We report of a 27-month-old boy with a recurrent infratentorial ependy
moma; the initial resection was at 14 months of age. Both resection sp
ecimens were histologically similar. In addition to neoplastic ependym
al cells forming perivascular pseudorosettes, a second population of c
ells with identical nuclear morphology displayed large hyaline, refrac
tile cytoplasmic inclusions, causing these cells to superficially rese
mble gemistocytic astrocytes. These inclusions demonstrated strong gli
al fibrillary acidic protein (GFAP) immunoreactivity. Ultrastructurall
y, the inclusions appeared as fenestrated irregular-shaped bodies with
jagged edges and were made up of electron-dense granular material. Al
though these inclusions superficially resembled Rosenthal fibers, immu
noperoxidase stains for ubiquitin and alphaB-crystallin were negative.
Immunoelectron microscopy showed that these unusual non-filamentous i
nclusions were diffusely GFAP positive.