Detection of epileptogenic focal cortical dysplasia by depth, not subdural electrodes

Centers that perform presurgical epilepsy evaluations disagree on whether depth or subdural electrodes represent the optimal technique for invasive recording, especially in seizures originating outside the temporal lobe. A 13-year-old girl with a normal magnetic resonance imaging scan had unlocalized partial onset seizures, despite scalp and subdural grid ictal video/EEG recordings. Repeat video/EEG with depth electrodes showed a discrete site of continuous interictal spiking and seizure onset that was located 2-2.5 cm beneath the surface of the sensory cortex. The resected region showed focal cortical dysplasia and the patient had greater than 95% seizure frequency reduction at 3-year follow-up. We conclude that although subdural electrodes have many advantages when recording seizures outside the temporal lobes, depth electrodes may provide superior recordings when the epileptogenic region is beneath the cortical surface.