Observation of psammoma bodies in cultured meningiomas: analysis of three-dimensional structure using scanning and transmission electron microscopy.

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.