Ictal magnetic source imaging as a localizing tool in partial epilepsy

Objective: To determine the feasibility and usefulness of ictal magnetoencephalography (MEG) recordings in the presurgical evaluation of patients with epilepsy. Methods: Twenty patients with frequent or predictable seizures were studied with the intent to capture seizures using a large array single-probe 37-channel or dual-probe 74-channel biomagnetometer. Results: Successful ictal MEG recordings were made in 6 of 20 patients with neocortical epilepsy. In one other patient, a seizure was captured but movement artifact made MEG recordings impossible. As determined by invasive EEG recording and postsurgical outcome, ictal MEG provided localizing information that was superior to interictal MEG in three of the six patients. Localization of ictal onset by MEG was at least equivalent to invasive EEG in five of the six patients, and was superior in two patients as determined by postsurgical outcome. Conclusion: Larger studies are necessary to confirm that ictal MEG recordings in patients with frequent or easily provoked neocortical seizures can contribute localizing information equivalent or superior to invasive EEG recording.