Pigmented ependymoma with signet-ring cells and Rosenthal fibers: a rare variant of ependymoma.

We report a rare case of ependymoma with vacuolar features, signet cells, pigmentation and numerous Rosenthal fibers arising in the fourth ventricle of a 35-year-old woman. The tumor was composed of cells with cytoplasmic vacuoles, signet cells and clear cells. The clear cells were compactly arranged resembling oligodendroglioma. Pseudovascular and ependymal rosettes were observed only in focal areas. Additionally, some tumor cells contained brown cytoplasmic pigment, which was histochemically compatible with lipofuscin and neuromelanin. On immunohistochemical examination, the tumor cells were positive for S100, glial fibrillary acidic protein and vimentin, and negative for synaptophysin, cytokeratin, neurofilament and HMB45. Epithelial membrane antigen staining showed dot-like and small vesicular reactivity. The case is presented to increase familiarity with these extraordinary variants of ependymoma.