Somatosensory evoked potentials in hemimegalencephaly and lissencephaly: anatomo-functional correlations.

Four patients with hemimegalencephaly and four with lissencephaly were studied by median nerve somatosensory evoked potentials. The peripheral conduction velocity and the conduction time between the brachial plexus (Erb's point) and cervical cord were normal in both malformations. In hemimegalencephaly, the cortical components were absent on the malformed hemisphere but normal on the healthy side, whereas in lissencephaly an abnormal, prolonged N20 wave was recorded bilaterally. The difference presumably relates to the absence of normal cortical lamination in hemimegalencephaly and to the presence of a 'four-layered' cortex in lissencephaly.