Feasibility, Safety, and Performance of Full-Scalp Subdural EEG - A Report on Minimally Invasive Electrode Implantation

Background and Purpose

Since Berger first recorded human scalp electrical signals and discovered the alpha rhythm in 1929, the recording capabilities of electroencephalography (EEG) have significantly improved in terms of spatial coverage (increased number of electrodes), temporal length (days), and digitization. Traditional scalp EEG is the standard method for diagnosing transient neurological disorders, such as epilepsy or sleep disorders. However, current clinical practice is limited to short-term (days) traditional EEG recordings, which cannot capture brain (functional) changes over longer time scales (months). To optimize the management of chronic brain diseases (such as epilepsy), there is an urgent need to find a way to monitor brain electrical activity during daily life.

This study aimed to develop a device capable of full-scalp subdural EEG (Epios) recording and to validate the feasibility of safely inserting electrode wires through a minimally invasive technique (primary outcome). As a secondary outcome, the study validated that subdural EEG is not inferior to traditional scalp EEG in measuring physiological brain oscillations and pathological discharges.

Authors and Publication Information

This research was conducted by Dr. Ellen van Maren, Dr. Sigurd L. Alnes, Dr. Janir Ramos Da Cruz, and other doctors and medical doctors, involving institutions such as the University Hospital of Bern and Inselspital in Switzerland, the Wyss Center for Bio and Neuroengineering in Geneva, and other universities and research centers. The paper was published in the journal Neurology®, issue number Neurology® 2024;102:e209428, on June 2024.

Research Process

Participants and Methods

The study participants were 8 individuals undergoing intracranial EEG for drug-resistant epilepsy treatment, during which subdural electrodes were inserted between the scalp and skull using a custom tool in the same surgery. Postoperatively, safety was monitored for up to 9 days in the hospital ward, and sleep-wake, ictal, and interictal EEG signals were quantitatively compared between subdural and scalp EEG using windowed cone transformation and spectral concordance. The consistency between subdural and scalp EEG was evaluated using Bland-Altman analysis, and the intraclass correlation coefficient (ICC) was calculated.

Practical Steps and Experiments

1. Electrode Implantation and Initial Safety Monitoring: During surgery, up to 28 subdural electrodes were inserted through minimally invasive techniques, via a 1 cm incision, along with standard postoperative safety monitoring.
2. Signal Recording and Comparison: Postoperative EEG signals were compared and analyzed at multiple levels with traditional scalp EEG, including physiological brain oscillations (such as alpha, delta, sigma, and beta waves) and pathological discharges.

Results

Safety

Electrodes inserted through minimally invasive techniques did not cause serious adverse events for up to 9 days. The 5 perioperative adverse events reported by some participants were related to the surgery but were resolved without serious consequences.

Physiological Signal Recording

Subdural electrodes provided maintenance-free continuous EEG recordings and demonstrated non-inferiority in measuring peak alpha power and consistency assessment (ICC > 0.8, no bias).

Pathological Signal Recording

Subdural electrodes performed consistently with scalp electrodes in recording abnormal discharges and epileptic seizure signals, allowing for highly consistent localization and monitoring of brain propagation.

Data Analysis and Device Performance

The intraclass correlation coefficient (ICC) and Bland-Altman analysis confirmed high consistency between subdural and scalp electrodes in measuring brain electrical signals. Postoperative CT co-registered with preoperative MRI for some participants confirmed the expected electrode positions, validating the initial safety of the device and technique.

Discussion

Research Value

This study was the first to demonstrate that a full-scalp subdural EEG system (Epios) can be safely implanted through minimally invasive surgery and provide high-quality electrical signal recordings for up to nine days. Its performance validation showed that this new system is not inferior to traditional scalp EEG in recording physiological and pathological brain electrical signals, with the advantage of full-scalp coverage, making it applicable for chronic brain disease monitoring.

Clinical and Research Application Prospects

Compared to existing intracranial devices, the Epios system can provide broader brain signal coverage, enabling monitoring without prior knowledge of the seizure onset zone. For chronic epilepsy patients, this system is particularly suitable for long-term recording, improving the ability to detect and localize abnormal discharges, guiding drug treatment optimization, and providing more data support for presurgical planning.

Research Highlights

1. Technological Innovation: Introduced a novel design of a trident-shaped electrode that can be implanted subdurally through a small incision, achieving full-scalp coverage.
2. Scientific Research Methods: Adopted rigorous experimental methods and multi-level data analysis to validate the safety and performance of the device.
3. Potential for Clinical Application: Has the potential to change the current monitoring methods for epilepsy and other brain diseases, enabling long-term out-of-hospital monitoring.

Through innovative design and rigorous validation methods, this study has laid a solid foundation for the clinical and research applications of a full-scalp subdural EEG recording system.