Simultaneous closure of a perilymphatic fistula and placement of cochlear implant in a case of complex inner ear malformation.

Key Clinical Message: In young infants, under the age of one-year, cochlear malformation with profound hearing loss complicated by a perilymphatic fistula (PLF), presents a serious clinical challenge, warranting immediate audiological and surgical intervention. Timely PLF detection and closure, along with an early CI can significantly improve the prognosis of such patients and helps them in achieving their maximum hearing and developmental potential, in the long term. Abstract: Inner ear malformation (IEM) with incomplete partition and cystic cochlea is mostly accompanied by profound hearing loss. It gets further complicated with other malformations such as a perilymphatic fistula (PLF). This case concerns an 8-month-old child cochlear malformation and profound hearing loss. Surgical intervention identified a PLF at the stapedial footplate, which was successfully closed. The surgery also included the placement of a cochlear implant (CI) in the right ear, via the round window. The left ear was equipped with hearing aids, with persistent hearing thresholds at 70-80 db. At the age of 6 years, the child showed a good hearing outcome with the CI, with only moderate speech delay. Cochlear malformation accompanied by a perilymphatic leakage warrants immediate surgical closure of the PLF, to minimize the risk of bacterial meningitis. Wherever possible, the feasibility of a CI should be explored in such cases and a CI should be placed for treatment of hearing loss. Audiological and speech outcomes may vary with the use of the CI, especially in cases of IEM. However, an early CI coupled with timely PLF detection and closure can help children with profound hearing loss, in achieving their maximum hearing and developmental potential, in the long run.

Cochlear implantation impairs intracochlear microcirculation and counteracts iNOS induction in guinea pigs.

Introduction: Preservation of residual hearing remains a great challenge during cochlear implantation. Cochlear implant (CI) electrode array insertion induces changes in the microvasculature as well as nitric oxide (NO)-dependent vessel dysfunction which have been identified as possible mediators of residual hearing loss after cochlear implantation. Methods: A total of 24 guinea pigs were randomized to receive either a CI (n = 12) or a sham procedure (sham) by performing a cochleostomy without electrode array insertion (n = 12). The hearing threshold was determined using frequency-specific compound action potentials. To gain visual access to the stria vascularis, a microscopic window was created in the osseous cochlear lateral wall. Cochlear blood flow (CBF) and cochlear microvascular permeability (CMP) were evaluated immediately after treatment, as well as after 1 and 2 h, respectively. Finally, cochleae were resected for subsequent immunohistochemical analysis of the iNOS expression. Results: The sham control group showed no change in mean CBF after 1 h (104.2 ± 0.7%) and 2 h (100.8 ± 3.6%) compared to baseline. In contrast, cochlear implantation resulted in a significant continuous decrease in CBF after 1 h (78.8 ± 8.1%, p < 0.001) and 2 h (60.6 ± 11.3%, p < 0.001). Additionally, the CI group exhibited a significantly increased CMP (+44.9% compared to baseline, p < 0.0001) and a significant increase in median hearing threshold (20.4 vs. 2.5 dB SPL, p = 0.0009) compared to sham after 2 h. Intriguingly, the CI group showed significantly lower iNOS-expression levels in the organ of Corti (329.5 vs. 54.33 AU, p = 0.0003), stria vascularis (596.7 vs. 48.51 AU, p < 0.0001), interdental cells (564.0 vs. 109.1 AU, p = 0.0003) and limbus fibrocytes (119.4 vs. 18.69 AU, p = 0.0286). Conclusion: Mechanical and NO-dependent microvascular dysfunction seem to play a pivotal role in residual hearing loss after CI electrode array insertion. This may be facilitated by the implantation associated decrease in iNOS expression. Therefore, stabilization of cochlear microcirculation could be a therapeutic strategy to preserve residual hearing.

Continuous Feature-Based Tracking of the Inner Ear for Robot-Assisted Microsurgery.

Robotic systems for surgery of the inner ear must enable highly precise movement in relation to the patient. To allow for a suitable collaboration between surgeon and robot, these systems should not interrupt the surgical workflow and integrate well in existing processes. As the surgical microscope is a standard tool, present in almost every microsurgical intervention and due to it being in close proximity to the situs, it is predestined to be extended by assistive robotic systems. For instance, a microscope-mounted laser for ablation. As both, patient and microscope are subject to movements during surgery, a well-integrated robotic system must be able to comply with these movements. To solve the problem of on-line registration of an assistance system to the situs, the standard of care often utilizes marker-based technologies, which require markers being rigidly attached to the patient. This not only requires time for preparation but also increases invasiveness of the procedure and the line of sight of the tracking system may not be obstructed. This work aims at utilizing the existing imaging system for detection of relative movements between the surgical microscope and the patient. The resulting data allows for maintaining registration. Hereby, no artificial markers or landmarks are considered but an approach for feature-based tracking with respect to the surgical environment in otology is presented. The images for tracking are obtained by a two-dimensional RGB stream of a surgical microscope. Due to the bony structure of the surgical site, the recorded cochleostomy scene moves nearly rigidly. The goal of the tracking algorithm is to estimate motion only from the given image stream. After preprocessing, features are detected in two subsequent images and their affine transformation is computed by a random sample consensus (RANSAC) algorithm. The proposed method can provide movement feedback with up to 93.2 µm precision without the need for any additional hardware in the operating room or attachment of fiducials to the situs. In long term tracking, an accumulative error occurs.

Electrophysiological and histomorphological changes of cochlea in miniature pigs after abrasion of round window niches.

Background: In operations of cochlea implantation (CI), many surgeons choose to drill a window on the bone wall of cochlea basic rotation, when more and more patients receive CI with residual hearing, what damage this step would result in is unclear.Objective: To study the effect to inner ear hair cells which is caused by drilling during CI.Methods: 6 miniature pigs are equally divided into two groups, Round window niche of each pig in the experimental group was milled, while the pigs in control group wasn't. After implanting depth of 6.5, 11.5 and 20 mm, round window electrocochleography was recorded to analyze the change of cochlea microphonic (CM) potentials respectively, histomorphological changes was observed.Results: Thresholds of CM in experimental group were higher than that of control group at different depth, amplitudes were smaller. In further group, cilia of inner hair cells (IHC) at bottom rotation were significantly damaged. After operation, ABR hearing threshold of experimental group was higher, differences at low frequency region were more obvious.Conclusions: Damage caused by mulling round window niche may seriously affect the function of the hair cells. Damage of the IHC is greater than OHC. CI through round window may protect residual hearing.

Automated detection of electrically evoked stapedius reflexes (eSR) during cochlear implantation.

INTRODUCTION: In cochlear implantation, objective fitting methods are needed to optimize audiological results in small children or patients with poor compliance. Intraoperatively measured electrically evoked stapedius reflexes (eSR) can be used as a marker for the patient's discomfort level. The aim of this study was to develop and evaluate an automated detection method for eSR and to compare it to the detection rate of the surgeon and independent observers. METHODS: Cochlear implantation using a fully digital surgical microscope was performed. Movements of the stapedius tendon were recorded and analyzed by means of computer vision technique. Differences in eSR elicited by stimulating electrodes at different cochlear locations (basal, middle and apical) were analyzed. The eSR detection rate of the image processing algorithm was compared to the surgeon's detection rate and to those of two less experienced observers. RESULTS: A total of 387 electrically impulses were applied. The stimulation of middle turn electrodes showed significantly higher detection rates (50.4%) compared to the basal (40.0%; p = 0.001) and apical (43.6%; p = 0.03) turn. The software identified significantly more of the applied stimuli (58.4%) compared to the surgeon (46.3%; p = 0.0007), the intermediate observer (37.7%; p < 0.0001) and the unexperienced observer (41.3%; p < 0.0001). CONCLUSION: The feasibility of an automated intraoperative software-based detection of eSR is demonstrated. By improving the eSR detection methods and their clinical applicability, their utility in objective cochlear implant fitting may be substantially increased.

Protection of Spiral Ganglion Neurons and Prevention of Auditory Neuropathy.

In the auditory system, the primary sensory neurons, spiral ganglion neurons (SGNs), transmit complex acoustic information from hair cells to the second-order sensory neurons in the cochlear nucleus for sound processing, thus building the initial bridge between the physical world of sound and the perception of that sound. Cochlear SGN loss causes irreversible hearing impairment because this type of neural cell cannot regenerate. A better understanding of the molecular mechanisms of formation, structure, degeneration, and protection of SGNs will help to design potential therapeutic strategies for preservation and replacement of them in the cochlear implant recipient. In this review, we described and summarized the following about SGNs: (1) their cell biology and their peripheral and central connections, (2) mechanisms of their neuronal damage and their protection, and (3) the neural and synaptic mechanism of auditory neuropathy and current options for hearing rehabilitation from auditory neuropathy. The updates of the research progress and the significant issues on these topics were discussed.

Investigation of ultra-low insertion speeds in an inelastic artificial cochlear model using custom-made cochlear implant electrodes.

PURPOSE: Latest research on cochlear implantations focuses on hearing preservation during insertion of the implant's electrode array by reducing insertion trauma. One parameter which may influence trauma is insertion speed. The objective of this study was to extend the range of examined insertion speeds to include ultra-low velocities, being lower than manually feasible, and investigate whether these reduce insertion forces. METHODS: 24 custom-made cochlear implant test samples were fabricated and inserted into an artificial scala tympani model using 12 different insertion speeds while measuring the resulting insertion forces. Three commercially available slim straight electrode carriers were inserted using the same setup to analyze whether the results are comparable. RESULTS: Insertions of the test samples using high insertion speeds (2.0/2.8 mm/s) showed significantly higher insertion forces than insertions done with low insertion speeds (0.2 mm/s) or ultra-low insertion speeds (< 0.1 mm/s). The insertions with commercial slim straight electrode arrays showed significantly reduced insertion forces when using a low insertion speed as well. CONCLUSIONS: Slow insertions showed significantly reduced insertion forces. Insertion speeds which are lower than manually feasible showed even lower insertion forces.

Radiation dose reduction in postoperative computed position control of cochlear implant electrodes in lambs - An experimental study.

OBJECTIVE: Cochlear implants (CI) are standard treatment for prelingually deafened children and postlingually deafened adults. Computed tomography (CT) is the standard method for postoperative imaging of the electrode position. CT scans accurately reflect electrode depth and position, which is essential prior to use. However, routine CT examinations expose patients to radiation, which is especially problematic in children. We examined whether new CT protocols could reduce radiation doses while preserving diagnostic accuracy. METHODS: To investigate whether electrode position can be assessed by low-dose CT protocols, a cadaveric lamb model was used because the inner ear morphology is similar to humans. The scans were performed at various volumetric CT dose-indexes CTDIvol)/kV combinations. For each constant CTDIvol the tube voltage was varied (i.e., 80, 100, 120 and 140kV). This procedure was repeated at different CTDIvol values (21mGy, 11mGy, 5.5mGy, 2.8mGy and 1.8mGy). To keep the CTDIvol constant at different tube voltages, the tube current values were adjusted. Independent evaluations of the images were performed by two experienced and blinded neuroradiologists. The criteria diagnostic usefulness, image quality and artifacts (scaled 1-4) were assessed in 14 cochlear-implanted cadaveric lamb heads with variable tube voltages. RESULTS: Results showed that the standard CT dose could be substantially reduced without sacrificing diagnostic accuracy of electrode position. The assessment of the CI electrode position was feasible in almost all cases up to a CTDIvol of 2-3mGy. The number of artifacts did not increase for images within this dose range as compared to higher dosages. The extent of the artifacts caused by the implanted metal-containing CI electrode does not depend on the radiation dose and is not perceptibly influenced by changes in the tube voltage. Summarizing the evaluation of the CI electrode position is possible even at a very low radiation dose. CONCLUSIONS: CT imaging of the temporal bone for postoperative electrode position control of the CI is possible with a very low and significantly radiation dose. The tube current-time product and voltage can be reduced by 50% without increasing artifacts. Low-dose postoperative CT scans are sufficient for localizing the CI electrode.

Cochlear implantation in children with bacterial meningitic deafness: The influence of the degree of ossification and obliteration on impedance and charge of the implant.

OBJECTIVES: To determine impedance values and charge consumption following cochlear implantation post-meningitic deaf children depending on the grade of cochlear ossification and obliteration. METHODS: Post-meningitic deaf (n=49) and control (n=43) children treated with cochlear implants were included in the study. Impedance and charge values were calculated for each group. The degree of ossification of the cochlea was evaluated from a high-resolution computed tomography (HRCT) scan whereas the degree of obliteration was determined intraoperatively by the surgeon. RESULTS: Pneumococci were the principal pathogen responsible for bacterial meningitis, followed by meningococci. In HRCT scans, the degree of ossification was 1 and 2 in 29% of patients. The results of the intraoperative assessment of the cochlea showed obliteration grade 1 in 38% and grade 2 in 23% of cases. Children in the meningitis group showed significant higher impedances comparing to the control group. A significantly increased charge consumption was observed in patients with a grade 2 ossification when compared to those without ossification (P=0.02). Discussion Cochlea implanted children with meningitis-related deafness exhibit higher impedances, especially in the region of the basal and middle turn, however, not depending on the degree of cochlear ossification. High impedances and charge in the meningitis group may be explained by alterations in the central auditory pathway or on the electrode surface. CONCLUSION: To optimize the outcome in post-meningitic deaf children, surgery is advisable at an early stage prior to the onset of cochlear ossification.