Advanced MEG Source Analysis for Epileptogenic Focus Localization in Patients with Non-Lesional MRI

Accurate determination of the epileptogenic focus can be challenging, especially when electroencephalography (EEG) and/or imaging studies (e.g. MRI) are inconclusive. A significant number of patients who undergo presurgical MEG testing have neocortical epilepsy with normal (non-lesional) MRI. The methodology we developed first identifies potential current sources in the brain that could account for the spontaneous MEG signals that are recorded in the sensor space, and subsequently measures directional information flow in the space of the identified current dipole sources. Applying this methodology to the interictal MEG recordings from two patients with neocortical epilepsy and non-lesional MRIs, who were seizure-free at least 6 months after surgery and resection of their epileptogenic focus, we were able to correctly localize the focus irrespectively of the presence or absence of interictal epileptic spikes in the data. It is anticipated that the promise of the proposed methodology to noninvasively identify the location of obscure neocortical epileptogenic foci, a yet unfulfilled goal for many patients with focal epilepsy and normal MRIs, could lead to a paradigm shift in the diagnosis and treatment of epilepsy by decreasing the need for prolonged hospitalization, improving selection of surgical candidates, and guiding the placement of intracranial electrodes when needed.