Abstracts

Rationale: Epilepsy surgery offers a potential cure for children with medically intractable epilepsy. Often the epileptic focus is hard to localize using scalp electroencephalogram (EEG) and the placement of subdural grids and strips is necessary. When the seizure focus is deep, even these subdural electrodes may not be able to accurately localize the seizure onset. The use of depth electrodes can improve identification of the seizure focus especially when it is deep within the cortex. Methods: From January 2006 until May 2008, 30 patients with medically refractory epilepsy underwent grid and strip placement at Children’s Hospital of Pittsburgh. Six patients had stereotactic placement of depth electrodes into the brain parenchyma around a suspected lesion using Brain Lab technology. Two patients had cortical dysplasia, one patient had tuberous sclerosis (TS), two patients had a low grade tumor and one had an area of presumed ischemia. One patient with cortical dysplasia seized only during cortical stimulation and will not be included in this review. Continuous video/EEG recordings were obtained and all patients’ typical seizures were recorded. The EEG’s were reviewed by at least two epileptolgists to determine seizure onset. All patients underwent a cortical resection with follow-up ranging from 6 months to 2 ½ years. Results: Patients had three to five 4 contact depth electrodes placed around their lesion with a 48-64 contact grid placed on the cortical surface over the depth electrodes. Four patients also had subdural strips placed ranging from 6-8 contacts and one patient had an interhemispheric grid placed with 16 contacts recording from each side. Location was temporal (1 patient), frontal (3 patients), and occipital (1 patient). Three patients had a clear seizure onset from one or more of the depth electrodes which preceded spread to the grids or strips. Once the seizures spread to the grids they were diffuse and difficult to localize. One patient had seizure onset from the depth electrodes at the same time as the grid, this patient had TS with the monitored tuber located close to the cortical surface. One patient had seizure onset first from the interhemispheric grid then spreading to the depth electrodes and last spreading to the grid. All patients had follow-up visits and none of them had complications from the depth electrodes. Outcomes were Engel class I for 4 patients (80 %) and Engel class II for 1 patient (20%). Conclusions: This study shows that that depth electrodes placed around a suspected lesion can improve localization of the seizure foci and may improve outcomes. Depth electrodes identified a smaller region of seizure onset than the standard subdural grids in patients with deep lesions enabling a smaller resection. While this study is preliminary with only a few patients, depth electrodes were safe, appeared to better define the seizure focus and may enable a smaller resection while still yielding good results at follow-up.