The accumulation of crystals in the vesicles and the coalescence of calcified vesicles and calcified adjacent tonofibrils resulted in the formation of a large calcified body. Mineralized precipitates were confirmed as calcium and phosphorus by means of an energy dispersive X-ray microanalyzer; the precipitates were composed of hydroxyapatite which was substantiated crystallographically with an X-ray diffractometer. These findings suggest that membrane-bound vesicles derived from degenerated keratinized cells play an important role in the initial process of calcification. The tonofibrils may also serve to orient apatite crystal precipitation.