Thickness of the human round window membrane in different forms of otitis media

Comparative Histopathologic Analysis of Inner Ear Damage in Meningitis: Otogenic Versus Meningogenic Routes

OBJECTIVE

To distinguish the patterns of inner ear changes between meningogenic and otogenic routes in meningitis cases. Our hypothesis is that pinpointing distinct patterns linked to each route could aid in the development of diagnostic strategies and targeted therapies.

METHODS

Temporal bones (TBs) from patients with a history of meningitis and histopathological evidence of labyrinthitis were divided into two groups (otogenic and meningogenic). Inner ear histopathological examination was performed to identify qualitative and semi-quantitative changes. This assessment encompassed inflammation patterns, indications of early ossification, hair cell loss, and alterations in the lateral wall, round window membrane, cochlear aqueduct and vestibular aqueduct.

RESULTS

Thirty-six TBs were included in the study (otogenic, 21; meningogenic, 15). Generalized labyrinthitis was more common in otogenic cases (100% vs. 53%, p < 0.001). Early signs of cochlear ossification were exclusively observed in otogenic cases (9 TBs). The spiral ligament of otogenic cases has shown a uniform loss of fibrocytes across all cochlear turns, while meningogenic cases showed more severe loss in the apical turn. Otogenic cases exhibited a higher prevalence of severe inflammation of the cochlear aqueduct and endolymphatic sac. Meningogenic cases showed more severe loss of vestibular hair cells in the otolithic organs.

CONCLUSION

Otogenic cases displayed a higher prevalence of changes in the spiral ligament and signs of early ossification, whereas meningogenic cases were associated with a higher degree of vestibular damage. Our findings emphasize the importance of considering the infection route and its implications for timely diagnosis and development of pathology-oriented treatment strategies.

LEVEL OF EVIDENCE

NA Laryngoscope, 2024.

Microbubble-assisted ultrasound for inner ear drug delivery

Treating pathologies of the inner ear is a major challenge. To date, a wide range of procedures exists for administering therapeutic agents to the inner ear, with varying degrees of success. The key is to deliver therapeutics in a way that is minimally invasive, effective, long-lasting, and without adverse effects on vestibular and cochlear function. Microbubble-assisted ultrasound ("sonoporation") is a promising new modality that can be adapted to the inner ear. Combining ultrasound technology with microbubbles in the middle ear can increase the permeability of the round window, enabling therapeutic agents to be delivered safely and effectively to the inner ear in a targeted manner. As such, sonoporation is a promising new approach to treat hearing loss and vertigo. This review summarizes all studies on the delivery of therapeutic molecules to the inner ear using sonoporation.

Sheep as a large animal model for hearing research: comparison to common laboratory animals and humans

Sensorineural hearing loss (SNHL), caused by pathology in the cochlea, is the most common type of hearing loss in humans. It is generally irreversible with very few effective pharmacological treatments available to prevent the degenerative changes or minimise the impact. Part of this has been attributed to difficulty of translating "proof-of-concept" for novel treatments established in small animal models to human therapies. There is an increasing interest in the use of sheep as a large animal model. In this article, we review the small and large animal models used in pre-clinical hearing research such as mice, rats, chinchilla, guinea pig, rabbit, cat, monkey, dog, pig, and sheep to humans, and compare the physiology, inner ear anatomy, and some of their use as model systems for SNHL, including cochlear implantation surgeries. Sheep have similar cochlear anatomy, auditory threshold, neonatal auditory system development, adult and infant body size, and number of birth as humans. Based on these comparisons, we suggest that sheep are well-suited as a potential translational animal model that bridges the gap between rodent model research to the clinical use in humans. This is especially in areas looking at changes across the life-course or in specific areas of experimental investigation such as cochlear implantation and other surgical procedures, biomedical device development and age-related sensorineural hearing loss research. Combined use of small animals for research that require higher throughput and genetic modification and large animals for medical translation could greatly accelerate the overall translation of basic research in the field of auditory neuroscience from bench to clinic.

Models of Cochlea Used in Cochlear Implant Research: A Review

As the first clinically translated machine-neural interface, cochlear implants (CI) have demonstrated much success in providing hearing to those with severe to profound hearing loss. Despite their clinical effectiveness, key drawbacks such as hearing damage, partly from insertion forces that arise during implantation, and current spread, which limits focussing ability, prevent wider CI eligibility. In this review, we provide an overview of the anatomical and physical properties of the cochlea as a resource to aid the development of accurate models to improve future CI treatments. We highlight the advancements in the development of various physical, animal, tissue engineering, and computational models of the cochlea and the need for such models, challenges in their use, and a perspective on their future directions.

Human cochlear microstructures at risk of electrode insertion trauma, elucidated in 3D with contrast-enhanced microCT

Cochlear implant restores hearing loss through electrical stimulation of the hearing nerve from within the cochlea. Unfortunately, surgical implantation of this neuroprosthesis often traumatizes delicate intracochlear structures, resulting in loss of residual hearing and compromising hearing in noisy environments and appreciation of music. To avoid cochlear trauma, insertion techniques and devices have to be adjusted to the cochlear microanatomy. However, existing techniques were unable to achieve a representative visualization of the human cochlea: classical histology damages the tissues and lacks 3D perspective; standard microCT fails to resolve the cochlear soft tissues; and previously used X-ray contrast-enhancing staining agents are destructive. In this study, we overcame these limitations by performing contrast-enhanced microCT imaging (CECT) with a novel polyoxometalate staining agent Hf-WD POM. With Hf-WD POM-based CECT, we achieved nondestructive, high-resolution, simultaneous, 3D visualization of the mineralized and soft microstructures in fresh-frozen human cochleae. This enabled quantitative analysis of the true intracochlear dimensions and led to anatomical discoveries, concerning surgically-relevant microstructures: the round window membrane, the Rosenthal's canal and the secondary spiral lamina. Furthermore, we demonstrated that Hf-WD POM-based CECT enables quantitative assessment of these structures as well as their trauma.

Optical Coherence Tomography-Based Atlas of the Human Cochlear Hook Region

Advancements in intracochlear diagnostics, as well as prosthetic and regenerative inner ear therapies, rely on a good understanding of cochlear microanatomy. The human cochlea is very small and deeply embedded within the densest skull bone, making nondestructive visualization of its internal microstructures extremely challenging. Current imaging techniques used in clinical practice, such as MRI and CT, fall short in their resolution to visualize important intracochlear landmarks, and histological analysis of the cochlea cannot be performed on living patients without compromising their hearing. Recently, optical coherence tomography (OCT) has been shown to be a promising tool for nondestructive micrometer resolution imaging of the mammalian inner ear. Various studies performed on human cadaveric tissue and living animals demonstrated the ability of OCT to visualize important cochlear microstructures (scalae, organ of Corti, spiral ligament, and osseous spiral lamina) at micrometer resolution. However, the interpretation of human intracochlear OCT images is non-trivial for researchers and clinicians who are not yet familiar with this novel technology. In this study, we present an atlas of intracochlear OCT images, which were acquired in a series of 7 fresh and 10 fresh-frozen human cadaveric cochleae through the round window membrane and describe the qualitative characteristics of visualized intracochlear structures. Likewise, we describe several intracochlear abnormalities, which could be detected with OCT and are relevant for clinical practice.

Inner Ear Diagnostics and Drug Delivery via Microneedles

Objectives: Precision medicine for inner ear disorders has seen significant advances in recent years. However, unreliable access to the inner ear has impeded diagnostics and therapeutic delivery. The purpose of this review is to describe the development, production, and utility of novel microneedles for intracochlear access. Methods: We summarize the current work on microneedles developed using two-photon polymerization (2PP) lithography for perforation of the round window membrane (RWM). We contextualize our findings with the existing literature in intracochlear diagnostics and delivery. Results: Two-photon polymerization lithography produces microneedles capable of perforating human and guinea pig RWMs without structural or functional damage. Solid microneedles may be used to perforate guinea pig RWMs in vivo with full reconstitution of the membrane in 48–72 h, and hollow microneedles may be used to aspirate perilymph or inject therapeutics into the inner ear. Microneedles produced with two-photon templated electrodeposition (2PTE) have greater strength and biocompatibility and may be used to perforate human RWMs. Conclusions: Microneedles produced with 2PP lithography and 2PTE can safely and reliably perforate the RWM for intracochlear access. This technology is groundbreaking and enabling in the field of inner ear precision medicine.

Inner Ear Drug Delivery for Sensorineural Hearing Loss: Current Challenges and Opportunities

Most therapies for treating sensorineural hearing loss are challenged by the delivery across multiple tissue barriers to the hard-to-access anatomical location of the inner ear. In this review, we will provide a recent update on various pharmacotherapy, gene therapy, and cell therapy approaches used in clinical and preclinical studies for the treatment of sensorineural hearing loss and approaches taken to overcome the drug delivery barriers in the ear. Small-molecule drugs for pharmacotherapy can be delivered via systemic or local delivery, where the blood-labyrinth barrier hinders the former and tissue barriers including the tympanic membrane, the round window membrane, and/or the oval window hinder the latter. Meanwhile, gene and cell therapies often require targeted delivery to the cochlea, which is currently achieved via intra-cochlear or intra-labyrinthine injection. To improve the stability of the biomacromolecules during treatment, e.g., RNAs, DNAs, proteins, additional packing vehicles are often required. To address the diverse range of biological barriers involved in inner ear drug delivery, each class of therapy and the intended therapeutic cargoes will be discussed in this review, in the context of delivery routes commonly used, delivery vehicles if required (e.g., viral and non-viral nanocarriers), and other strategies to improve drug permeation and sustained release (e.g., hydrogel, nanocarriers, permeation enhancers, and microfluidic systems). Overall, this review aims to capture the important advancements and key steps in the development of inner ear therapies and delivery strategies over the past two decades for the treatment and prophylaxis of sensorineural hearing loss.

[A case of obliteration of a round window in otosclerosis]

The article presents a brief review of the literature on the anatomy and physiology of the round window (RW) niche, the causes of occlusion, the diagnosis of this pathology, the features of auditory disorders and tactics when it is detected in patients with otosclerosis (OS). A clinical case of diagnosis and effective surgical treatment for obliteration of RW in a patient with advanced OS, which occurred in 2019 in 0.7% of cases, is described. Removal of RW niche obliteration was carried out with a curette and microcresis by smoothing the canopy over RW until partial visualization of the secondary membrane. It was this stage of the operation that made it possible to restore the normal hydrodynamics of the inner ear fluids and contributed to a functional result. Thus, the diagnosis of RW obliteration in patients with OS is difficult, but possible when using computed tomography of the temporal bones and assessing the mobility of the RW membrane or analyzing changes in hearing at the end of the operation, if it is performed under local anesthesia. The simultaneous performance of stapedoplasty and the removal of bone obliteration of RW makes it possible to safely achieve functional rehabilitation in patients with OS.

The safety of povidone-iodine solution in tympanoplasty: a randomised, triple-blind, placebo-controlled study

Objective

Nowadays, povidone-iodine is commonly used as a disinfectant in head and neck procedures. The present study investigated the effect of povidone-iodine, which is used as a disinfectant solution in tympanoplasty, on patients’ hearing.

Methods

A povidone-iodine solution was used as disinfection in chronic otitis media patients undergoing tympanoplasty. In the intervention group, 5% povidone-iodine, was applied to the external auditory canal and remained there for 10 minutes. In the control group, povidone-iodine was used but not allowed to enter the external auditory canal by inserting cotton wool into the canal. To evaluate the adverse effect of povidone-iodine on hearing, the bone conduction level was compared between groups at baseline and one month after exposure.

Results

Bone conduction levels at frequencies 500 Hz, 1 kHz, 2 kHz, 3 kHz, 4 kHz and 8 kHz and mean of bone conduction level in 500 Hz, 1 kHz and 2 kHz were measured and compared respectively between intervention and control group. No significant difference was seen between bone conduction levels of above frequencies and mean frequencies before and one month after surgery. (P-value = 0.321, 0.432, 0.219, 0.489, 0.61, 0.112, 0.324 respectively)

Conclusions

According to the present study, currently available 5% povidone-iodine did not affect hearing and therefore, can be comfortably used for preparation and disinfection in otologic surgeries.

A Review on Recent Advancement on Age-Related Hearing Loss: The Applications of Nanotechnology, Drug Pharmacology, and Biotechnology

Aging is considered a contributing factor to many diseases such as cardiovascular disease, Alzheimer’s disease, and hearing loss. Age-related hearing loss, also termed presbycusis, is one of the most common sensory impairments worldwide, affecting one in five people over 50 years of age, and this prevalence is growing annually. Associations have emerged between presbycusis and detrimental health outcomes, including social isolation and mental health. It remains largely untreatable apart from hearing aids, and with no globally established prevention strategies in the clinical setting. Hence, this review aims to explore the pathophysiology of presbycusis and potential therapies, based on a recent advancement in bile acid-based bio-nanotechnologies. A comprehensive online search was carried out using the following keywords: presbycusis, drugs, hearing loss, bile acids, nanotechnology, and more than 150 publications were considered directly relevant. Evidence of the multifaceted oxidative stress and chronic inflammation involvement in cellular damage and apoptosis that is associated with a loss of hair cells, damaged and inflamed stria vascularis, and neuronal signalling loss and apoptosis continues to emerge. New robust and effective therapies require drug delivery deeper into the various layers of the cochlea. Bile acid-based nanotechnology has gained wide interest in its permeation-enhancing ability and potential for numerous applications in treating presbycusis.

Investigating the Geometry and Mechanical Properties of Human Round Window Membranes Using Micro-Fringe Projection

HYPOTHESIS

The geometry and the mechanical property of the round window membrane (RWM) have a fundamental impact on the function of cochlea.

BACKGROUND

Understanding the mechanical behavior of RWM is important for cochlear surgery and design for the cochlear implant. Although the anatomy of RWM has been widely studied and described in the literature, argument remains regarding the true shape of RWM. The mechanical properties of RWM are also scarcely reported due to the difficulty of the measurement of the small size RWM.

METHODS

In this paper, micro-fringe projection was used to reconstruct the 3-dimensional geometries of 14 RWMs. Mechanical properties of the RWMs were subsequently measured using finite element (FE) model and an inverse method. The three-dimensional surface topographies and the curvatures of the two major directions reconstructed from the micro-fringe projection both demonstrated wide variations among samples.

RESULTS

The diameters of the RWMs vary from 1.65 to 2.2 mm and the curvatures vary from -0.97 to 3.76 mm-1. The nonlinear elasticity parameters in the Ogden model for each sample was measured and the average effective Young's modulus is approximately 1.98 MPa.

CONCLUSION

The geometries and mechanical properties of the human RWM measured in the work could potentially be applied to surgery design and on modeling analysis for the cochlea.

3D-Printed Microneedles Create Precise Perforations in Human Round Window Membrane in Situ

HYPOTHESIS

Three-dimensional (3D)-printed microneedles can create precise holes on the scale of micrometers in the human round window membrane (HRWM).

BACKGROUND

An intact round window membrane is a barrier to delivery of therapeutic and diagnostic agents into the inner ear. Microperforation of the guinea pig round window membrane has been shown to overcome this barrier by enhancing diffusion 35-fold. In humans, the challenge is to design a microneedle that can precisely perforate the thicker HRWM without damage.

METHODS

Based on the thickness and mechanical properties of the HRWM, two microneedle designs were 3D-printed to perforate the HRWM from fresh frozen temporal bones in situ (n = 18 total perforations), simultaneously measuring force and displacement. Perforations were analyzed using confocal microscopy; microneedles were examined for deformity using scanning electron microscopy.

RESULTS

HRWM thickness was determined to be 60.1 ± 14.6 (SD) μm. Microneedles separated the collagen fibers and created slit-shaped perforations with the major axis equal to the microneedle shaft diameter. Microneedles needed to be displaced only minimally after making initial contact with the RWM to create a complete perforation, thus avoiding damage to intracochlear structures. The microneedles were durable and intact after use.

CONCLUSION

3D-printed microneedles can create precise perforations in the HRWM without damaging intracochlear structures. As such, they have many potential applications ranging from aspiration of cochlear fluids using a lumenized needle for diagnosis and creating portals for therapeutic delivery into the inner ear.

Three-Dimensional Analysis of Round Window Membrane in the Chinchilla Model with Acute Otitis Media Induced with Streptococcus Pneumoniae 7F

Objective:

The purpose of this study was to investigate the morphological changes of round window membrane (RWM) in chinchillas with Streptococcus pneumoniae (S. pneumoniae) serotype 7F induced acute otitis media (AOM) by two dimensional (2D) and three dimensional (3D) measurements.

Methods:

Temporal bone specimens taken from 12 chinchillas were divided into two groups. The control group consisted of healthy animals that were injected with intrabullar saline. The subjects in the experimental group were induced with AOM by intrabullar injection of S. pneumoniae 7F. The 2D and 3D measurements of RWM were compared between the groups.

Results:

Dramatic changes were noted in the RWM of the experimental group compared to the control group. The thickness [mean ± standard deviation (SD)] of the RWM was significantly (p<0.05) increased in the experimental group compared to the control group by 2D measurements taken at three different points of RWM. Moreover, 3D measurements revealed that the volume (mean ± SD) of RWM was significantly (p=0.009) increased in the experimental group.

Conclusion:

The results of our study, which indicated significant change in RWM in both 2D and 3D measurements, may shed light on the relationship between AOM and inner ear diseases. Based on our results, we recommend evaluating 3D analyses of RWM, which provide useful data, to better understand the changes in the membrane.

Characterization of the Sheep Round Window Membrane

Intratympanic injection is a clinically used approach to locally deliver therapeutic molecules to the inner ear. Drug diffusion, at least in part, is presumed to occur through the round window membrane (RWM), one of the two openings to the inner ear. Previous studies in human temporal bones have identified a three-layered structure of the RWM with a thickness of 70-100 μm. This is considerably thicker than the RWM in rodents, which are mostly used to model RWM permeability and assess drug uptake. The sheep has been suggested as a large animal model for inner ear research given the similarities in structure and frequency range for hearing. Here, we report the structure of the sheep RWM. The RWM is anchored within the round window niche (average vertical diameter of 2.1 ± 0.3 mm and horizontal diameter of 2.3 ± 0.4 mm) and has a curvature that leans towards the scala tympani. The centre of the RWM is the thinnest (55-71 μm), with increasing thickness towards the edges (< 171 μm), where the RWM forms tight attachments to the surrounding bony niche. The layered RWM structure, including an outer epithelial layer, middle connective tissue and inner epithelial layer, was identified with cellular features such as wavy fibre bundles, melanocytes and blood vessels. An attached "meshwork structure" which extends over the cochlear aqueduct was seen, as in humans. The striking anatomical similarities between sheep and human RWM suggest that sheep may be evaluated as a more appropriate system to predict RWM permeability and drug delivery in humans than rodent models.

Ototoxicity of povidone-iodine - A case report

Objective

The ototoxicity of povidone-iodine has been documented in animal studies. However, there is limited evidence of these ototoxic effects in humans. This is the first report to show the ototoxic effects of povidone-iodine in a human subject.

Patient

A 36-year-old woman came to our hospital complaining of left unilateral persistent hearing loss. One month before presentation, her child had accidentally struck her on her left ear. She applied approximately three drops of povidone-iodine (10% weight/volume) into her left auditory canal. Immediately after application, she felt severe pain and vertigo. An audiogram revealed severe left unilateral sensorineural hearing loss. Magnetic resonance imaging showed mild enhancement of the left vestibule and basal turn of the left cochlea.

Conclusions

Even a single application of povidone-iodine could cause significant hearing loss and disequilibrium. It should, therefore, be used with caution.

Middle-ear dexamethasone delivery via ultrasound microbubbles attenuates noise-induced hearing loss

OBJECTIVES/HYPOTHESIS

In this study, we expanded our previous investigation by testing the efficiency of trans-round window membrane dexamethasone (DEX) delivery mediated by ultrasound (US)-aided microbubbles (MBs) and its preventive effects regarding noise exposure in animal models.

STUDY DESIGN

Live animal model.

METHODS

Forty-two pigmented male guinea pigs were divided into the following three groups: an US-MBs (USM) group, in which the tympanic bulla was filled with DEX and MBs and exposed to US; a round window soaking (RWS) group, without the US irradiation; and a control group. The above-mentioned manipulations were performed 2 hours prior to white noise exposure. The cochlear damage, including auditory threshold shifts, hair cell loss, and expression of cochlear HMGB1, was evaluated.

RESULTS

The enhanced DEX delivery efficiency of the USM group was approximately 2.4× to 11.2× greater than that of the RWS group. After the noise exposure, the RWS group showed significant cochlear protection compared with the control group, and more significant and dominant protective effects were demonstrated in the USM group.

CONCLUSIONS

The application of US-MBs provides a safe and more effective approach than spontaneous diffusion, which is commonly used in clinical practice; thus, this technique holds potential for future inner-ear drug delivery.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:1907-1914, 2019.

Anatomical basis of drug delivery to the inner ear

The isolated anatomical position and blood-labyrinth barrier hampers systemic drug delivery to the mammalian inner ear. Intratympanic placement of drugs and permeation via the round- and oval window are established methods for local pharmaceutical treatment. Mechanisms of drug uptake and pathways for distribution within the inner ear are hard to predict. The complex microanatomy with fluid-filled spaces separated by tight- and leaky barriers compose various compartments that connect via active and passive transport mechanisms. Here we provide a review on the inner ear architecture at light- and electron microscopy level, relevant for drug delivery. Focus is laid on the human inner ear architecture. Some new data add information on the human inner ear fluid spaces generated with high resolution microcomputed tomography at 15 μm resolution. Perilymphatic spaces are connected with the central modiolus by active transport mechanisms of mesothelial cells that provide access to spiral ganglion neurons. Reports on leaky barriers between scala tympani and the so-called cortilymph compartment likely open the best path for hair cell targeting. The complex barrier system of tight junction proteins such as occludins, claudins and tricellulin isolates the endolymphatic space for most drugs. Comparison of relevant differences of barriers, target cells and cell types involved in drug spread between main animal models and humans shall provide some translational aspects for inner ear drug applications.

Surgical anatomy of the round window-Implications for cochlear implantation

BACKGROUND

The round window is an important portal for the application of active hearing aids and cochlear implants. The anatomical and topographical knowledge about the round window region is a prerequisite for successful insertion for a cochlear implant electrode.

OBJECTIVE OF REVIEW

To sum up current knowledge about the round window anatomy and to give advice to the cochlear implant surgeon for optimal placement of an electrode.

TYPE OF REVIEW

Systematic Medline search.

SEARCH STRATEGY

Search term "round window[Title]" with no date restriction. Only publications in the English Language were included. All abstracts were screened for relevance, that is a focus on surgical anatomy of the round window. The search results were supplemented with hand searching of selected reviews and reference lists from included studies.

EVALUATION METHOD

Subjective assessment.

RESULTS

There is substantial variability in size and shape of the round window. The round window is regarded as the most reliable surgical landmark to safely locate the scala tympani. Factors affecting the optimal trajectory line for atraumatic electrode insertion are anatomy of the round window, the anatomy of the intracochlear hook region and the variable orientation and size of the cochlea's basal turn.

CONCLUSIONS

The very close relation to the sensitive inner ear structures necessitates a thorough anatomic knowledge and careful insertion technique, especially when implanting patients with residual hearing. In order to avoid electrode migration between the scalae and to achieve protect the modiolus and the basilar membrane, it is recommended to aim for an electrode insertion vector from postero-superior to antero-inferior.

Safety of transtympanic application of probiotics in a chinchilla animal model

Background

Chronic suppurative otitis media can be recalcitrant and difficult to treat, particularly with the increasing occurrence of antibiotic resistance. Lactobacillus plantarum is a probiotic that has been shown to decrease S. aureus and P. aeruginosa growth in wounds, making it a good candidate for the treatment of chronic suppurative otitis media. However, before it can be applied in the ear, its ototoxicity potential must be evaluated.

Methods

A prospective controlled trial was conducted in a chinchilla animal model at the Animal care research facilities of the Montreal Children’s Hospital Research Institute to determine whether Lactobacillus plantarum is ototoxic when applied transtympanically. Ten chinchillas each had one ear randomly assigned to receive 10⁹ CFU/mL of Lactobacillus plantarum solution, while the contralateral ear received saline. Auditory brainstem responses were measured bilaterally at 8, 20, 25 kHz before, at 7–10 days after application, and at 28 days after application of probiotic or saline. Facial nerve and vestibular function were assessed clinically.

Results

There were no statistically significant differences in hearing thresholds between control and experimental ears at 28 days after application. A difference of 11 dB was noted in the 25 kHz range at day 7–10, but resolved by day 28. No animals receiving probiotics developed vestibular nerve dysfunction. There was no histologic evidence of auditory hair cell damaged evidenced by scanning electron microscopy.

Conclusion

Our study suggests that a single application of Lactobacillus plantarum at 10⁹ CFU/mL does not cause ototoxicity in a chinchilla animal model. These preliminary safety evaluations and the pathogen inhibitory effects of L. plantarum demonstrated by previous studies present this probiotic as a candidate of interest for further investigation.

Electronic supplementary material

The online version of this article (10.1186/s40463-017-0242-y) contains supplementary material, which is available to authorized users.

Sensorineural hearing loss after otitis media with effusion and subacute mastoiditis after viral infections of the upper respiratory tract: A comparative study of conservative and surgical treatment

Involvement of the middle ear after viral infections of the upper airways may lead to serous otitis media with effusion in the absence of bacterial infection. This can be accompanied by a concomitant shading of the mastoid air cells, which could manifest as a reduced opacity on computed tomography (CT) in the absence of a history of chronic mastoiditis or acute inflammatory signs. This can lead to a subsequent impairment of inner ear function. CT scans reveal an extended pneumatization of the temporal bones in affected patients. Inner ear hearing impairment can probably be attributed to a concomitant labyrinthine reaction-the so-called toxic inner ear lesion. If no remission occurs within 5 days after initial conservative treatment (paracentesis or hemorrheologic infusions), surgical treatment with a mastoidectomy can accelerate hearing restoration. We conducted a retrospective, nonrandomized study of short- and long-term hearing outcomes in patients with a toxic inner ear lesion who had been treated with conservative measures alone (CONS group) or with surgery (SURG group) in a tertiary care referral center. Our study group was made up of 52 consecutively presenting patients (57 ears) who had been seen over a 10-year period; there were 20 patients (21 ears) in the CONS group and 32 patients (36 ears) in the SURG group. Initially, 15 CONS patients (75%) and 18 SURG patients (56%) complained of dizziness or a balance disorder. The initial averaged sensorineural hearing loss (over 0.5, 1.0, 2.0, and 3.0 kHz) was 32.4 ± 15.6 dB in the CONS group and 35.4 ± 12.0 dB in the SURG group. At follow-up (mean: 31.7 mo), the SURG group experienced a significantly greater improvement in hearing (p = 0.025). We conclude that patients with viral otitis media and concomitant noninflammatory mastoiditis with impairment of inner ear function (sensorineural hearing loss) experience a better hearing outcome when a mastoidectomy is performed during primary treatment.

Morphological changes in the round window membrane associated with Haemophilus influenzae-induced acute otitis media in the chinchilla

OBJECTIVE

The round window membrane (RWM) encloses the round window, the opening into the scala tympani (ST) from the middle ear. During the course of acute otitis media (AOM), structural changes of the RWM can occur that potentially affect sound transmission into and out of the cochlea. The relationship between such structural changes and conductive hearing loss during AOM has remained unclear. The focus of the current study was to compare the thickness distribution across the RWM surface between normal ears and those with AOM in the chinchilla. We assessed the occurrence of AOM-associated histological changes in this membrane compared to uninfected control animals after AOM of two relatively short durations.

MATERIAL AND METHODS

AOM was induced by transbullar injection of the nontypeable Haemophilus influenzae strain 86-028NP into two groups of adult chinchillas (n = 3 each). Bullae were obtained from the two infected groups, at 4 days or 8 days post challenge. Structures and thickness of these RWMs were compared between the two infected treatment groups and to RWMs from uninfected control animals (n = 3) at seven different RWM locations.

RESULTS

RWM thickness in infected chinchillas increased significantly at locations along the central line on the 4th day post bacterial challenge compared to values found for uninfected control animals. Lymphocyte infiltration and edema were the primary contributors to these thickness increases. No significant further increases in RWM thickness were observed when RWMs from chinchillas ears infected for 4 and 8 days were compared. Thickness and structural changes at the RWM lateral and medial areas were less visually obvious and not statistically significant among the three treatment groups. These latter RWM regions clearly were less affected during AOM than the central areas.

CONCLUSIONS

This histological study establishes that H. influenzae-induced AOM causes significant acute changes in chinchilla RWM structure that are characterized by region-specific increases in thickness. Our new morphological findings comparing normal and diseased chinchilla RWMs identify yet another biomechanical mechanism by which nontypeable H. influenzae may contribute to hearing loss in AOM.

Intratympanic Gene Delivery of Antimicrobial Molecules in Otitis Media

Otitis media (OM) in children is clinically important because of its detrimental effects on the development of language and motor coordination and is the most common reason for prescription of antibiotics. A recent bacteriological change in OM pathogens such as emergence of antibiotic resistance and vaccination-mediated pathogenic shift urges us to develop a new non-antibiotic strategy. The middle ear epithelium abundantly secretes a variety of antimicrobial molecules suppressing the viability of the common OM pathogens. Recently, we have demonstrated that the adenoviral vector is able to deliver the β-defensin 2 gene to the middle ear epithelial cells in vitro and in vivo, and adenovirus-mediated overexpression of β-defensin 2 is protective for experimental OM. There are many hurdles limiting successful clinical application of gene delivery to the respiratory epithelium of the tubotympanum; however, intratympanic gene therapy with β-defensin 2 is a promising alternative or adjuvant strategy for the management of OM.

Microperforations significantly enhance diffusion across round window membrane

HYPOTHESIS

Introduction of microperforations in round window membrane (RWM) will allow reliable and predictable intracochlear delivery of pharmaceutical, molecular, or cellular therapeutic agents.

BACKGROUND

Reliable delivery of medications into the inner ear remains a formidable challenge. The RWM is an attractive target for intracochlear delivery. However, simple diffusion across intact RWM is limited by what material can be delivered, size of material to be delivered, difficulty with precise dosing, timing, and precision of delivery over time. Further, absence of reliable methods for measuring diffusion across RWM in vitro is a significant experimental impediment.

METHODS

A novel model for measuring diffusion across guinea pig RWM, with and without microperforation, was developed and tested: cochleae, sparing the RWM, were embedded in 3D-printed acrylic holders using hybrid dental composite and light cured to adapt the round window niche to 3 ml Franz diffusion cells. Perforations were created with 12.5-μm-diameter needles and examined with light microscopy. Diffusion of 1 mM Rhodamine B across RWM in static diffusion cells was measured via fluorescence microscopy.

RESULTS

The diffusion cell apparatus provided reliable and replicable measurements of diffusion across RWM. The permeability of Rhodamine B across intact RWM was 5.1 × 10(9-) m/s. Manual application of microperforation with a 12.5-μm-diameter tip produced an elliptical tear removing 0.22 ± 0.07% of the membrane and was associated with a 35× enhancement in diffusion (P < 0.05).

CONCLUSION

Diffusion cells can be applied to the study of RWM permeability in vitro. Microperforation in RWM is an effective means of increasing diffusion across the RWM.

Ototoxicity of gentian violet on the guinea pig cochlea

PURPOSE

Gentian violet (GV) is an antimicrobial and antifungal agent that has been used widely to treat intractable discharge in the ear. The purpose of this report is to warn clinicians about the ototoxic effect of GV in the middle ear.

MATERIALS AND METHODS

GV ototoxicity was evaluated by measuring compound action potentials (CAPs) in the VIIIth nerve in adult Hartley guinea pigs. The middle ear cavities of the animals were filled with GV solution (0.5% or 0.13%), and CAPs were measured after intervals of 5 and 30 minutes and 1, 2, 6, and 24 hours. After all measurements were completed, the temporal bones were harvested for histopathologic evaluation. Celloidin-embedded specimens were cut into 20-μm slices and examined using light microscopy. The bacteriostatic activity of GV was evaluated using a disk-diffusion assay.

RESULTS

A 0.5% GV solution produced a mild elevation in the CAP threshold at 30 minutes, a greater reduction at 1 hour, and complete abolishment of CAP at 24 hours. A 0.13% GV solution caused mild elevation in the CAP threshold at 2 hours and severe elevation at 6 hours. Massive new bone formation was found in the middle ear cavity at 6 weeks. GV concentrations of 0.13% and 0.06% were effective against all bacteria tested, with the exception of Pseudomonas aeruginosa.

CONCLUSIONS

Although GV has marked antibacterial and antifungal activities, its use should be limited to the external ear canal. GV exerts an ototoxic effect in a concentration- and time-dependent manner, and so the use of this drug in the middle ear cavity is not recommended.

Chronic otitis media in children: an evidence-based guide for diagnosis and management

AIM

To provide an easy-to-follow evidence-based diagnostic and therapeutic algorithm for the management of chronic otitis media (COM) in children.

MATERIALS/METHODS

Literature review and critical analysis of the available evidence in Medline and other scientific database sources.

DATA SYNTHESIS

Otorrhea and hearing loss are the cardinal symptoms of COM, while oto-microscopy and imaging techniques can confirm the diagnosis. Conservative treatment is acceptable to some extent (i.e. mild cases of COM without cholesteatoma). It involves topical drops (quinolones as first choice drugs- strength of recommendation B), as well as performing aural toilet (strength of recommendation B), and avoiding water ingress. Tympanoplasty without mastoidectomy is expected to improve hearing in cases of non-cholesteatomatous COM (strength of recommendation C), and positively affect the children's quality of life (strength of recommendation B). Less experienced surgeons and inflamed, wet middle ear mucosa represent the two most important factors, which could lead to reperforations (strength of recommendation C). The surgical management of COM with cholesteatoma tends to employ the least invasive surgical technique, in order to obtain a small self-cleaning mastoid cavity, as well as good hearing results (strength of recommendation C).

CONCLUSION

The treatment of choice in most cases of pediatric COM is surgery. Figure 1 proposes a detailed and easy-to-follow evidence-based algorithm with regard to the diagnosis and management of COM in children.

Dynamic properties of round window membrane in guinea pig otitis media model measured with electromagnetic stimulation

The round window, one of two openings into the cochlea from the middle ear, plays an important role in hearing and is known to be structurally altered during otitis media. However, there have been no published studies systematically describing the changes in biomechanical properties of the round window membrane (RWM) that accompany bacterial otitis media. Here we describe the occurrence of significant changes in the dynamic properties of the RWM between normal guinea pigs and those with acute otitis media (AOM) that are detectable by electromagnetic force stimulation and laser Doppler vibrometry (LDV) measurements. AOM was induced by transbullar injection of streptococcus pneumoniae into the middle ear, and RWM specimens were prepared three days after challenge. Vibration of the RWM induced by coil-magnet coupling was measured by LDV over frequencies of 0.2-40 kHz. The experiment was then simulated in a finite element model, and the inverse-problem solving method was used to determine the complex modulus in the frequency domain and the relaxation modulus in the time domain. Results from 18 ears (9 control ears and 9 AOM ears) established that both the storage modulus and loss modulus of the RWM from ears with AOM were significantly lower than those of RWM from uninfected ears. The average decrease of the storage modulus in AOM ears ranged from 1.5 to 2.2 MPa and the average decrease of the loss modulus was 0.025-0.48 MPa. Our findings suggest that middle ear infection primarily affects the stiffness of the RWM due to the morphological changes that occur in AOM ears. We also conclude that the coil-magnet coupling method for assessment of RWM function may provide a valuable new approach to characterizing the mechanical response of the RWM when reverse driving is selected for middle ear implantable devices. This article is part of a special issue entitled "MEMRO 2012".

Dynamic properties of human round window membrane in auditory frequencies running head: dynamic properties of round window membrane

Round window is one of the two openings into cochlea from the middle ear. Mechanical properties of round window membrane (RWM) affect cochlear fluid motion and play an important role in the transmission of sound into cochlea. However, no measurement of mechanical properties of RWM has been reported because of the complication of its location and small size. This paper reports the first investigation on dynamic properties of human RWM using acoustic stimulation and laser Doppler vibrometry measurement. The experiments on RWM specimens were subsequently simulated in finite element (FE) model and an inverse-problem solving method was used to determine the complex modulus in frequency-domain and the relaxation modulus in time-domain. The results show that the average storage modulus of human RWM changes from 2.32 to 3.83 MPa and the average loss modulus from 0.085 to 0.925 MPa over frequencies of 200-8000 Hz. The effects of specimen geometry and experimental condition on complex modulus measurements were discussed through FE modeling analysis. Dynamic properties of RWM reported in this paper provide important data for the study of middle ear and cochlear mechanics.

Pseudo-sudden deafness

OBJECTIVES

We describe the symptom complex and management of a clinical entity we refer to as "pseudo-sudden deafness," which is an episode of acute otitis media that leads to sensorineural hearing loss with reduced speech discrimination.

METHODS

We included 8 adult patients with audiometrically confirmed, asymmetric sensorineural hearing loss with decreased speech discrimination that presented after an episode of acute otitis media. Magnetic resonance imaging ruled out retrocochlear disease. Both physical examination and myringotomy helped confirm the diagnosis of serous otitis media (SOM). Myringotomy, tympanostomy tubes, oral antibiotics, and otic antibiotic-steroid drops were used to treat the SOM. Oral steroids were used to treat the sensorineural component.

RESULTS

Pretreatment and posttreatment audiograms showed an improvement in speech discrimination score, pure tone thresholds, or both after treatment for underlying SOM and sensorineural hearing loss in 6 of the 8 patients.

CONCLUSIONS

Patients who present with an acute onset of unilateral sensorineural hearing loss with decreased speech discrimination may be mistakenly thought to have idiopathic sudden sensorineural hearing loss when, in fact, they may have an SOM-induced phenomenon that is potentially reversible. The distinguishing feature is a preexisting otitis media, which must be treated first, before the administration of steroids.

Contrast enhancement of the inner ear after intravenous administration of a standard or double dose of gadolinium contrast agents

CONCLUSION

Imaging of the endolymphatic space was possible in most cases after administering a standard dose of gadolinium (Gd) by using heavily T2-weighted 3D fluid-attenuated inversion recovery (hT(2)W-3D-FLAIR) magnetic resonance imaging (MRI).

OBJECTIVES

The aim of this study was to characterize the contrast enhancement in the inner ear after intravenous injection of Gd and to compare the signal intensity after a double dose or standard dose of Gd.

METHODS

We injected a standard dose of gadodiamide hydrate (DTPA-BMA) or a double dose of gadoteridol (HP-DO3A) intravenously in patients affected by Meniere's disease and performed hT(2)W-3D-FLAIR 3 T MRI. Contrast enhancement of the basal turn of the cochlea was evaluated semiquantitatively.

RESULTS

Endolymphatic hydrops was observed in the cochlea and vestibule of the affected ears of patients with Meniere's disease in both the double-dose group and the standard-dose group.

A new device for delivering drugs into the inner ear: otoendoscope with microcatheter

OBJECTIVES

Intratympanic injection (ITI) of drugs into the inner ear is an attractive way to deliver therapy. However, if the round window membrane (RWM) cannot be visualized, adhesions need to be removed first before ITI can be performed. We developed and tested a novel otoendoscopy device that allows visualization of the RWM for the purpose of ITI.

METHODS

Our otoendoscope consists of a catheter channel for delivering drugs and a suction channel.

RESULTS

The novel otoendoscope for inner ear drug delivery has a fine needle with catheter, which can be used to remove or perforate round window niche (RWN) mucosal adhesions. The elliptical shape of the otoendoscope effectively captures the field in the light-guided area, resulting in bright images.

CONCLUSIONS

Our otoendoscope can be used to apply drugs directly onto the surface of the RWM and to verify the correct placement of an inner ear drug delivery system, ensuring that it is safely in place.

Round window membrane in Ménière's disease: a human temporal bone study

OBJECTIVES

To disclose the histopathologic findings of the thickness of the round window membrane and the presence of false round window membrane in Ménière's disease.

METHODS

Twelve temporal bones from 6 patients with bilateral Ménière's disease, 44 temporal bones from 23 patients with unilateral Ménière's disease, and 102 age-matched normal temporal bones from 56 individuals were histopathologically examined. The thickness of the round window membrane was calculated from 3 different places. In addition, the presence of false round window membrane was investigated in temporal bones with Ménière's disease and compared to the normal temporal bones.

RESULTS

A significant difference in the mean thickness of the round window membrane was observed in temporal bones with Ménière's disease compared with normal temporal bones. There was no significant difference in the thickness of the round window membrane between the diseased side and contralateral side in patients with unilateral Ménière's disease. A false round membrane was observed in 9 (25.7%) of 35 Ménière's disease cases and in 5 (4.9%) of 102 normal temporal bones.

CONCLUSION

The thickened nature of the round window membrane and the frequent presence of false round window membrane in patients with Ménière's disease may impede the intratympanic injection treatments. The thickened middle layer of the round window membrane may be related to perilymphatic pressure changes observed in patients with Ménière's disease.

Contrast-enhanced MRI of the inner ear after intratympanic injection of meglumine gadopentetate or gadodiamide hydrate

CONCLUSION

The degree of contrast enhancement of the cochlea after intratympanic administration of meglumine gadopentetate (Gd-DTPA) or gadodiamide hydrate (Gd-DTPA-BMA) varies widely among patients with inner ear diseases. There was no morphological change in the stria vascularis after Gd-DTPA or Gd-DTPA-BMA was placed on the round window of guinea pigs.

OBJECTIVES

We investigated the degree of contrast enhancement of the inner ear after intratympanic administration of ionized and nonionized gadolinium (Gd) contrast agents in patients with inner ear diseases. The inner ear toxicities of these agents were investigated in guinea pigs.

METHODS

3D-FLAIR MRI was conducted 1 day after the intratympanic injection of eightfold-diluted Gd-DTPA or Gd-DTPA-BMA in 73 patients with inner ear diseases. Gd enhancement of the basal turn of the cochlea was evaluated as the signal intensity (SI) ratio between the affected and nonaffected sides. In guinea pigs, nondiluted Gd-DTPA, Gd-DTPA-BMA or saline was placed on the round window for 1 h and the stria vascularis was observed using electron microscopy.

RESULTS

The SI ratio ranged from 1.5 to 16.5 in the Gd-DTPA group and from 2.5 to 21 in the Gd-DTPA-BMA group. Electron microscopy showed no significant differences in the stria vascularis of guinea pigs in any of the groups.

Middle ear exploration in patients with Ménière's disease who have failed outpatient intratympanic gentamicin therapy

OBJECTIVE

Treatment of medically refractory Ménière's disease (MD) with intratympanic (IT) gentamicin has now become a standard therapy. This procedure is effective in controlling vertigo attacks, but approximately 10% of patients do not have an adequate response. The objective of the current study was to evaluate the option of middle ear exploration with direct application of gentamicin to the round window (MEE-G) in patients with persistent MD after transtympanic injection of gentamicin.

STUDY DESIGN

A retrospective chart review of 191 patients with MD treated with IT gentamicin revealed 16 who failed to have symptomatic relief after transtympanic injection. Options discussed with these patients included labyrinthectomy, vestibular nerve section, and MEE-G.

SETTING

Tertiary referral center.

PATIENTS

Eight patients opted for MEE-G.

INTERVENTION

Patients were taken to the operating room for MEE-G. After removal of the round window obstruction, gentamicin-soaked pledgets were placed for at least 30 minutes.

MAIN OUTCOME MEASURES

Control of MD-related vertigo and need for additional therapy.

RESULTS

At the time of MEE-G, all 8 patients were found to have adhesions, bone dust blocking the round window, or a thickened round window membrane. In 6 of these patients, vertigo symptoms due to MD either resolved with no further therapy (4 patients) or with subsequent IT gentamicin injections in clinic (2 patients). The remaining 2 patients underwent a vestibular nerve section, which resolved MD symptoms in each case.

CONCLUSION

Anatomic barriers to the round window membrane may be a significant cause of IT gentamicin failure, and MEE-G can be considered before ablative therapy in this subset of patients with Ménière's disease.

Change in cochlear response in an animal model of otitis media with effusion

Our previous studies confirm that middle ear mobility is reduced in the presence of otitis media with effusion (OME). Variations in middle ear function may result in changes in cochlear response in OME ears. With the long-term goal of evaluating cochlear function in OME ears, the aim of this study was to measure the displacement of the basilar membrane (BM) in guinea pig ears with OME. Vibrations of the BM at the apex and basal turn were measured in an in vitro preparation extracted 3 and 14 days after injection of lipopolysaccharide in the middle ear of guinea pigs. The results show that the displacement sensitivity of the BM at the apex and the basal turn to sound pressure in the ear canal was reduced up to 25 dB at their characteristic frequencies, respectively. Cochlear gain with respect to umbo movement was also changed in ears with OME in both groups. This study provides data for analysis of the change of BM vibration in a guinea pig OME model.

Permeability of the round window membrane is influenced by the composition of applied drug solutions and by common surgical procedures

INTRODUCTION

Intratympanic drug delivery has become widely used in the clinic, but little is known regarding how clinically used drug preparations affect round window membrane (RWM) permeability or how much drug is actually delivered to the cochlea. This study evaluated the effect of clinically relevant carrier solutions and of suction near the RWM on the permeability properties of the RWM.

METHODS

RWM permeability was assessed by perfusion of the marker trimethylphenylammonium into the round window niche while monitoring entry into perilymph using trimethylphenylammonium-selective electrodes sealed into scala tympani.

RESULTS

High-osmolarity solution increased RWM permeability by a factor of 2 to 3, benzyl alcohol (a preservative used in some drug formulations) increased permeability by a factor of 3 to 5, and suctioning near the RWM increased permeability by a factor of 10 to 15.

CONCLUSION

Variations in available drug formulations can potentially alter RWM permeability properties and affect the amount of drug delivered to the inner ear. Drug solution osmolarity, benzyl alcohol content, and possible drying of the RWM during suctioning the middle ear can all have a substantial influence of the perilymph levels of drug achieved.

Sensorineural hearing loss in patients with chronic otitis media

Chronic otitis media is generally associated with some degree of hearing loss, which is often the patient's chief complaint. This hearing loss is usually conductive, resulting from tympanic membrane rupture and/or changes in the ossicular chain due to fixation or erosion caused by the chronic inflammatory process. When cholesteatoma or granulation tissue is present in the middle ear cleft, the degree of ossicular destruction is even greater. An issue that has recently gained attention is additional sensorineural hearing loss due to chronic otitis media. While the conductive loss can be minimized through surgery, sensorineural hearing loss constitutes a permanent after effect, attenuated only through the use of a hearing aid. However, a few groups have reported a decrease in sensorineural function in these patients as well. This survey study performed at a referral center evaluates the occurrence of sensorineural hearing loss in ambulatory patients with this disease. We reviewed the files of patients with unilateral chronic otitis media. One hundred and fifty patients met the inclusion criteria: normal otoscopy and normal hearing in the contralateral ear.

MAIN OUTCOME MEASURE

bone-conduction threshold averages were calculated for frequencies of 500, 1,000, 2,000, 3,000 and 4,000 Hz, with comparison between the normal ear and the ear with chronic otitis media. Thresholds were examined separately for each frequency. The bone-conduction threshold averages for the normal side were lower than those for the ear with chronic otitis media. The threshold shift was statistically significant for each frequency (P<0.0001, Student's t test). There were differences between the groups when analyzed for age (500 and 1,000 Hz) or the presence of cholesteatoma (1,000 Hz). This study shows that chronic otitis media is associated with a decrease in cochlear function.

Gentamicin is primarily localized in vestibular type I hair cells after intratympanic administration

Intratympanic (IT) gentamicin injections are effective in the control of episodic vertigo due to Ménière's disease. Histological studies in animals have found that the loss of type I vestibular hair cells far exceeds that of type II cells after IT gentamicin treatment. The objective of this study was to determine whether this selective toxicity for type I hair cells might be due to selective concentration of the drug by these cells. Gentamicin was localized within the vestibular epithelium by both direct and indirect methods. Gentamicin conjugated to Texas Red(R) was used as a direct tracer, and anti-gentamicin antibody provided an indirect means of localization. Conjugated or unconjugated gentamicin was injected into the left tympanic space of chinchillas. The animals were killed and fixed 1 or 3 weeks post-treatment. Confocal fluorescence microscopy was used to determine the localization of gentamicin in semicircular canal cristae. Results from the animals killed within 1 week of administration showed that numerous type I hair cells still remained throughout the epithelium. The mean intensity in grayscale units (0-255) of anti-gentamicin labeling for type I hair cells was 28.14 (95% CI 24.60-31.69), for type II hair cells was 17.09 (14.99-19.20), and for support cells was 5.35 (5.34-5.46; p < 0.001, ANOVA). Anti-gentamicin antibody labeling appeared in the majority of type I hair cells throughout their cytoplasm, but with greater intensity at the apex (p < 0.001). Intensity of fluorescence with Texas-Red conjugated gentamicin was 25.38 (22.83-27.94) in type I hair cells, 15.60 (14.73-16.48) in type II cells, and 12.62 (12.06-13.17) in support cells (p < 0.001, ANOVA). These results suggest that type I hair cells are more susceptible to gentamicin because they more avidly take up or retain the drug in the early period after administration.

Safety of ofloxacin (OFLX) and fosfomycin sodium (FOM) ear drops

OBJECTIVE

The objective of this study is to evaluate the safety of two ear drops, Ofloxacin (OFLX: Taribid Otic Solution, Daiichi Seiyaku) and Fosfomycin sodium (FOM: Fosmicin S, Meiji Seiyaku).

METHODS

Albino guinea pigs were used as experimental animals, and the ototoxicity was evaluated by means of threshold changes in the compound action potentials (CAP), when topically applied to the middle ear cavity of the guinea pig. The sound stimuli applied were; click sound, with tone bursts of 8 kHz, 4 kHz, and 2 kHz. In one group of animals, after one application of the ear drops in the right middle ear cavity, the change in CAP was compared with a contralateral saline control at 24h, one week, and four weeks. In other group of animals, the ear drops were applied into the middle ear cavity for seven consecutive days and the CAP was measured at 24h.

RESULTS

At 24h the CAP threshold for click, 8 and 4 kHz elevated significantly for both the saline and ear drop treatment, but the threshold returned to normal when measured at 7 days and 28 days. Seven consecutive days of ear drops administration resulted in no reduction in the CAP for either ear drops.

CONCLUSIONS

Based on the lack of changes in the CAP, these two ear drops studied did not show any significant ototoxicities.

Round window membrane and labyrinthine pathological changes: an overview

The round window membrane is considered the most likely pathway from the middle to the inner ear. Various substances placed in the middle ear have been seen to pass through the round window membrane. Once toxic substances or inflammatory mediators such as cytokines and nitric oxide enter the inner ear, various inner ear sequelae such as labyrinthitis, endolymphatic hydrops, sensorineural hearing loss or more insidious diseases can occur.

Intratympanic gentamicin for the treatment of Ménière's disease and other forms of peripheral vertigo

Titration therapy with intratympanic gentamicin offers class A or B control of vertigo in 87% (range, 75%-100%) of patients with unilateral Ménière's disease. The risk of additional hearing loss is about 21% (range,0-37%). Vertigo may recur, however, in nearly one third of patients over time. These recurrences can also be treated by intratympanic gentamicin with a similar risk of hearing loss. The salient effect of intratympanic gentamicin is probably the reduction of vestibular function through damage to hair cells, but a complete ablation of function does not seem to be necessary for vertigo control.

Determinants of sensorineural hearing loss in chronic middle-ear disease

A statistical study was carried out on SNHL in CSOM. The study group consisted of 1,828 patients suffering from CSOM who underwent surgery at our centre from 1982 to 2001, out of these 510 cases with unilateral CSOM were selected for this study by a strict selection criteria so as to eliminate covariables such as exposure to acoustic trauma, head injury, previous ear surgery and hereditary causes. The healthy ear served as control. We determined the average SNHL in relation to the age of onset, duration of disease, examining it in relation to other eventual aural complications such as cholesteatoma, ossicular chain erosion und otorrhea.On the basis of data obtained we observed consistent co-relation between severity of SNHL and duration of the disease, presence of cholesteatoma, ossicular erosion, attic and subtotal perforations. These findings suggest that more severe middle ear disease may result in SNHL and thus early intervention in cases of chronic suppurative Otitis media is desired.

Round window membrane in young and aged C57BL/6 mice

Although there have been many studies on the round window membrane (RWM), little information has been reported about changes in the membrane associated with aging. We have undertaken morphological studies of RWMs using young (7-8 weeks old) and aged (27-29 months old) C57BL/6 mice. The RWM was thinner in mice from the aged group compared with that of the young group. The cell density in the epithelial and inner layers was also reduced in the aged group. In the middle layer of the RWM in aged mice, transmission electron microscopy revealed many degenerated short and thick elastic fibers. Confocal laser microscopy using fluorescein isothiocyanate(FITC)-wheat germ agglutinin (WGA) staining was used to identify WGA-positive fibers in the middle layer of the RWM, which changed in a similar manner to the fibers in aging skin.

Round window gentamicin absorption: an in vivo human model

OBJECTIVE/HYPOTHESIS

Using a novel human labyrinthine sampling model, in vivo gentamicin absorption through the round window can be measured.

STUDY DESIGN

A prospective study.

METHODS

Gentamicin was delivered either transtympanically (preoperative) or through a facial recess approach (intraoperative). The lateral semicircular canal and vestibule were opened, and by means of a microsyringe, labyrinthine fluid was aspirated. A sample of serum was also drawn. In all patients cerebrospinal fluid was also drawn. The samples were analyzed using a standard chemistry analyzer.

RESULTS

Intratympanic gentamicin diffused through the round window membrane and achieved concentrations in the labyrinthine fluid ranging from 0 to 16 mg/L. Intratympanic gentamicin was absorbed into the systemic circulation in 4 of 11 patients with serum levels ranging from 0.3 to 0.4 mg/L. No gentamicin was detected in the cerebrospinal fluid.

CONCLUSIONS

Intratympanic gentamicin diffuses rapidly through the round window membrane and achieves significant levels in the inner ear. Thus, this new model can be used to assess round window permeability to clinically relevant medications such as steroids and ototopical antibiotics.

Clinical aspects of round window membrane permeability under normal and pathological conditions

Current research and an overall review of 25 years of round window membrane studies are presented. The approach, rationale and concepts that have evolved from these studies are described. Ultrastructural studies of the round window membrane of humans, monkeys, felines and rodents have disclosed three basic layers: an outer epithelium, a middle core of connective tissue and an inner epithelium. Interspecies variations are mainly in terms of thickness, being thinnest in rodents and thickest in humans. Morphologic evidence suggests that the layers of the round window participate in resorption and secretion of substances to and from the inner ear, and that the membrane could play a role in the defense system of the ear. Different substances, including antibiotics and tracers, when placed in the middle ear side traverse the membrane. Tracers placed in perilymph become incorporated into the membrane by the inner epithelial cells. Permeability is selective and factors affecting permeability include size, concentration, electrical charge, thickness of the membrane and tacilitating agents. Passage of substances through the membrane is by different pathways, the nature of which is seemingly decided at the outer epithelium of the membrane. Round window membrane studies have provided increased knowledge of the anatomy and function of this structure, as well as new insights into pathology and pathogenesis. The concepts that have evolved from these studies are potentially useful for understanding middle and inner ear interactions, and for eventual drug delivery (based on permeability) to the inner ear.