Occipitoatlantoaxial malformation with atlantoaxial subluxation in a cat

Occipitoatlantoaxial malformation and atlantoaxial subluxation was diagnosed in a three-year-old castrated male domestic shorthair cat. Clinical signs included ataxia, postural reaction deficits, abnormal spinal reflexes, and behaviour changes. Radiographic examination revealed malformation and hypoplasia of the occipital condyles, hypoplasia of the dens, and atlantoaxial subluxation. Electroencephalographic (EEG) findings included high voltage slow activity and sharp waves with superimposed low voltage fast activity in the occipital leads and sinusoidal beta waves in the frontal leads. Basilar artery compression as a result of atlantoaxial instability is suspected to have caused the behavioural changes and EEG abnormalities in this patient. The cat was treated by stabilisation of the atlantoaxial subluxation by ventral cross pin fixation, odontectomy, and arthrodesis of the atlantoaxial articulation. The patient responded well to treatment and was neurologically normal 18 months after surgery.