IMMUNOHISTOCHEMICAL OBSERVATION OF FOCI OF MUSCLE ACTIN-POSITIVE TUMOR-CELLS IN MENINGIOMAS

Objective.-It has been suggested that muscle actin is expressed in som e meningiomas. The purpose of this study was to examine this hypothesi s in a large number of meningiomas and to examine possible explanation s for this expression. Design.-Sixty-five meningiomas were examined us ing immunohistochemistry for muscle actin. Meningiomas with foci of mu scle actin-positive cells (n = 6) were further examined using monoclon al antibodies for desmin, epithelial membrane antigen, cytokeratin, an d von Willebrand factor. These specimens were also stained for reticul in. Setting.-All tissues were obtained from surgical biopsy specimens at a large academic medical center. Main Outcome Measures.-Meningioma cells were considered to express muscle actin if the expression was sh own to localize specifically in meningothelial cells and whorls that w ere also positive for epithelial membrane antigen. Results.-Seventeen of 65 meningiomas were shown to contain muscle actin-positive cells. S cattered cells were positive in 11 cases, and in the remaining six cas es we observed foci of muscle actin-positive cells, which had a propen sity to form cellular whorls. These foci expressed epithelial membrane antigen, but stains for desmin, cytokeratin, von Willebrand factor, a nd reticulin were negative. Conclusions.-Our findings Suggest that men ingioma cells elaborate muscle actin without showing differentiation i nto specific cell types.