The use of simultaneous SEEG and MEG in localising seizure onset zone

ObjectivesBoth Magnetoencephalography (MEG) and stereo-electroencephalography (SEEG) are used in presurgical epilepsy assessment, with contrasting advantages and limitations. It is not known whether combined recording using both modalities can maintain inherent advantages whilst overcoming these limitations e.g. recording from deep brain sources whilst preserving good spatial resolution.Methods24 adult and paediatric patients who underwent SEEG study for pre-surgical evaluation of focal drug-resistant epilepsy, were recorded using simultaneous SEEG-MEG, of which 14 had abnormal interictal activity during recording. The 14 patients were divided into two groups; those with presumed superficial (n=7) and deep (n=7) brain interictal activity.ResultsThere was no significant difference between SEEG and MEG in identifying superficial spikes (p=0.135) and SEEG was significantly better at detecting deep spikes (p=0.002). Mean distance across patients between SEEG channel with highest average spike amplitude and MEG dipole was 26.6+/-3.6 mm for superficial sources, and 21.5 +/- 2.04 mm for deep sources, even though for some of the latter (n=4) no MEG spikes were detected and MEG dipole was fitted to a SEEG interictal activity triggered average. Removal of MEG dipole was associated with 1 year seizure freedom in 5/6 patients with superficial source, and 4/6 patients with deep source.ConclusionsAlthough SEEG has greater sensitivity in identifying interictal activity from deeper sources, an MEG source can be localised using SEEG information, thereby providing useful whole brain context to SEEG and potential role in epilepsy surgery planning.