Intracerebral papillary ependymoma in a cow.

Intracranial neoplasms are rare in cattle. Bovine ependymomas have been reported only sporadically, with limited morphologic descriptions and, to our knowledge, without immunohistochemical characterization. Here, we describe the gross, histologic, and immunophenotypic features of a papillary ependymoma in the brain of a 7.5-y-old cow that was a bovine spongiform encephalopathy suspect. Grossly, a large, intraparenchymal, well-demarcated mass occupied the left cerebral hemisphere, extending from the frontal to the occipital lobe and communicating with the left lateral ventricle. Histologically, the neoplasm was composed of elongated-to-columnar cells arranged predominantly in perivascular pseudorosettes with prominent papillary architecture. Immunohistochemically, >95% of neoplastic cells had strong cytoplasmic glial fibrillary acidic protein immunolabeling, which was accentuated in perivascular processes; ~20% of neoplastic cells were also immunolabeled for vimentin. Neoplastic cells lacked immunolabeling for pan-cytokeratin, S100, oligodendrocyte transcription factor 2, NeuN, synaptophysin, and E-cadherin. The combined morphologic and immunophenotypic findings supported a diagnosis of papillary ependymoma and excluded morphologic mimics.