Distribution of epithelial membrane antigen in normal and neoplastic human ependyma.

The ependyma and choroid plexus of 23 normal brains and 20 ependymal tumors were examined immunohistochemically for expression of epithelial membrane antigen (EMA) using a specific monoclonal antibody. The ependyma of normal brains showed three patterns of immunoreactivity: membrane immunoreactivity confined to the luminal surface; irregular punctate intracytoplasmic immunoreactivity in the subependymal layer; and spherical and ring-like intracytoplasmic immunoreactivity in the subependymal layer. Of 13 differentiated ependymomas 11 reflected the immunoreactive patterns of normal ependyma. The anaplastic ependymomas and ependymoblastomas had no immunoreactivity. Our results indicate that EMA has a highly selective distribution in the ependyma, and is a marker for differentiated ependymoma.