Case Report: Glioneuronal Hamartoma in the Cerebral Cortex of a Juvenile Cynomolgus Monkey (Macaca fascicularis).

Two dark and raised foci were observed on the left hemisphere of the brain of a 3-year-old cynomolgus monkey during the routine necropsy procedures of a preclinical toxicity study. Microscopic examination revealed a lesion in the cerebral cortex at the junction of the parietal and occipital lobes, consisting of disorganized, but generally well-circumscribed collections of mixed glial and neuronal cells within a fibrillar stroma. Numerous eosinophilic granular bodies, brown pigment-laden macrophages, and lymphocytic infiltrates were also noted. Immunohistochemical staining for glial fibrillary acidic protein, neurofilament, and Ki-67, as well as histochemical stains Masson's Trichrome and Klüver-Barrera confirmed the presence of both glial and neuronal cells within a collagenous stroma, without significant proliferation. Both histopathological and immuno/histochemical stains were consistent with a glioneuronal hamartoma. This report describes the first case of such a lesion in a nonhuman primate.