In contrast to the inner structure, three-dimensional structure of psammona 
bodies in meningiomas is not well defined. This study examined three cultured 
meningiomas, in which surface observation of psammoma bodies might be easier 
than in the tumor tissues since influence of interposing connective tissue is 
minimized in tissue culture. Early culture revealed that psammoma bodies with 
frank calcification were suspended in the tissue culture medium, and so were 
they collected, centrifuged, and then processed for electron microscopy. 
Ultrastructurally, psammoma bodies were mostly spherical in shape and composed 
of a core of dense calcification and surrounding collagen fiber bundles. Apart 
from psammoma bodies, round bodies with concentric lamination like a 
transversely cut onion were frequently noted by light microscopy. These bodies 
were composed mainly of tangles of collagen fibers emerged from surrounding 
tumor cell processes. The results suggest that psammoma bodies in meningiomas 
arise in part from meningothelial whorls due to collagen production by tumor 
cells followed by obliteration and disappearance of tumor cell processes, 
although some of the alternative pathways for psammoma body formation proposed 
by other investigators cannot be ruled out by this study.