Immunohistochemical observation of foci of muscle actin-positive tumor cells in meningiomas.

OBJECTIVE

It has been suggested that muscle actin is expressed in some meningiomas. The purpose of this study was to examine this hypothesis in a large number of meningiomas and to examine possible explanations for this expression.

DESIGN

Sixty-five meningiomas were examined using immunohistochemistry for muscle actin. Meningiomas with foci of muscle actin-positive cells (n = 6) were further examined using monoclonal antibodies for desmin, epithelial membrane antigen, cytokeratin, and von Willebrand factor. These specimens were also stained for reticulin.

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 shown to localize specifically in meningothelial cells and whorls that were also positive for epithelial membrane antigen.

RESULTS

Seventeen of 65 meningiomas were shown to contain muscle actin-positive cells. Scattered cells were positive in 11 cases, and in the remaining six cases we observed foci of muscle actin-positive cells, which had a propensity to form cellular whorls. These foci expressed epithelial membrane antigen, but stains for desmin, cytokeratin, von Willebrand factor, and reticulin were negative.

CONCLUSIONS

Our findings suggest that meningioma cells elaborate muscle actin without showing differentiation into specific cell types.