[Ultrastructural study of a Masson's "humid meningioma"].

The authors report the ultrastructural analysis of a Masson's humic meningioma. The tumor presents at the electronic microscopic examination every sign of secretive hyperactivity and does not show any degenerative characteristics. The existence of an important extracellular material rich in pre-collagenic fibres accounts for lacunar texture of this neoplasia at optic microscopic investigation; the role played by tumoral cells in the elaboration of the material is taken into account and seems to corroborate histogenic ecto-mesenchymatous theory of arachnoidal cells.