Source localization determined by magnetoencephalography and electroencephalography in temporal lobe epilepsy: comparison with electrocorticography: technical case report.

OBJECTIVE AND IMPORTANCE: Source modeling by magnetoencephalography (MEG) and electroencephalography (EEG) may be useful techniques for noninvasive localization of epileptogenic zones for surgery in patients with partial seizures.

CLINICAL PRESENTATION: Simultaneous recordings of MEG and EEG, obtained in two patients, were coregistered on each patient's magnetic resonance image for direct comparison of these two methods with intracranial electrocorticography.

TECHNIQUE: The average difference between MEG and EEG for localization of the same interictal spikes was approximately 2 cm in one patient and 3.8 cm in the other patient. One patient experienced a complex partial seizure during testing, which permitted comparison between interictal and ictal source localization by both MEG and EEG. The EEG ictal localization differed from the interictal one, whereas the MEG ictal and interictal localizations were more similar. In this patient, the MEG interictal source seemed to localize close to the ictal source, whereas EEG did not. The patients underwent temporal lobectomy after electrocorticography, and the results were compared with the findings of MEG and EEG. Although the results of both techniques agreed with the findings of electrocorticography, in one patient the MEG localization seemed to be more accurate. Both patients experienced good surgical outcomes.

CONCLUSION: Both MEG and EEG source localization can add useful and complementary information for epilepsy surgery evaluation. MEG seemed to be more accurate than EEG, especially when comparing interictal versus ictal localization. Further study is needed to evaluate the validity of source localization as useful noninvasive techniques to localize the epileptogenic zone.