Implementing intraoperative high-density electrocorticography during epilepsy surgery

Objective: 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. Methods: 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. Results: 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. Significance: 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.