Juan Anso

A Neuromonitoring Approach to Facial Nerve Preservation During Image-guided Robotic Cochlear Implantation.

Hypothesis: A multielectrode probe in combination with an optimized stimulation protocol could provide sufficient sensitivity and specificity to act as an effective safety mechanism for preservation of the facial nerve in case of an unsafe drill distance during image-guided cochlear implantation. Background: A minimally invasive cochlear implantation is enabled by image-guided and robotic-assisted drilling of an access tunnel to the middle ear cavity. The approach requires the drill to pass at distances below 1 mm from the facial nerve and thus safety mechanisms for protecting this critical structure are required. Neuromonitoring is currently used to determine facial nerve proximity in mastoidectomy but lacks sensitivity and specificity necessaries to effectively distinguish the close distance ranges experienced in the minimally invasive approach, possibly because of current shunting of uninsulated stimulating drilling tools in the drill tunnel and because of nonoptimized stimulation parameters. To this end, we propose an advanced neuromonitoring approach using varying levels of stimulation parameters together with an integrated bipolar and monopolar stimulating probe. Materials and Methods: An in vivo study (sheep model) was conducted in which measurements at specifically planned and navigated lateral distances from the facial nerve were performed to determine if specific sets of stimulation parameters in combination with the proposed neuromonitoring system could reliably detect an imminent collision with the facial nerve. For the accurate positioning of the neuromonitoring probe, a dedicated robotic system for image-guided cochlear implantation was used and drilling accuracy was corrected on postoperative microcomputed tomographic images. Results: From 29 trajectories analyzed in five different subjects, a correlation between stimulus threshold and drill-to-facial nerve distance was found in trajectories colliding with the facial nerve (distance <0.1 mm). The shortest pulse duration that provided the highest linear correlation between stimulation intensity and drill-to-facial nerve distance was 250 &mgr;s. Only at low stimulus intensity values (⩽0.3 mA) and with the bipolar configurations of the probe did the neuromonitoring system enable sufficient lateral specificity (>95%) at distances to the facial nerve below 0.5 mm. However, reduction in stimulus threshold to 0.3 mA or lower resulted in a decrease of facial nerve distance detection range below 0.1 mm (>95% sensitivity). Subsequent histopathology follow-up of three representative cases where the neuromonitoring system could reliably detect a collision with the facial nerve (distance <0.1 mm) revealed either mild or inexistent damage to the nerve fascicles. Conclusion: Our findings suggest that although no general correlation between facial nerve distance and stimulation threshold existed, possibly because of variances in patient-specific anatomy, correlations at very close distances to the facial nerve and high levels of specificity would enable a binary response warning system to be developed using the proposed probe at low stimulation currents.

Feasibility of Using EMG for Early Detection of the Facial Nerve During Robotic Direct Cochlear Access

Hypothesis Facial nerve monitoring can be used synchronous with a high-precision robotic tool as a functional warning to prevent of a collision of the drill bit with the facial nerve during direct cochlear access (DCA). Background Minimally invasive direct cochlear access (DCA) aims to eliminate the need for a mastoidectomy by drilling a small tunnel through the facial recess to the cochlea with the aid of stereotactic tool guidance. Because the procedure is performed in a blind manner, structures such as the facial nerve are at risk. Neuromonitoring is a commonly used tool to help surgeons identify the facial nerve (FN) during routine surgical procedures in the mastoid. Recently, neuromonitoring technology was integrated into a commercially available drill system enabling real-time monitoring of the FN. The objective of this study was to determine if this drilling system could be used to warn of an impending collision with the FN during robot-assisted DCA. Materials and Methods The sheep was chosen as a suitable model for this study because of its similarity to the human ear anatomy. The same surgical workflow applicable to human patients was performed in the animal model. Bone screws, serving as reference fiducials, were placed in the skull near the ear canal. The sheep head was imaged using a computed tomographic scanner and segmentation of FN, mastoid, and other relevant structures as well as planning of drilling trajectories was carried out using a dedicated software tool. During the actual procedure, a surgical drill system was connected to a nerve monitor and guided by a custom built robot system. As the planned trajectories were drilled, stimulation and EMG response signals were recorded. A postoperative analysis was achieved after each surgery to determine the actual drilled positions. Results Using the calibrated pose synchronized with the EMG signals, the precise relationship between distance to FN and EMG with 3 different stimulation intensities could be determined for 11 different tunnels drilled in 3 different subjects. Conclusion From the results, it was determined that the current implementation of the neuromonitoring system lacks sensitivity and repeatability necessary to be used as a warning device in robotic DCA. We hypothesize that this is primarily because of the stimulation pattern achieved using a noninsulated drill as a stimulating probe. Further work is necessary to determine whether specific changes to the design can improve the sensitivity and specificity.

Robotic cochlear implantation: surgical procedure and first clinical experience

Abstract Conclusion: A system for robotic cochlear implantation (rCI) has been developed and a corresponding surgical workflow has been described. The clinical feasibility was demonstrated through the conduction of a safe and effective rCI procedure. Objectives: To define a clinical workflow for rCI and demonstrate its feasibility, safety, and effectiveness within a clinical setting. Method: A clinical workflow for use of a previously described image guided surgical robot system for rCI was developed. Based on pre-operative images, a safe drilling tunnel targeting the round window was planned and drilled by the robotic system. Intra-operatively the drill path was assessed using imaging and sensor-based data to confirm the proximity of the facial nerve. Electrode array insertion was manually achieved under microscope visualization. Electrode array placement, structure preservation, and the accuracy of the drilling and of the safety mechanisms were assessed on post-operative CT images. Results: Robotic drilling was conducted with an accuracy of 0.2 mm and safety mechanisms predicted proximity of the nerves to within 0.1 mm. The approach resulted in a minimal mastoidectomy and minimal incisions. Manual electrode array insertion was successfully performed through the robotically drilled tunnel. The procedure was performed without complications, and all surrounding structures were preserved.

Instrument flight to the inner ear

Image-guided robotic surgery, designed for operating on small structures, is demonstrated for robotic cochlear implantation. Surgical robot systems can work beyond the limits of human perception, dexterity, and scale, making them inherently suitable for use in microsurgical procedures. However, despite extensive research, image-guided robotics applications for microsurgery have seen limited introduction into clinical care to date. Among others, challenges are geometric scale and haptic resolution at which the surgeon cannot sufficiently control a device outside the range of human faculties. Mechanisms are required to ascertain redundant control on process variables that ensure safety of the device, much like instrument flight in avionics. Cochlear implantation surgery is a microsurgical procedure, in which specific tasks are at submillimetric scale and exceed reliable visuo-tactile feedback. Cochlear implantation is subject to intra- and interoperative variations, leading to potentially inconsistent clinical and audiological outcomes for patients. The concept of robotic cochlear implantation aims to increase consistency of surgical outcomes, such as preservation of residual hearing, and to reduce invasiveness of the procedure. We report successful image-guided, robotic cochlear implantation in human. The robotic treatment model encompasses computer-assisted surgery planning, precision stereotactic image guidance, in situ assessment of tissue properties, and multipolar neuromonitoring, all based on in vitro, in vivo, and pilot data. The model is expandable to integrate additional robotic functionalities such as cochlear access and electrode insertion. Our results demonstrate the feasibility and possibilities of using robotic technology for microsurgery on the lateral skull base. It has the potential for benefit in other microsurgical domains for which there is no task-oriented robotic technology available at present.

Electrical Impedance to Assess Facial Nerve Proximity during Robotic Cochlear Implantation

Reported studies pertaining to needle guidance suggest that tissue impedance available from neuromonitoring systems can be used to discriminate nerve tissue proximity. In this pilot study, the existence of a relationship between intraoperative electrical impedance and tissue density, estimated from computer tomography (CT) images, is evaluated in the mastoid bone of in vivo sheep. In five subjects, nine trajectories were drilled using an image-guided surgical robot. Per trajectory, five measurement points near the facial nerve were accessed and electrical impedance was measured (≤1 KHz) using a multipolar electrode probe. Micro-CT was used postoperatively to measure the distances from the drilled trajectories to the facial nerve. Tissue density was determined from coregistered preoperative CT images and, following sensitivity field modeling of the measuring tip, tissue resistivity was calculated. The relationship between impedance and density was determined for 29 trajectories passing or intersecting the facial nerve. A monotonic decrease in impedance magnitude was observed in all trajectories with a drill axis intersecting the facial nerve. Mean tissue densities intersecting with the facial nerve (971–1161 HU) were different (p <0.01) from those along safe trajectories passing the nerve (1194–1449 HU). However, mean resistivity values of trajectories intersecting the facial nerve (14–24 Ωm) were similar to those of safe passing trajectories (17–23 Ωm). The determined relationship between tissue density and electrical impedance during neuromonitoring of the facial nerve suggests that impedance spectroscopy may be used to increase the accuracy of tissue discrimination, and ultimately improve nerve safety distance assessment in the future.

Genauigkeit und Machbarkeit robotische Multi-Port Cochleaimplantation – Evaluierung am Phantom

Untersuchungsziel Der Multi-Port Ansatz fur die robotische Cochleaimplantation bietet Vorteile bezuglich Instru-mentenmanipulation und Visualisierung und eine Beruhrung von Trommelfell und Gehorkno-chelchen kann vermieden werden. In dieser Studie wurde die Machbarkeit einer minimal-invasiven Cochleaimplantation uber einen Multi-Port Zugang untersucht. Methodik In Bilddaten (CT, 0.15 x 0.15 x 0.2 mm) eines Schlafenbeinmodels (Phacon) wurden vier Trajektorien (∅ 1.8 mm, l = 21.5 bis 31.8 mm) von der Oberflache des Felsenbeins kollisions-frei zu anatomischen Strukturen zum runden Fenster geplant: retro-facial (RF), suprameatal (SM), sub-facial (SF) und durch den Rezessus Facialis (FR) und mittels eines CI-Robotersystems (Universitat Bern) realisiert. Es wurden sechs Insertionsversuche durchge-fuhrt (Visualisierung mittels EndoGnost, 0.55 mm Durchmesser, 0° Winkel, PolyDiagnost und Manipulation mit einer geraden Nadel, Medicon). Jeder Zugang bestand aus je einer Trajek-torie fur Elektrodeninsertion (immer FR), Visualisierung und Instrumentenmanipulation (Kom-bination aus RF, SM und SF). Pro Kombination wurden die endoskopisch darstellbaren sowie fur die Instrumente erreichbaren anatomischen Strukturen, die erreichte Elektrodeninserti-onstiefe und die dafur benotigte Zeit bestimmt. Anhand eines postoperativen CT wurden die Trajektorien geometrisch vermessen. Ergebnisse Der mittlere Bohrfehler betrug 0.15 mm. (SM 0.12 mm; FR 0.2 mm; RF 0.07 mm; SF 0.2 mm). Fur eine volle Insertion des Elektrodenarrays war ein Zugang bestehend aus den Trajektorien FR, RF und SF am geeignetsten (12 von 12 Elektroden innerhalb von 4:30 Minu-ten). Visualisierung und Instrumentenmanipulation via Trajektorien RF respektive SF ermog-lichten freie Sicht auf bzw. Erreichbarkeit des runden Fensters und erlaubten die zusatzliche manuelle Unterstutzung bei der Einfuhrung des Elektrodenarrays. Ein Multi-Port Zugang be-stehend aus den Trajektorien SF fur Visualisierung und RF fur Instrumentenmanipulation er-moglichte Visualisierung vieler anatomischer Strukturen, jedoch war die Trajektorie RF we-gen dem Winkel zum runden Fenster als Hilfestellung zur Elektrodeninsertion mittels eines ri-giden Instrumentes nutzlos. Die ubrigen Zugange waren mangels Visualisierung oder Er-reichbarkeit des runden Fensters ungeeignet fur eine verlassliche Insertion. Schlussfolgerung Die Moglichkeit eines Multi-Port Zugang zum runden Fenster bestehend aus drei Trajektorien ohne Beeinflussung anatomischer Strukturen konnte initial im Phantom bestatigt werden. Verschiedene Kombinationen von Zugangen wurden miteinander verglichen. Visualisierung und Manipulation durch die RF und SF verlaufenden Trajektorien ermoglichte die Darstellung und Erreichbarkeit aller zur Cochleaimplantation notigen Strukturen.

Roboterassistierte Cochlea-Implantation

Im Sommer 2016 wurde in der Schweiz doppelt Tunnelbohrgeschichte geschrieben. Neben der feierlichen Eroffnung des Gotthard-Basistunnels konnte in Bern in ganzlich anderen Grossenordnungen eine weitere Weltpremiere gefeiert werden: Die erste roboterassistierte Cochlea-Implantation am Patienten.