A case of oligodendroglioma in a sea otter (Enhydra lutris).

A 19-year-old male sea otter (Enhydra lutris) exhibited systemic seizures, declining consciousness, temporary cardiopulmonary arrest, and right-side rotation. The sea otter died approximately one month after its initial seizure. Postmortem magnetic resonance imaging examination revealed a high-intensity region in the left frontal lobe. At necropsy, a gelatinous lesion in the left frontal lobe of the brain was revealed. Histopathologically, the lesion consisted of neoplastic proliferation of round to polyhedral monomorphic cells with a honeycomb growth pattern, small round nuclei, and cytoplasmic halos. The neoplastic cells were immunopositive for oligodendrocyte transcriptional factor-2 (OLIG2) and immunonegative for glial fibrillary acidic protein (GFAP). In this study, we describe the clinical signs and histopathological features of oligodendroglioma, which have rarely been reported in sea otters.