Hyaline inclusions (Pseudopsammoma bodies) in meningiomas: immunocytochemical demonstration of epithel-like secretion of secretory component and immunoglobulins A and M.

Three meningotheliomatous meningiomas showed prominent formation of hyaline inclusions (pseudopsammoma bodies). Immunocytochemical examination by means of indirect immunofluorescence and PAP techniques demonstrated strong labeling of these inclusions by antisera to human secretory component (SC), immunoglobulin (Ig) A and IgM. A similar staining pattern was found in intracytoplasmic globules of a metastatic carcinoma. Hyaline structures of various types in atypical, psammomatous, and hemangiopericytic meningiomas were not stained with the antisera employed. By histochemical, immunocytochemical, and ultrastructural criteria, pseudopsammoma bodies in meningiomas are identical with intracytoplasmic inclusions of some epithelial neoplasms, especially of mammary and gastric carcinomas. Our study strongly corroborates Kepes' (1961, 1975) concept of secretory differentiation in meningiomas, and demonstrates an epithelial character at least of some meningiomas.