Current Understanding of Hearing Loss in Sporadic Vestibular Schwannomas: A Systematic Review

ObjectiveHearing loss is the most common initial symptom in patients with sporadic vestibular schwannomas (SVS). Hearing preservation is an important goal of both conservative and surgical therapy. However, the mechanism of SVS-associated hearing loss remains unclear. Thus, we performed this systematic review to summarize the current understanding of hearing loss in the SVS and distill a testable hypothesis to further illuminate its underlying mechanism.MethodsA systematic review querying four databases (PubMed, Medline, Embase, and Web of Science) was performed to identify studies evaluating hearing loss in patients with SVS and exploring the potential mechanisms of hearing impairment.ResultsA total of 50 articles were eligible and included in this review. After analysis, the retrieved studies could be categorized into four types: (1) 29 studies explore the relationship between hearing loss and the growth pattern of the tumor (e.g., tumor size/volume, growth rate, tumor location, etc.); (2) ten studies investigate the potential role of cochlear dysfunction in hearing deterioration, including structural abnormality, protein elevation in perilymph, and cochlear malfunctioning; (3) two studies looked into SVS-induced impairment of auditory pathway and cortex; (4) in the rest nine studies, researchers explored the molecular mechanism underlying hearing loss in SVS, which involves molecular and genetic alterations, inflammatory response, growth factors, and other tumor-associated secretions.ConclusionsMultiple factors may contribute to the hearing impairment in SVS, including the growth pattern of tumor, cochlear dysfunction, impairment of auditory pathway and cortex, genetic and molecular changes. However, our current understanding is still limited, and future studies are needed to explore this multifactorial hypothesis and dig deeper into its underlying mechanism.

Noise-Induced Cochlear Damage Involves PPAR Down-Regulation through the Interplay between Oxidative Stress and Inflammation

The cross-talk between oxidative stress and inflammation seems to play a key role in noise-induced hearing loss. Several studies have addressed the role of PPAR receptors in mediating antioxidant and anti-inflammatory effects and, although its protective activity has been demonstrated in several tissues, less is known about how PPARs could be involved in cochlear dysfunction induced by noise exposure. In this study, we used an in vivo model of noise-induced hearing loss to investigate how oxidative stress and inflammation participate in cochlear dysfunction through PPAR signaling pathways. Specifically, we found a progressive decrease in PPAR expression in the cochlea after acoustic trauma, paralleled by an increase in oxidative stress and inflammation. By comparing an antioxidant (Q-ter) and an anti-inflammatory (Anakinra) treatment, we demonstrated that oxidative stress is the primary element of damage in noise-induced cochlear injury and that increased inflammation can be considered a consequence of PPAR down-regulation induced by ROS production. Indeed, by decreasing oxidative stress, PPARs returned to control values, reactivating the negative control on inflammation in a feedback loop.

Multiscale photonic imaging of the native and implanted cochlea

The cochlea of our auditory system is an intricate structure deeply embedded in the temporal bone. Compared with other sensory organs such as the eye, the cochlea has remained poorly accessible for investigation, for example, by imaging. This limitation also concerns the further development of technology for restoring hearing in the case of cochlear dysfunction, which requires quantitative information on spatial dimensions and the sensorineural status of the cochlea. Here, we employed X-ray phase-contrast tomography and light-sheet fluorescence microscopy and their combination for multiscale and multimodal imaging of cochlear morphology in species that serve as established animal models for auditory research. We provide a systematic reference for morphological parameters relevant for cochlear implant development for rodent and nonhuman primate models. We simulate the spread of light from the emitters of the optical implants within the reconstructed nonhuman primate cochlea, which indicates a spatially narrow optogenetic excitation of spiral ganglion neurons.

Cochlear Dysfunction after Kanamycin Injection in Multidrug Resistant Tuberculosis Patients

Background: Longterm exposure to aminoglycoside such as kanamycin to cochlear cells is known to be associated with damage to outer hair cells in the organ Cortiand type 1 sensory hair cells in the vestibular organs which ultimately causes permanent damage to hair cells. Hair cell damage occurs from the basal cochlea (high frequency area) to the apex cochlea (low frequency area) and followed by damage from the auditory nerve. Evaluation of cochlear dysfunction on multidrug resistant tuberculosis (MDR TB) patients have been rarelyreported in the literature based on distortion product otoacoustic emission (DPOAE).Objectives: To prove cochlear dysfunction after kanamycin injection in MDR TB patient based on DPOAE examination of the overall frequencies and specific frequency.Methods: An observational longitudinal analytic with pre and post design without control group conducted in the infection division of MDR TB Outpatients Pulmonology Department and Otorhinolaryngology Community division of ORL-HNS Department Dr. Soetomo general hospital Surabaya, within 3 months in 2018, 15 ear with the best baseline examination were taken by consecutive sampling and statistical analysis for cochlear dysfunction based on overall frequency and specific frequency DPOAE examination using Mc Nemar test.Results: Based on DPOAE examination of overall frequencies there was no cochlear dysfunction (p > 0.05) but a significant difference was found at frequency of 10,000 Hertz (Hz) (p = 0.002 ).Conclusion:On ototoxicity monitoring there was no cochlear dysfunction after 4 weeks Kanamycin injection but cochlear dysfunction occurs at a specific frequency of 10,000 Hz.

Cochlear Dysfunction after Kanamycin Injection in Multidrug Resistant Tuberculosis Patients

Long-term exposure to aminoglycoside such as kanamycin to cochlear cells is known to be associated with damage to outer hair cells in the organ Corti and type 1 sensory hair cells in the vestibular organs which ultimately causes permanent damage to hair cells. Hair cell damage occurs from the basal cochlea (high frequency area) to the apex cochlea (low frequency area) and followed by damage from the auditory nerve. Evaluation of cochlear dysfunction on multidrug resistant tuberculosis (MDR TB) patients have been rarely reported in the literature based on distortion product otoacoustic emission (DPOAE). Objectives: To prove cochlear dysfunction after kanamycin injection in MDR TB patient based on DPOAE examination of the overall frequencies and specific frequency. This was an observational longitudinal analytic with pre and post design without control group conducted in the infection division of MDR TB Outpatients Pulmonology Department and Otorhinolaryngology Community division of ORL-HNS Department, Dr. Soetomo General Hospital, Surabaya, within 3 months in 2018, 15 ear with the best baseline examination were taken by consecutive sampling and statistical analysis for cochlear dysfunction based on overall frequency and specific frequency DPOAE examination using Mc Nemar test. Based on DPOAE examination of overall frequencies there was no cochlear dysfunction (p>0.05) but a significant difference was found at frequency of 10,000 Hertz (Hz) (p=0.002). On ototoxicity monitoring there was no cochlear dysfunction after 4 weeks Kanamycin injection but cochlear dysfunction occurs at a specific frequency of 10,000 Hz.

Lateralization of cochlear dysfunction as a specific biomarker of Parkinson’s disease

In the last decade, animal studies highlighted the sensitivity of hearing function to lack of specific cochlear dopamine receptors, while several studies on humans reported association between hearing loss and Parkinson’s disease, partially recovered after levodopa administration in de novo patients. Taken together, these observations suggest investigating the possible use of cochlear function outcome variables, particularly, otoacoustic emissions, as sensitive biomarkers of Parkinson’s disease. Any lateralization of hearing dysfunction correlated with Parkinson’s disease lateralization would 1) further confirm their association, and 2) provide a disease-specific differential outcome variable. Differential indicators are particularly useful for diagnostic purposes, because their effectiveness is not limited by physiological inter-subject fluctuations of the outcome variable. Recent advances in the acquisition and analysis techniques of otoacoustic emissions suggest using them for evaluating differential cochlear damage in the two ears. In this study, we quantitatively evaluated hearing function in a population of subjects with Parkinson’s disease, to investigate the occurrence of hearing loss, and, particularly, whether hearing dysfunction shows lateralization correlated to motor symptoms. Pure tone audiometry and distortion product otoacoustic emissions were used as outcome variables in eighty patients (mean age 65 ± 9 years) and forty-one controls (mean age 64 ± 10 years). An advanced customized acquisition and analysis system was developed and used for otoacoustic testing, which guarantees response stability independent of probe insertion depth, and has the sensitivity necessary to accurately assess the low levels of otoacoustic response typical of elderly subjects. To our knowledge, this is the first study introducing the distinction between ipsilateral and contralateral ear, with respect to the body side more affected by Parkinson’s disease motor symptoms. Significant asymmetry was found in the auditory function, as both otoacoustic responses and audiometric hearing levels were worse in the ipsilateral ear. Significantly worse hearing function was also observed in patients with Parkinson’s disease compared to controls, confirming previous studies. Several pathophysiological mechanisms may be hypothesized to explain asymmetric cochlear damage in Parkinson's disease, including the impairment of dopamine release and the involvement of extra-dopaminergic circuits, with the cholinergic pathway as a likely candidate. The observed asymmetry in the audiological response of patients with Parkinson’s disease suggests that lateralization of hearing dysfunction could represent a specific non-motor signature of the disease. The possible diagnostic use of cochlear dysfunction asymmetry as a specific biomarker of Parkinson’s disease deserves further investigation, needing a more precise quantitative assessment, which would require a larger sample size.