Case Report: Fremitus Nystagmus in Superior Canal Dehiscence Syndrome.

Superior canal dehiscence syndrome (SCDS) is a structural bony defect of the roof of the superior semi-circular canal into the middle cranial fossa and is responsible for the creation of a third window, which alters the dynamics of the inner ear. During humming, vibratory waves entering the vestibulum and cochlea are re-routed through the dehiscence, leading to stimulation of the otolithic and ampullary vestibular organs. This is responsible for the torsional-vertical nystagmus known as "fremitus nystagmus". In this case report, we video-document a rare case of fremitus nystagmus and its resolution after plugging of the superior semi-circular canal

Pharmacological and Behavioral Strategies to Improve Vision in Acquired Pendular Nystagmus.

BACKGROUND Acquired pendular nystagmus (APN) is a back and forth, oscillatory eye movement in which the 2 oppositely directed slow phases have similar waveforms. APN occurs commonly in multiple sclerosis and causes a disabling oscillopsia that impairs vision. Previous studies have proven that symptomatic therapy with gabapentin or memantine can reduce the nystagmus amplitude or frequency. However, the effect of these medications on visual acuity (VA) is less known and to our knowledge the impact of non-pharmacological strategies such as blinking on VA has not been reported. This is a single observational study without controls (Class IV) and is meant to suggest a future strategy for study of vision in patients with disabling nystagmus and impaired vision. CASE REPORT A 49-year-old woman with primary progressive multiple sclerosis with spastic paraparesis and a history of optic atrophy presented with asymmetrical binocular APN and bothersome oscillopsia. We found that in the eye with greater APN her visual acuity improved by 1 line (from 0.063 to 0.08 decimals) immediately after blinking. During treatment with memantine, her VA without blinking increased by 2 lines, from 0.063 to 0.12, but improved even more (from 0.12 to 0.16) after blinking. In the contralateral eye with a barely visible nystagmus, VA was reduced by 1 line briefly (~500 ms) after blinking. CONCLUSIONS In a patient with APN, blinking transiently improved vision. The combination of pharmacological treatment with memantine and the blinking strategy may induce better VA and less oscillopsia than either alone

A Sleeve-Based, Micromotion Avoiding, Retractable and Tear-Opening (SMART) Insertion Tool for Cochlear Implantation

Objective: In classical cochlear implantation, the insertion of the electrode array is strongly affected by the local anatomy and human kinematics. Herein, we present a concept for an insertion tool that allows to optimize the insertion trajectory beyond anatomical constraints and stabilizes the electrode array in manual implantation. A novel sleeve-based design allows the instrument to be compliant and potentially protective to intracochlear structures, while a tear-open mechanism allows it to be removed after insertion by simply retracting the tool. Methods: Conventional and tool-guided manual insertions were performed by expert cochlear implant surgeons in an analog temporal bone model that allows to simultaneously record intracochlear pressure, insertion forces and electrode array deformation. Results: Comparison between conventional and tool-guided insertions demonstrate a substantial reduction of maximum insertion forces, force variations, transverse intracochlear electrode array movement, and pressure transients. Conclusion: The presented tool can be utilized in manual cochlear implantation and significantly improves key metrics associated with intracochlear trauma. Significance: The instrument may ultimately help improve hearing outcomes in cochlear implantation. The versatile design may be used in both manual cochlear implantation and motorized and robotic insertion, as well as image-guided surgery

Quantifying the influence of magnetic vestibular stimulation on spatial tasks

Strong magnetic fields induce dizziness, vertigo, and nystagmus due to Lorentz forces acting on the cupula in the semi-circular canals (Roberts et al. 2012). Studies using passive motion, galvanic or caloric vestibular stimulation have shown that vestibular information can interfere with cognitive tasks with spatial components (e.g., Falconer & Mast, 2012). In this study, we were interested if magnetic vestibular stimulation (MVS) in a 7 Tesla MRI scanner influences performance in cognitive tasks with spatial components. 30 participants solved a mental rotation task in a 7T MR scanner with an egocentric and an allocentric strategy. The findings of previous studies suggest that only the egocentric strategy should be affected by altered vestibular information. The allocentric strategy served as a control condition. The strength of MVS was manipulated within participants by letting them solve the task inside the bore with two different head positions, resulting in a stronger and a weaker stimulation condition (Wyssen et al., in press). Response time analyses showed that overall participants responded slower under stronger stimulation than under weaker stimulation. This effect of magnetic vestibular stimulation on response times was only present in the egocentric mental rotation task but not when participants used the allocentric strategy. However, participants showed inter-individual differences, and the strength of the individual effect could not be linked to the individual stimulation strength quantified by nystagmus. The findings of our study suggest that MVS could influence cognitive tasks with spatial components in MRI scanners. The effect of magnetic vestibular stimulation should be considered in fMRI studies using ultra-high magnetic fields using spatial tasks, as it could be a possible confounder. In the future magnet ic vestibular stimulation could serve as a tool to investigate the interrelation of vestibular information and spatial cognition. References: (1) Roberts, D. C., Marcelli, V., Gillen, J. S., Carey, J. P., Della Santina, C. C., & Zee, D. S. (2011). MRI magnetic field stimulates rotational sensors of the brain. Curr. Biol., 21(19), 1635-1640. (2) Falconer C. J., Mast F.W. (2012). Balancing the mind: vestibular induced facilitation of egocentric mental transformations. Exp. Psychol., 59(6):332-9. (3) Wyssen, G., Morrison, M., Korda, A., Wimmer, W., Otero-Millan, J., Ertl, M., Szukics, A.A., Wyss, T., Wagner, F., Caversaccio, M.D., Mantokoudis, G., Mast, F.W. (in press). Measuring the Influence of Magnetic Vestibular Stimulation on Nystagmus, Self-Motion Perception, and Cognitive Performance in a 7T MRT. J. Vis. Exp., e64022

In-Vitro Study of Speed and Alignment Angle in Cochlear Implant Electrode Array Insertions

Objective: The insertion of the electrode array is a critical step in cochlear implantation. Herein we comprehensively investigate the impact of the alignment angle and feed-forward speed on deep insertions in artificial scala tympani models with accurate macro-anatomy and controlled frictional properties. Methods: Motorized insertions (n=1033) were performed in six scala tympani models with varying speeds and alignment angles. We evaluated reaction forces and micrographs of the insertion process and developed a mathematical model to estimate the normal force distribution along the electrode arrays. Results: Insertions parallel to the cochlear base significantly reduce insertion energies and lead to smoother array movement. Non-constant insertion speeds allow to reduce insertion forces for a fixed total insertion time compared to a constant feed rate. Conclusion: In cochlear implantation, smoothness and peak forces can be reduced with alignment angles parallel to the scala tympani centerline and with non-constant feed-forward speed profiles. Significance: Our results may help to provide clinical guidelines and improve surgical tools for manual and automated cochlear implantation

Influence of magnetic vestibular stimulation on self-motion perception

Ultrahigh magnetic fields (UHF) induce dizziness, vertigo and nystagmus due to Lorentz forces acting on the cupula in the semi-circular canals, an effect called magnetic vestibular stimulation (MVS) (Roberts et al., 2011; Ward et al., 2015). As the effect of the magnetic field on the cupula remains constant throughout the exposure, MVS is specifically suitable for studying cognitive performance under vestibular stimulation. The effect of MVS can be set near to zero by tilting the head 30° forward towards the body, allowing to compare different strengths of MVS within subjects (Mian et al., 2016). Furthermore, MVS serves as a suitable non-invasive model for unilateral failure of the vestibular system, which enables studying compensatory processes (Ertl and Boegle, 2019). We conducted our study in a Siemens Terra 7 Tesla Scanner and tested 8 young, healthy participants and plan to include 30 more. The study had two main goals. First, to investigate the process of perception-reflex uncoupling, as under MVS self-motion perception differs from measured nystagmus in direction as well as time course. While horizontal nystagmus was predominant, most participants report a percept of roll rotation, and less frequent a percept of yaw rotation or a mixture of both when moving in to and out of the magnetic field. This matches previous studies (Mian et al., 2013). Reported percepts did not correspond fully to measured reflexive eye-movements. Overall, stronger nystagmus indicated stronger percepts. Roll percepts make sense because the brain integrates the prior knowledge and sensory evidence. In supine position, yaw but not roll rotation would also elicit change in direction of gravity. Second, to quantify influence of continuous vestibular stimulation on cognitive functions with spatial components. Behavioral and neuroimaging studies have shown repeatedly that caloric, galvanic and motion platform-induced vestibular stimulation can affect performance in spatial tasks, such as mental rotation (Klaus et al., 2019; Falconer & Mast, 2012). The influence of MVS on spatial cognition is relevant for fMRI studies as MVS can be a confounder, especially in studies using UHFs. In our study, we did not find a meaningful effect of MVS on mental body rotation performance, neither in allocentric nor in egocentric strategy. In the future, we aim to compare healthy participants and patients with vestibular disorders to investigate adaption and habituation mechanisms

Performing Intracochlear Electrocochleography during Cochlear Implantation.

Electrocochleography (ECochG) measures inner ear potentials generated in response to acoustic stimulation of the ear. These potentials reflect the residual function of the cochlea. In cochlear implant candidates with residual hearing, the implant electrode can directly measure ECochG responses during the implantation process. Various authors have described the ability to monitor the inner ear function by continuous ECochG measurements during the surgery. The measurement of ECochG signals during surgery is not trivial. There are no interpretable signals in up to 20% of cases. For a successful recording, a standardized procedure is recommended to achieve the highest measurement reliability and avoid possible pitfalls. Therefore, seamless collaboration between the CI surgeon and CI technician is key. This video consists of an overview of the system setup and a stepwise procedure of performing intracochlear ECochG measurements during CI surgery. It shows the surgeon's and the CI technician's roles in the process, and how a smooth collaboration between the two is made possible

Systematic review and meta-analysis of the diagnostic accuracy of spontaneous nystagmus patterns in acute vestibular syndrome.

OBJECTIVES For the assessment of patients presenting with acute prolonged vertigo meeting diagnostic criteria for acute vestibular syndrome (AVS), bedside oculomotor examinations are essential to distinguish peripheral from central causes. Here we assessed patterns of spontaneous nystagmus (SN) observed in AVS and its diagnostic accuracy at the bedside. METHODS MEDLINE and Embase were searched for studies (1980-2022) reporting on the bedside diagnostic accuracy of SN-patterns in AVS patients. Two independent reviewers determined inclusion. We identified 4,186 unique citations, examined 219 full manuscripts, and analyzed 39 studies. Studies were rated on risk of bias (QUADAS-2). Diagnostic data were extracted and SN beating-direction patterns were correlated with lesion locations and lateralization. RESULTS Included studies reported on 1,599 patients, with ischemic strokes (n = 747) and acute unilateral vestibulopathy (n = 743) being most frequent. While a horizontal or horizontal-torsional SN was significantly more often found in peripheral AVS (pAVS) than in central AVS (cAVS) patients (672/709 [94.8%] vs. 294/677 [43.4%], p < 0.001), torsional and/or vertical SN-patterns were more prevalent in cAVS than in pAVS (15.1 vs. 2.6%, p < 0.001). For an (isolated) vertical/vertical-torsional SN or an isolated torsional SN specificity (97.7% [95% CI = 95.1-100.0%]) for a central origin etiology was high, whereas sensitivity (19.1% [10.5-27.7%]) was low. Absence of any horizontal SN was more frequently observed in cAVS than in pAVS (55.2 vs. 7.0%, p < 0.001). Ipsilesional and contralesional beating directions of horizontal SN in cAVS were found at similar frequency (28.0 vs. 21.7%, p = 0.052), whereas for pAVS a contralesional SN was significantly more frequent (95.2 vs. 2.5%, p < 0.001). For PICA strokes presenting with horizontal SN, beating direction was ipsilesional more often than contralesional (23.9 vs. 6.4%, p = 0.006), while the opposite was observed for AICA strokes (2.2 vs. 63.0%, p < 0.001). CONCLUSIONS (Isolated) vertical and/or torsional SN is found in a minority (15.1%) of cAVS patients only. When present, it is highly predictive for a central cause. A combined torsional-downbeating SN-pattern may be observed in pAVS also in cases with isolated lesions of the inferior branch of the vestibular nerve. Furthermore, in cAVS patients the SN beating direction itself does not allow a prediction on the lesion side

Objectification of intracochlear electrocochleography using machine learning.

Introduction Electrocochleography (ECochG) measures inner ear potentials in response to acoustic stimulation. In patients with cochlear implant (CI), the technique is increasingly used to monitor residual inner ear function. So far, when analyzing ECochG potentials, the visual assessment has been the gold standard. However, visual assessment requires a high level of experience to interpret the signals. Furthermore, expert-dependent assessment leads to inconsistency and a lack of reproducibility. The aim of this study was to automate and objectify the analysis of cochlear microphonic (CM) signals in ECochG recordings. Methods Prospective cohort study including 41 implanted ears with residual hearing. We measured ECochG potentials at four different electrodes and only at stable electrode positions (after full insertion or postoperatively). When stimulating acoustically, depending on the individual residual hearing, we used three different intensity levels of pure tones (i.e., supra-, near-, and sub-threshold stimulation; 250-2,000 Hz). Our aim was to obtain ECochG potentials with differing SNRs. To objectify the detection of CM signals, we compared three different methods: correlation analysis, Hotelling's T2 test, and deep learning. We benchmarked these methods against the visual analysis of three ECochG experts. Results For the visual analysis of ECochG recordings, the Fleiss' kappa value demonstrated a substantial to almost perfect agreement among the three examiners. We used the labels as ground truth to train our objectification methods. Thereby, the deep learning algorithm performed best (area under curve = 0.97, accuracy = 0.92), closely followed by Hotelling's T2 test. The correlation method slightly underperformed due to its susceptibility to noise interference. Conclusions Objectification of ECochG signals is possible with the presented methods. Deep learning and Hotelling's T2 methods achieved excellent discrimination performance. Objective automatic analysis of CM signals enables standardized, fast, accurate, and examiner-independent evaluation of ECochG measurements