Integration of intraoperative ultrasound and depth-electrode electrocorticography for resection guidance in epilepsy surgery: technical workflow and feasibility.

BACKGROUND

Complete resection of the epileptogenic zone (EZ) is the strongest predictor of seizure freedom in drug-resistant epilepsy (DRE). However, even in MRI-positive cases with anatomo-electro-clinical concordance, the EZ may not be clearly delineated, complicating intraoperative decision-making. Intraoperative ultrasound (ioUS) provides real-time anatomical feedback, while depth-electrode intraoperative electrocorticography (iECoG) enables electrophysiological delineation of epileptogenic tissue beyond the cortical surface, sampling deep regions not accessible to subdural electrodes. Their integration may improve intraoperative precision in defining resection limits and optimizing resective surgery.

METHODS

This study describes the workflow and feasibility of combining ioUS and depth-electrode iECoG for intraoperative guidance in MRI-positive focal DRE with an ill-defined EZ. In all cases, concordant anatomo-electro-clinical data identified a single EZ for which SEEG was not required, yet the suspected EZ remained poorly delineated. ioUS was used for real-time lesion visualization, verification of electrode trajectories, and guidance of resection depth and extent. Pre- and post-resective depth-electrode iECoG and ioUS were used in combination to delineate the resection margins, by identifying interictal epileptiform discharges (IEDs) and confirming lesion boundaries and resection completeness.

RESULTS

Six patients underwent resective surgery using the combined ioUS-iECoG workflow. The technique was feasible and safe in all cases, with no intraoperative or postoperative complications (37 depth-electrode insertions). iECoG revealed IEDs in four patients (66%), prompting resection extension in two. MRI confirmed complete resection in all cases. At last follow-up (6-40 months), 5/6 patients were seizure-free (Engel I). Histopathology revealed FCD IIb in three cases, a gliotic lesion related to an encephalocele in one, a gliotic scar post-arachnoid cyst marsupialization in another, and a tuberous sclerosis-related lesion in a case of tuberous-sclerosis-complex.

CONCLUSION

The integration of ioUS and depth-electrode iECoG offers real-time anatomical and electrophysiological data, refining EZ delineation and resection assessment in complex MRI-positive epilepsy cases where SEEG is not clinically indicated.