A new "practical" plane for Eustachian tube measurements and its application in predicting middle ear dysfunction in patient with acquired cholesteatomas.

SETTING: The Eustachian tube plays a vital role in middle ear physiology. There has been evidence that Eustachian tube (ET) and angle are correlated with middle ear function. The measurements of these Eustachian tube features are now made possible with computed tomography and multiplanar reconstruction techniques. However, there has not been a standardised protocol devised to these measurements in limited window cone-beam CT scans of temporal bones. OBJECTIVE: The primary object of the present study is to establish and validate a new landmark in closer proximity to the middle ear that is consistently captured, thereby allowing ET angle and length to be measured from the majority of cone-beam CT scans. Secondarily, the ET anatomies of patients with middle ear dysfunction manifesting as acquired cholesteatoma are analysed with this new method of measurement. METHODS: This study undertook a step-by-step method to first validate the methods of ET measurement with Reid's standard plane, then identifying an alternative landmark, thus a new plane visible on limited window cone-beam CT scans of temporal bones and lastly, validating the application of this new plane in the measurements of ET angle and length. This new method of measurement was coined the Ku-Copson plane and was applied to 30 cochlear implant patients and 30 patients with acquired cholesteatomas. Their ET anatomies were analysed and compared. RESULTS: It was found that the new Ku-Copson mandibular fossa plane was a reliable and accurate plane for the measurement of ET angle and length. Furthermore, it was found that patients with acquired cholesteatomas have statistically significant smaller ET angles and shorter ET lengths when compared with patients with cochlear implants, of normal middle ear function. CONCLUSION: The newly proposed method utilising the right mandibular fossa as an anatomical landmark for ET angles and lengths measurement appears to be viable. The close proximity of this landmark to the middle ear means that it is highly likely to be captured in most cone-beam CT scans of the petrous temporal bones. This enables the retrospective examination ET angles and lengths to be conducted on CB CT scans. This study reports statistically significant difference in ET anatomy in patients with middle ear dysfunction.

Surgical approach to the facial recess influences the acceptable trajectory of cochlear implantation electrodes.

PURPOSE: To provide practical guidance to the operative surgeon by mapping the location, where acceptable straight-line virtual cochlear implant electrode trajectories intersect the facial recess. In addition, to investigate the influence of facial recess preparation, virtual electrode width and surgical approach to the cochlea on these available trajectories. METHODS: The study was performed on imaging data from eight cadaveric temporal bones within the University of Melbourne Virtual Reality (VR) Temporal Bone Surgery Simulator. The facial recess was opened to varying degrees, and acceptable trajectory vectors with varying diameters were calculated for electrode insertions via cochleostomy or round window membrane (RWM). The percentage of acceptable insertion vectors through each location of the facial recess was visually represented using heatmaps. RESULTS: Seven of the eight bones allowed for acceptable vector trajectories via both cochleostomy and RWM approaches. These acceptable trajectories were more likely to lie superiorly within the facial recess for insertion via the round window, and inferiorly for insertion via cochleostomy. Cochleostomy insertions required a greater degree of preparation and skeletonisation of the junction of the facial nerve and chorda tympani within the facial recess. The width of the virtual electrode had only marginal impact on the availability of acceptable trajectories. Heatmaps emphasised the intimate relationship the acceptable trajectories have with the facial nerve and chorda tympani. CONCLUSION: These findings highlight the differences in the acceptable straight-line trajectories for electrodes when implanted via the round window or cochleostomy. There were notable exceptions to both surgical approaches, likely explained by the variation of hook region anatomy. The methodology used in this study holds promise for translation to patient specific surgical planning.

Development of a virtual reality clinically oriented temporal bone anatomy module with randomised control study of three-dimensional display technology.

Objective: To investigate the effectiveness of a virtual reality (VR), three-dimensional (3D) clinically orientated temporal bone anatomy module, including an assessment of different display technologies. Methods: A clinically orientated, procedural and interactive anatomy module was generated from a micro-CT of a cadaveric temporal bone. The module was given in three different display technologies; 2D, 3D with monoscopic vision, and 3D with stereoscopic vision. A randomised control trial assessed the knowledge acquisition and attitudes of 47 medical students though a pretutorial and post-tutorial questionnaire. The questionnaire included questions identifying anatomic structures as well as understanding structural relations and clinical relevance. Furthermore, a five-point Likert scale assessed the students' attitudes to the module and alternative learning outcomes, such as interest in otology and preparedness for clinical rotations. Results: As a whole cohort, the total test score improved significantly, with a large effect size (p≤0.005, Cohen's d=1.41). The 23 students who returned the retention questionnaire had a significant improvement in total test score compared with their pretutorial score, with a large effect size (p≤0.005, Cohen's d=0.83). Display technology did not influence the majority of learning outcomes, with the exception of 3D technologies, showing a significantly improvement in understanding of clinical relevance and structural relations (p=0.034). Students preferred 3D technologies for ease of use, perceived effectiveness and willingness to use again. Conclusions: The developed VR temporal bone anatomy tutor was an effective self-directed education tool. 3D technology remains valuable in facilitating spatial learning and superior user satisfaction.

Comparison of Experts and Residents Performing a Complex Procedure in a Temporal Bone Surgery Simulator.

OBJECTIVE: To investigate the use of automated metrics from a virtual reality (VR) temporal bone surgery simulator to determine how the performance of experts and trainees differs when performing a complex otological procedure (mastoidectomy with posterior tympanotomy and cochleostomy). STUDY DESIGN: Cohort study. METHODS: Using the University of Melbourne VR temporal bone surgery simulator, seven ENT consultants and seven ENT residents performed two trials of the surgical approach to cochlear implantation on a virtual temporal bone. Simulator recordings were used to calculate a range of automated metrics for each stage of the procedure, capturing efficiency, technique characteristics, drilled bone regions, and damage to vital anatomical structures. RESULTS: Results confirm that experts drilled more efficiently than residents. Experts generally used larger burrs and applied higher forces, resulting in faster material removal. However, they exercised more caution when drilling close to anatomical structures. Residents opened the temporal bone more widely, but neglected important steps in obtaining a clear view toward the round window, such as thinning the external ear canal wall and skeletonizing the medial aspect of the facial nerve. Residents used higher magnification and reoriented the temporal bone more often than experts. CONCLUSION: VR simulation provides metrics that allow the objective analysis of surgical technique, and identification of differences between the performance of surgical residents and their senior colleagues. The performance of residents could be improved with more guidance regarding how much force they should apply, what burr size they should use, how they should orient the bone, and for cochlear implant surgery guidance regarding anatomical regions requiring particular attention, to visualize the round window.

Supporting skill acquisition in cochlear implant surgery through virtual reality simulation.

OBJECTIVES: To evaluate the effectiveness of a virtual reality (VR) temporal bone simulator in training cochlear implant surgery. METHODS: We compared the performance of 12 otolaryngology registrars conducting simulated cochlear implant surgery before (pre-test) and after (post-tests) receiving training on a VR temporal bone surgery simulator with automated performance feedback. The post-test tasks were two temporal bones, one that was a mirror image of the temporal bone used as a pre-test and the other, a novel temporal bone. Participant performances were assessed by an otologist with a validated cochlear implant competency assessment tool. Structural damage was derived from an automatically generated simulator metric and compared between time points. RESULTS: Wilcoxon signed-rank test showed that there was a significant improvement with a large effect size in the total performance scores between the pre-test (PT) and both the first and second post-tests (PT1, PT2) (PT-PT1: P = 0.007, r = 0.78, PT-PT2: P = 0.005, r = 0.82). CONCLUSION: The results of the study indicate that VR simulation with automated guidance can effectively be used to train surgeons in training complex temporal bone surgeries such as cochlear implantation.