Quantitative EEG analyses and surgical outcome after corpus callosotomy

Abstract

Purpose: To clarify the relation between quantitative electroencephalogram (EEG) findings and outcome following corpus callosotomy (CC). Methods: The degree of bilateral synchrony and morphologic similarity of spike-wave discharges was analyzed by using a cross-correlation analysis and the measurements of amplitude differences between bilateral homologous regions in 22 patients who underwent anterior CCs for intractable symptomatic generalized epilepsies (SGE; 17 patients) and frontal lobe epilepsy (five patients). Results: Interictal generalized synchronous spike-wave (GSSW) bursts in the SGE patients were disrupted and changed to unilateral spike- waves (USWs) in 11 patients and to bilaterally independent spike-waves (BISWs) in six. The USW group had better surgical outcome than the BISW group. Pre-operatively, the USW group had significantly lower interhemispheric synchrony (IS) and fewer regional changes in the side leading in time and the side dominant for amplitude, suggesting unilaterally predominant epileptogenesis that triggered the secondary bilateral synchrony. Postoperatively, the BISW group had a more marked reduction in IS because of independent discharges from bilateral epileptogenic areas, and the USW group had a greater amplitude difference because of unilateralized spike-waves. In addition, an excellent surgical outcome was related to (a) the preoperative degree of the morphologic similarity of the bilateral spike-waves (only a small variation during a burst of spike-waves) and the few instances of regional changes in the side leading in time and in the side dominant for amplitude; and (b) to large postoperative amplitude differences. Conclusion: Preoperative quantitative EEG analyses enabled us to predict the underlying conditions of epileptogenesis and the surgical outcomes in patients undergoing CC.