Pleomorphic xanthoastrocytoma within the medulla oblongata of a young dog.

A 13-week-old male intact Poodle mix dog developed an acute onset of vestibular ataxia, tetraparesis, and vomiting. The patient presented ambulatory, tetraparetic, and ataxic with a head tilt to the left and a disconjugate nystagmus (rotary nystagmus with fast phase to the right in right eye and vertical nystagmus in left eye). There were absent postural reactions in the left pelvic and left thoracic limbs and decreased right-sided postural reactions. Magnetic resonance imaging demonstrated an intra-axial mass within the left midcaudal medulla oblongata. On gross dissection, there was a left-sided neoplasm in the medulla oblongata with surrounding hemorrhage. The histologic findings indicated that the mass was a pleomorphic xanthoastrocytoma. This tumor, an uncommon variant of an astrocytoma most often seen in children and young adult humans, has yet to be described in dogs.