Calcification in the stroma of adult telencephalic choroid plexus was studied of 
20 postmortem brains and one biopsy by light microscopy, transmission and 
scanning electron microscopy and compared with calcification in psammoma bodies 
in normal arachnoid, five spinal meningiomas and in calcospherites of six pineal 
glands. Fifteen fetal and newborn choroid plexuses were also examined by light 
microscopy. Calcium deposition was observed in the subepithelial regions of the 
adult choroid plexus, in the walls of blood vessels but was mostly seen in 
spherical psammoma bodies. Collagen whorls 20-60 microns in diameter and 
surrounded by arachnoid cells, were observed in the stroma of the choroid 
plexus; calcium, phosphorous and iron were deposited in the collagen whorls to 
form psammoma bodies. Matrix vesicles and spicules resembling hydroxyapatite 
were associated with the arachnoid cells surrounding the collagen whorls and 
with the collagen fibres within the whorls. The dense amorphous calcified core 
of each psammoma body was surrounded by an outer coating of entwined collagen 
fibres readily visible by scanning electron microscopy. Similar psammoma bodies 
were occasionally observed in normal arachnoid. Psammoma bodies in meningiomas 
resembled those in the choroid plexus stroma. Calcospherites in the pineal 
differed from psammoma bodies; they were lobulated, more irregular in shape and 
did not have a collagen base. The results of this study suggest that psammoma 
bodies in the choroid plexus, as in meningiomas, form by a process of dystrophic 
calcification associated with arachnoid cells and collagen fibres. The presence 
of iron in the choroid plexus psammoma bodies may be a result of haemorrhage 
into the stroma. The mechanism of calcification in pineal remains unclear.