Simultaneous subdural grid and depth electrodes in patients with refractory complex partial seizures

Simultaneous implantation of intracerebral depth electrodes and subdural electrode grids is an extension of available techniques for invasive monitoring and seizure localization in epilepsy surgery candidates. This combined approach is described in 10 selected patients with refractory complex partial epilepsy, in whom previous intensive video/EEG monitoring with scalp or depth electrodes had indicated a lateralized seizure onset. All patients required subdural grids for further localization, functional mapping, or both. Ipsilateral depth electrodes were placed in mesial temporal or other regions through the same craniotomy. Four patients had seizures originating in the mesial temporal lobe, and the onsets were first seen in the temporal lobe depth electrodes. The other six patients had seizures beginning in lateral cortical structures, and the onsets were first seen in the subdural grid (overlying known structural lesions in four patients). The information from both electrode sources guided the surgical resections. All patients were improved after surgery; six are seizure-free with at least 12 months of followup. This preliminary experience indicates that simultaneous placement of depth and subdural grid electrodes is useful in localizing the site of seizure onset and in guiding surgical resections.