Abstracts

Rationale: 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 macroelectrodes and microelectrode arrays is not yet defined. Here we report our preliminary experience from 24 patients who had implantation of hybrid electrodes. Methods: In this Mayo Clinic IRB approved study twenty-four consecutive patients undergoing chronic iEEG monitoring had hybrid depth and subdural grid and strip electrodes, containing both clinical macro and research micro-electrodes, implanted after informed consent. Data from 198 consecutive craniotomies for standard clinical subdural grid insertion (prior to the 24 patients studied) were used for comparison to investigate the relative risk of complications. Results: For the 24 consecutive patients implanted with hybrid electrodes the average age of patients implanted was 35 ± 12 years of age (range 21-65). There were 18 females and 6 males total. Hospitalization duration was 11 ± 4 days (range 5 to 20), with duration of implantation 7.0 ± 3.2 (range 3 to 15 days). Focal seizure identification with subsequent resection occurred in 91% of patients. One patient was re-operated for neurologic deterioration secondary to cerebral swelling and a 5 mm subdural hematoma. There were no infections. Overall complication rate was 4.2% (1 of 24 cases with a complication), which did not significantly differ from our previously reported complication rate with standard subdural and depth intracranial electrodes of 6.6%. There were no permanent deficits or deaths related to implantation. Conclusions: We demonstrate the use of hybrid subdural strip and grid electrodes containing high-density microwire arrays and standard clinical macroelectrodes. The hybrid electrodes provide high spatial resolution electrophysiology of neocortex that is not possible with standard clinical iEEG. In our initial 24 patients, the complication rate is acceptable and it appears there is no increased risk associated with hybrid electrodes compared to standard subdural and depth iEEG. More research is required to show whether hybrid electrode recordings will improve localization of epileptic brain and tracking the generation of neocortical seizures.