Phase I trial: Safety and feasibility of intracranial electroencephalography using hybrid subdural electrodes containing macro- and microelectrode arrays

Object. Cerebral cortex electrophysiology is poorly sampled using standard, low spatial resolution clinical intracranial electrodes. Adding microelectrode arrays to the standard clinical macroelectrode arrays increases the spatial resolution and may ultimately improve the clinical utility of intracranial electroencephalography (iEEG). However, the safety of hybrid electrode systems containing standard clinical macroelectrode and microelectrode arrays is not yet known. The authors report on their preliminary experience in 24 patients who underwent implantation of hybrid electrodes. Methods. In this study, 24 consecutive patients underwent long-term iEEG monitoring with implanted hybrid depth and subdural grid and strip electrodes; both clinical macroelectrodes and research microelectrodes were used. The patients included 18 women and 6 men with an average age of 35 ± 12 years (range 21-65). The mean hospital stay was 11 ± 4 days (range 5-20), with mean duration of implantation 7.0 ± 3.2 days (range 3-15). Data from the 198 consecutive craniotomies for standard clinical subdural grid insertion (prior to surgery in the 24 patients described here) were used for comparison to investigate the relative risk of complications. Results. Focal seizure identification and subsequent resection was performed in 20 patients. One patient underwent a subsequent operation after neurological deterioration secondary to cerebral swelling and a 5-mm subdural hematoma. There were no infections. The overall complication rate was 4.2% (only 1 patient had a complication), which did not significantly differ from the complication rate previously reported by the authors of 6.6% when standard subdural and depth intracranial electrodes were used. There were no deaths or permanent neurological deficits related to electrode implantation. Conclusions. The authors demonstrate the use of hybrid subdural strip and grid electrodes containing high-density microwire arrays and standard clinical macroelectrodes. Hybrid electrodes provide high spatial resolution electrophysiology of the neocortex that is impossible with standard clinical iEEG. In this initial study in 24 patients, the complication rate is acceptable, and there does not appear to be increased risk associated with the use of hybrid electrodes compared with standard subdural and depth iEEG electrodes. More research is required to show whether hybrid electrode recordings will improve localization of epileptic foci and tracking the generation of neocortical seizures.