The accuracy of computer-aided surgery in neurotologic approaches to the temporal bone: A cadaver study

Role of Navigation in Oral and Maxillofacial Surgery: A Surgeon's Perspectives

Surgeries related to the maxillofacial area deal with an intricate network of anatomical structures. With the complexity of the vital structures, it necessitates a surgical team to respect each anatomical boundary. In the past, there was an exceptionally high number of cases with surgical errors. These errors were not because of flaws in the surgeon’s skills or techniques but owing to lack of resources. Visualisation is one of the key factors that determines the precision of any surgical outcome. Advances in surgical planning have led to the introduction of a “Navigation” system that helps surgeons to see more, know more and ultimately do more for their patients. The usefulness of the navigation system in oral surgeries has been indicated by its surgical applications in craniomaxillofacial trauma, orthognathic surgeries, head and neck pathological resections, complex skull base surgeries and surgery involving temporomandibular joint. A vast majority of research literature has suggested remarkable improvement in surgical outcomes under the guidance of 3d planning and navigation. However, with such an inordinate advancement, financial expenses and a gradual learning curve are always a constraining factor in surgical navigation. This article overviews indication of navigation in craniofacial surgeries with a focus on applied aspect, planning and solution to the future problem.

Evolution and Stagnation of Image Guidance for Surgery in the Lateral Skull: A Systematic Review 1989-2020

Objective: Despite three decades of pre-clinical and clinical research into image guidance solutions as a more accurate and less invasive alternative for instrument and anatomy localization, translation into routine clinical practice for surgery in the lateral skull has not yet happened. The aim of this review is to identify challenges that need to be solved in order to provide image guidance solutions that are safe and beneficial for use during lateral skull surgery and to synthesize factors that facilitate the development of such solutions. Methods: Literature search was conducted via PubMed using terms relating to image guidance and the lateral skull. Data extraction included the following variables: image guidance error, imaging resolution, image guidance system, tracking technology, registration method, study endpoints, clinical target application, and publication year. A subsequent search of FDA 510(k) database for identified image guidance systems and extraction of the year of approval, intended use, and indications for use was performed. The study objectives and endpoints were subdivided in three time phases and summarized. Furthermore, it was analyzed which factors correlated with the image guidance error. Factor values for which an error ≤0.5 mm (μ_error + 3σ_error) was measured in more than one study were identified and inspected for time trends. Results: A descriptive statistics-based summary of study objectives and findings separated in three time intervals is provided. The literature provides qualitative and quantitative evidence that image guidance systems must provide an accuracy ≤0.5 mm (μ_error + 3σ_error) for their safe and beneficial application during surgery in the lateral skull. Spatial tracking accuracy and precision and medical image resolution both correlate with the image guidance accuracy, and all of them improved over the years. Tracking technology with accuracy ≤0.05 mm, computed tomography imaging with slice thickness ≤0.2 mm, and registration based on bone-anchored titanium fiducials are components that provide a sufficient setting for the development of sufficiently accurate image guidance. Conclusion: Image guidance systems must reliably provide an accuracy ≤0.5 mm (μ_error + 3σ_error) for their safe and beneficial use during surgery in the lateral skull. Advances in tracking and imaging technology contribute to the improvement of accuracy, eventually enabling the development and wide-scale adoption of image guidance solutions that can be used safely and beneficially during lateral skull surgery.

Accuracy of a Modern Intraoperative Navigation System for Temporal Bone Surgery in a Cadaveric Model

Objectives

To determine the accuracy of a modern navigation system in temporal bone surgery. While routine in other specialties, navigation has had limited use in the temporal bone due to issues of accuracy, perceived impracticality, and value.

Study Design

Prospective observational study.

Setting

Temporal bone laboratory.

Subjects and Methods

Eighteen cadaveric specimens were dissected after rigid fiducials were implanted and computed tomography scans were obtained. Target registration and target localization errors were then measured at various points.

Results

The mean overall target registration error was 0.48 ± 0.29 mm. The mean target localization error was 0.54 mm at the sinodural angle, 0.48 mm at the lateral semicircular canal, 0.55 mm at the round window, 0.39 mm at the oval window, and 0.52 mm at the second genu of the facial nerve.

Conclusion

A modern navigation system demonstrated submillimeter accuracy for all points of interest. Its use in clinical as well as training settings has yet to be fully elucidated.

Image-guided Localization of the Internal Auditory Canal via the Middle Cranial Fossa Approach

OBJECTIVE: We sought to determine the accuracy of an electromagnetic image guidance surgical navigation system in localizing the midpoint of the internal auditory canal (IAC) and other structures of the temporal bone through the middle cranial fossa approach.

MATERIALS AND METHODS: Seven fresh cadaveric whole heads were dissected via a middle cranial fossa approach. High-resolution CT scans were used with an InstaTrak 3500 Plus electromagnetic image guidance system (General Electric, Fairfield, CT). We evaluated the accuracy of identifying several middle cranial fossa landmarks including the midpoint of the IAC; the labyrinthine segment of the facial nerve; and the arcuate eminence, the carotid artery, and foramen spinosum.

RESULTS: We were able to identify the middle of the IAC within 2.31 mm (range 0.65-7.52 mm, SD 2.39 mm). The arcuate eminence could be identified within 1.86 mm (range 1.49-2.37 mm, SD 0.36 mm). We noted some interference when the handpiece was within 6 to 8 cm of the microscope.

CONCLUSION: Although computer-aided navigational tools are no substitute for thorough knowledge of temporal bone anatomy, we found the InstaTrak system reliable in identifying the midpoint of the IAC to within 2.4 mm through a middle fossa approach.

Evaluation of intraoperative cone beam computed tomography and optical drill tracking in temporal bone surgery

OBJECTIVES/HYPOTHESIS

A prototype system for intraoperative cone beam computed tomography (CBCT) imaging has been developed and augmented with real time optical tracking of a surgical drill. We hypothesize that this system provides sufficient accuracy for guidance of temporal bone surgery.

STUDY DESIGN

Basic research.

METHODS

Measurements of drill localization accuracy using CBCT imaging were obtained with a custom three-dimensional calibration object. Integrated CBCT imaging and drill tracking were prospectively evaluated on 12 cadaver temporal bones. Six inexperienced and six experienced surgeons conducted four surgical tasks: cortical mastoidectomy, posterior tympanotomy, cochleostomy, and a translabyrinthine approach to the internal auditory canal. Questionnaires provided expert feedback on tracking accuracy and system usability.

RESULTS

Target registration error measurements of drill tracking accuracy and precision yielded a mean of 0.76 mm, a maximum of 1.30 mm, and a standard deviation of 0.21 mm. Anatomical landmark identification tasks (e.g., facial nerve, incus, semicircular canals, cochlea) provided additional validation of system accuracy. The usability and utility of the guidance system were positively rated by both groups of surgeons, with further modifications underway to improve tracking line of sight and registration workflow. Experienced but in particular inexperienced surgeons indicated significant benefits in cases involving extensive disease, abnormal anatomy, and loss of anatomical landmarks.

CONCLUSIONS

The integration of intraoperative CBCT imaging with optical tracking provides sufficient accuracy to localize anatomical structures within the temporal bone using an otological drill. Future studies will explore the role of this technology in complex oncological resections, in surgery for congenital anomalies, and as a tool for teaching.

Image-guided, endoscopic-assisted drilling and exposure of the whole length of the internal auditory canal and its fundus with preservation of the integrity of the labyrinth using a retrosigmoid approach: a laboratory investigation

OBJECTIVE

Hearing loss after removal of vestibular schwannomas with preservation of the cochlear nerve can result from labyrinthine injury of the posterior semicircular canal and/or common crus during drilling of the posterior wall of the internal auditory meatus. Indeed, there are no anatomic landmarks that intraoperatively identify the position of the posterior semicircular canal or of the common crus. We investigated the usefulness of image guidance and endoscopy for exposure of the internal auditory canal (IAC) and its fundus without labyrinthine injury during a retrosigmoid approach.

METHODS

A retrosigmoid approach to the IAC was performed on 10 whole fresh cadaveric heads after acquiring high-resolution computed tomographic scans (120 kV; slice thickness, 1 mm; field of vision, 40 cm; matrix, 512 x 512) with permanent bone-implanted reference markers. Drilling of the posterior wall of the IAC was executed with image guidance. Its most lateral area was visualized using endoscopy.

RESULTS

Target registration error for the procedure was 0.28 to 0.82 mm (mean, 0.46 mm; standard deviation, 0.16 mm). The measured length of the IAC along its posterior wall was 9.7 +/- 1.6 mm. The angle of drilling (angle between the direction of drill and the posterior petrous surface) was 43.3 +/- 6.0 degrees, and the length of the posterior wall of the IAC drilled without violating the integrity of the labyrinth was 7.2 +/- 0.9 mm. The surgical maneuvers in the remaining part of the IAC, including the fundus, were performed using an angled endoscope.

CONCLUSION

Frameless navigation using high-resolution computed tomographic scans and bone-implanted reference markers can provide a "roadmap" to maximize safe surgical exposure of the IAC without violating the labyrinth and leaving a small segment of the lateral IAC unexposed. Further exposure and surgical manipulation of this segment, including the fundus without additional cerebellar retraction and labyrinthine injury, can be achieved using an endoscope. Use of image guidance and an endoscope can help in exposing the entire posterior aspect of the IAC including its fundus without violating the labyrinth through a retrosigmoid approach. This technique could improve hearing preservation in vestibular schwannoma surgery.

Review of temporal bone dissection teaching: how it was, is and will be

Objective:

We aimed to review the history of anatomical dissection, and to examine how modern educational techniques will change the way temporal bone dissection is taught to otolaryngology trainees.

Method:

Review of the literature using Medline, Embase and PubMed database searches.

Results:

Temporal bone anatomy has traditionally been taught using cadaveric specimens. However, resources such as three-dimensional reconstructed models and ‘virtual reality’ temporal bone simulators have a place in educating the otolaryngology trainee.

Conclusion:

We should encourage the use of fresh frozen cadaveric temporal bone specimens for future otologists. Artificial three-dimensional models and virtual reality temporal bone simulators can be used to educate junior trainees, thus conserving the scarce resource of cadaveric bones.

Medical navigation system for otologic surgery based on hybrid registration and virtual intraoperative computed tomography

An image-guided surgical system for otologic surgery was developed and clinically evaluated. With reliable hybrid registration, real-time patient movement compensation and virtual intraoperative computed tomography imaging have been originally proposed. In contrast to the commercially available systems that mainly use 2-D images for pointing probes, in this system, the surgical drill position is navigated and displayed in the 3-D space with real-time surface rendering. In a temporal bone model study, the navigation accuracy was 1.12 +/- 0.09 mm with regard to the target registration error. Initial clinical evaluation of the proposed method was performed in five cochlea implantation surgeries. Accurate insertion of the electrodes into the cochlea was achieved, and the facial nerve was protected from injury in all surgeries. The proposed method could be applied to various surgeries for accurate targeting and protection of critical organs.

Intraoperative cone-beam CT for guidance of temporal bone surgery

OBJECTIVES

To describe our preclinical experience with Cone Beam CT (CBCT) in image-guided surgery of the temporal bone.

STUDY DESIGN AND SETTINGS

A mobile isocentric C-arm (PowerMobil, Siemens Medical Systems, Erlangen, Germany) modified to include a flat-panel detector (Varian Imaging Products, Palo Alto, CA) and a motorized orbit was developed to acquire multiple projections in rotation about a subject. Initial experiments imaging steel wire in air were used to investigate the system's spatial resolution in 3D image reconstruction. Subsequently temporal bone dissection was performed on five cadaver heads using the modified C-arm as an image guidance system.

RESULTS

We obtained a spatial resolution of 0.85 mm. The image acquisition time was 120 seconds and the radiation dose approximately one-tenth of a conventional CT scan.

CONCLUSION

CBCT provided submillimeter accuracy at high speed with low radiation dosage to offer utility as an intraoperative imaging system.

SIGNIFICANCE

CBCT offers technology that approximates "near-real-time" image guidance.

EBM RATING

C-4.