Postoperative multichannel magnetoencephalography in patients with recurrent seizures after epilepsy surgery

Objective - Assessment of usefulness of magnetoencephalography (MEG) as a novel non-invasive technique in the diagnostic evaluation of patients with recurrent seizures after unsuccessful epilepsy surgery. Material and methods - Seventeen patients in whom epilepsy surgery had failed underwent reevaluation by means of MEG in addition to standard presurgical investigations (EEG MRI, SPECT. and neuropsychologic testing). Results - Source analysis of interictal epileptic MEG discharges revealed dipole localizations immediately adjacent to the borders of previous resection in 10 of 17 patients. Standard non-invasive presurgical evaluation suggested epileptogenicity over the general area of previous resection in all patients, but did not provide any detailed spatial localizing data. Invasive EEG recordings confirmed the MEG focus localization in all of 5 patients who were selected for reoperation. Second operation at the site of previous resection achieved complete seizure control in 3 and cessation of tonic-clonic seizures in 1 of these patients. Conclusion - MEG may provide useful information in the diagnostic reevaluation of postoperative epileptic patients in whom skull and dura defects produce a "breach effect" which alters non-invasive and invasive EEG.