Globular glial fibrillary acidic protein-reactive cytoplasmic inclusions in ependymoma: an immunoelectron-microscopic study.

We report of a 27-month-old boy with a recurrent infratentorial ependymoma; the initial resection was at 14 months of age. Both resection specimens were histologically similar. In addition to neoplastic ependymal cells forming perivascular pseudo-rosettes, a second population of cells with identical nuclear morphology displayed large hyaline, refractile cytoplasmic inclusion, causing these cells to superficially resemble gemistocytic astrocytes. These inclusions demonstrated strong glial fibrillary acidic protein (GFAP) immunoreactivity. Ultrastructurally, the inclusions appeared as fenestrated irregular-shaped bodies with jagged edges and were made up of electron-dense granular material. Although these inclusions superficially resembled Rosenthal fibers, immunoperoxidase stains for ubiquitin and alpha B-crystallin were negative. Immunoelectron microscopy showed that these unusual non-filamentous inclusions were diffusely GFAP positive.