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

Ependymoma with "granular cell" features: report of two cases

We report two cases of ependymoma which showed prominent "granular cell" changes of the cytoplasm. The patients were a 7-year-old boy with a tumor in the cerebellum (case 1) and a 70-year-old man with a tumor in the frontal lobe (case 2). The tumor of case 1 showed a histopathological appearance of ependymoma containing many focal aggregates of large polygonal cells in which the cytoplasm was stuffed with numerous eosinophilic granules. The tumor of case 2 predominantly showed the features of papillary ependymoma, and some tumor cells were swollen and contained similar eosinophilic granules. Intracytoplasmic granules in both tumors were immunoreactive for GFAP and ubiquitin, but not for epithelial membrane antigen, CD68 or mitochondria. Ultrastructurally, they were found as aggregates of membrane-bound, electron-dense, globular structures. Karyotypic analysis of the tumor in case 1 demonstrated 2, 11 and 12 trisomies. Intracytoplasmic eosinophilic granules occasionally occur in astrocytic and oligodendroglial neoplasms, but an appearance of similar granules is very rare in ependymoma. The two cases presented here may represent a new histopathological variant of ependymoma, and the term "granular cell ependymoma" is appropriate for them.

Pediatric embryonal tumor of the cerebellum with rhabdoid cells and novel intracytoplasmic inclusions: distinction from atypical teratoid/rhabdoid tumor

We report a case of embryonal tumor with novel inclusion bodies occurring in the cerebellum of a 12-year-old girl. The tumor was histopathologically composed of small undifferentiated cells intermingled with a small number of rhabdoid cells, which had an ultrastructural feature of intermediate filament whorls. Immunohistochemically, the neoplasm showed a polyphenotype, including glial fibrillary acidic protein (GFAP), S-100, synaptophysin, chromogranin A, cytokeratin, vimentin, smooth muscle actin, and desmin. However, epithelial membrane antigen (EMA) immunoreactivity was absent. The MIB-1 labeling index was high (25.6%). Ultrastructurally, there was no evidence of neuronal or myogenic differentiation. The small neoplastic cells contained numerous small intracytoplasmic inclusions stained pink by eosin and red by Masson's trichrome stain. The inclusion body was a densely packed, granulovesicular structure at the electron microscopic level, and was immunoreactive for vimentin, GFAP, desmin, and actin. Reverse transcription-PCR and immunohistochemistry showed the expression of INI1 at the RNA and protein levels, respectively. In conclusion, this tumor was differentiated from atypical teratoid/rhabdoid tumor by the absence of EMA and the presence of INI1 mRNA and protein, and diagnosed as an unclassified, embryonal tumor. Eosinophilic, granulovesicular inclusions of the tumor cells are novel cytoplasmic inclusions in the brain tumor.

Equine papillary ependymoma

A 17-year-old Arabian gelding with progressive neurologic signs had a velvety, reddish brain tumor protruding from the ventral midline caudal to the optic chiasma. Histologically, the tumor had a papillary formation with a single layer of elongate cells radially oriented around a central fibrovascular core. Intracytoplasmic globular inclusions were positive for glial fibrillary acidic protein and weakly positive for vimentin. Ultrastructurally, these inclusions were comprised of whorling intermediate filaments. Neoplastic cells also had cytoplasmic interdigitations and numerous zona adherens and often rested on a basal lamina. The tumor was diagnosed as a papillary ependymoma.