Magnetoencephalography in focal epilepsy

The introduction of whole-head magnetoencephalographic (MEG) systems facili tating simultaneous recording from the entire brain surface has led to a ma jor breakthrough in the MEG evaluation of epilepsy patients. MEG localizati ons estimates of the interictal spike zone showed excellent agreement with invasive electrical recordings and were useful to clarify the spatial relat ionship of the irritative zone and structural lesions. MEG appears to be es pecially useful for study of patients with neocortical epilepsy, and helped to guide the placement of subdural grid electrodes in patients with nonles ional epilepsies. MEG could differentiate between patients with mesial and lateral temporal seizure onset. Spike propagation in the temporal lobe and the spatio-temporal organization of the interictal spike complex could be s tudied noninvasively. MEG was useful to delineate essential brain regions b efore surgical procedures adjacent to the central fissure. MEG appears to b e more sensitive than scalp EEG for detection of epileptic discharges arisi ng from the lateral neocortex, whereas only highly synchronized discharges arising from mesial temporal structures could be recorded. A major limitati on of MEG has been the recording of seizures because long-term recordings c annot be performed on a routine basis with the available technology. Becaus e MEG and EEG yield both complementary and confirmatory information, combin ed MEG-EEG recordings in conjunction with advanced source modeling techniqu es should improve the noninvasive evaluation of epilepsy patients and furth er reduce the need for invasive procedures.