Polymicrogyria refers to an intracranial malformation marked by development of numerous disorganized microgyria. Intracranial malformations may occur because of an inherent developmental defect or secondary to in utero injury to the brain with subsequent hypoplasia and atrophy. Malformations of the brain include hydrocephalus, hydranencephaly, porencephaly, holoprosencephaly, corpus callosum agenesis, lissencephaly, polymicrogyria, meningoencephalocele, intracranial cysts, cerebellar malformations, and hamartomas. In growing animals these malformations can cause neurologic disorders, although some anomalies may not produce clinical signs until adulthood.3

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A large number of conditions can lead to polymicrogyria, including inflammatory diseases of the brain and certain genetic diseases. In some cases, environmental causes such as congenital infections have been reported. The disease is diagnosed using computer tomography and magnetic resonance imaging tests and is confirmed by biopsy of the brain.2 Clinical signs vary depending on the location of the abnormal cortex, although most animals experience epilepsy. When polymicrogyria affects both hemispheres, affected dogs may experience multiple types of seizures that are are hard to control.4 Polymicrogyria appears to be a familial trait in the Standard Poodle. Affected puppies seem normal at birth, but eventually develop hydrocephalus, seizures, vision loss, and changes in behavior and gait. Severely affected animals are usually euthanized at an early age.

microgyrus (pl. microgyria) - an abnormally small convolution of the brain
polymicrogyria - an intracranial malformation marked by development of numerous disorganized microgyria
hypoplasia - incomplete development
atrophy - loss of function
hydranencephaly - absence of the cerebral hemispheres
porencephaly - cysts or abnormal cavities in the brain tissue
holoprosencephaly - abnormal development of the forebrain
corpus callosum agenesis - absence of all or part of the corpus
corpus - a mass of fibers connecting the cerebral hemispheres
lissencephaly - abnormal development of the gyri of the cerebral cortex
meningoencephalocele - hernial protrusion of the meninges and brain substance through a defect in the skull
hamartomas - benign tumor-like nodules


  1. Lowell Ackerman. Genetic Connection: A Guide to Health Problems in Purebred Dogs.
  2. Jurney C, Haddad J, Crawford N, Miller AD, Van Winkle TJ, Vite CH, Sponenberg P, Inzana KD, Cook CR, Britt L, O'Brien DP.. Polymicrogyria in standard poodles.
  3. MacKillop E. Magnetic resonance imaging of intracranial malformations in dogs and cats.
  4. Behavioral Aspects of Epilepsy: Principles and Practice. Dr. Dorothve Trenitv, MD,MPH, Steven Schachter, Gregory Holmes, MD

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