Paradoxical vestibular disease with trigeminal nerve-sheath tumor in a dog

A thirteen-year old spayed female poodle was referred because of atrophy of temporal and masseter muscles on the left and head tilt and episodical cir cling to the right side. Additionally, decreased facial sensation, absent m enace reaction, palpebral and corneal reflexes on the left side, as well as ipsilateral hemiparesis and tongue palsy were noticed. Generalised vestibu lar ataxia and hypermetria in the front limbs were present. Based on the cl inical signs, the presumptive anatomical localization of the lesion was the cerebellopontine angle including parts of the caudal brainstem with involv ement of the trigeminal, facial and hypoglossal nerves. Involvement of eith er flocculonodular lobe or the caudal cerebellar peduncle on the left side causing paradoxical vestibular disease was suspected. On magnetic resonance imaging a large enhancing lesion in the area of the left cerebellopontine angle involving the trigeminal nerve and compressing cerebellum and brainst em was seen. Because of the poor prognosis the dog was euthanized on the ow ner's request. This space occupying lesion could be identified as a trigemi nal neurofibrosarcoma/schwannoma on post mortem histopathological examinati on.