Combining Intraoperative Ultrasound with Depth-Electrode iECoG in Epilepsy Surgery

Overview

This report reviews the integration of intraoperative ultrasound (ioUS) with depth-electrode intraoperative electrocorticography (iECoG) to improve surgical resection precision in drug-resistant epilepsy (DRE) patients with MRI-visible lesions. The combined approach enhances real-time anatomical and electrophysiological mapping, facilitating accurate delineation of epileptogenic zones (EZ) especially in deep or complex lesions.

Background

Approximately 30% of persons with epilepsy suffer from drug-resistant epilepsy, for whom surgical resection of the epileptogenic zone offers the best chance for seizure freedom. Accurate localization and complete resection of the EZ are critical, yet challenging, particularly in MRI-positive cases where lesion boundaries may not perfectly correspond to the EZ. Traditional intraoperative electrocorticography using subdural grids has limitations in deep or sulcal lesions. The combined use of ioUS and depth-electrode iECoG provides real-time anatomical visualization alongside electrophysiological data, potentially improving surgical outcomes.

Data Highlights

A retrospective consecutive series of MRI-positive DRE patients underwent tailored resection guided by combined depth-electrode iECoG and ioUS between 2022 and 2024. Preoperative evaluation included HARNESS protocol MRI, prolonged video-EEG, and [21]F-FDG PET. Advanced neuroimaging post-processing and multidisciplinary planning defined electrode trajectories and resection boundaries. Intraoperatively, ioUS identified lesion echogenic features and guided depth electrode placement for electrophysiological sampling along lesion margins.

Key Findings

• Depth-electrode iECoG combined with ioUS enables precise intraoperative localization of epileptogenic tissue, especially in deep or sulcal lesions.
• Real-time ultrasound delineates lesion boundaries, complementing electrophysiological data to refine resection margins.
• Conventional subdural strip iECoG was less informative in cases with complex lesion morphology or subcortical extension.
• Preoperative planning with advanced imaging and neuronavigation supports tailored electrode trajectories and resection strategies.
• The combined approach is feasible and reproducible in a clinical setting for MRI-positive DRE patients without SEEG investigation.

Clinical Implications

Integrating ioUS with depth-electrode iECoG provides surgeons with enhanced intraoperative guidance, improving the accuracy of epileptogenic zone delineation and potentially reducing postoperative seizure recurrence. This approach is particularly valuable for lesions with unclear anatomical boundaries or deep location, where conventional methods may be insufficient. Adoption of this combined technique may optimize surgical outcomes in selected DRE patients.

Conclusion

The combined use of intraoperative ultrasound and depth-electrode electrocorticography is a feasible and effective strategy to improve anatomical and electrophysiological delineation of epileptogenic zones in epilepsy surgery. This integrated approach holds promise for enhancing surgical precision and patient outcomes in drug-resistant epilepsy.

References

1. Penfield and Jasper 1930s -- Introduction of iECoG
2. Recent reviews 2015-2020 -- Impact of iECoG on seizure outcome
3. Studies 2022-2024 -- Use of ioUS and depth-electrode iECoG in epilepsy surgery