Abstracts

Rationale: We have recently reported the beneficial results of corpus callosotomy for infantile spasms (IS). Although no definite criteria have been determined to promote this therapy as a viable alternate, approximately 50% of patients achieved satisfactory seizure reduction postoperatively. In other types of epilepsy, the effects of corpus callosotomy on background EEG, such as transformation of bilaterally synchronous epileptiform discharges into lateralized discharges, appear to correlate closely with good surgical results (Matsuzaka et al., 1999). However, regarding IS, the impact of this surgery on EEG features, particularly hypsarrhythmia, has not been fully investigated. A case report concerning corpus callosotomy for IS stated that bilateral hypsarrhythmia became unilateral after the procedure (Pinard et al., 1993). The present study quantitatively analyzed pre- and postoperative EEG data to test the lateralizing effects of corpus callosotomy on hypsarrhythmia. Methods: Among patients with IS who underwent corpus callosotomy, we retrospectively reviewed EEG data from 15 patients (age at operation, 5-27 months), excluding cases displaying rhythmic spike-and-wave bursts and/or prominent suppression-burst pattern. Preoperative EEGs showed typical or modified hypsarrhythmia. Characteristic EEG features mainly comprising irregular high-amplitude slow activities were extracted from artifact-free sleep records that were part of pre- and postoperative long-term video-EEG monitoring. Using a Fast Fourier Transformation, spectral powers were integrated into frequency bands of delta (< 3.5 Hz), theta (< 8 Hz), alpha (< 13 Hz) and beta (< 30 Hz), corresponding to the five electrode sites in each hemisphere (F3/4, C3/4, P3/4, O1/2, and T3/4). Aggregated spectral power values for each frequency band in each hemisphere were designated as left/right hemispheric spectral power (HSP). Laterality indices (LIs) of HSP were calculated as (L-R)/(L+R), where L and R are values of subjected measure. Pre- and postoperative LIs of HSP were individually compared by frequency bands and correlated with postoperative seizure reductions.