Abstract

Background: Stereoelectroencephalography (SEEG) is a common diagnostic surgical procedure for patients with medically refractory epilepsy. We aimed to describe our initial experience with the recently released NeuroOne Evo SEEG electrode product (Zimmer Biomet, Warsaw, IN) and review technical specifications for other currently approved depth SEEG electrodes.

Methods: We performed a record review on the first five patients implanted with NeuroOne Evo SEEG electrode product using the robotic stereotactic assistance robot platform and described our surgical technique in detail. We recorded technical specifications of all currently Food and Drug Administration-approved SEEG electrodes for comparison.

Results: Our initial 5 surgical patients were reviewed. The average total time of operation was 92 min, with an average of 16.8 electrodes. The estimated time per electrode insertion was

Conclusion: NeuroOne SEEG electrodes can be implanted with efficiency and provide a valuable additional tool for the epilepsy surgeon. A tapered drill bit prevents the bolt from being placed beyond the inner cortex and may reduce the risk of brain contusion or inadvertent advancement of anchor bolts, and the electrode internal stylet also affords the potential to reduce the number of trajectory passes.

MeSH Terms: Epilepsy, EEG, Drug-resistant Epilepsy, Intracranial EEG

Keywords: AdTech, DiXi, NeuroOne, Positron emission tomography (PMT), Stereoelectroencephalography

INTRODUCTION

Stereoelectroencephalography (SEEG) is a widely utilized technique in invasive monitoring for medically refractory epilepsy when less invasive techniques are unable to distinguish potential epileptogenic areas effectively. In this procedure, multiple electrodes are surgically implanted into the brain using one of several targeting methods. Stereotactic head frames and surgical robots are common tools used for insertion. Robotic insertion has been shown to lower average operative time and perhaps improve accuracy.[ 3 , 5 , 6 , 9 , 11 ] The procedure is generally considered to have a low complication rate, with hemorrhage being the most common adverse event at 1–3%.[ 1 , 2 , 6 , 10 ] Electrode design and placement techniques have been relatively unchanged to date, and most electrode manufacturers recommend similar steps for the placement of each electrode. These include accessing the cranial vault, placement of a fixed skull bolt, opening of the dura, creation of a tract for the electrode to traverse, and placement of the electrode, which is subsequently fixed to the skull bolt.

Currently, Food and Drug Administration-approved SEEG electrode products include those from AdTech (Oak Creek, WI), PMT (Chanhassen, MN), DiXI (Chaudefontaine, France), and NeuroOne (Zimmer Biomet, Warsaw, IN, USA) companies. NeuroOne is the most recently approved of these, and little has been published about this electrode system to date.[ 4 ]

SEEG is becoming a more and more prevalent method of intracranial monitoring when advanced diagnostics are required to localize a patient’s epilepsy. Due to the minimally invasive nature of SEEG, our center frequently employs this technique in refractory epilepsy that scalp electroencephalography (EEG) is unable to categorize confidently. The NeuroOne electrode design provides for reduced steps during implantation and makes the process of implantation more efficient. The authors report our initial experience and the technical specifications of the NeuroOne electrodes, with the goal of making the reader aware of new devices in epilepsy surgery, which could enhance safety and reduce steps involved in the implantation process.

MATERIALS AND METHODS

We performed a case series review of our first five consecutive patients with Zimmer NeuroOne EVO SEEG electrodes inserted at the University of California, Irvine Douglas, over approximately 6 months in 2023. The clinical, radiographic, and surgical history of each epilepsy patient was reviewed retrospectively through medical record review [ Table 1 ]. No identifiable information was maintained for our report. The total operative time recorded was based on nursing operative documentation. The senior surgeon (Author SV) performed all procedures. Technical specifications of currently approved electrode products are listed in Table 2 . Images of NeuroOne electrode insertion equipment are displayed in Figure 1 . To be selected for SEEG implantation, each patient care plan was agreed upon at a multidisciplinary care conference. SEEG was performed to clarify the localization of epilepsy when focal epilepsy was suspected but not diagnosed with noninvasive methods, when bilateral epileptiform activity was suspected, and in other instances.

Figure 1:

Various equipment components used with NeuroOne stereoelectroencephalography electrodes.

Table 1:

Patient demographics from initial cases with NeuroOne electrode product.

Table 2:

Comparison data from each currently FDA-approved SEEG depth electrode product.

Surgical and medical device photographs were collected without any identifying features or patient identifiers, and, as is standard practice at our institution, each patient has consented before surgery to the possibility of publishing any photographs or videos obtained in connection with their clinical and surgical information in a de-identified fashion. This study was performed in line with the principles of the Declaration of Helsinki. Local Institutional Review Board Approval was granted before study initiation. This case series has been reported in line with the PROCESS guideline.

Surgical procedure

Procedures were performed under general endotracheal anesthesia. After preprocedural time-out and clipping of hair, the head was fixed into place with a Leksell stereotactic frame (Elekta Solutions, Sweden) or Mayfield skull clamp system (Integra Neurosciences, Plainsboro, NJ) and then attached to the robotic stereotactic assistance (ROSA) robot (Zimmer Biomet, Warsaw, IN, USA). Facial registration was performed using the built-in robotic software and laser capabilities, utilizing both preoperative computed tomography (CT) and double-contrast magnetic resonance imaging. This registration process takes between 20 and 40 min. Once the robot is calibrated, the patient is prepped and draped. Electrode trajectories were preplanned and loaded onto the robot.

Figure 2:

Postoperative X-rays on each patient after stereoelectroencephalography placement.

RESULTS

Our initial five cases with NeuroOne EVO electrodes proceeded without any apparent technical issues. It is reasonable to expect an average time of <2 min per electrode insertion with this system. We did not have any intracranial hemorrhage on immediate postoperative CT scans. Monitoring yielded diagnostic information in all patients, and there were no apparent hardware complications. Surgical removal of the electrode and anchor bolt systems after monitoring proceeded without any complications, and incisions (closed with staples) were well healed at 2-week follow-up appointments for each patient.

DISCUSSION

There are several small alterations to surgical techniques utilized in our series that make electrode insertion more efficient. The use of a robot to aid in the efficiency and accuracy of electrode insertion has been documented previously.[ 3 , 5 , 6 , 11 ] Our technique to use the drill-guide attachment on the robot arm as a drill safety stop reduces time with each burr hole and reduces the inadvertent advancement of the drill. The tapered design of the NeuroOne drill bit is uniquely designed to prevent the anchor bolt and the drill from extending into the cranial vault or excessively deep placement of the anchor bolt. This appears to be a useful safety feature during drill use for both experienced surgeons and those in training. In our institutional-specific practice, we utilize the ROSA robot drill attachment as a safety stop for the drill. With the separate attachable safety stop, the surgeon must use a flathead screwdriver to adjust the safety stop on the drill bit; each time, more length of the drill bit needs to be exposed. Using the robot drill-guide attachment, the surgeon can easily move the drill guide several millimeters further along the robotic trajectory each time the drill needs to be advanced, and with less chance of the safety-stop unintentionally moving. A final nuance with the potential to reduce operative time is the absence of a preelectrode pass through the brain with a stylet to create a tract for the electrode to traverse. The NeuroOne electrodes have a built-in stylet that provides significant rigidity to obviate the need for the creation of a tract. Once the dura has been perforated adequately, the risk of errant placement of electrodes is significantly reduced.

Other benefits of a built-in stylet model are the lack of need for a separate stylet, which adds cost to the procedure, and the avoidance of potential deformation or bending of a stylet with repeated use. A disposable stylet can be opened for each case should the surgeon desire to create an additional trajectory pass before inserting the SEEG electrode. As we accumulate experience with NeuroOne electrode insertion, we anticipate that high accuracy of placement will eliminate the need for utilizing this (or multiple) additional stylets and perhaps reduce cost.

Another potential benefit of not using a separate stylet is a reduced rate of intracranial hemorrhage due to a reduced number of trajectory passes. Multiple authors cite a relationship between the number of electrode passes in deep brain stimulation and hemorrhage risk, and one could assume a similar correlation in SEEG.[ 12 ] The overall hemorrhage rate in SEEG has been quoted at 1–3% and is likely escalated with an increasing number of electrodes and frontal lobe location.[ 2 , 10 ] This reduced number of trajectory passes with an internal stylet may, of course, be offset as the total number of electrodes for each procedure increases. The most common type of hemorrhage after SEEG is intraparenchymal, which would not be easily detected intraoperatively.[ 10 ] For the surgeon, electrode diameter is important when planning the site of brain entry and reducing the chance of surface vessel contact. NeuroOne has a relatively thin electrode profile, which may reduce the chance of a vascular collision in either circumstance. McGovern et al. demonstrated that hemorrhage risk in SEEG is related to the total number of electrodes, underlying the importance of establishing a focused monitoring hypothesis when possible.[ 8 ] They demonstrated a 2.2% symptomatic hemorrhage risk after SEEG but a 19.1% radiographic hemorrhage risk for all types of intracranial bleeding.[ 8 ] Worthy of mention is a very recent publication from Lee et al., which showed a larger radial error in trajectory targeting when using an internal-stylet technique as opposed to an external, manually measured stylet pass before inserting the final SEEG electrode with robotic assistance.[ 7 ] In addition to the internal-stylet method, greater trajectory entry angle and greater target depth were also correlated with greater targeting error.[ 7 ] It will be of great interest to see if we find similar results and acceptable accuracy in our future experience with NeuroOne electrodes and their internal stylet feature.

The thin profile of NeuroOne electrodes provides an additional technical specification that might reduce hemorrhage risk. With a diameter of 0.8 mm, NeuroOne has a slim profile [ Table 2 ]. A range between 5 and 16 contacts, each 2 mm in length, allows for sufficient recording coverage. Contact spacing ranges from 1.5 to 3.2 mm for larger electrodes to offer more customized surface contact per brain region. In comparison, DIXI Medical, USA (DIXI) SEEG electrodes (Chaudefontaine, France) have a similar diameter (0.8 mm) and a semi-rigid structure intended to allow the surgeon to choose between utilizing a preelectrode stylet and using the electrode alone to create the trajectory. The stylet is listed as a single-use item. DIXI electrodes exhibit a fixed distance of 1.5 mm between all contacts, and a nonsterile attachment cable is typically used [ Table 2 ]. PMT Medical Corporation, Chanhassen, MN (PMT) offers the surgeon an option of selecting an electrode with or without internal stylet on order, which is unique among the existing companies. In theory, PMT electrodes (without a stylet) may be the least rigid of existing products, which may predispose to trajectory deflection; the exact incidence of this is unknown. AdTech (Oak Creek, WI) SEEG electrodes have a wide range of contact sizes and diameters, some of which are available through special order. Some of the special-order electrodes have a diameter over twice as large as their competitors, leaving a bigger trajectory footprint and a need for careful preoperative planning to avoid vascular structures if these models are used. The ideal number of contacts will be different depending on the area of tissue monitored and the suspected epileptogenic and irritative zones. Connection cables for AdTech are typically advertised as a sterile, single-use product.

With a learning curve for insertion considered, it would be reasonable to infer small cost savings from the shortened duration of anesthesia if the surgeon fully realizes the potential surgical time benefits of the NeuroOne tapered drill and internal stylet.

Although this series is one of the earliest reports of NeuroOne SEEG electrodes, it includes a very limited number of patients. Due to an overall low complication rate with SEEG, a larger number of electrode insertions would be necessary to compare operative times, technical issues, or hardware complications between these and other electrode models. The same statement could be made about the diagnostic capabilities of this electrode versus other available designs. This text is intended to be a review of some technical specifications of this new SEEG product and not a lengthy review of the indications for SEEG. There are many similarities between currently approved electrode models. The lack of a separate stylet for NeuroOne electrode insertion may prompt the concern of electrode deviation; the risk of this event is unknown and would be elicited with a large volume of consecutive cases. Finally, as the variable of cost is influenced by many factors – insurance, availability, and hospital contractual agreements, it may be difficult to generalize trends.

CONCLUSION

Our initial experience with NeuroOnc SEEG products gives us positive expectations for continued use in epilepsy surgery. Their low profile, variability in contact spacing, and semi-rigid internal stylet design suggest that they can be both versatile and efficient for the surgeon in terms of OR time and cost. There are multiple similarities in design between the existing electrode companies, which will make studying some differences challenging, whether this may be hardware complications, successful use in monitoring data, or risk of complications in a procedure with already low complication rates.

Author contributions

NW: Conceptualization, data curation, formal analysis, writing of original draft, review, and editing; AH: Conceptualization, review, and editing; SV: Conceptualization, formal analysis, review and editing, supervision.

Ethical approval

The research/study was approved by the Institutional Review Board at the University of California Irvine, number 3656, dated 10/01/2023.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Video available on:

https://doi.org/10.25259/SNI_277_2024

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

Acknowledgments

We would like to recognize all surgical device company representatives who have worked at UCI in their efforts to provide accurate information and assist with patient care.

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