Epileptogenic zone localization using magnetoencephalography predicts seizure freedom in epilepsy surgery.
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 (χ(2) = 26.4, p < 0.001). MEG reliability was comparable in patients with or without localized scalp electroencephalography (EEG), and overall, localizing MEG findings predicted seizure freedom with an odds ratio of 5.11 (95% confidence interval [CI] 2.23-11.8).


CONCLUSIONS
MEG is a valuable tool for noninvasive interictal spike mapping in epilepsy surgery, including patients with nonlocalized findings receiving long-term EEG monitoring, and localization of the epileptogenic zone using MEG is associated with improved seizure outcomes.
UCSF Comprehensive Epilepsy Center, University of California, San Francisco, San Francisco, California, U.S.A.|Department of Neurological Surgery, University of California, San Francisco, San Francisco, California, U.S.A.|Biomagnetic Imaging Lab, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, U.S.A.
Dario J
DJ
Englot
UCSF Comprehensive Epilepsy Center, University of California, San Francisco, San Francisco, California, U.S.A.|Biomagnetic Imaging Lab, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, U.S.A.
Srikantan S
SS
Nagarajan
UCSF Comprehensive Epilepsy Center, University of California, San Francisco, San Francisco, California, U.S.A.|Department of Neurological Surgery, University of California, San Francisco, San Francisco, California, U.S.A.
Brandon S
BS
Imber
UCSF Comprehensive Epilepsy Center, University of California, San Francisco, San Francisco, California, U.S.A.|Department of Neurological Surgery, University of California, San Francisco, San Francisco, California, U.S.A.
Kunal P
KP
Raygor
Biomagnetic Imaging Lab, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, U.S.A.
Susanne M
SM
Honma
Biomagnetic Imaging Lab, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, U.S.A.
Danielle
D
Mizuiri
UCSF Comprehensive Epilepsy Center, University of California, San Francisco, San Francisco, California, U.S.A.|Biomagnetic Imaging Lab, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, U.S.A.
Mary
M
Mantle
UCSF Comprehensive Epilepsy Center, University of California, San Francisco, San Francisco, California, U.S.A.|Biomagnetic Imaging Lab, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, U.S.A.|Department of Neurology, University of California, San Francisco, San Francisco, California, U.S.A.
Robert C
RC
Knowlton
UCSF Comprehensive Epilepsy Center, University of California, San Francisco, San Francisco, California, U.S.A.|Biomagnetic Imaging Lab, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, U.S.A.|Department of Neurology, University of California, San Francisco, San Francisco, California, U.S.A.
Heidi E
HE
Kirsch
UCSF Comprehensive Epilepsy Center, University of California, San Francisco, San Francisco, California, U.S.A.|Department of Neurological Surgery, University of California, San Francisco, San Francisco, California, U.S.A.|Biomagnetic Imaging Lab, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, U.S.A.
Edward F
EF
Chang
D000328:Adult; D058256:Brain Waves / Q000502:physiology*; D016009:Chi-Square Distribution; D015331:Cohort Studies; D004569:Electroencephalography; D004827:Epilepsy / Q000601:surgery; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012640:Seizures / Q000175:diagnosis* / Q000473:pathology*; D016896:Treatment Outcome
Epilepsy surgery; Epileptogenic zone; Interictal spike; Magnetic source imaging; Magnetoencephalography