To assess the outcome of stereoEEG following unsuccessful grid/strip implant.

Invasive EEG utilizes two distinct strategies to determine seizure onset zone. The grids/strips approach utilizes large cortical surface electrode arrays. The stereoEEG (SEEG) or all-depth approach employs multiple depth electrodes to cover the cortical surface and reach deeper brain regions. The merits of using stereoEEG approach following a failed grids/strips approach are not currently well defined. The present study evaluates the success of seizure onset localization in six patients, each of whom initially underwent monitoring with subdural strips/grids with later SEEG monitoring.

This is a retrospective chart review of six pre-surgical patients. Imaging studies, 3-dimensional implantation graphics, and scalp electrode recording results are described to facilitate understanding of the areas suspicious for seizure focus when relevant to the patient’s outcome.

Of six patients implanted with grids/strips, three underwent bilateral lead placement and three had unilateral leads. Of these six patients, localization was unsuccessful in five who therefore did not undergo surgical treatment. One patient was localized and underwent surgery without change in seizure frequency. On subsequent sEEG, unilateral leads were used in one patient, with bilateral leads in the remainder. Four patients with unsuccessful strip/grid localization had success with SEEG. Three of these patients were not candidates for surgical resection and thus an RNS was placed. One had decreased seizure frequency following RNS placement, one no longer experienced debilitating seizures, and one has only rarely had seizures. The fourth patient for whom localization was successful was a candidate for surgery but refused intervention and had no reduction in seizure frequency. 

Inadequate localization was main rationale for performing SEEG following grids/strips implant. In most instances, successful localization with SEEG was possible although surgical resection was not pursued. Treatment with RNS resulted in decrease in seizure frequency in two of four patients.