Interictal electromagnetic source imaging in focal epilepsy: practices, results and recommendations

Electromagnetic source imaging of interictal epileptiform activity with electroencephalography or magnetoencephalography seems a logical first step in locating the epileptogenic zone in partial epilepsy. However, a lack of standardization contributes to an undeserved low-key 'image' of electromagnetic source imaging. After a clinical and technical review, we propose a practical guide how to apply electromagnetic source imaging.

We found 25 clinical studies of electromagnetic source imaging in targeting epilepsy surgery in the recent literature, mostly using magnetoencephalography. Feasibility of electromagnetic source imaging is around 75%. Whether magnetoencephalography is superior to electroencephalography is still unresolved, because fair comparisons are lacking. Clinical studies have not yet adopted all technical possibilities. Localization accuracy seems high, but studies lack uniformity regarding methods, goals and outcome parameters. Therefore, the final place of electromagnetic source imaging in the presurgical work-up is still to be determined. The diagnostic potential is probably highest in extratemporal epilepsies, and lowest in mesial temporal lobe epilepsy.

Electromagnetic source imaging has evolved technically and can provide valuable localization information in the presurgical evaluation of patients with epilepsy. Standardization of the technique is required, before further clinical studies can better establish its role in presurgical evaluation of focal epilepsy. A relatively easy, stepwise data acquisition and analysis protocol are proposed.