Abstracts

Rationale: We evaluated the effects of anterior corpus callosotomy (ACC) based on the pre- and postoperative gradient magnetic field topography (GMFT) findings on interictal magnetoencephalography (MEG) spikes in patients with intractable epilepsy and drop-attacks. Methods: We used retrospective data of 8 patients with symptomatic generalized epilepsy who underwent anterior two-third CC for drop-attacks. The etiologies of epilepsy were Lennox-Gastaut syndrome (n=4), tuber sclerosis (n=1), periventricular nodular heterotopias (n=1), and unknown (n=2). All patients had generalized spikes and wave discharges on preoperative scalp EEG. MEG spikes were examined in all patients pre- and postoperatively. We evaluated the spreading (bilateral or unilateral hemispheric) patterns, their distribution (anterior or posterior), and interhemispheric time difference (ITD) using GMFT with MEG. We compared postoperative changes of the rate of these categorized spikes and ITD in patients with good and poor seizure outcomes. Results: Good seizure outcome was obtained in 5 patients who achieved drop-attack cessation. Postoperatively, the rates of anterior bilateral hemispheric (anterior BH) spikes were significantly (p=0.001615) decreased in the good outcome group (range: 48.44-73.83%; mean±SD: 57.38±9.728%, preoperatively; and 0-20.20%, 10.72±10.43%, postoperatively). Furthermore, the rates of posterior BH spikes were also significantly (p=0.013881) decreased postoperatively (7.273-28.13%; 17.19±9.875%, preoperatively; and 0-5.556%, 2.766±2.603%, postoperatively). Both the anterior and posterior BH spikes were replaced by the anterior unilateral hemispheric (anterior UH) spikes, postoperatively. However, there were no differences in rates of anterior and posterior BH spikes between the pre- and postoperative values in the poor outcome group. The preoperative mean ITD in patients ranged from 11.53 to 18.82 msec. In 4 of 5 patients of the good outcome group, the preoperative mean ITD of anterior BH spikes ranged from 13.44 to 15.70 msec, and was prolonged postoperatively to 18.94-26.67 msec. The postoperative ITD was not applicable because of the disappearance of BH spikes in a patient of the good outcome group. In 3 patients of the poor outcome group, the preoperative value ranged from 11.53 to 18.82 msec, and it was also prolonged postoperatively to 19.62-21.64 msec. Conclusions: MEG using GMFT analysis revealed the characterization of interictal spikes, which were observed as generalized spike and wave discharges on scalp EEG. The good seizure outcome correlated with postoperative reduced rates of both the anterior and posterior BH spikes, and prolongation of ITD of the anterior BH spikes. These results may lead to elucidation of the mechanism of ACC effect.