EQUINE PAPILLARY EPENDYMOMA

A 17-year-old Arabian gelding with progressive neurologic signs had a velvety, reddish brain tumor protruding from the ventral midline cauda l to the optic chiasma. Histologically, the tumor had a papillary form ation 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 whorli ng intermediate filaments. Neoplastic cells also had cytoplasmic inter digitations and numerous zona adherens and often rested on a basal lam ina. The tumor was diagnosed as a papillary ependymoma.