Quantitative EEG Analyses and Surgical Outcome after Corpus Callosotomy
Epilepsia 1999; 40(9): 1269-78 
Tetsuo Matsuzaka (1), Kenji Ono (2), Hiroshi Baba (3), Mitsuhiro Matsuo (1), Shigeki Tanaka (1), Naohisa Kamimura (1), and Yoshiro Tsuji (1)
Departments of Pediatrics (1) and Physiology (2), Nagasaki University School of Medicine; Division of Neurosurgery (3), National Nagasaki-Chuo Hospital, Japan.
Purpose: To clarify the relationship between quantitative EEG findings and the outcome of corpus callosotomy.
Methods: The degree of bilateral synchrony and synmorphism of spike-wave discharges were analyzed using cross-correlation analysis and the measurement of amplitude difference between bilateral homologous regions in 22 patients who underwent anterior corpus callosotomy for intractable symptomatic generalized epilepsies (SGE) (17 patients) and frontal lobe epilepsy (5 patients).
Results: Interictal generalized synchronous spike-wave (GSSW) bursts in SGE were disrupted and changed to unilateral spike-wave (USW) (11 patients) and bilaterally independent spike-wave (BISW) (6 patients).  The surgical outcome in the USW group was better than that in the BISW group.  Preoperatively, the USW group had a significantly lower interhemispheric synchrony (IS) and fewer regional changes in the leading side of time and in the dominant side of amplitude, suggesting unilaterally predominant epileptogenesis which triggers the secondary bilateral synchrony.   Postoperatively, the BISW group had a more marked reduction in IS due to independent discharges from bilateral epileptogenic areas, and the USW group had a more prominent amplitude difference due to unilateralized spike-waves.  In addition, an excellent surgical outcome was related to the preoperative factors of a high degree of morphological similarity (synmorphism) of the bilateral spike-waves, with only a small variation during a burst of spike-waves, and few regional changes in the leading side of time and in the dominant side of amplitude, and to the postoperative factor of large amplitude difference. 
Conclusion: Quantitative EEG analyses enable us to predict the underlying conditions of epileptogenesis and the surgical outcomes of corpus callosotomy, even from the preoperative EEGs.