Malignant meningioma: ultrastructure and observations on histogenesis.

A malignant meningioma was studied by light and electron microscopy. Histologically, the tumour was composed predominantly of spindle shaped cells arranged in interlacing bundles with numerous mitoses and much nuclear atypia. There were many necrotic foci as well as invasion of the cerebral cortex, dura mater and blood vessels. Ultrastructurally, the main findings included moderate plasma membrane interdigitation, many intracytoplasmic filaments, and junctional attachments of three kinds: desmosomes, hemidesmosomes, and zonulae adhaerentes. These subcellular features are suggestive of arachnoidal cell origin.