Abstracts

Rationale: The evaluation of the resective epilepsy surgery candidates with medically refractory partial seizures, who undergo several localization tests to determine the epileptogenic region. We wanted to establish the relative predictive value of MEG (Magnetoencephalography) as compared to other standard tests to predict the epileptogenic region as defined by invasive electrode recording (invER) including ECoG. MEG that directly measures neuronal activity has theoretical advantages over the FDG-PET, SPECT, and functional MRI. MEG is an expensive tool and the added yield of this procedure needs to be validated. As interictal MEG is a marker of the irritative zone our hypothesis was that it would predict the irritative zone as defined by invER.Methods: Patients with poorly localized medically refractory partial seizures still considered to be surgical candidates underwent an MEG evaluation utilizing a large array biomagnetometer. We included in our cohort only patients that had invasive electrode implantation. Single equivalent dipole solutions with a goodness of fit>0.98 were superimposed on the patient’s own MR images. All patients underwent a standard pre-surgical work up that included MRI of Brain, FDG-PET Brain scan, an inpatient routine scalp (sEEG) and video-EEG monitoring. We devised a concordance scale with invasive electrode testing as follows. A score of 5 was given if MEG localizations correlated with ictal invasive electrode findings, score 4 was given if interictal MEG co-localized to interictal invasive electrode findings in the same lobe, score 3 corresponded to lateralized localizations, score 0 represented absent dipoles, and -3 was given for discordant contralateral localizations.Results: MEG, brain MRI, scalp EEG, and FDG-PET brain scan were obtained in 145 patients, 62 of them subsequently underwent resective Epilepsy Surgery between 2001-2005 at the UCLA and CSMC Seizure Disorder Centers. The patient’s demographic data distribution was: age from 2 to 65 year old; gender - 80 female; epilepsy duration was from 2 to 55 years, mean 15.53 years. Only 65 patients underwent invER. The correlation of MEG and standard tests to invER testing was assessed using T tests. Mean score of diagnostic modalities as compared to invER was as follows: MEG/invER – mean (m) 4.241935484, variance (v) 2.57985193; PET/invER – mean 2.813559322, (v) 6.602571596; sEEG/invER - (m) 3.448275862, (v) 5.83061101; intraoperative ECoG/invER - (m) 4.595744681, (v) 1.637372803; MRI/invER – (m) 3.103448276, (v) 5.427707199. Statistical analysis demonstrated that MEG as compared to invER testing in our patient group had the highest concordance rate as compared to all other tests performed during the pre-surgical evaluation. Conclusions: Interictal MEG has one of the highest concordance score in comparison to invasive electrode testing. Noninvasive MEG may not be inferior to the intracranial ictal and intraoperative ECoG recording. Interictal MEG studies could possibly be used as reliable guide for resective Epilepsy surgery in the patients with medically intractable seizures.