Magnetoencephalographic Characteristics of Interictal Spikes in TLE

Purpose: To characterize the localization of interictal spikes by magnetoencephalography (MEG) in patients with mesial temporal lobe epilepsy (TLE). Methods: We studied 5 patients with mesial TLE who had convergent localization information based on presurgical evaluation and became seizure free after anterior temporal lobectomy (ATL). Simultaneous MEG and scalp EEG were recorded before and 6-12 months after surgery using a whole-scalp neuromagnetometer. We visually searched interictal spikes simultaneously occurring on both MEG and EEG channels and analyzed the spikes by MEG dipole modeling. Results: Spikes were localized in anterior temporal region, although most spikes were not exactly located in mesial temporal structure. The dipole orientation was horizontal for 86% (83-94%) of interictal spikes in 4 patients and vertical for 86% of interictal spikes in 1 patient. According to the postoperative MR images with superimposed spike coordinates, 91% (68-100%) of preoperative spike dipoles were situated within the resection demarcation of ATL. Conclusions: In patients with mesial TLE, most interictal spikes were localized in anterior temporal lobe within the resection demarcation of ATL. The dipole orientation can be either horizontal or vertical.