In Silico Assessment of Safety and Efficacy of Screw Placement for Pediatric Image-Guided Otologic Surgery.

Introduction: Current high-accuracy image-guided systems for otologic surgery use fiducial screws for patient-to-image registration. Thus far, these systems have only been used in adults, and the safety and efficacy of the fiducial screw placement has not yet been investigated in the pediatric population. Materials and Methods: In a retrospective study, CT image data of the temporal region from 11 subjects meeting inclusion criteria (8-48 months at the time of surgery) were selected, resulting in n = 20 sides. These datasets were investigated with respect to screw stability efficacy in terms of the cortical layer thickness, and safety in terms of the distance of potential fiducial screws to the dura mater or venous sinuses. All of these results are presented as distributions, thickness color maps, and with descriptive statistics. Seven regions within the temporal bone were analyzed individually. In addition, four fiducial screws per case with 4 mm thread-length were placed in an additively manufactured model according to the guidelines for robotic cochlear implantation surgery. For all these screws, the minimal distance to the dura mater or venous sinuses was measured, or if applicable how much they penetrated these structures. Results: The cortical layer has been found to be mostly between 0.7-3.3 mm thick (from the 5th to the 95th percentile), while even thinner areas exist. The distance from the surface of the temporal bone to the dura mater or the venous sinuses varied considerably between the subjects and ranged mostly from 1.1-9.3 mm (from the 5th to the 95th percentile). From all 80 placed fiducial screws of 4 mm thread length in the pediatric subject younger than two years old, 22 touched or penetrated either the dura or the sigmoid sinus. The best regions for fiducial placement would be the mastoid area and along the petrous pyramid in terms of safety. In terms of efficacy, the parietal followed by the petrous pyramid, and retrosigmoid regions are most suited. Conclusion: The current fiducial screws and the screw placement guidelines for adults are insufficiently safe or effective for pediatric patients

Otosclerosis under microCT: New insights into the disease and its anatomy

Purpose: Otospongiotic plaques can be seen on conventional computed tomography (CT) as focal lesions around the cochlea. However, the resolution remains insufficient to enable evaluation of intracochlear damage. MicroCT technology provides resolution at the single micron level, offering an exceptional amplified view of the otosclerotic cochlea. In this study, a non-decalcified otosclerotic cochlea was analyzed and reconstructed in three dimensions for the first time, using microCT technology. The pre-clinical relevance of this study is the demonstration of extensive pro-inflammatory buildup inside the cochlea which cannot be seen with conventional cone-beam CT (CBCT) investigation. Materials and Methods: A radiological and a three-dimensional (3D) anatomical study of an otosclerotic cochlea using microCT technology is presented here for the first time. 3D-segmentation of the human cochlea was performed, providing an unprecedented view of the diseased area without the need for decalcification, sectioning, or staining. Results: Using microCT at single micron resolution and geometric reconstructions, it was possible to visualize the disease's effects. These included intensive tissue remodeling and highly vascularized areas with dilated capillaries around the spongiotic foci seen on the pericochlear bone. The cochlea's architecture as a morphological correlate of the otosclerosis was also seen. With a sagittal cut of the 3D mesh, it was possible to visualize intense ossification of the cochlear apex, as well as the internal auditory canal, the modiolus, the spiral ligament, and a large cochleolith over the osseous spiral lamina. In addition, the oval and round windows showed intense fibrotic tissue formation and spongiotic bone with increased vascularization. Given the recently described importance of the osseous spiral lamina in hearing mechanics and that, clinically, one of the signs of otosclerosis is the Carhart notch observed on the audiogram, a tonotopic map using the osseous spiral lamina as region of interest is presented. An additional quantitative study of the porosity and width of the osseous spiral lamina is reported. Conclusion: In this study, structural anatomical alterations of the otosclerotic cochlea were visualized in 3D for the first time. MicroCT suggested that even though the disease may not appear to be advanced in standard clinical CT scans, intense tissue remodeling is already ongoing inside the cochlea. That knowledge will have a great impact on further treatment of patients presenting with sensorineural hearing loss

Robotic Milling of Electrode Lead Channels During Cochlear Implantation in an ex-vivo Model.

Objective: Robotic cochlear implantation is an emerging surgical technique for patients with sensorineural hearing loss. Access to the middle and inner ear is provided through a small-diameter hole created by a robotic drilling process without a mastoidectomy. Using the same image-guided robotic system, we propose an electrode lead management technique using robotic milling that replaces the standard process of stowing excess electrode lead in the mastoidectomy cavity. Before accessing the middle ear, an electrode channel is milled robotically based on intraoperative planning. The goal is to further standardize cochlear implantation, minimize the risk of iatrogenic intracochlear damage, and to create optimal conditions for a long implant life through protection from external trauma and immobilization in a slight press fit to prevent mechanical fatigue and electrode migrations. Methods: The proposed workflow was executed on 12 ex-vivo temporal bones and evaluated for safety and efficacy. For safety, the difference between planned and resulting channels were measured postoperatively in micro-computed tomography, and the length outside the planned safety margin of 1.0 mm was determined. For efficacy, the channel width and depth were measured to assess the press fit immobilization and the protection from external trauma, respectively. Results: All 12 cases were completed with successful electrode fixations after cochlear insertions. The milled channels stayed within the planned safety margins and the probability of their violation was lower than one in 10,000 patients. Maximal deviations in lateral and depth directions of 0.35 and 0.29 mm were measured, respectively. The channels could be milled with a width that immobilized the electrode leads. The average channel depth was 2.20 mm, while the planned channel depth was 2.30 mm. The shallowest channel depth was 1.82 mm, still deep enough to contain the full 1.30 mm diameter of the electrode used for the experiments. Conclusion: This study proposes a robotic electrode lead management and fixation technique and verified its safety and efficacy in an ex-vivo study. The method of image-guided robotic bone removal presented here with average errors of 0.2 mm and maximal errors below 0.5 mm could be used for a variety of other otologic surgical procedures

Robotic milling of the electrode lead channel during cochlear implantation

A new fixation technique for the electrode lead of cochlear implants is proposed for the robotic middle and inner ear access technique, and studied for safety and efficacy in an ex-vivo model

Computer Assistance, Image Guidance and Robotics in Otologic Surgery

Cochlear implants have transformed the field of otology after becoming the standard care for hearing rehabilitation in patients with severe to profound sensorioneural hearing loss that has progressed to the point that benefit from hearing aids is limited. Only 50 years ago there were no effective treatment for deafness or severe to profound hearing losses. Since Alessandro Volta in the early 1800’s provided the first account of electrical stimulation of the auditory system, a fascinating series of experiments involving electrically evoked hearing has been described, culminating with the first cochlear implant performed by Dr House in 1961. At that time, patients had some basic frequency discrimination and could identify words in small closed sets.1 The changing point for CI came when Dr House enlisted the partnership of Mr Jack Urban, an electrical engineer, resulting on landmark changes in the history of CIs.1 The current technique for cochlear implantation (CI) surgery requires a mastoidectomy to gain access to the cochlea for electrode array insertion, drilling in close proximity to bone-embedded nerves, blood vessels and other structures, which can result in complications for the patient.2 Within all fields of surgery there has been a push towards minimizing the invasiveness of procedures to limit co-morbidity as well as costs.3 On the past 20 years, bioengineering and surgical principles were united to reduce surgical trauma by using image-guided surgical systems (IGS) that drill a single tunnel towards the cochlea. Using pre and intraoperatively acquired CT (computed tomography) image, these systems allow surgeons to determine the boundaries of the surgical field and positions of vital anatomical structures.3 Credits for introducing IGS to Otolaryngology goes to Schlöndorff.4,5 Early attempts to minimize CI surgery included the endomeatal approach, where a trough was drilled in the posterior external auditory canal (EAC) to accommodate the connecting wire from the internal receiver to the electrode array. This approach was complicated by infection, wire extrusion into the EAC, and cholesteatoma6,7. Later efforts have focused on smaller incision sites8,9, micromastoids, known as “Veria Operation”10 and single drill troughs to the middle ear via the attic11. Research on RCI (robotic cochlear implantation) has so far focused on individual elements of the procedure, such as image-based surgical planning, guided keyhole trajectory using surgical templates, industrial robotic manipulators, and skull- mounted passive kinematic structures. Design for electrode insertion systems and reproducible options for cochlear access using robotic force feedback control, have also been addressed. For the past 20 years, groups around the world have contributed for the creation and refinement of minimally invasive surgical approaches, starting with the creation of anatomical datasets for surgical training and temporal bone study. The steps to achieve the current status of the robotic surgical procedure will be described in this chapter

Image-Based Planning of Minimally Traumatic Inner Ear Access for Robotic Cochlear Implantation.

Objective: During robotic cochlear implantation, an image-guided robotic system provides keyhole access to the scala tympani of the cochlea to allow insertion of the cochlear implant array. To standardize minimally traumatic robotic access to the cochlea, additional hard and soft constraints for inner ear access were proposed during trajectory planning. This extension of the planning strategy aims to provide a trajectory that preserves the anatomical and functional integrity of critical intra-cochlear structures during robotic execution and allows implantation with minimal insertion angles and risk of scala deviation. Methods: The OpenEar dataset consists of a library with eight three-dimensional models of the human temporal bone based on computed tomography and micro-slicing. Soft constraints for inner ear access planning were introduced that aim to minimize the angle of cochlear approach, minimize the risk of scala deviation and maximize the distance to critical intra-cochlear structures such as the osseous spiral lamina. For all cases, a solution space of Pareto-optimal trajectories to the round window was generated. The trajectories satisfy the hard constraints, specifically the anatomical safety margins, and optimize the aforementioned soft constraints. With user-defined priorities, a trajectory was parameterized and analyzed in a virtual surgical procedure. Results: In seven out of eight cases, a solution space was found with the trajectories safely passing through the facial recess. The solution space was Pareto-optimal with respect to the soft constraints of the inner ear access. In one case, the facial recess was too narrow to plan a trajectory that would pass the nerves at a sufficient distance with the intended drill diameter. With the soft constraints introduced, the optimal target region was determined to be in the antero-inferior region of the round window membrane. Conclusion: A trend could be identified that a position between the antero-inferior border and the center of the round window membrane appears to be a favorable target position for cochlear tunnel-based access through the facial recess. The planning concept presented and the results obtained therewith have implications for planning strategies for robotic surgical procedures to the inner ear that aim for minimally traumatic cochlear access and electrode array implantation

Image-guidance and robotic technology to support surgery on the lateral skull base

The lateral skull base embeds important anatomy such as the hearing and balance organs, facial and taste nerves as well as blood supply for the brain, many of which structures are at submillimetric scale. Surgery at the lateral skull base is at the limits of human perception and dexterity, thus increasing chances for side effects and complications such as destruction of residual hearing or nerves. The geometric scale and fragility of lateral skull base anatomy requires constant visual access, and dexterity with haptic feedback with resolutions of <<0.5 mm (Krombach et al. 2005) and <<1mN (Schurzig et al. 2010) respectively. To overcome human limitations and improve surgical outcomes, the use of image based 1) intervention planning for 2) image-guidance of surgical tools and 3) surgical robotic systems that can carry out tasks at this scales automatically, manipulate in the micrometer range and feel in the micronewton range has been proposed. Software based annotation of anatomical structures in lateral skull base (Nobel et al. 2009), planning of cochlear access procedures (Klenzner et al. 2014, Gerber et al. 2014) and elements of photo realistic rendering (Tsai et al. 2019) have been proposed and made their way to clinics. In contrast, commercially available ENT navigation systems have been demonstrated to be of very limited use due to inaccuracies present (Labadie et al. 2004, Majdani et al. 2009). Robotic technology has been proposed and investigated for automated drilling and milling tasks in the temporal bone (Baron et al. 2010, Bell et al. 2012) with successful clinical introduction (Weber & Caversaccio et al. 2017). In addition, head mounted and patient individual template systems have been successfully applied in clinics (Labadie et al. 2014). With this contribution, a general overview of the state of the art image-guidance and robotics for microsurgery in the lateral skull base will be given with an outlook of what can be expected in the near future

Safety and Efficacy of Screw Placement for Pediatric Image-Guided Surgery

Retrospective study for fiducial screw placement for Image Guided Surgery in pediatric subjects

Planning of tunnel-based robotic access to the inner ear

A new planning strategy for tunnel-based robotic access to the inner ear is proposed based on the study of three- dimensional models of the middle and inner ear anatomy. With the goal of minimizing access- and insertion-related trauma to increase consistency, especially with respect to preservation of residual hearing during cochlear implantation, a trend for more promising trajectory placement can be identified

Feasibility of Pediatric Robotic Cochlear Implant in Phantoms

Objective: To demonstrate the feasibility of robotic cochlear implant surgery in subject specific pediatric phantoms. Study Design: Pilot study. Materials and Methods: Computed tomographic preoperative encrypted data of 10 pediatric subjects (total of 20 sides) between 8 months and 48 months old, who underwent cochlear implant surgery were studied. Four datasets (n¼8 sides) were selected for investigation of the complete robotic procedure including middle and inner ear access and electrode insertion. Results: The planning of the safe trajectory for the robotic approach was possible in 17 of the cases. In three sides, planning the trajectory was not possible due to the small size of the facial recess. Bone thickness study demonstrated average sufficient bone thickness at the site of screw implantation in general. The complete robotic procure including the drilling and insertion was successfully carried out on all the created phantoms. Conclusion: With this work we have demonstrated the feasibility of planning and performing a robotic middle and inner ear access and cochlear implantation (CI) in phantom models of pediatric subjects. To develop and validate the proposed procedure for use in children, next stage optimization of the current surgical workflow and adaptation of the surgical material to pediatric population is necessary