MEG Versus EEG HR for the Localization of the Epileptogenic Zone as Part of the Pre-surgical Assessment of Epilepsy

MEG Versus EEG HR for the Localization of the Epileptogenic Zone as Part of the Pre-surgical Assessment of Epilepsy

Drug-resistant partial epilepsies are disabling diseases for which surgical treatment may be indicated. The determination of the area to be operated (or 'epileptogenic zone') is based on a bundle of clinical arguments and neuroimaging, having a direct impact on surgical success.

Epileptic patients have electrical abnormalities that can be detected with surface electrophysiological examinations such as surface EEG or MagnetoEncephalography (MEG). The intracerebral source of these abnormalities can be localized in the brain using source modeling techniques from MEG signals or EEG signals if a sufficient number of electrodes is used (> 100, so-called high EEG technique Resolution = EEG HR). EEG HR and MEG are two infrequent state-of-the-art techniques.

The independent contribution of EEG HR and MEG for the localization of the epileptogenic zone has been shown in several studies. However, several modeling studies have shown that MEG and EEG HR have a different detection capacity and spatial resolution depending on the cortical generators studied. Modeling studies suggest that MEG has better localization accuracy than EEG for most cortical sources.

No direct comparison of the locating value of MEG and EEG HR for the localization of the epileptogenic zone has been performed to date in a large-scale clinical study.

In this prospective study, 100 patients with partial epilepsy who are candidates for epilepsy surgery, and for some of them with intracranial EEG recording, will benefit from two advanced electrophysiological examinations including magnetoencephalographic recording (MEG). ) interictal electrophysiological abnormalities and high-resolution EEG recording (128 electrodes) in addition to the usual examinations performed as part of the pre-surgical assessment, prior to cortectomy and / or intracranial EEG recording.

Based on recent work conducted in humans, we postulate:

• that the MEG and the EEG HR make it possible to precisely determine the epileptogenic zone, by using two approaches of definition of the epileptogenic zone (zone operated in the cured patients, zone at the origin of the crises during the intracranial recordings), but that the MEG is a little more precise than the EEG HR for the determination of the epileptogenic zone (we will try to highlight a difference of about 10%)
• that the quantitative study of the complementarity between EEG HR and MEG for modeling sources of epileptic spikes will show an added value in the use of both methods compared to the use of only one of the two methods
• that it is possible to determine the epileptogenic zone by determining the MEG model zone having the highest centrality value (hub) within the intercritical network by studying networks using graph theory.

Inclusion Criteria:

• patients with partial epilepsy for at least 2 years and for whom are decided and planned: either i) a surgical procedure to resect the epileptogenic zone without prior intracranial EEG recording either ii) an intracranial EEG record needed before a possible cortectomy procedure
• Routine scalp EEG revealing known paroxysmal interictal abnormalities (at least 5 points on a 20-minute plot performed less than 2 years before inclusion in the study)
• Patient giving written consent

Exclusion Criteria:

• patient aged over 60 or under 18
• patients with contraindications to brain MRI and MEG
• women of childbearing age for whom a urine pregnancy test performed during the first visit would detect a pregnancy