1-A-D-26. Pre-operative magnetoencephalographic spike localization in patients with surgically-cured epilepsy

This study investigated the characteristic localization of magnetoencephalographic (MEG) “green” spikes unrelated to epileptogenicity. Preoperative interictal MEG spike localization was compared with surgical resection areas in 17 patients, who achieved complete seizure freedom after withdrawal from antiepileptic medications. No MEG spikes were detected in two patients. In three patients, all MEG spike-areas were resected. Eleven patients had MEG spikes in both resection and other areas. Spike localization remote from resection-area was classified into three types: (1) antero-mesial temporal spikes ( n = 4); (2) contralateral temporal spikes ( n = 3); and (3) posterior temporo-parietal spikes ( n = 5). Both the antero-mesial and contralateral temporal spikes were found only in patients with mesial temporal lobe epilepsy (TLE). The posterior temporo-parietal spikes were found in patients with mesial TLE, as well as other epilepsies. Mesial temporal spikes generated from the hippocampus can propagate to the anterior temporal neocortex and contralateral temporal lobe. Since these temporal neocortical spikes did not reflect epileptogenicity, seizure freedom was achieved after amygdalohippocampectomy. Temporo-parietal spikes found in TLE and other epilepsies can be a “green” MEG spikes. MEG has high sensitivity to activity in the temporo-parietal area, to where spikes propagate easily.