Chronic trismus in a cat with an extra-axial mass causing compression of the pons.

Case summary: A 15-year-old spayed female domestic shorthair cat presented with a 5-month history of dysphagia that progressed to an inability to open the mouth, resulting in poor prehension of food and subsequent weight loss. Neurological examination revealed an ambulatory vestibular ataxia with reduced postural reactions in all four limbs. There was a head tilt to the right and a positional rotatory nystagmus. The mandibular range of motion was greatly reduced at 20 mm compared with a normal cat (mean 62 ± 8 mm, median 63, range 41-84). MRI of the brain revealed a solitary, large, extra-axial mass at the level of the pons, extending from the level of the caudal colliculi to the level of the cerebellar nuclei. The cat was subsequently euthanased and post-mortem histopathology was declined. Relevance and novel information: To our knowledge, this is the first case report of a pontine lesion causing trismus in a cat, and, although rare, should be considered as a differential diagnosis for trismus in the feline population.