Fine structure of psammoma bodies at the outer aspect of blood vessels in meningioma.

Psammoma bodies at the perivascular area in five cases of meningioma were examined with the electron microscope. In general, meningocytic cells invest the outer aspect of blood vessels, which are constituted by multilayered basal laminae, collagen fibers, microfibrils, and pericytes. Remnants of degenerated cells are observed in some areas of the perivascular space. Matrix vesicles and matrix giant bodies with or without mineralized deposits are also present in those areas. Energy dispersive, X-ray microanalysis evidenced the presence of both calcium and phosphorus (probably hydroxyapatite) mineralized precipitates. Production of psammoma bodies in the perivascular area may indicate that matrix vesicles and matrix giant bodies are derived from degenerated cells, which then sequestrate hydroxyapatite crystals to form psammoma bodies.