Pineal parenchymal tumor in a domestic rabbit.

An 11-y-old male lionhead rabbit (Oryctolagus cuniculus) was presented with progressive hindlimb weakness and right-sided neurologic deficits, and was subsequently euthanized due to poor prognosis. Autopsy revealed a 1.6 × 1.1 × 1.0-cm, well-circumscribed, extra-axial mass compressing the occipital lobe and affecting both telencephalic hemispheres. Histologic and immunohistochemical analyses demonstrating positivity for synaptophysin and neuron-specific enolase, along with a Ki67 proliferative index of ~20%, were highly suggestive of a high-grade pineal parenchymal tumor (PPT). The tumor was densely cellular with marked atypia and frequent binucleation, and lacked pineocytomatous rosettes-features most consistent with a pineal parenchymal tumor of intermediate differentiation in humans. No evidence of metastasis was observed. Pineal tumors are exceptionally rare in domestic animals, with limited documentation in species such as dogs, horses, goats, cattle, and birds. To our knowledge, PPT has not been reported previously in a rabbit, underscoring the diagnostic challenges associated with intracranial neoplasms in this species.