Implementing intraoperative high-density electrocorticography during epilepsy surgery

In intraoperative electrocorticography (ioECoG)-tailored epilepsy surgery, standard low-density (LD) electrode grids (16-20 electrodes, 10 mm inter-electrode distance) are used, covering ±20 cm² of cortex. High-density (HD) grids have shown advantages in basic research. We wanted to evaluate the clinical use of HD grids during epilepsy surgery. We assessed how often HD-ioECoG might have altered the presurgical hypothesis by recording highly localized epileptic spikes and high-frequency oscillations (HFOs) and by facilitating spike-onset localization.

Patients undergoing HD-ioECoG-tailored epilepsy surgery (64 electrodes, 5 mm inter-electrode distance; 2048 Hz sampling) were selected from our registry (2021-2023). We assessed clinical reports to evaluate the impact on surgical strategy. Intraoperative decision-making was guided mainly by interictal spikes. We visually marked spikes and HFOs (ripples 80-250 Hz and fast ripples [FRs] 250-500 Hz) in 1-min artifact-free epochs. We assessed number of events, and compared channels covering the resected and non-resected tissue and surgical outcome with logistic mixed models. We assessed focal events, which occurred in few channels and could be missed on LD grids. We analyzed spike-onset localization with Granger's causality.

We included 36 HD grid positions from 20 patients. HD-ioECoG would have confirmed the original surgical plans in 11 patients and adapted it in 6. We found 41-5485 spikes, 0-2243 ripples (one patient none), and 0-1008 FR (three patients none) per patient. More FRs occurred in channels covering the resected areas than outside (p < .001), particularly in patients who became seizure-free (p < .001). Of the spikes, ripples, and FRs, 6.1%, 19.5%, and 46.7%, respectively, occurred on one or two channels; 58.3% of the HD spike-onset locations might be localized differently with standard LD grids.

HD-ioECoG can be used clinically for epilepsy surgery guidance. HD-ioECoG captured increased detail when identifying focal epileptic events, especially FRs, and pinpointing spike onsets, which may be missed with LD-ioECoG.