Magnetic source localization and morphological changes in temporal lobe epilepsy: comparison of MEG/EEG, ECoG and volumetric MRI in presurgical evaluation of operated patients

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Abstract
Is MEG source analysis able to precisely locate the primary focal epileptic activity? 22 patients with pharmacoresistant temporal lobe epilepsy were recorded during presurgical evaluation simultaneously with multichannel MEG/EEG and invasive (subdural) electrodes to evaluate the increase of information gained by MEG concerning the localization of focal epileptic activity and lesions. With this systematic study it should become clearer how often MEG can establish a diagnostic bridge between function and morphology. In addition, MEG localization accuracy of focal epileptic activity was to be validated empirically by invasive EEG recordings and postsurgical outcome. Spikes in the MEG were used for magnetic source localization, and the result was combined with magnetic resonance imaging (MRI). All patients definitly suffered from temporal lobe epilepsy and revealed a structural abnormality in MRI. 17 patients with lesions in the temporal lobe were operated meanwhile and became markedly improved or seizure free. In 7 of 8 patients with a tumor and validated operation outcome, a very close correlation of the 3D-magnetic source localization and the border of the tumor in the brain was found (distance less than 10 mm). In 8 of 9 patients with a temporal/hippocampal atrophy and validated operation outcome, dipoles of epileptiform activity were located within the atrophic lobe. Therefore, it is concluded that magnetic source analysis provides 3D information concerning spatial correlation of lesion and irritative zone in temporal lobe epilepsy. This quantitative spatial relation may be very important for planning invasive recordings and selective surgical procedures. For this purpose the quantification of focal epileptic activity in extent and strength will be investigated additionally to the localization. With the help of focus quantification the relation of localization as well as distribution of trigger (PFA in the irritative zone) and amplifier for seizure generation in the epileptogenic zone can be analysed.