Grid electrode technology: electrophysiological tool for cavernous nerve mapping

Introduction

Intraoperative neurophysiological monitoring (IONM) represents an advancing technology for consideration during pelvic surgeries such as radical prostatectomy. This real-time navigational system involves surveying intrapelvic nerves that critically mediate pelvic functions whereby actions are guided intraoperatively that maximally preserve their functional integrity.

Electrode-containing grids may well be used in this system as a tool for electrophysiological testing and relaying intrapelvic nerve signals. By design, such grids contain electrodes that are embedded as an array into some type of flexible base material such as polyurethane or silicone. In use for cortical/epilepsy surgeries, such grids are laid on the surface of the brain and in sulci to determine foci of epileptic discharge, after which the neurosurgeon is guided to ablate these foci precisely (1). For radical prostatectomy, it is postulated that electrode-containing grids would be situated within the pelvis aligned with the periprostatic cavernous nerve network thereby guiding nerve localization and preservation with a similar precision-guided surgical intent.

We propose the application of grid electrode technology for periprostatic cavernous nerve mapping during radical prostatectomy. In this brief report, we describe basic characteristics of grid electrode technology, the procedures we used for designing and testing prototypical electrode-containing grids for this application, and observations from a pilot surgical investigation.

Methods

This project employed an engineering design process (2). Process stages were conceptualization, feasibility assessment, definition of design requirements, preliminary design, prototyping and evaluation (3). Feasibility evaluations of grid prototypes were extended to simulated robotic-assisted radical prostatectomy studies using human male cadavers. Additionally, by way of alpha testing, grids were evaluated for performance and functionality in pilot studies of radical prostatectomy.

The study protocol was approved by the Institutional Review Board of the Johns Hopkins University School of Medicine to proceed with clinical investigation of IONM during radical prostatectomy [IRB No. 00300979, Automated Intraoperative Monitoring to Improve Functional Outcomes following Radical Prostatectomy (Neurovrd)]. A study cohort consisted of men with early stage, localized prostate cancer undergoing open and robot-assisted radical prostatectomy surgeries. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. Consent is waived, in accordance with institutional policy and ethics committee approval.

At this preliminary stage of our research in this field, additional elements of production planning and production were not applicable.

Results

Grid electrode technology

Electrophysiological studies, which are used commonly for evaluating neuromuscular abnormalities, apply various types of electrodes to record electrical signals or muscle responses. Conventional recording utilizes surface electrodes that are commonly disc-shaped and applied to the surface of a tissue or needle electrodes that are inserted into a tissue or muscle (4).

Nerve signaling is assessed based on recordings between electrodes according to a specified testing method, or montage (5,6). A referential montage is one option, whereby an electrode is placed close to the origin of the neurological activity of interest (Channel A, active electrode) and another electrode (or more electrodes) is placed at some location nearby (Channel B, referential electrode). The true voltage amount is determined as a differential measurement of the signals of the active electrode and referential electrodes. A bipolar montage represents an alternative method, in which both electrodes are placed close to the origin of the neurological activity of interest. This method localizes the origin of the neurological activity and, when applied to neural tissue, serves readily as a nerve signal localization technique.

The arrangement of multiple electrodes within a grid offers a technique for localizing nerves according to the nerve signal recording. A conventional configuration for a grid is rectangular consisting of rows and columns of electrodes that are equally spaced (Figure 1). For example, a 2×3 electrode arrangement describes a grid featuring two columns of three electrodes each. The electrodes are customarily 2 mm in diameter with a 4 mm distance from center to center and a 2 mm distance from edge to edge. In accordance with bipolar montage methodology, recordings from paired electrodes within a grid represent discrete channels. When utilizing multiple channels within the dimensions of a grid, a pattern of neurological activity is deciphered based on the assimilation of data from these channels.

Figure 1 Grid prototypes. Graphic depicting rectangular configurations of grids containing electrodes (2×3 and 4×6 arrays) arranged equidistantly in rows and columns.

An additional application of grids for nerve signal localization is that they can be programmed to produce and record a nerve signal all within the functional properties of the grid, obviating remote neurostimulation. This application utilizes paired grid electrodes: one electrode for delivering an electrical current and an adjacent electrode for recording the nerve signal response (7).

Grid design specifications

In developing grid electrode technology for radical prostatectomy, it is important to consider the variable prostate sizes and shapes in addition to the anatomical location of the prostate in the pelvic region. In a retropubic surgical space, a functional grid may be laid over the prostate anterolaterally and a portion of the pelvic floor adjacently, spanning the extent of the periprostatic cavernous nerves. Plausible grid dimensions should meet the proportions of the surgical field. Additionally, desirable physical properties of grids for this application include pliability with a gelatinous texture, so that they readily mold to the shape and contours of the prostate and surrounding structures, and adherence, so that all electrodes of the grids effectively contact the periprostatic nerve tissue.

An inherent design aspect of electrodes within a grid is their electrical connectivity. A wire extending from each electrode is soldered to the conductive (platinum or stainless steel) disc and merged as a lead exiting the grid (Figure 2).

Figure 2 Electrical connectivity of grids. Schematic depicting wires extending from individual electrodes contained in a grid design (right) merged into cables that extend into a nerve stimulator device via an electrical outlet (left).

Prototype testing, engineering and cadaveric studies

We evaluated the feasibility of stock cortical grids that are used for epilepsy surgery as reference sources. These grids are commercially available in various sizes, conventionally designed with platinum electrodes constructed at 4 mm center-to center distance intervals (Figure 1). For our initial evaluation, we customized these at various sizes, appraising how they would fit in the pelvic region overlying the surfaces of the prostate and adjacent pelvic sidewalls. However, these stock cortical grids presented a consistent limitation related to their stiffness. The base material thickness of these grids is 0.75 mm, limiting their formability and adherence for our surgical application. Taking this limitation into account, we next constructed grids at 0.3 mm thickness, conjecturing that they would have improved pliability relative to stock cortical grids. We also designed, produced and tested “butterfly grids”, considering the possible advantage of their configuration for molding over the prostate (Figure 3).

Figure 3 Butterfly grid. Graphic depicting the design of a butterfly configured grid with interstices for molding over characteristically diverse prostates. The blue dots represent locations for individual electrodes.

We performed cadaveric dissection laboratory studies to assess the optimal physical properties of grids with respect to true anatomical conditions and clinical testing requirements and to establish the surgical application technique. In a robot-assisted radical prostatectomy simulation workshop using fresh male cadaveric specimens (sourced through the institutional Minimally Invasive Surgical Training and Innovation Center), grid prototypes were positioned after retropubic exposure overlying the prostate and off-midline of the prostate and extending to the pelvic floor bilaterally. Five surgeons independently completed a post-workshop questionnaire rating the characteristics of these grids and providing specifications of a grid product that they would likely use in actual surgical cases. This assessment established the intraoperative utility of 0.3 mm thick rectangular grids composed of 4×5 electrode arrays with 10 mm interelectrode distances, which handled and positioned well (Figure 4). By recording from electrodes that are situated within a grid at approximate 10 mm separation and applying a bipolar montage methodology, channels are created for localizing neurological activity sufficiently within 1–2 mm of paired electrodes (8).

Figure 4 Pelvic grid product. Graphic depicting a rectangular grid product composed as a 4×5 array of electrodes (black dots) ready for use in pelvic surgery. The inner face of the grid is presented that would contact pelvic tissues.

Pilot clinical studies

We piloted the performance of grids in a real intraoperative setting of patients undergoing open (n=5) and robot-assisted (n=3) radical prostatectomy. Patients received standard preoperative and intraoperative procedures, with the additional temporary placement of needle electrodes at the sacral spinal cord (L4–L5 vertebral level) for intrapelvic neurostimulation, an intraoperative procedure for delivering electrical current delivery that produces cavernous nerve signaling and penile tumescence (9,10). Baseline evaluations of the function of the grid prototypes were done prior to prostate dissection.

Electrophysiological grid recordings were done as part of a proprietary neurophysiological monitoring Sentinel^® platform. The procedures involved neurostimulation using a sacral spinal neurostimulatory protocol (9,10), after which neural signals and neuronally mediated responses in the pelvic region were recorded. Recorded neural signals using the grids were assessed as action potentials using a bipolar montage technique. Grids were placed across the anterolateral aspects of the prostate, such that nerve signals were shown to be feasibly recorded at multiple locations corresponding with the positions of the electrodes (Figures 5,6). They were connected by cables to a recording machine that is assembled within the IONM platform. This machine served to display continuous nerve signal recordings at multiple channels graphically as a series of waveforms (Figure 7).

Figure 5 Grid positioning at the anterior prostate. Graphic depicting the use of a customized 4×5 electrode-containing rectangular grid situated anteriorly over the prostate with retropubic exposure during open radical prostatectomy.

Figure 6 Grid positioning at the lateral prostate. Graphic depicting the use of a customized 3×3 electrode-containing rectangular grid situated laterally toward the prostatic apex with retropubic exposure during robot-assisted radical prostatectomy.

Figure 7 Electrophysiological grid recording. Schematic (left) depicting a six-channel montage with each channel referenced to nerve signal recordings between two adjacent electrodes (bipolar testing method). Graphic (right) depicting continuous recordings of action potentials using an eight-channel montage as a series of waveforms. With a grid placed unilaterally over the anterolateral surface of the prostate in a retropubic exposure, the top channel (#1) corresponds with the midline of the prostate and the bottom channel (#8) corresponds with the lateralmost aspect of the prostate adjacent to the pelvic sidewall. The waveform oscillations with neurostimulation determine locations of nerve signals; for example, a phase reversal in channel #1 having a lower amplitude compared with that of channel #2, whereas a lower amplitude signal but in the same direction in channel #3 compared with channel #2, indicates the existence of a nerve signal between electrodes for channels #1 and #2.

Neurostimulated nerves were localized by the amplitude and latency of action potentials and the polarity of waveforms (Figure 7). Reverse polarity in waveforms in sequence with other waveforms indicated an electrode position opposite from a nerve localization (Figure 7). Notably, action potential amplitude measurements varied side to side in individual subjects and between subjects, attesting to the intersubject variability in cavernous nerve signaling within the cavernous neural network. Dominant nerve signals were determined and correlated with erection responses, and a 12–30% decrement in amplitude per mm distance from the nerve signal of origin was calculated.

Neuronally mediated responses to neurostimulation involved erection monitoring using near infrared spectrophotometry (10). Quantifiable erection responses affirmed the function of sacral spinal neurostimulated cavernous nerve signaling.

Discussion

We present an evaluation of intrapelvic grids for localizing erectogenic cavernous nerves considering their potential application within an IONM platform for cavernous nerve mapping during radical prostatectomy. Our study accessed electrode-containing grid technology and applied it to a methodical engineering design and testing process. Thereafter, we settled on a grid product that is worthy of further evaluation in clinical trials of IONM for radical prostatectomy surgeries.

Our prototypical grid for radical prostatectomy displays several opportune characteristics for use in IONM. By containing multiple electrodes, it spans the periprostatic cavernous neural network, allowing comprehensive neural stimulation. The structure of the grid by design and testing adequately molds over the prostate and is versatile for various prostate sizes and shapes. Its flexibility is also ideal for passage through access ports and instrumentation with robot-assisted surgical procedures.

We acknowledge our preliminary clinical investigation references baseline conditions and does not specify their use during surgical dissection of the prostate. The next clinical trial phase will involve the evaluation of grids throughout surgical stages, which would indicate how they are useful amid tissue perturbations. This next phase may also involve further engineering refinements of the grid, including resolving the optimal quantity and arrangement of electrodes for this purpose.

In conclusion, we present the concept, design, and preliminary application of an intrapelvic grid that may be incorporated into an IONM platform for radical prostatectomy. Our findings support the feasibility of grid technology for both recording and localizing neurostimulated nerve impulses with the pelvis. Ongoing studies are necessary to advance grid technology definitively for this purpose. This demonstration suggests that grid technology in combination with IONM is potentially useful for gynecologic and colorectal pelvic surgeries as well. Alternate grid designs may be customized for products applied in these specialties.

Acknowledgments

None.

Footnote

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0344/prf

Funding: The work was supported by Neurovascular Research & Design.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0344/coif). A.L.B., K.P. and J.H.O. report that this work was supported by Neurovascular Research & Design. A.L.B. serves as a principal investigator for an institutional clinical trial sponsored by Neurovascular Research & Design. He receives Clinical trial sponsorship from Comphya SA and Neurovascular Research & Design and Sexual medicine fellowship support from Boston Scientific. He also serves as a Board of Directors member for the American Urological Association, Executive Officer for the International Society for Sexual Medicine, and Board member for Mentoring Male Teens in the Hood. K.P. is an independent contractor hired by NeuroVascular Research & Design to conduct this research. A.G. reports receiving consulting fees with Leeve, CIVCO, fortec. J.H.O. works for Neurovascular Research and Design, the company that paid for this study. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Institutional Review Board of the Johns Hopkins University School of Medicine (No. 00300979). Consent is waived, in accordance with institutional policy and ethics committee approval.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Bekelis K, Radwan TA, Desai A, et al. Subdural interhemispheric grid electrodes for intracranial epilepsy monitoring: feasibility, safety, and utility: clinical article. J Neurosurg 2012;117:1182-8. [Crossref] [PubMed]
2. Haik Y, Shahin TM, Sivaloganathan S. Engineering Design Process. 2nd ed. Stamford, CT: Cengage Learning; 2011.
3. Ejiko MI. Engineering design process and its common stages. Res Rev J Eng Tech 2023;12:19-20.
4. Stålberg E. Some electrophysiological methods for the study of human muscle. J Biomed Eng 1980;2:290-8. [Crossref] [PubMed]
5. Szelényi A, Kothbauer KF, Deletis V. Transcranial electric stimulation for intraoperative motor evoked potential monitoring: Stimulation parameters and electrode montages. Clin Neurophysiol 2007;118:1586-95. [Crossref] [PubMed]
6. Thatcher KL, Nielsen KE, Sandler EB, et al. Optimizing transcutaneous spinal stimulation: excitability of evoked spinal reflexes is dependent on electrode montage. J Neuroeng Rehabil 2025;22:2. [Crossref] [PubMed]
7. Reppel M, Pillekamp F, Lu ZJ, et al. Microelectrode arrays: a new tool to measure embryonic heart activity. J Electrocardiol 2004;37:104-9. [Crossref] [PubMed]
8. Crespo M, Campillo SR, Casado-Arroyo R, et al. Assessment of the Interelectrode Distance Effect over the Omnipole with High Multielectrode Arrays. Annu Int Conf IEEE Eng Med Biol Soc 2023;2023:1-4. [Crossref] [PubMed]
9. Burnett AL, El-Achkar A, Patel K, et al. PD02-11 Sacral neurostimulated urethral function monitoring: A method to assess the male continence mechanism at pelvic surgery. Journal of Urology 2025;213:e46.
10. Burnett AL, El-Achkar A, Patel K, et al. MP35-04 Sacral neurostimulation with penile near-infrared spectrophotometry: An intraoperative technique for erectile function assessment during pelvic surgery. Journal of Urology 2025;213:e1218.