A 7 year old female spayed mixed breed dog was presented for evaluation of a cyst-like mass in her brain. Her clinical signs began with a vestibular ataxia. At that time, she was treated with enrofloxacin for a presumptive bilateral ear infection, thought to be the cause of her ataxia. Her ataxia became progressively worse despite treatment with enrofloxacin. She was referred to a clinic for a brain MRI. The MRI revealed a slightly right-sided, circular, intraparenchymal lesion most consistent with a cyst at the level of the pons/midbrain/medulla. Her ataxia worsened, and she was referred to the Cornell University Hospital for Animals Neurology service for further evaluation. On presentation she had neurologic signs that neurolocalized to the brainstem, and had green discharge in both external ear canals. Her MRI was evaluated for surgical planning, and it was decided that surgical decompression of the cyst would be the best option, given that the fluid-filled structure itself could not be removed due to its location, and shunt placement within the brainstem was not feasible. A rostrotentorial approach was tried first. Decompression could not be accomplished through this approach due to excessive bleeding. A suboccipital craniotomy was then performed, the cerebellum lifted, and the cyst was decompressed with a needle. The dog recovered over a week in ICU, and very slowly regained the ability to walk and eat without becoming nauseous. She was discharged to the care of her owner with a guarded prognosis. At her one month recheck her clinical signs were improved, but at two months she had again begun to develop vestibular signs. She went to her referring veterinarian to be euthanized. A necropsy was not performed.