Interictal epileptiform discharges propagation revealed by MEG/foramen ovale-EEG co-recording in patients with temporal lobe epilepsy candidate to neurosurgery.

OBJECTIVE

The spatio-temporal propagation of the Interictal Epileptiform Discharges (IEDs) can reveal mesial temporal lobe (mTL) involvement in focal temporal seizures. We investigated whether simultaneous recording with magnetoencephalography (MEG), electroencephalography (EEG), and Foramen Ovale Electrodes (FOE) recording improve the definition of the Epileptogenic Zone (EZ) in temporal lobe epilepsies with uncertain lateralization.

METHODS

Sixteen patients with drug-resistant epilepsy, suspected mTL involvement, and inconclusive lateralizing signs underwent simultaneous MEG, EEG, and FOE recordings. IEDs were localized using sub-averaging and hierarchical clustering of source maps to identify consistent spatiotemporal propagation patterns. Based on MEG data, patients were classified as having "good" (unilateral, localized EZ) or "poor" surgical candidacy. These classifications were compared to FOE-EEG assessments. MEG accuracy was then evaluated in relation to surgical outcomes (Engel class > I = poor outcome).

RESULTS

All patients showed mTL involvement. In seven patients, MEG revealed primary mTL activation; in nine, mTL involvement was secondary. The agreement between MEG-based and FOE-based surgical eligibility in the patients with good or poor sbad surgical eligibility and in the entire sample was 87.5%, 75.0% and 81.3%, respectively. The accuracy of MEG-based analysis in identifying suitable candidates for the surgery was 85.7%.

SIGNIFICANCE: Simultaneous MEG/EEG/FOE recordings enhance characterization of IED propagation, offering complementary insight into mTL involvement. This multimodal approach improves localization of the EZ and helps predict surgical outcomes in drug-resistant mTLE, particularly in cases with ambiguous lateralization.