Symptomatic granular cell tumor involving the pituitary gland in a dog: A case report and review of the literature

A granular cell tumor involving the pituitary gland, optic chiasm and ventr al pyriform lobes was discovered in a 12-year-old Labrador Retriever. Clini cal signs included acute blindness, seizures, ataxia, weakness, and behavio ral changes. The diagnosis was established by histopathologic and ultrastru ctural examination of neoplastic tissues collected at necropsy. Granular ce ll tumors involving the central nervous system are well documented in human s but rarely have been described in dogs. The location of the neoplasm and the clinical symptoms seen in this dog closely parallel those of a rare syn drome in humans commonly described as symptomatic parasellar or pituitary g ranular cell tumors. The cell of origin for these tumors is still highly de bated, and attempts to characterize human granular cell tumors through immu nohistochemistry have produced conflicting results. An immunohistochemical profile of this neoplasm revealed focal positive staining for vimentin with a lack of staining for neuron-specific enolase, glial fibrillary acidic pr otein, S-100, and synaptophysin. All neoplastic cells were strongly positiv e with the periodic acid-Schiff reaction.