Accuracy of High-Resolution Computed Tomography Compared to High-Definition Ear Endoscopy to Assess Cholesteatoma Extension.

OBJECTIVE: To correlate radiographic evidence of cholesteatoma in the retrotympanum with intraoperative endoscopic findings in cholesteatoma patients and to evaluate the clinical relevance of radiographic evidence of cholesteatoma in the retrotympanum. STUDY DESIGN: Case series with chart review. SETTING: Tertiary referral center. METHODS: Seventy-six consecutive cases undergoing surgical cholesteatoma removal with preoperative high-resolution computed tomography (HRCT) were enrolled in this study. A retrospective analysis of the medical records was conducted. The extension of cholesteatoma regarding different middle ear subspaces, into the antrum and mastoid were reviewed radiologically in preoperative HRCT and endoscopically from surgical videos. Additionally, facial nerve canal dehiscence, infiltration of the middle cranial fossa, and inner ear involvement were documented. RESULTS: Comparison of radiological and endoscopic cholesteatoma extension revealed statistically highly significant overestimation of radiological cholesteatoma extension for all retrotympanic regions (sinus tympani 61.8% vs 19.7%, facial recess 69.7% vs 43.4%, subtympanic sinus 59.2% vs 7.9%, and posterior sinus 72.4% vs 4.0%) and statistically significant overestimation for mesotympanum (82.9% vs 56.6%), hypotympanum (39.5% vs 9.2%), and protympanum (23.7% vs 6.6%). No statistically significant differences were found for epitympanum (98.7% vs 90.8%), antrum (64.5% vs 52.6%), and mastoid (26.3% vs 32.9%). Statistically significant radiological overestimation of facial nerve canal dehiscence (54.0% vs 25.0%) and invasion of tegmen tympani (39.5% vs 19.7%) is reported. CONCLUSION: Radiologic cholesteatoma extension in different middle ear subspaces is overestimated compared to the intraoperative extension. The preoperative relevance of radiological retrotympanic extension might be limited in the choice of approach and transcanal endoscopic approach is always recommended first.

Assessment of jugular bulb variability based on 3D surface models: quantitative measurements and surgical implications.

PURPOSE: High-riding jugular bulbs (JBs) among other anatomical variations can limit surgical access during lateral skull base surgery or middle ear surgery and must be carefully assessed preoperatively. We reconstruct 3D surface models to evaluate recent JB classification systems and assess the variability in the JB and surrounding structures. METHODS: 3D surface models were reconstructed from 46 temporal bones from computed tomography scans. Two independent raters visually assessed the height of the JB in the 3D models. Distances between the round window and the JB dome were measured to evaluate the spacing of this area. Additional distances between landmarks on surrounding structures were measured and statistically analyzed to describe the anatomical variability between and within subjects. RESULTS: The visual classification revealed that 30% of the specimens had no JB, 63% a low JB, and 7% a high-riding JB. The measured mean distance from the round window to the jugular bulb ranges between 3.22 ± 0.97 mm and 10.34 ± 1.41 mm. The distance measurement (error rate 5%) was more accurate than the visual classification (error rate 15%). The variability of the JB was higher than for the surrounding structures. No systematic laterality was found for any structure. CONCLUSION: Qualitative analysis in 3D models can contribute to a better spatial orientation in the lateral skull base and, thereby, have important implications during planning of middle ear and lateral skull base surgery.

Variability of the retrotympanum and its association with mastoid pneumatization in cholesteatoma patients.

PURPOSE: This study aimed to investigate the variability of the retrotympanum in patients undergoing surgical treatment for cholesteatoma. METHODS: We included 59 ears of patients undergoing middle ear surgery for cholesteatoma who had preoperative computed tomography scans. A retrospective analysis of the medical records was conducted. The sinus tympani (ST), subtympanic sinus (STS) and facial recess (FR) were classified into types A-C based on the relationship of their extension to the facial nerve. The mastoid and petrous apex were assessed and categorized as normal pneumatized or sclerotic. RESULTS: Type A extension was the most frequently found in all sinuses (ST 64%, FR 77%, STS 69%), Type B extension was found more often in ST (34%) and STS (24%) than in FR (15%). A very deep extension was found only rarely (ST 2%, FR 8%, STS 7%). A sclerotic mastoid was found in 67% of cases. Those cases showed a statistically significant difference regarding retrotympanum pneumatization when compared with normal mastoid. CONCLUSION: The most frequent variant of retrotympanic pneumatization in relation to the facial nerve was type A in all subsites in cholesteatoma patients. The variability among patients with cholesteatoma is different to previously published results in healthy subjects. Moreover, the pneumatization of the retrotympanum is associated with mastoid pneumatization.

Topographic Anatomy of the Medial Labyrinthine Wall: Implications for the Transcanal Endoscopic Approach to the Internal Auditory Canal.

HYPOTHESIS: To characterize transcanal endoscopic landmarks of the medial labyrinthine wall and correlate these with anatomical features of the fundus of the internal auditory canal (IAC). BACKGROUND: The transcanal transpromontorial approach (TTA) enables minimally invasive access to the IAC. The establishment of a landmark-based dissection technique for the approach is crucial to avoid injury to the facial nerve. METHODS: Twenty temporal bones were dissected endoscopically through the TTA. Furthermore, high-resolution computed tomography (CT) scans from ten adult normal temporal bones were analyzed and three-dimensionally reconstructed. RESULTS: A stepwise dissection technique for the TTA was demonstrated depending on a newly described landmark used in the identification of the facial nerve. The proposed landmark, which was named the intervestibulocochlear crest (IVCC), is an integrated part of the otic capsule. It can be differentiated after the excision of the lateral labyrinthine wall as a laterally based bony pyramid between the cochlea and the vestibule. Its medially directed apex blends with the central part of the falcifrom crest and points to the distal part of the meatal facial nerve. The IVCC is best detected on axial CT images at the level of the tympanic facial nerve. The union between the IVCC and the falciform crest appears radiologically as a short stem or mini-martini glass. CONCLUSION: The proposed IVCC is a novel landmark with a consistent relationship to the IAC fundus and the facial nerve. It may be utilized in conjunction with the falciform crest to identify the facial nerve during minimally invasive transcanal surgeries.

Hearing-Preserving Approaches to the Internal Auditory Canal: Feasibility Assessment from the Perspective of an Endoscope.

OBJECTIVE: Minimally invasive transcanal transpromontorial endoscopic approaches to the internal auditory canal sacrifice the cochlea. Two hearing-preserving approaches, the exclusively endoscopic transcanal infracochlear approach and the endoscope-assisted transmastoid retrolabyrinthine approach, have been controversially discussed in the literature. In this study, we examine the feasibility of these 2 approaches by means of three-dimensional surface models, a population-based analysis of the available surgical space, and dissections in human whole-head specimens. METHODS: We reconstructed three-dimensional surface models based on clinical high-resolution computed tomography scans of 53 adult temporal bones. For both approaches, we measured the maximal extensions and the area of the surgical access windows located between landmarks on the surrounding anatomic structures. We then identified the limiting extensions and derived the cumulative distribution to describe the available surgical space. Dissections were performed to validate the corridors and landmark selection. RESULTS: The limiting extension for the infrachochlear approach is 7.0 ± 2.7 mm from the round window to the dome of the jugular bulb. The limiting extension for the retrolabyrinthine approach is 6.4 ± 1.5 mm from the dura of the posterior fossa to the facial nerve. The cumulative distribution shows that 80% of the cohort have access window extensions ≥3 mm for both approaches. CONCLUSIONS: This study shows that in a high percentage of the measured cohort, the access windows are sufficiently large for endoscopic approaches to the internal auditory canal. With appropriate instrumentation, these hearing-preserving minimally invasive approaches may evolve into alternatives to surgical treatment.

Exclusive Endoscopic Laser-Stapedotomy: Feasibility of an Ovine Training Model.

OBJECTIVE: Stapedotomy is an effective treatment for conductive hearing loss associated with otosclerosis. However, the procedure, especially using the endoscopic technique requires extensive training and experience for optimal results. Due to limited training options in endoscopic stapes surgery, we aim to develop an ovine stapedotomy model and assess its feasibility for surgeons at different training levels. METHODS: A fully endoscopic ovine laser-stapedotomy model was developed and described. During repetitive dissections, surgical time required for the different steps to assess the training curve and associated intraoperative complications were recorded in three surgeons of different training level. Additionally, subjective feedback was assessed. RESULTS: Successful endoscopic laser-stapedotomy was performed in 25 cases in the ovine model. Assessment of surgical time revealed a stable curve for the experienced surgeon (mean 15:01 min) for the whole training with no intraoperative complications. The fellow showed a gradual reduction of surgical time from 27:21 (first five cases) to 24:10 minutes (last five cases) and the resident a reduction from 42:38 to 21:08 minutes respectively. The assessed learning curve for the trainees revealed a significant association between the operative time and observed intraoperative complications. DISCUSSION: In this study, an ex-vivo model for exclusively endoscopic laser-stapedotomy was developed and tested for feasibility. We suggest the ovine model as a cost-effective, easily available, and realistic training model for future otologic surgeons. The surgeons were able to improve their performance with satisfactory results despite the small number of cases.

Endoscopic-Assisted Lateral Corridor to the Infratemporal Fossa: Proposal and Quantitative Comparison to the Endoscopic Transpterygoid Approach.

Objective This study was aimed to propose an expanded endoscopic-assisted lateral approach to the infratemporal fossa (ITF) and compare its area of exposure and surgical freedom with the endoscopic endonasal transptergyoid approach (EETA). Methods Anatomical dissections were performed in five cadaver heads (10 sides). The ITF was first examined through the endoscopically assisted lateral corridor, herein referred to as the endoscopic-assisted transtemporal fossa approach (TTFA). After that, the EETA was performed and coupled with two sequential maxillary procedures (medial maxillectomy [MM], and endoscopic-assisted Denker's approach [DA]). Using the stereotactic neuronavigation, measurements of the area of exposure and surgical freedom at the foramen ovale were determined for the previously mentioned approaches. Results Bimanual exploration of the ITF through the endoscopic-assisted lateral approach was achieved in all specimens. The DA (729 ± 49 mm 2 ) provided a larger area of exposure than MM (568 ± 46 mm 2 ; p < 0.0001). However, areas of exposure were similar between the DA and the TTFA (677 ± 35 mm 2 ; p = 0.09). The surgical freedom offered by the TTFA (109.3 ± 19 cm 2 ) was much greater than the DA (24.7 ± 4.8 cm 2 ; p < 0.0001), and the MM (15.2 ± 3.2 cm 2 , p < 0.0001). Conclusion The study demonstrates the feasibility of the proposed approach to provide direct access to the extreme extensions of the ITF. The lateral corridor offers an ideal working area in the posterior compartment of the ITF without crossing over important neurovascular structures. The new technique may be used alone in selected primary ITF lesions or in combination with endonasal approaches in pathologies spreading laterally from the nose or nasopharynx.

Endoscopic Anatomy of the Chorda Tympani: Systematic Dissection, Novel Anatomic Classification, and Surgical Implications.

HYPOTHESIS: A transcanal endoscopic approach enables visualization of the variable course of the chorda tympani inside the middle ear. BACKGROUND: The chorda tympani is the longest intrapetrous branch of the facial nerve. Despite having been investigated in several studies, a description of its tympanic tract from an endoscopic point of view is lacking in the literature. METHODS: We performed transcanal endoscopic dissections of 44 human cadaveric head and ear specimens. The entry point of the chorda tympani into the middle ear was classified into four categories according to its location, and as covered or dehiscent according to its appearance. The chordal eminence (CE) was defined as absent, shallow, intermediate, prominent, or fused, based on its shape and extension. The relationship of the chorda tympani to adjacent bony and ligamental structures was assessed. RESULTS: The tympanic tract of the chorda tympani was divided into three portions. The periannular segment was dehiscent in 54.5% of specimens, with type II being the most frequent entry point configuration (52.3%). In the interossicular segment, the nerve consistently passed lateral to the incus and medial to the malleus. The course of the intrapetrous segment was independent from the conformation of the tensor fold and supratubal recess. CONCLUSION: The transcanal endoscopic approach allows a detailed description of tympanic segment of the chorda tympani. Novel anatomic classifications of the chorda tympani and CE are proposed herein to highlight their possible surgical implications during otologic procedures.

Training model for salvage procedures in endoscopic stapes surgery.

PURPOSE: The learning curve in endoscopic stapes surgery, is flat and long. There is limited space during training for advanced and salvage procedures, which could be necessary in unexpected intraoperative scenarios. The aim of the present study is to develop an ex-vivo animal model for training in salvage and advanced procedures in endoscopic stapes surgery METHODS: After defining the difficult intraoperative scenarios requiring a salvage procedure during stapes surgery, we used the ovine model to create those intraoperative situations. After assessing the suitability of the model for that purpose, it was validated by subjective feedback rating (scale from 1 to 10) and by comparing the relevant anatomical structures for stapes surgery with the human. Finally, an optimal sequence of surgical steps was defined. RESULTS: 8 Fresh frozen lamb heads (16 ears) were studied. The selected intraoperative scenarios were: floating footplate, footplate fracture, luxation of the incus or necrosis of the long process, overhanging facial nerve, obliterative otosclerosis. The simulation resulted feasible and close to real. The mean overall rating for surgical scenarios ranged from 7.5 to 8.8 for residents and was consistent with the rating of senior surgeons, ranging from 7.67 and 9.0. Anatomical measures of the oval window area resulted similar between the ovine and the human. CONCLUSION: The ex-vivo ovine model is a suitable model for training in salvage and advanced procedures in exclusively endoscopic stapes surgery. The model can be used both for the training and maintenance of the acquired advanced skills in endoscopic stapes surgery.

Relationship Between the Cochlear Aqueduct and Internal Auditory Canal: Surgical Implications for Transcanal Transpromontorial Approaches to the Lateral Skull Base.

HYPOTHESIS: The cochlear aqueduct (CA) is subject to considerable anatomical variability. We hypothesize a topographical relationship between the CA and the internal auditory canal (IAC). BACKGROUND: The CA represents the lower limit of dissection during transcanal transpromontorial approaches to the lateral skull base due to its close relationship to the lower cranial nerves and jugular vein. METHODS: Three-dimensional models from high-resolution computed tomography scans of normal human temporal bones were created using threshold-based segmentation. The CA was classified into four categories. Five points were determined on the three-dimensional models to measure the surgically relevant relationships. RESULTS: Segmentation was performed on 26 high-resolution computed tomography scans. The average length of the virtual and visual part of the CA was 6.6 mm (SD ±1.7 mm) and 5.5 mm (SD ±1.3 mm) respectively. The mean distance between the IAC and the medial end of the visual part of the CA was 3.8 mm (±0.7 mm), while the average distance between the IAC and the lateral end was 1.4 mm (±0.6 mm). The distance between the visual part of the CA and the IAC increased by 0.25 mm per from the fundus of the IAC. CONCLUSION: A close relationship between the CA and the IAC could be established, despite the anatomical variability of the CA. The distance between CA and IAC increases by 0.25 per mm from the fundus to the porus of the IAC. These findings quantify the inferior limit of dissection of the transcanal transpromontorial approach to the lateral skull base.

Quantification and Comparison of Droplet Formation During Endoscopic and Microscopic Ear Surgery: A Cadaveric Model.

OBJECTIVES: The COVID-19 pandemic and the disproportional spread of the disease among otorhinolaryngologists raised concerns regarding the safety of health care staff. Therefore, a quantitative risk assessment for otologic surgery would be desirable. This study aims to quantitatively compare the risk of perioperative droplet formation between microscopic and endoscopic approaches. STUDY DESIGN: Experimental research. SETTING: Temporal bone laboratory. METHODS: The middle ear of whole head specimens was injected with fluorescein (0.2 mg/10 mL) before endoscopic and microscopic epitympanectomy and mastoidectomy. Fluorescent droplet deposition on the surgical table was recorded under ultraviolet light, quantified, and compared among the interventions. Drilling time, droplet proportion, fluorescein intensity, and droplet size were assessed for every procedure. RESULTS: A total of 12 procedures were performed: 4 endoscopic epitympanectomies, 4 microscopic epitympanectomies, and 4 mastoidectomies. The mean (SD) proportion of fluorescein droplets was 0.14‰ (0.10‰) for endoscopic epitympanectomy and 0.64‰ (0.31‰) for microscopic epitympanectomy. During mastoidectomy, the deposition of droplets was 8.77‰ (6.71‰). Statistical comparison based on a mixed effects model revealed a significant increase (0.50‰) in droplet deposition during microscopic epitympanectomy as compared with endoscopic epitympanectomy (95% CI, 0.16‰ to 0.84‰). CONCLUSIONS: There is considerable droplet generation during otologic surgery, and this represents a risk for the spread of airborne infectious diseases. The endoscopic technique offers the lowest risk of droplet formation as compared with microscopic approaches, with a significant 4.5-fold reduction of droplets between endoscopic and microscopic epitympanectomy and a 62-fold reduction between endoscopic epitympanectomy and cortical mastoidectomy.

Transcanal Transpromontorial Approach to Lateral Skull Base: Maximal Area of Exposure and Surgical Extensions.

OBJECTIVE: To determine the possible surgical extensions and maximal area of exposure (AOE) achievable through the transcanal transpromontorial approach (TTA) to the internal auditory canal (IAC) and cerebellopontine angle. We hypothesize a possible extension of indication for this minimally invasive approach to the lateral skull base. METHODS: In this experimental anatomic study, the expanded TTA was first carried out in 4 temporal bones to define the anatomic boundaries of the maximal exposure, from 2 perspectives, the middle ear and the porus of the IAC. Consecutively, these identified boundaries were translated on segmented 3-dimensional (3D) surface models of 32 temporal bone high-resolution computed tomography scans. RESULTS: The dissections performed were the basis followed during the determination of the AOE on the 3D surface models. The measurements revealed that the AOE at the middle ear was 152.9 ± 33.6 mm2, whereas it was 151.9 ± 24.8 mm2 at the porus of the IAC. The mean superoinferior and anteroposterior extensions at the middle ear were 14.7 ± 2.5 mm and 16.9 ± 2.5 mm, respectively. On the other hand, the mean superoinferior and anteroposterior extensions at the IAC porus were 10.3 ± 1.3 mm and 18.5 ± 1.9 mm, respectively. CONCLUSIONS: Consistent with the minimally invasive approaches, the AOE is limited; however, if compared with traditional approaches, it appears of considerable size. Our results may assist the surgeon in the selection process of the appropriate candidates for the TTA and to tailor the approach to the disease.

Acquisition of basic ear surgery skills: a randomized comparison between endoscopic and microscopic techniques.

BACKGROUND: Endoscopic ear surgery is gaining increasing popularity and has an important impact on teaching middle ear anatomy and basic surgical skills among residents and fellows. Due to the wide-angled views offered, the approach significantly differs from the established microscopic technique. This randomized study compares the acquisition of basic ear-surgery skills using the endoscopic and microscopic technique under standardized conditions. We aim to investigate the required surgical times, attempts and accidental damages to surrounding structures (errors) in surgeons with different training levels. METHODS: Final-year medical students (n = 9), residents (n = 14) and consultants (n = 10) from the Department of Otorhinolaryngology, Head and Neck Surgery at the University Hospital of Bern, Switzerland were enrolled in the present study. After randomization every participant had to complete a standard set of grasping and dissecting surgical tasks in a temporal bone model. After the first session the participants were crossed over to the other technique. RESULTS: Time required for completion of the surgical tasks was similar for both techniques, but highly dependent on the training status. A significant increase in the number of damages to the ossicular chain was observed with the microscopic as compared to the endoscopic technique (p < 0.001). Moreover, students beginning with the endoscopic technique showed an overall significantly lower amount of time to complete the tasks (p = 0.04). From the subjective feedback a preference towards the endoscopic technique mainly in medical students was observed. CONCLUSIONS: The endoscopic approach is useful and beneficial for teaching basic surgical skills, mainly by providing a reduction of damage to surrounding tissues with similar operating times for both techniques. Moreover, medical students performed significantly faster, when first taught in the endoscopic technique. Especially for young surgeons without previous training in ear surgery, the endoscope should be considered to improve surgical skills in the middle ear.

Clinical Applicability of a Preoperative Angular Insertion Depth Prediction Method for Cochlear Implantation.

OBJECTIVE: Evaluation of the accuracy and clinical applicability of a single measure cochlear implant angular insertion depth prediction method. BACKGROUND: Cochlear implantation outcomes still vary extensively between patients. One of the possible reasons could be variability in intracochlear electrode array placement. For this reason, single measure methods were suggested to preoperatively predict angular insertion depths. Based on a previously performed accuracy study in human temporal bones, we were interested in determining the extent to which the method could be applied in a clinical setting. METHODS: A retrospective analysis was performed on pre- and postoperative radiographic images of 50 cochlear implant recipients. Preoperatively predicted angular insertion depths were compared with angular insertion depths measured on postoperative ground truth. The theoretical prediction error was computed under the assumption that all achieved insertions were matching the preoperatively assumed linear insertion depth. More importantly, the clinical prediction error was assessed using two different software tools performed by three experienced surgeons. RESULTS: Using the proposed method we found a theoretical prediction error of 5 degrees (SD = 41 degrees). The clinical prediction error including the cases with extracochlear electrodes was 70 degrees (SD = 96 degrees). CONCLUSIONS: The presented angular insertion depth prediction method is a first practical approach to support the preoperative selection of cochlear implant electrode arrays. However, the presented procedure is limited in that it is unable to predict the occurrence of insertion results with extracochlear electrodes and requires user training.

Comparison of 3- vs 2-Dimensional Endoscopy Using Eye Tracking and Assessment of Cognitive Load Among Surgeons Performing Endoscopic Ear Surgery.

IMPORTANCE: Endoscopic ear surgery (EES) is an emerging technique to treat middle ear diseases; however, the interventions are performed in 2-dimensional (2D) endoscopic views, which do not provide depth perception. Recent technical developments now allow the application of 3-dimensional (3D) endoscopy in EES. OBJECTIVE: To investigate the usability, advantages, and disadvantages of 3D vs 2D endoscopy in EES under standardized conditions. DESIGN, SETTING, AND PARTICIPANTS: This cohort study conducted at a tertiary academic medical center in Bern, Switzerland, included 16 residents and consultants of the Department of Otorhinolaryngology, Head & Neck Surgery, Inselspital, Bern. INTERVENTIONS: Each participant performed selected steps of a type I tympanoplasty and stapedotomy in 3D and 2D views in a cadaveric model using a randomized, Latin-square crossover design. MAIN OUTCOMES AND MEASURES: Time taken to perform the EES, number of attempts, and accidental damage during the dissections were compared between 3D and 2D endoscopy. Eye tracking was performed throughout the interventions. Cognitive load and subjective feedback were measured by standardized questionnaires. RESULTS: Of the 16 surgeons included in the study (11 inexperienced residents; 5 experienced consultants), 8 were women (50%); mean age was 36 years (range, 27-57 years). Assessment of surgical time revealed similar operating times for both techniques (181 seconds in 2D vs 174 seconds in 3D). A total of 64 surgical interventions were performed. Most surgeons preferred the 3D technique (10 for 3D vs 6 for 2D), even though a higher incidence of eye strain, measured on a 7-point Likert scale, was observed (3D, 2.19 points vs 2D, 1.44 points; mean difference , 0.74; 95% CI, 0.29-1.20; r = 0.67). Eye movement assessment revealed a higher duration of fixation for consultants in 2D (0.79 seconds) compared with 3D endoscopy (0.54 seconds), indicating a less-efficient application of previously acquired experiences using the new technique. Residents (mean [SD], 49.02 [16.4]) had a significantly higher workload than consultants (mean [SD], 27.21 [12.20]), independent of the used technique or task. CONCLUSIONS AND RELEVANCE: Three-dimensional endoscopy is suitable for EES, especially for inexperienced surgeons whose mental model of the intervention has yet to be consolidated. The application of 3D endoscopy in clinical routines and for educational purposes may be feasible and beneficial.

Assessment of Middle Ear Anatomy Teaching Methodologies Using Microscopy versus Endoscopy: A Randomized Comparative Study.

Teaching methodologies for the anatomy of the middle ear have not been investigated greatly due to the middle ear's highly complex structure and hidden location inside of the temporal bone. The aim of this randomized study was to quantitatively compare the suitability of using microscope- and endoscope-based methods for teaching the anatomy of the middle ear. We hypothesize that the endoscopic approach will be more efficient compared to the microscopic approach. To answer the study questions, 33 sixth-year medical students, residents and otorhinolaryngology specialists were randomized either into the endoscopy or the microscopy group. Their anatomical knowledge was assessed using a structured anatomical knowledge test before and after each session. Each participant received tutoring on a human cadaveric specimen using one of the two methods. They then performed a hands-on dissection. After 2-4 weeks, the same educational curriculum was repeated using the other technique. The mean gains in anatomical knowledge for the specialists, residents, and medical students were +19.0%, +34.6%, and +23.4%, respectively. Multivariate analyses identified a statistically significant increase in performance for the endoscopic method compared to the microscopic technique (P < 0.001). For the recall of anatomical structures during dissection, the endoscopic method outperformed the microscopic technique independently of the randomization or the prior training level of the attendees (P < 0.001). In conclusion, the endoscopic approach to middle ear anatomy education is associated to an improved gain in knowledge as compared to the microscopic approach. The participants subjectively preferred the endoscope for educational purposes.

Quantitative Analysis of Surgical Freedom and Area of Exposure in Minimal-Invasive Transcanal Approaches to the Lateral Skull Base.

HYPOTHESIS: We aim to provide objective data regarding the area of exposure (AOE) and the surgical freedom (SF) offered by the transcanal approaches to the lateral skull base. BACKGROUND: Minimal-invasive transcanal lateral skull base procedures have been recently developed and their clinical feasibility demonstrated. The reduced access size requires careful analysis and selection of suitable cases, qualifying for a minimal-invasive approach. METHODS: We performed the mentioned approaches in standardized dissection using human whole heads. Surgical freedom is defined as the degree of movement liberty of the surgical instrument at predefined landmarks. We assessed SF at anatomical landmarks throughout the lateral skull base. Moreover, we measured the AOE, defined as the surface on the lateral skull base reached by every approach. RESULTS: We performed a total of 48 dissections under stereotactic image guidance in a total of 12 sides. The mean SF was assessed for the inferior petrous apex 602 mm, for the geniculate ganglion 1,916 mm, and for the fundus of internal auditory canal 1,337 mm. The AOE was measured for the infracochlear approach 55 mm, suprageniculate approach 67 mm, transpromontorial approach 11 mm, and for the expanded transpromontorial approach 93 mm at the fundus and 108 mm at the porus of the internal auditory canal. CONCLUSION: This study provides a quantitative description of minimal-invasive transcanal approaches to the lateral skull base. The AOE offered by the expanded transcanal transpromontorial approach is inferior but comparable to the reported AOE of transmastoidal approaches. The reported objective measurements may provide important information for future preoperative planning and patient counseling.

Minimally Invasive Lateral Endoscopic Multiport Approach to the Infratemporal Fossa: A Cadaveric Study.

BACKGROUND: Expanded endoscopic endonasal approaches to the infratemporal fossa (ITF) are increasingly performed owing to improved visualization and less morbidity compared with classic open approaches. Only a few studies in the literature investigated lateral endoscopic access to the ITF. The aim of this study was to examine the ITF with the minimally invasive endoscopically assisted Gillies approach with a trial of its expansion through a double port technique. METHODS: The ITF was examined in 10 sides of 5 cadaveric heads using a lateral endoscopic assisted approach. A double portal technique was developed to allow bimanual dissection. Specific long angled skull base instruments were used for dissection under stereotactic guidance. RESULTS: The endoscopic assisted Gillies approach permitted minimally invasive access to the complete anteroposterior extension of the ITF with sufficient mobility of surgical instruments. A new anatomic classification for the ITF from a lateral endoscopic perspective was introduced. The addition of the second port allowed bimanual dissection. CONCLUSIONS: This cadaveric study shows the feasibility of an endoscopically assisted lateral approach to the ITF. The addition of a posterior port expands the approach through increasing the working area and enabling a bimanual dissection technique. Performed alone or combined with an anterior endoscopic transnasal approach, this technique offers minimally invasive access to the ITF. The development of specifically designed instruments would further improve this promising approach.