Abstracts

Rationale: Magnetoencephalography and Magnetic Source Imaging(MEG/MSI) is the most recent significant advance in the noninvasive localization of seizure foci. Mesial Temporal Lobe Epilepsy(MTLE) is the most common form of intractable epilepsy that requires epilepsy surgery as estimated by the NIH.It was the purpose of this study to determine the yield of MEG/MSI in mesial temporal lobe epilepsy. Methods: This is a retrospective study of intractable mesial temporal lobe epilepsy patients who underwent MEG/MSI for seizure focus localization. The total number of intractable mesial temporal lobe epilepsy patients who underwent a MEG/MSI study was six. Mesial Temporal lobe epilepsy(MTLE) was defined as findings characteristic of MTLE in seizure description, Video-EEG, MRI Brain and PET. A whole head 306 channel MEG system was used with the sensor array equipped with 102 triple-sensor elements evenly distributed over the surface of the patient s head. The helmet array is configured with 306 independently sampled sensors. The recording was done in six 10 minute epochs for a total of 60 minutes. Results: In 3 out 6 patients we identified MEG spikes in the ipsilateral temporal lobe. In these 3 patients the unilateral temporal dipoles, were localized to the same temporal lobe as determined by the other diagnostic modalities - seizure description, Video-EEG monitoring, MRI Brain and PET. In the other 3 patients no MEG spikes were identified despite recording for a total of 60 minutes. So the yield of MEG/MSI in MTLE in our study was 50%. MEG systems with different configurations of magnetometers and gradiometers can potentially have different senstivity in detection of mesial temporal spikes. Conclusions: Magnetoencephalography can detect mesial temporal spikes in about 50% of cases. In these cases it localizes the seizure focus accurately. Larger prospective studies will be needed to better establish the utility of MEG/MSI in MTLE.