Meningiomas. Diagnostic value of immunoperoxidase staining for epithelial membrane antigen.

Meningiomas are composed of cells which display both mesenchymal and epithelial features. To investigate the epithelial nature of these cells, we studied the distribution of epithelial membrane antigen (EMA) in 22 meningiomas; for comparison, we also studied eight central schwannomas, neoplasms with which meningiomas sometimes may be confused histologically. All 22 meningiomas (12 transitional, six meningotheliomatous, three fibroblastic, and one psammomatous) demonstrated immunoreactive EMA, whereas all eight schwannomas were EMA-negative. There was no consistent relationship between histologic growth pattern and nature of EMA staining in the meningiomas: meningothelial areas, spindle cell areas, and whorls all showed EMA immunoreactivity of varying degrees. We also evaluated the distribution of S-100 protein and keratin in these tumors. All schwannomas showed diffuse S-100 positivity, which was often more intense in the nuclei than in the cytoplasm. In nine meningiomas (41%), S-100 immunostaining was observed, but this was usually focal, and nuclear staining was never more intense than cytoplasmic staining. One meningioma, but none of the schwannomas, showed clusters of keratin-positive cells. We conclude the following: EMA immunoreactivity is a characteristic feature of meningiomas, regardless of pattern of growth, and the combination of immunoperoxidase staining for EMA and S-100 protein may be used to distinguish meningiomas from schwannomas in problematic cases.