Abstracts

Rationale: Temporal lobectomy (TL) is the most commonly performed procedure for the treatment of patients with medically refractory epilepsy. After surgery, 60 to 70% of patients are free of seizures. However, seizures recur in some of patients who obtained seizure freedom after TL. The aim of this study is to reveal the epileptic source localization in patients with recurrence of seizures after TL with dense-array Electroencephalography (dEEG). Methods: Four patients, aged 9 to 41 years, were included in this study. Seizures recurred in 1-2 years after TL. All patients had complex partial seizures and underwent anterior temporal lobectomy. 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). The dEEG recordings were performed only after the seizure recurrence. Results: Epileptic source detection was performed with inter-ictal spikes using dEEG. The dEEG demonstrated epileptic sources clearly on MRIs. Epileptic sources were estimated in orbitofrontal cortex, temporal pole in the temporal lobe, or residual temporal cortex posterior to the resected area. Conclusions: The 256-channel dEEG provides important information regarding the existence of epileptic sources in patients with recurrence of seizures. These results indicate an importance of accurate identification of the epileptic source before TL. Funding: None