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Objectives: The aim of this study was to assess the outcomes of cochlear implantation in children with inner ear malformations (IEMs). Methods: A retrospective review of 212 children who received implants from September 1994 to May 2004 was performed. Forty-six of them had radiologic evidence of IEMs. The preoperative evaluations, intraoperative findings, postoperative complications, and performance outcomes were analyzed. For the comparative analysis of performance outcomes, the children with IEMs were matched and compared with children with a normal inner ear who had received implants. Statistical analysis was performed with a repeated-measures analysis of variance. Results: All of the children were studied with computed tomography and magnetic resonance imaging. Three-dimensional volume rendering of magnetic resonance images was performed in cases that were difficult to interpret because of structural complexity. The operative findings included aberrant facial nerves in 2 children and cerebrospinal fluid gushers in 22 children. Intraoperative fluoroscopic examination was performed to evaluate electrode placement. There were no serious postoperative complications. All children with IEMs achieved open-set speech perception abilities, except for the children with a narrow internal auditory canal (IAC), and showed progressive improvement of their speech perception abilities over time. There were no statistically significant differences in performance measured by the Common Phrases test between the 2 groups. Although the repeated-measures analysis of variance indicated that children with IEMs performed more poorly than those with a normal inner ear on the Phonetically Balanced Kindergarten test for phonemes, statistical significance was not found at 2 years after implantation. The children with a narrow IAC benefited from the implantation and used the device every day, although their speech perception abilities were limited. Conclusions: The results of the present study show that cochlear implantation can be performed relatively safely in deaf children with IEMs and that they receive considerable benefit from their implants. Substantial benefit can be expected from implantation in children with most kinds of IEMs, except for a narrow IAC, which is often associated with limited results.

The aim of robot-assisted cochlear implant surgery (RACIS) is to access the inner ear with minimal trauma. High-resolution imaging, empowered with a highly accurate navigation system can enable the planning of a direct keyhole drilling trajectory toward the inner ear. The time has come to (re)define the ideal trajectory into the inner ear with robot-assisted tools that can drill with the highest accuracy. The trajectories of past RACIS procedures were analysed to gain insight into how to calculate the most ideal trajectory and to determine which trajectory parameters influence the course of the procedure. Data-analysis was performed on three groups of previously performed RACIS-procedures. Group 1 included the RACIS-procedures with a round window (RW) approach. Group 2 included the RACIS-procedures with difficulty entering the inner ear. Group 3 included the converted cases to conventional CI surgery due to inadequate intra-operative safety margins. The RW diameter was significantly smaller and its orientation significantly less favourable in group 2 compared to group 1. A smaller surface size and an unfavourable orientation of the RW in relation to the drilling trajectory are thus associated with a more difficult electrode array insertion in RACIS. Both must be taken into account when planning a drilling trajectory into the inner ear.

Estimation of cochlear length is gaining attention in the field of cochlear implants (CIs), mainly for selecting of CI electrode lengths. The currently available tools to estimate the cochlear duct length (CDL) are only valid for normal inner anatomy. However, inner ear malformation (IEM) types are associated with different degrees of cystic apices, limiting the application of CDL equations of normal anatomy inner ear. Therefore, this study aimed to understand the degree to which the outer wall (OW) is observed in different malformation types and to formulate mathematical equations to estimate the OW length (OWL) from cochlear parameters, namely the basal turn diameter (A-value) and width (B-value). Three-dimensional (3D) segmentation of promontory and fluid parts of the inner ear was performed to understand the extent to which the OW is visible to measure the OWL manually. Enlarged vestibular aqueduct syndrome (EVAS) was diagnosed in 37 ears, which consistently showed the extent of the OW to an angular depth of 540°, beyond which the cystic apex starts. Incomplete partition (IP) type I was observed in 30 ears, with the OW extending to only 360° of angular depth. IP type II was observed in 35 ears, with the OW extending to 450° of angular depth. IP type III was identified in 24 ears, with the OW observed for 540° of angular depth. Cavity-type malformations were observed in 36 ears, and circumference was measured in the axial view. A strong positive linear correlation was observed between the manually measured OWL and cochlear parameters for all malformation types analyzed. A multiple linear regression model was applied to formulate mathematical equations, which was further used to create a software application for estimating OWLs in IEM types, using cochlear parameters as inputs.

Purpose In patients with inner ear schwannomas (IES), reports on hearing rehabilitation with cochlear implants (CI) have increased over the past decade, most of which are case reports or small case series. The aim of this study is to systematically review the reported hearing results with CI in patients with IES considering the different audiologic outcome measures used in different countries. Methods According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline, a search of published literature was conducted. We included patients with IES (primary or with secondary extension from the internal auditory canal (IAC) to the inner ear, sporadic or NF2 related) undergoing cochlear implantation with or without tumour removal. The audiological results were divided into the categories “monosyllables”, “disyllables”, “multisyllabic words or numbers”, and “sentences”. Results Predefined audiological outcome measures were available from 110 patients and 111 ears in 27 reports. The mean recognition scores for monosyllabic words with CI were 55% (SD: 24), for bisyllabic words 61% (SD: 36), for multisyllabic words and numbers 87% (SD: 25), and 71% (SD: 30) for sentences. Results from for multisyllabic words and numbers in general showed a tendency towards a ceiling effect. Possible risk factors for performance below average were higher complexity tumours (inner ear plus IAC/CPA), NF2, CI without tumour removal (“CI through tumour”), and sequential cochlear implantation after tumour removal (staged surgery). Conclusion Hearing loss in patients with inner ear schwannomas can be successfully rehabilitated with CI with above average speech performance in most cases. Cochlear implantation thus represents a valuable option for hearing rehabilitation also in patients with IES while at the same time maintaining the possibility of MRI follow-up. Further studies should investigate possible risk factors for poor performance. Audiological tests and outcome parameters should be reported in detail and ideally be harmonized to allow better comparison between languages.

For 40 years, the amino acid acetyl-DL-leucine (or isoleucine – Tanganil®) has been used in clinical practice to reduce imbalance and autonomic manifestations associated with acute vertigo crises. In animal models, acetyl-DL-leucine accelerates vestibular compensation following unilateral labyrinthectomy, and has only minor effects on normal vestibular function. Our work in animal models suggested that acetyl-DL-leucine acted mainly on abnormally hyperpolarized and/or depolarized vestibular neurons by restoring their membrane potential towards a mean value of –65 to –60 mV. Acute vestibular disorders are associated with asymmetrical spontaneous activities of vestibular neurons, so this previous study suggested that acetyl-DL-leucine may reduce acute, vestibular-related imbalances in humans. To test this hypothesis, we investigated the efficacy of acetyl-DL-leucine during the acute stage following neurotomy or labyrinthectomy in patients undergoing surgery for unilateral vestibular acoustic neurinoma, or suffering from unilateral and intractable Ménière’s disease. By clinical testing of the vestibular function, patients were categorized according to the degree of compensation of the vestibular deafferentation prior to surgery. For patients who had achieved a close to perfect compensation before surgery, acetyl-DL-leucine had minor or no effect after surgery. For patients who displayed residual vestibular function before surgery, acetyl-DL-leucine eased the static vestibular syndromes, which followed neurotomy. Our findings tend to confirm the view that acetyl-DL-leucine mainly acts, in humans, on abnormally hyperpolarized and/or depolarized vestibular neurons by restoring their membrane potential towards normal values; this is consistent with findings in guinea pigs following unilateral labyrinthectomy. Moreover, it suggests that the degree of caloric paresis of the patients before neurotomy is useful both to predict the outcome of any acute vestibular syndrome following neurotomy and to assess the potential value of the administration of acetyl-DL-leucine to treat any such syndrome.

The human inner ear contains minute three-dimensional neurosensory structures that are deeply embedded within the skull base, rendering them relatively inaccessible to regenerative therapies for hearing loss. Here we provide a detailed characterisation of the functional architecture of the space that hosts the cell bodies of the auditory nerve to make them safely accessible for the first time for therapeutic intervention. We used synchrotron phase-contrast imaging which offers the required microscopic soft-tissue contrast definition while simultaneously displaying precise bony anatomic detail. Using volume-rendering software we constructed highly accurate 3-dimensional representations of the inner ear. The cell bodies are arranged in a bony helical canal that spirals from the base of the cochlea to its apex; the canal volume is 1.6 μL but with a diffusion potential of 15 μL. Modelling data from 10 temporal bones enabled definition of a safe trajectory for therapeutic access while preserving the cochlea’s internal architecture. We validated the approach through surgical simulation, anatomical dissection and micro-radiographic analysis. These findings will facilitate future clinical trials of novel therapeutic interventions to restore hearing.

Introduction Preserving the cochlear structures and thus hearing preservation, has become a prominent topic of discussion in cochlear implant (CI) surgery. Various approaches and soft surgical techniques have been described when approaching the inner ear. Robot-assisted cochlear implant surgery (RACIS) reaches the round window in a minimally invasive manner by following a trajectory of minimal trauma. This involves the drilling of a keyhole trajectory to the round window, through the facial recess, with no need for a complete mastoidectomy. It involves less drilling, less drilling time and less structural damage. A lot of attention has been paid to the structural traumatic causes of hearing loss but acoustic trauma during the exposure of the inner ear appears to be neglected topic. Aim The aim was to measure the noise exposure of the inner ear during the robotic drilling of the mastoid and bony overhang of the round window. The results were compared with the milling in conventional cochlear implantation surgery. Intervention RACIS on fresh frozen human cadavers. Outcome measurements The equivalent frequency-weighted and time-averaged sound pressure level L AF in dB and the noise dose in % derived from a noise damage model, both obtained during RACIS. Materials and methods The robotic drilling of 6 trajectories towards the inner ear were performed, including 4 trajectories through round window access and 2 trajectories through cochleostomy. The results were compared with the data of 7 cases of conventional CI surgery that have been described in literature. The induced equivalent sound pressure level L AF was determined via an accelleration sensor at the zygomatic arch and a calibration according to bone conduction audiometry. A noise dose for the whole procedure was calculated from the equivalent sound pressure level L AF and the exposure time using a noise damage model. A noise dose of 100% is considered a critical exposure limit and values above are considered potentially harmful, with the risk of hearing impairment. Results The maximum L AF was 82 dB during fiducial screw placement; 87 dB during middle ear access; 95 dB for the accesses through the round window and 88 dB for the accesses through cochleostomy. The noise dose due to the HEARO ® -procedure was always far below the critical value of 100%. There was no acoustic trauma of the inner ear in all cases with the noise dose being smaller than 0.1% in five out of the six cases. The maximum L AF in the seven cases of conventional CI surgery was 118 dB with a maximum cumulative noise dose of 172.6%. The critical exposure limit of 100% was exceeded in three cases of conventional CI surgery. Conclusion RACIS provokes significantly less acoustic trauma than conventional mastoid surgery in our findings. There were no observable differences in noise exposure levels between a cochleostomy or a round window approach where the bony overhang needed to be drilled.

Purpose Cochlear implantation in patients with vestibular schwannomas is of increasing importance and interest. Two remaining challenges are the assessment of conduction of the cochlear nerve and the possibility of postoperative surveillance with magnetic resonance imaging. The aim of the current study was to assess follow-up imaging and determine the visibility of the internal auditory canal after vestibular schwannoma resection and cochlear implantation as well as in patients with persistent vestibular schwannomas and cochlear implants in place. Visibility of the internal auditory canal, cerebellopontine angle, and labyrinth were evaluated and graded. Methods For this retrospective study, 15 MR examinations of 13 patients after translabyrinthine vestibular schwannoma resection and ipsilateral cochlear implantation were included. All patients had been implanted with an MED-EL cochlear implant. Magnetic resonance imaging was carried out on a 1.5T device. All patients were prepped according to the manufacturer’s recommendations. Results All 15 examinations were carried out without any adverse event during imaging, such as pain, magnet dislocation, or malfunction. The internal auditory canal and the cerebellopontine angle were sufficiently visible in all cases to allow for vestibular schwannoma follow-up. Conclusion Magnetic resonance imaging surveillance of the internal auditory canal following vestibular schwannoma resection and cochlear implantation is feasible and safe with modern implants with a 1.5T magnetic resonance imaging device using metal artifact reduction sequences. Necessary follow-up imaging should not be a contraindication for cochlear implantation in patients with vestibular schwannomas.

Purpose Drilling injuries of the inner ear are an underreported complication of lateral skull base (LSB) surgery. Inner ear breaches can cause hearing loss, vestibular dysfunction, and third window phenomenon. This study aims to elucidate primary factors causing iatrogenic inner ear dehiscences (IED) in 9 patients who presented to a tertiary care center with postoperative symptoms of IED following LSB surgery for vestibular schwannoma, endolymphatic sac tumor, Meniere’s disease, paraganglioma jugulare, and vagal schwannoma. Methods Utilizing 3D Slicer image processing software, geometric and volumetric analysis was applied to both preoperative and postoperative imaging to identify causal factors iatrogenic inner ear breaches. Segmentation analyses, craniotomy analyses, and drilling trajectory analyses were performed. Cases of retrosigmoid approaches for vestibular schwannoma resection were compared to matched controls. Results Excessive lateral drilling and breach of a single inner ear structure occurred in 3 cases undergoing transjugular ( n =2) and transmastoid ( n =1) approaches. Inadequate drilling trajectory breaching ≥1 inner ear structure occurred in 6 cases undergoing retrosigmoid ( n =4), transmastoid ( n =1), and middle cranial fossa approaches ( n =1). In retrosigmoid approaches the 2-cm visualization window and craniotomy limits did not provide drilling angles to the entire tumor without causing IED in comparison to matched controls. Conclusions Inappropriate drill depth, errant lateral drilling, inadequate drill trajectory, or a combination of these led to iatrogenic IED. Image-based segmentation, individualized 3D anatomical model generation, and geometric and volumetric analyses can optimize operative plans and possibly reduce inner ear breaches from lateral skull base surgery.

Purpose The internal auditory canal (IAC) plays a key role in lateral skull base surgery. Although several approaches to the IAC have been proposed, endoscope-assisted transcanal corridors to the IAC have rarely been studied. We sought to provide a step-by-step description of the transcanal transpromontorial approach to the IAC and analyze anatomic relationships that might enhance predictability and safety of this approach. Methods Ten cadaveric specimens were dissected and the extended transcanal transpromontorial approach to the IAC was established. Various morphometric measurements and anatomic landmarks were reviewed and analyzed. Results The proposed technique proved feasible and safe in all specimens. There was no inadvertent injury to the jugular bulb or internal carotid artery. The chorda tympani, a key landmark for the mastoid segment of the facial nerve, was identified in all dissections. The spherical recess of the vestibule and middle turn of cochlea are important landmarks for identification of the labyrinthine segment of the facial nerve. Identification of all boundaries of the working area is also essential for safe access. Among various morphometric measurements, the modiolus-IAC angle (≈ 150°) proved particularly consistent; given its ease of use and low variability, we believe it could serve as a landmark for identification and subsequent dissection of the IAC. Conclusions The extended transcanal transpromontorial approach to the IAC is feasible and safe. Relying on anatomic landmarks to ensure preservation of the involved neurovascular structures is essential for a successful approach. The modiolus-IAC angle is a consistent, reproducible landmark for IAC identification and dissection.