Polymicrogyria

Polymicrogyria is a disorder of late neuronal migration and cortical organization. Neurons, which will form the cortex originates within the germinal matrix and migrates outwardly. The neurons migrate along radial glial fibers to their final destination. Migration begins at approximately 7 weeks of gestation and is completed between 24 and 40 weeks of gestation. Inhibition of neuronal migration or organization can result in a dysplastic cortex. Polymicrogyria is mainly attributed to environmental factors such as hypoxia, intrauterine vascular insults, intrauterine infection, maternal drug abuse, and maternal alcoholism during intrauterine life. Polymicrogyria has also been associated with chromosomal abnormalities. The clinical features of the patients are cerebral polymicrogyria include seizure disorders, spastic hemiparesis, and mental retardation. Seizure disorders are frequent, but spastic hemiparesis and mental retardation are not always present [1,2].
Polymicrogyria can be either generalized or focal, unilateral or bilateral. Immature brain is not yet hardwired, therefore neonates suffering substantial cortical infarctions often have minimal neurological deficits. In polymicrogyria the extend of cortical involvement affects the symptom complexes and the clinical course. The patients with more limited involvement have a better clinical course. Symptom complexes are similar among patients with comparable involvement. Patients with bilateral or diffuse involvement present earlier with worse symptoms. Epilepsy is the most encountered symptom in unilateral polymicrogyria whereas cerebral palsy and speech delay is prominent in bilateral involvement. Microcephaly and mental-motor retardation are not seen in patients with unilateral frank involvement [2].
The preferred imaging modality for cortical dysplasias is MR imaging. But it may be difficult to differentiate pachygyria and polymicrogyria with MR imaging. Several differential MR imaging features may help differentiate the two conditions. These features are: 1-The surface of the cerebral cortex which is smooth in pachygyria and irregular in polymicrogyria. 2- The border between the gray matter and white matter which is smooth in pachygyria and pleated in polymicrogyria. 3- The cortical thickness which is variable in polymicrogyria and abnormally thick (two to four times thicker than normal) in pachygyria [3].