Abstracts

Rationale: Accurate detection of the epileptogenic zone (EZ) is an important factor in obtaining a good surgical outcome in pharmacoresistant patients with focal epilepsy. Recent studies have demonstrated that dense array electroencephalogram (dEEG) source imaging can contribute significantly to the presurgical evaluation for epilepsy because of its high spatial resolution. Therefore, the aim of our study was to confirm the usefulness of dEEG source imaging as a noninvasive tool for epilepsy surgery. Methods: Thirty-two patients with intractable focal epilepsy were recruited for this study. We conducted a dEEG recording with the Geodesic Sensor Net, which consisted of 256-channel electrodes covering the entire head, including the cheek and the neck area, with inter-electrode distances of 20-25 mm. The dEEG was recorded for 30-40 minutes in a resting position with the eyes closed. Subsequently, interictal epileptogenic discharges (IEDs), which were identified and reviewed by an EEG expert, were grouped according to similar patterns of spatial distribution. The classified IEDs were segmented (500ms before and 500ms after the spike peak) and averaged. The source estimated by the averaged IED was superimposed on an individual Magnetic Resonance Image (MRI) using low-resolution electromagnetic tomography (LORETA). Results: In 10 patients with temporal lobe epilepsy (TLE), the spike-sources were accurately visualized in the mesial temporal lobe. In 3 patients with TLE, the sources were localized to the lateral temporal cortex. Spike-sources were easily identified in the cortices of the basal frontal lobe, the mesial temporal lobe and the interhemispheric fissure by dEEG source imaging. Both the lesion and the spike-source were observed simultaneously using this imaging. In 4 TLE patents whose seizures persisted after temporal lobectomy, spike-sources were detected in the cortices of the basal frontal lobe, the lateral temporal lobe, or in the residual hippocampus. Conclusions: 256-Channel dEEG source imaging using an individual MRI can accurately localize EZs. This method has the potential to be a useful noninvasive work-up tool for epilepsy surgery. Funding: No funding.