Hybrid Approach for Intracranial Electrographic Seizure Localization with Combined Subdural and Depth Electrodes in Adults

Introduction: Intracranial electroencephalography guide surgical approaches for medically refractory epilepsy patients. Compared to surface subdural electrodes, stereotactically implanted electrodes for stereoelectroencephalography (SEEG) has gained significant popularity over the past decade. In addition to SEEG, we have been using a hybrid subdural and depth electrodes approach at our institution. We believe this hybrid approach combines the advantages of both methods and remains useful in certain types of epilepsy cases, such as lateral and dorsal cortical seizures. We aim to evaluate the risk factors, complications, and outcome of this hybrid subdural and depth electrode technique in adult population.

Methods: The authors performed a retrospective review of consecutive adult intracranial electrode monitoring at our institution from 2006 to 2020. All patients underwent combined subdural and depth electrodes implantation.

Results: We identified 96 adult patients with a mean age of 36 years ( 11). After an average 13.5 days of monitoring, seizure focus was detected in almost 94% of patients. In 29% of patients, seizure focus was only detected by subdural electrodes. On the other hand, seizure focus was detected only by depth electrodes in 15% of patients. Seventy-three patients (76%) underwent seizure-focused resection at time of electrode explanation. Out of 73 patients, 87% achieved Engel class I & II outcome with an average follow-up of 4.2 years. The two most common complications were intracranial hemorrhage (9.4%) and CSF leak (8.3%). Patient age, electrode contact number, diabetes, BMI>30, hypertension, smoking status, diabetes, and history of stroke were not associated with increased risks of complications.

Conclusion : In adults with medically intractable epilepsy, this combined intracranial electroencephalography approach using both subdural and depth electrodes remains a safe and effective procedure in detecting seizure focus to guide epilepsy surgery in selected patients.