Abstracts

Rationale: Magnetoencephalography (MEG) is based on the ability of superconducting quantum interference devices (SQUID) to study magnetic fields in the brain. There are limited studies citing the utility of MEG in the presurgical evaluation of pediatrics patients with refractory epilepsy. We discuss our experience in the use of MEG in our institutions and evaluate its concordance with video and subdural EEG findings. Methods: Between 2004 to 3/ 2009, 26 pediatric patients were referred to the National Institute of Health for MEG study. Ten of these patients underwent surgical resection. All patients had a presurgical workup, including brain MRI, video EEG, MEG and subsequently an intracranial EEG. Neuromagnetic data were recorded using a CTF 275 MEG composed of whole-head array of 275 radial 1st order gradiometer/SQUID. MEG data was analyzed using the equivalent current dipole method.Data were coregistered to MRI.Video EEG, and MEG findings were compared to the intracranial EEG results and surgical outcomes. Results: Ten patients with medically refractory localization related epilepsy underwent presurgical evaluation and subsequent epilepsy surgery (mean age: 12 yrs; range 5-17 yrs). Majority of the patients had >at least 2 seizures per week. Four patients had normal MRI, six had lesions: left MCA infarct, a right occipital cortical dysplasia, a right parietal meninigiomatosis, suprasellar mass (transcallosal partial resection), right frontotemporal atrophy and a left parietal surgical defect. MEG dipole analysis was concordant to the subdural EEG in 80% of the patient. With video EEG, the findings were only concordant in 40% of the patients, however in 50% of the cases, the laterality of the video EEG was concordant with the laterality of the subdural EEG findings. Video EEG, MEG and subdural EEG were concordant in only 3 patients. All patients underwent seizure focus resection. Eight patients had an Engels outcome of I or II and one patient had an Engels outcome of III with a mean follow-up time of 26 months. One patient was post op for 1 week and was not included in the surgical outcome data. In the four patients with normal MRI, the MEG findings agreed with the subdural EEG except for one. The surgical outcome was Engels II except one had a Engels III outcome despite concordant MEG and subdural EEG. Conclusions: Our findings further confirms the utility of MEG in providing a reliable method for seizure localization during presurgical evaluation in children. Majority of the patients with concordant MEG and subdural EEG had good seizure outcome.