BLINDNESS DUE TO POLYMICROGYRIA AND ASYMMETRICAL DILATION OF THE LATERAL VENTRICLES IN STANDARD POODLES

Polymicrogyria and asymmetric dilation of the lateral ventricles were seen in related Standard Poodles that had cortical blindness. Three of the affected dogs also had gait and postural abnormalities, and one o f these had seizures. Two of the affected dogs were littermates. Thoro ugh ophthalmologic and neurologic examinations (including electroretin ography, electromyography, cerebrospinal fluid analysis, plain radiogr aphs, and computerized tomography scans) revealed no significant abnor malities outside of the brain that would account for the blindness. Co mputerized tomography scans in three-dogs demonstrated bilateral dilat ion of the lateral ventricles which was more severe in the right All d ogs were necropsied between 5 and 9 months of age and had strikingly s imilar brain abnormalities. Numerous small irregular gyri with shallow sulci covered the middle and caudal dorsal and lateral cerebral corte x. The bony ridges of the inner calvaria in this area conformed to the underlying microgyral pattern. The lateral ventricles were asymmetric ally dilated with the right more severely affected, particularly in th e occipital area, and the cortical grey and white matter, including th e corpus callosum, were thinned in these areas. The third and fourth v entricles and mesencephalic aqueduct were normal. Histologically, ther e was thinning and simplification of the cortical grey matter with an increased density of medium to large neurons. The corona radiata and s ubcortical white matter were also thinner than normal with no evidence of demyelination or astrocytic scarring. This congenital anomaly of t he visual cortex causing blindness in the Standard Poodle appears to b e inherited as an autosomal recessive trait.