Cortical thickness in a case of congenital unilateral perisylvian syndrome

In congenital perisylvian syndrome, there is polymicrogyric cortex distributed in variable extensions around the sylvian fissure. Unilateral cases usually present with congenital hemiparesis, while bilateral cases have pseudobulbar paralysis of the oropharingoglossal region. Both unilateral and bilateral cases have a high rate of epilepsy. Polymicrogyric cortex is characterized by too many small convolutions. Often there are no intervening sulci, and almost no white matter can be seen under them. On MRI they appear to have increased thickness. Bilateral and symmetric polimycrogiria can be hard to recognize on standard MRIs. Accurate and automated methods for measuring the thickness of cerebral cortex are available. They have mainly been used to study a variety of disorders with diminished cortical thickness. We studied a case of right perisylvian polymicrogyria, who presented in adult life with epilepsy and had a normal neurological exam. Fischl and Dale's automated cortical thickness analysis rendered a very clear picture of increased cortical thickness with values up to 9 mm in the affected areas (normal cortical thickness varies between 1 and 4.5 mm). The thickest areas were seen over grossly abnormal gyri on the reconstructed cerebral cortex. On MEG he presented a prominent and monotonous 9 Hz activity that was located within the limits of a thick gyrus. There was a significant difference of thickness between homologous hemispheric areas. To our surprise some areas of the left hemisphere also appeared to have increased thickness, raising the question of a bilateral asymmetric case.