Intracranial meningioma in a baboon (Papio spp.).

Meningioma is the most common intracranial non-glial tumour of cats, dogs and man. Few spontaneously arising brain tumours have been reported in non-human primates. This report describes a meningioma in a captive baboon. Clinical signs exhibited by the animal included head pressing, visual impairment and vestibular disease. The tumour arose from the ventral aspect of the cranial cavity and compressed the overlying left side of the cerebellum and brainstem. Microscopically, the mass was characterized by pleomorphic spindle-shaped to polygonal cells arranged in sheaths, vague whorls and occasional papillary structures on vascular cores. Nuclear cytoplasmic invagination, syncytial-like cells and areas of mineralization were also evident. Immunohistochemically, the neoplastic cells expressed vimentin and S-100 protein, but not pancytokeratin, glial fibrillary acidic protein or epithelial membrane antigen. The features of this tumour are similar to those of meningiomas in other species.