The use of a surgical planning tool for evaluating the optimal surgical accessibility to the stapedius muscle via a retrofacial approach during cochlear implant surgery: a feasibility study

Sinus tympani revisited for planning retrofacial approach-radiologic study in pneumatized temporal bones and its surgical implications

BACKGROUND AND PURPOSE

Retrofacial approach (RFA) is an access route to sinus tympani (ST) and it is used in cholesteatoma surgery, especially when type C ST is encountered. It may also be used to gain an access to stapedius muscle to assess the evoked stapedius reflex threshold. The primary object of this study was to evaluate the morphology of sinus tympani and its relationship to facial nerve (FN) and posterior semicircular canal (PSC) in context of planning retrofacial approach in pneumatized temporal bones.

METHODS

CBCT of 130 adults were reviewed. The type of sinus tympani was assessed according to Marchioni's classification. Width of entrance to sinus tympani (STW), depth of ST (STD), distance between the posterior semicircular canal and facial nerve (F-PSC), distance between the latter plane to the floor of ST at the right angle (P-ST) were measured at level of round window (RW) and pyramidal ridge (PR).

RESULTS

All of the bones were well-aerated and classified in Dexian Tan pneumatization group 3 or 4. Type B of ST is dominant (70.8%) in adult population with no history of inflammatory otologic diseases, followed by type C (22.7%) and then type A (6.5%). The depth of ST (STD) presented significant deviations (ANOVA, p < 0.05) among all three types. STW reaches greater values on the level of PR. F-PSC does not correlate with type of ST. In over 75% of examined type C sinus tympani the distance P-ST was less than 1 mm.

CONCLUSIONS

The qualitative classification of the sinus tympani into types A, B and C, introduced by Marchioni is justified by statistically significant differences of depth between individual types of tympanic sinuses. The STW distance reaches greater values inferiorly-it may suggest that RFA should be performed in infero-superior manner rather than opposite direction. Preoperative assessment of temporal bones CT scans gives very important information about size of sinus tympani and distance between FN and PSC.

Cochlear Implantation: The use of OTOPLAN Reconstructed Images in Trajectory Identification

OBJECTIVES

This study aimed to define the best electrode trajectory line in cochlear implant (CI) surgery using the OTOPLAN (otology planning software) reconstructed 3D model and to investigate the surgical distance of the retro-facial approach as a direct access to the round window.

METHODS

Computed tomography (CT) scans of the normal temporal bone were included for analysis in this study. OTOPLAN reconstruction was used to build 3D models with specific ear structures for study analysis.

RESULTS

Twenty-five scans were included; the average age at the time of CT scan was 6.8±12 years. Twelve scans (48%) were right-sided and thirteen (52%) were left-sided. The best trajectory line to the round window was identified in all scans. The retro-facial approach was the optimal approach for 52% of cases (13/25). In all scans, the safe distance from the facial nerve were in favor of the retro-facial approach (P = 0.0011).

CONCLUSION

The OTOPLAN reconstructed imaging provided a good analysis of the retro-facial approach and helped in planning the surgical trajectory line towards the round window. Additionally, calculation of the surgical distance can help the surgeon compare the retro-facial approach to the standard facial recess for preoperative planning. These findings may help in robotic surgery.

Accessing the stapedius muscle via novel surgical retrofacial approach during cochlear implantation surgery: Intraoperative results on feasibility and safety

Human stapedius muscle (SM) can be directly and safely accessed via retrofacial approach, opening new approaches to directly measure the electrically evoked stapedius reflex threshold (eSRT). The measurement of the SM activity via direct surgical access represents a potential tool for objective eSRT fitting of cochlear implants (CI), increasing the benefit experienced by the CI users and leading to new perspectives in the development of smart implantable neurostimulators. 3D middle-ear reconstructions created after manual segmentation and related SM accessibility metrics were evaluated before the CI surgery for 16 candidates with assessed stapedius reflex. Retrofacial approach to access the SM was performed after facial recess exposure. In cases of poor exposition of SM, the access was performed anteriorly to the FN via drilling of the pyramidal eminence (PE). The total access rate of the SM via both the retrofacial and anterior approach of the FN was 100%. In 81.2% of cases (13/16), the retrofacial approach allowed to access the SM on previously categorized well exposed (8/8), partially exposed (4/5), and wholly concealed (1/3) SM with respect to FN. Following intraoperative evaluation in the remaining 18.8% (3/16), the SM was accessed anteriorly via drilling of the PE. Exposure of SM with respect to the FN and the sigmoid sinus’s prominence was a predictor for the suitable surgical approach. The retrofacial approach offers feasible and reproducible access to the SM belly, opening direct access to electromyographic sensing of the eSRT. Surgical planner tools can quantitatively assist pre-surgical assessment.

Accessing the Stapedius Muscle Via Novel Surgical Retrofacial Approach: A Cadaveric Feasibility Study

HYPOTHESIS

Despite the complete embodiment of the stapedius muscle (SM) into the pyramidal eminence, it is possible to safely gain access to the SM belly via a retrofacial approach. This presents a novel approach to directly measure the electrically evoked stapedius reflex threshold (eSRT).

BACKGROUND

Objective fitting of maximum comfortable loudness levels for cochlear implant users can improve the benefit introduced by the device. Sensing SM activity via direct surgical access represents a potential tool for objective eSRT fitting.

METHODS

Eighteen human temporal bones (TBs) were used. Micro-computed tomography was performed for six TBs. Standard computed tomography for six TBs. Manual 3D-segmentation of the relevant middle and inner ear anatomy was performed on 12 TBs. Mastoidectomy and posterior tympanotomy allowed the access to middle ear of all 18 the TBs. Once identified the mastoidal segment of the facial nerve (FN), the retrofacial access to the SM was drilled.

RESULTS

The total access rate was 72.2%. Only in the first three cases the posterior semi-circular canal was hit. The SM access was identified posterior to the FN at a 4 ± 0.78 mm distance from the stapes' head, almost halfway to the chorda tympani's branching point along the FN direction. The drilling depth to access the SM posterior to the external surface of FN on average was 2 ± 0.30 mm. The exposure took on average of 5 to 8 minutes.

CONCLUSIONS

The retrofacial approach seems to offer a feasible and reproducible access to the SM belly opening an avenue to electromyographic sensing of eSRT.

NeuroPlan: A Surgical Planning Toolkit for an MRI-Compatible Stereotactic Neurosurgery Robot

The adoption of robotic image-guided surgeries has enabled physicians to perform therapeutic and diagnostic procedures with less invasiveness and higher accuracy. One example is the MRI-guided stereotactic robotic-assisted surgery for conformal brain tumor ablation, where the robot is used to position and orient a thin probe to target a desired region within the brain. Requirements such as the remote center of motion and precise manipulation, impose the use of complex kinematic structures, which result in non-trivial workspaces in these robots. The lack of workspace visualization poses a challenge in selecting valid entry and target points during the surgical planning and navigation stage. In this paper, we present a surgical planning toolkit called the "NeuroPlan" for our MRI-compatible stereotactic neurosurgery robot developed as a module for 3D Slicer software. This toolkit streamlines the current surgical workflow by rendering and overlaying the robot's reachable workspace on the MRI image. It also assists with identifying the optimal entry point by segmenting the cranial burr hole volume and locating its center. We demonstrate the accuracy of the workspace rendering and burr hole parameter detection through both phantom and MR-images acquired from previously conducted animal studies.

Emerging artificial intelligence applications in otological imaging

PURPOSE OF REVIEW

To highlight the recent literature on artificial intelligence (AI) pertaining to otological imaging and to discuss future directions, obstacles and opportunities.

RECENT FINDINGS

The main themes in the recent literature centre around automated otoscopic image diagnosis and automated image segmentation for application in virtual reality surgical simulation and planning. Other applications that have been studied include identification of tinnitus MRI biomarkers, facial palsy analysis, intraoperative augmented reality systems, vertigo diagnosis and endolymphatic hydrops ratio calculation in Meniere's disease. Studies are presently at a preclinical, proof-of-concept stage.

SUMMARY

The recent literature on AI in otological imaging is promising and demonstrates the future potential of this technology in automating certain imaging tasks in a healthcare environment of ever-increasing demand and workload. Some studies have shown equivalence or superiority of the algorithm over physicians, albeit in narrowly defined realms. Future challenges in developing this technology include the compilation of large high quality annotated datasets, fostering strong collaborations between the health and technology sectors, testing the technology within real-world clinical pathways and bolstering trust among patients and physicians in this new method of delivering healthcare.