The concordance rate between the anatomical location of interictal magnetoencephalography (MEG) spike foci with the location of ictal onset zones identified by invasive ictal intracranial electroencephalographic (EEG) recordings was determined in 11 children evaluated for epilepsy surgery at the Hospital for Sick Children and University of Toronto, Ontario, Canada. In 10 of 11 patients, the anatomical location of epileptiform discharges determined by MEG corresponded to the ictal onset zone recorded by subdural electrodes. Functional EEG mapping of the somatosensory hand area was the same as the MEG localization. Seizures were completely or more than 90% controlled after surgery in 9 patients, at a mean follow-up of 24 months. Noninvasive magnetic source imaging by MEG and MRI provides an accurate presurgical localization of epileptic foci in children with refractory nonlesional extratemporal epilepsy and may obviate the need for invasive monitoring. 
COMMENT. MEG detects magnetic fields generated by intraneuronal electrical currents, and MEG spikes correlate precisely with irritative zones adjacent to an epileptogenic lesion. Unlike EEG, MEG is restricted to interictal recordings, but the procedure is noninvasive. This study demonstrates that the accuracy of MEG localization of epileptogenic foci is equal to that of the invasive ictal EEG recordings.