Nasopharyngeal oncocytoma in a cat.

A 5-year-old male neutered Siamese cat was referred because of nasal swelling, nasal discharge, and oral respiration. Computed tomography and necropsy following euthanasia revealed a firm tan mass in the nasopharynx, occluding the nasal passage. Histologically, the nasopharyngeal mass was composed of solid nests, anastomosing cords, and closely packed glands separated by a delicate fibrovascular stroma. Individual neoplastic cells were cylindrical to polyhedral in shape, had distinct cell borders, and contained moderate amounts of finely granular eosinophilic cytoplasm and round to oval nuclei. The cytoplasmic granules were positive on phosphotungstic acid-hematoxylin staining. Immunohistochemically, the neoplastic cells were positive for cytokeratin and negative for chromogranin A, neuron-specific enolase, and vimentin. Ultrastructurally, the neoplastic cells contained numerous mitochondria.