Ependymal cyst in a cynomolgus macaque (Macaca fascicularis)

Background A focal hypointense intracranial lesion was detected by magnetic resonance imaging in the right caudal occipital lobe of the cerebrum in an asymptomatic cynomolgus macaque (Macaca fascicularis). Results Following euthanasia, gross evaluation of the lesion revealed a 1 cm diameter, wedge‐shaped intracranial cavitation without apparent communication with the ventricles. Histologically, the lesion was lined by ciliated cuboidal to low columnar epithelium that showed immunopositivity for cytokeratin, S‐100, and GFAP. Conclusion Based upon the gross, histologic, and immunohistochemical findings, this lesion was classified as an ependymal cyst. In the human patients, ependymal cysts are benign, non‐infectious, non‐inflammatory lesions of the central nervous system that are believed to originate from aberrant migration of ependymal cells during development. To our knowledge, this is the first report of an ependymal cyst in a non‐rodent veterinary species and the first report of a benign intracranial cyst of any classification in a non‐human primate.