Effect of anterior callosotomy on bilaterally synchronous spike and wave and other EEG discharges

We analyzed pre- and postoperative interictal and ictal EEG patterns in relation to seizure outcome in 29 patients with intractable epilepsy who had undergone anterior callosotomy. Twenty-two patients had generalized bilaterally synchronous sharp or spike and slow wave discharges (GSW) and 7 did not: Postoperatively, patients with preoperative GSW showed disruption of synchrony, increased amplitude asymmetry, and a decreased amount of GSW. No significant decrease was noted in the amount of total epileptic discharge after operation. There was a significant relation between seizure outcome and decrease in amount of GSW. The degree of disruption of synchrony, total amount of epileptic discharge, and pre- and postoperative EEG patterns were not good indicators of seizure outcome. Postoperative changes in lateralization of epileptic foci consisted either of increased lateralization, less lateralization but increased independent discharges in the previously nonpredominant hemisphere, or appearance of some lateralization. There appears to be a spectrum of GSW: Both secondary bilateral synchrony and secondarily generalized corticoreticular epileptic discharges are distributed along this spectrum.