Epileptogenic zone localization using magnetoencephalography predicts seizure freedom in epilepsy surgery

• Published in: Epilepsia (Copenhagen) 2015-06, Vol.56 (6), p.949-958
• Main Authors: Englot, Dario J., Nagarajan, Srikantan S., Imber, Brandon S., Raygor, Kunal P., Honma, Susanne M., Mizuiri, Danielle, Mantle, Mary, Knowlton, Robert C., Kirsch, Heidi E., Chang, Edward F.
• Format: Article
• Language: English
• Subjects: Adult; Brain Waves - physiology; Chi-Square Distribution; Cohort Studies; Confidence intervals; Electroencephalography; Epilepsy; Epilepsy - surgery; Epileptogenic zone; Female; Humans; Interictal spike; Magnetic Resonance Imaging; Magnetic source imaging; Magnetoencephalography; Male; Predictive Value of Tests; Reproducibility of Results; Seizures - diagnosis; Seizures - pathology; Surgery; Treatment Outcome
• ISSN: 0013-9580; 1528-1167
• DOI: 10.1111/epi.13002

Summary Objective The efficacy of epilepsy surgery depends critically upon successful localization of the epileptogenic zone. Magnetoencephalography (MEG) enables noninvasive detection of interictal spike activity in epilepsy, which can then be localized in three dimensions using magnetic source imaging (MSI) techniques. However, the clinical value of MEG in the presurgical epilepsy evaluation is not fully understood, as studies to date are limited by either a lack of long‐term seizure outcomes or small sample size. Methods We performed a retrospective cohort study of patients with focal epilepsy who received MEG for interictal spike mapping followed by surgical resection at our institution. Results We studied 132 surgical patients, with mean postoperative follow‐up of 3.6 years (minimum 1 year). Dipole source modeling was successful in 103 patients (78%), whereas no interictal spikes were seen in others. Among patients with successful dipole modeling, MEG findings were concordant with and specific to the following: (1) the region of resection in 66% of patients, (2) invasive electrocorticography (ECoG) findings in 67% of individuals, and (3) the magnetic resonance imaging (MRI) abnormality in 74% of cases. MEG showed discordant lateralization in ~5% of cases. After surgery, 70% of all patients achieved seizure freedom (Engel class I outcome). Whereas 85% of patients with concordant and specific MEG findings became seizure‐free, this outcome was achieved by only 37% of individuals with MEG findings that were nonspecific to or discordant with the region of resection (χ2 = 26.4, p