Clinical and magnetic resonance imaging features of unilateral thalamic porencephaly in a dog.

A 1-year-3-month-old, female, neutered labrador retriever was presented with a history of circling behaviour since 2 months of age and a recently detected blindness affecting its right eye. Neurological examination revealed a left-sided head tilt, compulsive tight circling towards the left, postural reaction deficits in the right thoracic and pelvic limbs, absent menace response in the right eye and ventral positional strabismus of the left eye. The neurological examination findings were localised to the left thalamus. Magnetic resonance imaging of the head revealed porencephaly involving the left dorsal aspect of the thalamus. Furthermore, reduced volume of the left rostral colliculus, crus cerebri and optic chiasm, alongside marked thinning of the left cerebral hemispheric white matter tracts with associated left lateral ventriculomegaly, were present. Based on magnetic resonance imaging features and clinical history, a congenital or perinatal encephaloclastic porencephaly with secondary hypoplasia or atrophy of the associated thalamic projection pathways was prioritised.