Patterns of epithelial metaplasia in malignant gliomas. I. Papillary formations mimicking medulloepithelioma.

Adenoid-like formations resembling ducts and glands or forming a cribriform pattern have previously been described in malignant gliomas, resulting in some cases in a confusion with metastatic adenocarcinoma. The interpretation of these structures as being composed of anaplastic glial cells rests partly on the presence of transitions to more differentiated neoplastic astrocytes and partly on the positivity of some of these cells for glial fibrillary acidic protein. In this report two cases are presented in which the adenoid pattern was associated with papillary formations mimicking the arrangement of a medulloepithelioma. These structures represent a form of aberrant neoplastic differentiation in a malignant glioma rather than the expression of an embryonal neuroepithelial neoplasm.