Subepithelial basement membrane deposition and intermediate filament expression in choroid plexus neoplasms and ependymomas.

The pattern of basement membrane deposition was investigated in benign and malignant choroid plexus tumours using an immunocytochemical method to detect laminin, an intrinsic basement membrane component. The results were compared with intracranial ependymomas and myxopapillary ependymomas of the filum terminale. Expression of the intermediate filaments cytokeratin and glial fibrillar acidic protein (GFAP) and the epithelial marker carcino-embroyonic antigen (CEA) was also assessed. Laminin was detected in a subepithelial location in all the choroid plexus tumours but in none of the ependymomas, although basement membrane fragmentation was seen in the choroid plexus carcinomas. In contrast, GFAP was present in all the types of tumour examined. Cytokeratin (as detected by CAM 5.2) was present in all the choroid plexus lesions and also in the ependymomas arising in the spinal canal. CEA was not detected. We conclude that immunostaining for laminin assists distinction between choroid plexus tumors and papillary ependymomas and between benign and malignant choroid plexus tumours.