Communication between the perilymphatic scalae and spiral ligament visualized by in vivo MRI

Preliminary Evidence for the Effects of Gentamicin on Vertical Semicircular Canals

INTRODUCTION

Gentamicin is a vestibulotoxic antibiotic often used in patients with Ménière's disease for its vestibular ablative effects. Gentamicin's effect on the horizontal semicircular canal does not always correlate with the degree of vertigo control achieved by patients; its effect on the vertical semicircular canals remains unknown. We sought to examine the effect of intratympanic gentamicin on vertical semicircular canal function in patients with Ménière's disease using video head impulse testing.

METHODS

A retrospective case series was carried out at a tertiary academic center. Patients with Ménière's disease who received ≥1 intratympanic gentamicin injection from 2019-2022 and had video head impulse testing performed were included. Outcomes of interest were vertical semicircular canal function following intratympanic gentamicin, correlations between vertical semicircular canal function and horizontal semicircular canal function, and residual symptoms following injection.

RESULTS

Ten patients met inclusion criteria. Twenty percent had abnormal V-SCC function prior to any injection and 40% following the first injection. There was an association between abnormal vertical and horizontal semicircular canal function following the first intratympanic gentamicin injection, though the relationship did not reach statistical significance (p = 0.058). While patients with abnormal vertical semicircular canal function following the first injection were less likely to report ongoing vertigo attacks, the relationship was not statistically significant (p = 0.260).

CONCLUSIONS

Intratympanic gentamicin leads to changes in vertical semicircular canal function in at least a proportion of patients with Ménière's disease. Further study is required to better assess correlations between vertical semicircular canal function and symptom control following intratympanic gentamicin.

Improving diagnostic accuracy for probable and definite Ménière's disease using magnetic resonance imaging

PURPOSE

To determine whether magnetic resonance imaging (MRI) can improve diagnostic accuracy for definite and probable Ménière's disease (MD) based on perilymphatic enhancement (PE) and endolymphatic hydrops (EH).

METHODS

363 patients with unilateral MD (probable MD, n = 75 and definite MD, n = 288) were recruited. A three-dimensional zoomed imaging technique with parallel transmission SPACE real inversion recovery was performed 6 h after intravenous gadolinium injection to investigate the presence of PE and to evaluate the grading and location of EH. PE and EH characteristics were analyzed and compared between the probable and definite MD groups.

RESULTS

The cochlear and vestibular EH grading on the affected side was more severe in the definite MD group than that in the probable MD group (P < 0.001). The EH locations within the inner ear on the affected side also differed between the two groups (χ2 = 81.15, P < 0.001). The signal intensity ratio (SIR) on the affected side was significantly higher in the definite MD group than in the probable MD group (t = 2.18, P < 0.05). The assessment of the combination of PE and EH parameters within the inner ear revealed a higher area under the curve (AUC) in the definite MD group (0.82) compared with the AUCs of the parameters assessed alone.

CONCLUSION

The assessment of a combination of PE and EH parameters improved the diagnostic accuracy for probable and definite MD, suggesting that MRI findings may be clinically useful in the diagnosis of MD.

Magnetic Targeting of Gadolinium Contrast to Enhance MRI of the Inner Ear in Endolymphatic Hydrops

OBJECTIVES

1. Determine the feasibility and efficiency of local magnetic targeting delivery of gadolinium (Gad) contrast to the inner ear in rodents. 2. Assess any potential ototoxicity of magnetic targeting delivery of Gad in the inner ear. 3. Study the utility of magnetic targeting delivery of Gad to visualize and quantify endolymphatic hydrops (EH) in a transgenic mouse model.

STUDY DESIGN

Controlled in vivo animal model study.

METHODS

Paramagnetic Gad was locally delivered to the inner ear using the magnetic targeting technique in both rat and mouse models. Efficiency of contrast delivery was assessed using magnetic resonance imaging (MRI). Ototoxicity of Gad was examined with histology of the cochlea and functional audiological tests. The Phex mouse model was used to study EH, hearing loss, and balance dysfunction. Magnetic targeting delivery of Gad contrast was used in the Phex mouse model to visualize the effects of EH using MRI.

RESULTS

Magnetic targeting improved the delivery of Gad to the inner ear and the technique was reproducible in both rat and mouse models. The delivery method did not result in microstructural damage or any significant hearing loss in a normal animal. Magnetic targeting of Gad in the Phex mouse model allowed detailed visualization and quantification of EH.

CONCLUSION

This study provided the first evidence of the effectiveness and efficiency of the local magnetic targeting delivery of gadolinium contrast to the inner ear and its application to the visualization and quantification of EH. Laryngoscope, 133:914-923, 2023.

Dexamethasone does not affect endolymphatic hydrops (EH) in patients with Meniere’s disease within 24 h, and intratympanic administration of gadolinium plus dexamethasone simplifies high-quality imaging of EH using a novel protocol of 7 minutes

Background

Intratympanic administration of gadolinium chelate allows for a better visualization of endolymphatic hydrops (EH) using MRI than intravenous injection and was recently further improved to facilitate high-quality imaging of EH in 7 min. The aim of the present study was to simplify the intratympanic administration protocol by mixing gadolinium chelate with therapeutic dexamethasone and to evaluate the effects of this mixture on the visualization of EH in MRI.

Materials and methods

In an in vitro study, the potential impact of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) on the stability of dexamethasone was evaluated by analyzing dynamic changes in dexamethasone with high-performance liquid chromatography (HPLC) after mixing with Gd-DTPA. Ten patients with definite Meniere's disease (MD) were recruited to study the potential interference of dexamethasone on MRI visualization of EH, and 49 patients with MD were recruited to evaluate the effect of intratympanic injection of Gd-DTPA mixed with dexamethasone on MRI of EH using a 3T MR machine and a novel heavily T2-weighted 3-dimensional fluid-attenuated inversion recovery reconstructed using a magnitude plus zero-filled interpolation (hT₂FLAIR-MZFI) sequence.

Results

The retention times and peak area of dexamethasone in HPLC were not modified by the addition of Gd-DTPA. EH grading in the cochlea and vestibule was not influenced in any ear by intratympanic injection of dexamethasone. Excellent inner ear images were obtained from all patients, and EHs with various grades were displayed. There were significant correlations between diagnosis and cochlear EH (p < 0.01, Spearman's Rho), between diagnosis and vestibular EH (p < 0.01, Spearman's Rho), and between cochlear and vestibular EH (p < 0.01, Spearman's Rho). The distribution of Gd-DTPA plus dexamethasone negatively correlated with the grade of vestibular EH. Injury of the endolymph-perilymph barrier was detected in one cochlea and three vestibules of 59 inner ears with MD.

Conclusions

Intratympanic administration of Gd-DTPA plus dexamethasone yielded high-quality MRI images of EH in patients with MD using a novel 7-min protocol and simplified the clinical application. Intratympanic administration of Gd-DTPA plus dexamethasone might be used to test its therapeutic effect in future work.

Level of evidence

3.

The Additional Value of Endolymphatic Hydrops Imaging With Intratympanic Contrast for Diagnostic Work-Up-Experience From a Neurotology Center in Austria

Objective: To illustrate the merit of hydrops imaging during clinical workup of dizziness and balance disorders. Background: Ever since the first description of in-vivo endolymphatic hydrops imaging in 2007, this diagnostic tool has been implemented in an increasing number of centers. The more experience in its clinical application is gathered, the more it is possible to critically assess its potential value for the diagnostic workup. This article intends to provide information about the experience of handling and utilization of endolymphatic hydrops imaging in one of the first centers in Austria. Methods: Retrospective analysis and review of clinical cases. Results: Based on our experience of endolymphatic hydrops imaging (EHI), which was established in cooperation between our departments of radiology and otorhinolaryngology in 2017, we have exclusively used intratympanic application of a contrast agent prior to magnetic resonance imaging, as this approach provides high quality imaging results. In 42.6% of cases, EHI could lead to the diagnosis of MD or HED. Since precise vestibular examination is still necessary, EHI is not a tool to replace the clinical examination but rather to add significantly to the interpretation of the results. Conclusion: Endolymphatic hydrops imaging represents a valuable, safe and well-applicable tool for evaluating cases with inconclusive clinical results. However, its potential additional diagnostic benefits rely on a correct indication based on prior thorough vestibular investigations.

High-quality imaging of endolymphatic hydrops acquired in 7 minutes using sensitive hT2W-3D-FLAIR reconstructed with magnitude and zero-filled interpolation

Background

It is still challenging to detect endolymphatic hydrops (EH) in patients with Meniere’s disease (MD) using MRI. The aim of the present study was to optimize a sensitive technique generating strong contrast enhancement from minimum gadolinium–diethylenetriamine pentaacetic acid (Gd–DTPA) while reliably detecting EH in the inner ear, including the apex.

Materials and methods

All imaging was performed using a 3.0 T MR system 24 h after intratympanic injection of low-dose Gd–DTPA. Heavily T2-weighted 3-dimensional fluid-attenuated inversion recovery reconstructed with magnitude and zero-filled interpolation (hT₂W–FLAIR–ZFI) was optimized and validated in phantom studies and compared with medium inversion time inversion recovery imaging with magnitude reconstruction (MIIRMR). The following parameters were used in hT₂W–FLAIR–ZFI: repetition time 14,000 ms, echo time 663 ms, inversion time 2900 ms, flip angle 120°, echo train length 271, and field of view 166 × 196 mm².

Results

MRI obtained using hT₂W–FLAIR–MZFI yielded high-quality images with sharper and smoother borders between the endolymph and perilymph and a higher signal intensity ratio and more homogenous perilymph enhancement than those generated with MIIRMR (p < 0.01). There were predominantly grade II EHs in the cochleae and grade III EHs in the vestibule in definite MD. EH was detected in the apex of 11/16 ipsilateral ears, 3/16 contralateral ears in unilateral definite MD and 3/6 ears in bilateral MD.

Conclusions

The novel hT₂W–FLAIR–MZFI technique is sensitive and demonstrates strong and homogenous enhancement by minimum Gd–DTPA in the inner ear, including the apex, and yields high-quality images with sharp borders between the endolymph and perilymph.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00405-021-06912-4.

Magnetic resonance imaging and Ménière's disease-unavoidable alliance

Ménière's disease (MD) is a clinical syndrome characterized by recurrent episodes of spontaneous vertigo, unilateral fluctuating sensorineural hearing loss, tinnitus, and aural fullness. Endolymphatic hydrops is recognized as the pathophysiological substrate of the disease, having been demonstrated in anatomical pathological studies and more recently by magnetic resonance imaging (MRI). The current criteria of the disease, however, remain symptom based and do not include the demonstration of endolymphatic hydrops. The authors review MRI techniques and diagnostic criteria of endolymphatic hydrops and the role of MRI in MD is discussed.

Development of nanoparticle drug-delivery systems for the inner ear

Hearing loss has become the most common sensory nerve disorder worldwide, with no effective treatment strategy. Low-permeability and limited blood supply to the blood-labyrinth barrier limit the effective delivery and efficacy of therapeutic drugs in the inner ear. Nanoparticle (NP)-based drugs have shown benefits of stable controlled release and functional surface modification, and NP-based delivery systems have become a research hotspot. In this review, we discuss the development of new targeted drug-delivery systems based on the biocompatibility and safety of different NPs in the cochlea, as well as the advantages and disadvantages of their prescription methods and approaches. We believe that targeted NP-based drug-delivery systems will be effective treatments for hearing loss.

MRI detection of endolymphatic hydrops in Meniere's disease in 8 minutes using MIIRMR and a 20-channel coil after targeted gadolinium delivery

Background

Endolymphatic hydrops (EH) become visible in vertigo patients, particularly in those with Meniere's disease (MD), in vivo using gadolinium-enhanced MRI. However, the image quality is not satisfying after intravenous injection of gadolinium chelate (GdC), and occasional failure in GdC uptake has been noticed after traditional intratympanic injection. In the present report, targeted delivery of GdC and using a cost-effective MRI system to obtain high quality images of EH in only 8 min will be introduced.

Methods

39 MD patients were recruited in the study. First, 0.1 ml of 20-fold diluted gadolinium-diethylenetriamine acid (Gd-DTPA) was delivered onto the posterior upper part of the tympanic medial wall using a soft-tipped micro-irrigation catheter through an artificially perforated tympanic membrane. Inner ear MRI was performed 24 h after Gd-DTPA administration using a 3T MR machine and a 20-channel head/neck coil with an 8 min sequence of medium inversion time inversion recovery imaging with magnitude reconstruction (MIIRMR). The parameters were as follows: TR 16000 ms, TE 663 ms, inversion time 2700 ms, flip angle 180°, slices per slab 60.

Results

Efficient inner ear uptake of Gd-DTPA was detected 24 h after delivery and it created excellent contrast in the inner ear of all cases. High quality images demonstrating EH in the vestibule and cochlea were obtained.

Conclusion

Targeted delivery of minimum Gd-DTPA (0.1 ml, 20-fold dilution) onto the posterior upper portion of the tympanic medial wall and MRI with MIIRMR in a 3T machine and 20-channel head/neck coil are clinically practical to obtain high quality images displaying EH.

Correlations Between the Degree of Endolymphatic Hydrops and Symptoms and Audiological Test Results in Patients With Menière's Disease: A Reevaluation

OBJECTIVE

This study was performed to reevaluate the diagnostic significance of clinically well-accepted audiological tests in indicating endolymphatic hydrops (EH) in Menière's disease (MD).

STUDY DESIGN

Retrospective case review.

SETTINGS

Hospital.

PATIENTS

Fifty patients (52 affected ears) diagnosed with MD were enrolled.

INTERVENTION

Diagnostic.

MAIN OUTCOME MEASURE

To analyze the correlations between endolymphatic hydrops and results of audiological test including the pure-tone audiometry threshold, suprathreshold function tests, electrocochleogram, and glycerol test.

RESULTS

Three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging demonstrated EH in either the vestibule or cochlea to various degrees in all of the MD patients, 24 hours after intratympanic gadolinium chelate injection. Both vestibular and cochlear EH were significantly correlated with PTA threshold. However, EH was not associated with alternate binaural loudness balance or the tone decay test, although a correlation was observed with the short-increment sensitivity index. There was also a correlation between vestibular EH, but not cochlear EH, and the negative summating potential/action potential (-SP/AP) ratio. Neither vestibular EH nor cochlear EH was correlated with the glycerol test results. In addition, the frequency of vertigo attacks, the existence of tinnitus, and aural fullness did not correlate with EH.

CONCLUSIONS

Disrupted ionic homeostasis in the inner ear, but not the EH, may contribute to changes in the -SP/AP ratio. The relevance of glycerol test in identifying EH through detection of hearing changes needs further investigation in the future.

On the classification of hydropic ear disease (Menière's disease)

More than 150 years after its initial description by Prosper Menière, the disease named after him is still at the center of scientific debates. Two recent developments have specifically created a breeding ground for controversy: (1) Since its first description 10 years ago, magnetic resonance imaging diagnosis of endolymphatic hydrops in living patients has seen an increasing and worldwide application. (2) The Bárány Society Classification Committee published diagnostic criteria for Menière's disease in 2015 and proposed a concept of the disease that has elicited widespread criticism. In order to promote the understanding of the underlying controversies and arguments, this article gives an overview of and discusses relevant classification proposals for Menière's disease, including the new classification system of hydropic ear disease.

Pharmacokinetics and tissue distribution of neurotrophin 3 after intracochlear delivery

Neurotrophin therapy has potential to reverse some forms of hearing loss. However, cochlear pharmacokinetic studies are challenging due to small fluid volumes. Here a radioactive tracer was used to determine neurotrophin-3 retention, distribution and clearance after intracochlear administration. ¹²⁵I-neurotrophin-3 was injected into guinea pig cochleae using a sealed injection technique comparing dosing volumes, rates and concentrations up to 750 μg/mL. Retention was measured by whole-cochlear gamma counts at five time points while distribution and clearance were assessed by autoradiography. Smaller injection volumes and higher concentrations correlated with higher retention of neurotrophin-3. Distribution of neurotrophin-3 was widespread throughout the cochlear tissue, decreasing in concentration from base to apex. Tissue distribution was non-uniform, with greatest density in cells lining the scala tympani and lower density in neural target tissue. The time constant for clearance of neurotrophin-3 from cochlear tissues was 38 h but neurotrophin-3 remained detectable for at least 2 weeks. Neurotrophin-3 was evident in the semi-circular canals with minor spread to the contralateral cochlea. This study is the first comprehensive evaluation of the disposition profile for a protein therapy in the cochlea. The findings and methods in this study will provide valuable guidance for the development of protein therapies for hearing loss.

Clinical manifestations of hydropic ear disease (Menière's)

INTRODUCTION

Hydropic ear disease, initially described by and named after Prosper Menière, is one of the most frequent vertigo disorders and one of the most frequent inner ear disorders. It is the syndrome of endolymphatic hydrops which until 2007 could be diagnostically confirmed only by post-mortem histology. In the past, various attempts to formulate clinical diagnostic criteria have been undertaken but were hampered by the inability to ascertain the diagnosis in living patients. With the milestone achievement of endolymphatic hydrops imaging, today the pathology can be ascertained. In this study, we have performed a detailed analysis of the clinical features of hydropic ear disease for the first time by examining a large cohort of patients with morphologically confirmed endolymphatic hydrops using a detailed physician-administered neurotologic face-to-face interview.

RESULTS

During a hydropic vertigo attack, the patients report nausea, vomiting, sweating, urge to defecate, urge to urinate, phosphenes, headache, photophobia, phonophobia and even transient loss of consciousness. A third of the patients does not experience auditory symptoms during the vertigo attacks. Vertigo attacks last less than 20 min in more than one-fourth of the patients. Audiometric hearing loss has its greatest diagnostic value at the frequencies of 1 kHz and below. Cochleovestibular symptom onset simultaneity is associated with a high frequency of drop-attacks. Migraine and autoimmune disorders are not associated with hydropic ear disease.

CONCLUSION

This study marks the beginning of the clinical characterization of hydropic ear disease. The findings have important implications for the future formulation of clinical diagnostic criteria.

Oxidative Stress in the Blood Labyrinthine Barrier in the Macula Utricle of Meniere's Disease Patients

The blood labyrinthine barrier (BLB) is critical in the maintenance of inner ear ionic and fluid homeostasis. Recent studies using imaging and histopathology demonstrate loss of integrity of the BLB in the affected inner ear of Meniere's disease (MD) patients. We hypothesized that oxidative stress is involved in the pathogenesis of BLB degeneration, and to date there are no studies of oxidative stress proteins in the human BLB. We investigated the ultrastructural and immunohistochemical changes of the BLB in the vestibular endorgan, the macula utricle, from patients with MD (n = 10), acoustic neuroma (AN) (n = 6) and normative autopsy specimens (n = 3) with no inner ear disease. Each subject had a well-documented clinical history and audiovestibular testing. Utricular maculae were studied using light and transmission electron microscopy and double labeling immunofluorescence. Vascular endothelial cells (VECs) were identified using isolectin B4 (IB4) and glucose-transporter-1 (GLUT-1). Pericytes were identified using alpha smooth muscle actin (αSMA) and phalloidin. IB4 staining of VECS was consistently seen in both AN and normative. In contrast, IB4 was nearly undetectable in all MD specimens, consistent with the significant VEC damage confirmed on transmission electron microscopy. GLUT-1 was present in MD, AN, and normative. αSMA and phalloidin were expressed consistently in the BLB pericytes in normative, AN specimen, and Meniere's specimens. Endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and nitrotyrosine were used as markers of oxidative stress. The VECs of the BLB in Meniere's had significantly higher levels of expression of iNOS and nitrotyrosine compared with normative and AN specimen. eNOS-IF staining showed similar patterns in normative and Meniere's specimens. Microarray-based gene expression profiling confirmed upregulation of iNOS mRNA from the macula utricle of Meniere's patients compared with AN. Nitrotyrosine, a marker recognized as a hallmark of inflammation, especially when seen in association with an upregulation of iNOS, was detected in the epithelial and stromal cells in addition to VECs in MD. Immunohistochemical and ultrastructural degenerative changes of the VEC suggest that these cells are the primary targets of oxidative stress, and pericyte pathology including degeneration and migration, likely also plays a role in the loss of integrity of the BLB and triggering of inflammatory pathways in MD. These studies advance our scientific understanding of oxidative stress in the human inner ear BLB and otopathology.

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.

Menière and Friends: Imaging and Classification of Hydropic Ear Disease

BACKGROUND

Over 75 years ago, endolymphatic hydrops was discovered as the pathologic correlate of Menière's disease. However, this pathologic finding could be ascertained only in postmortem histologic studies. Due to this diagnostic dilemma and the variable manifestation of the various audiovestibular symptoms, diagnostic classification systems based on clinical findings have been used hitherto.

METHODS

A review of the literature of magnetic resonance (MR) imaging of hydropic ear disease.

RESULTS

Recent developments of high resolution MR imaging of the inner ear have now enabled us to visualize in vivo endolymphatic hydrops in patients with suspected Menière's disease. The existing knowledge from temporal bone histologic studies and from the emerging evidence on imaging based evaluation of patients with suspected Menière's disease indicate that endolymphatic hydrops not only is responsible for the full-blown clinical triad of simultaneous attacks of auditory and vestibular dysfunction, but also for other clinical presentations such as "vestibular" and "cochlear Menière's disease."

CONCLUSION

As a consequence, we propose the term "Hydropic Ear Disease" as a new terminology which is based on symptomatic and imaging characteristics of these clinical entities to clarify and simplify their diagnostic classification.

Is oval window transport a royal gate for nanoparticle delivery to vestibule in the inner ear?

Drug delivery to the inner ear by nanomedicine strategies has emerged as an effective therapeutic approach for the management of inner ear diseases including hearing and balance disorders. It is well accepted that substance enters the perilymph from the middle ear through the round window membrane (RWM), but the passage through the oval window (OW) has long been neglected. Up to now, researchers still know little about the pathway via which nanoparticles (NPs) enter the inner ear or how they reach the inner ear following local applications. Herein, we engineered fluorescence traceable chitosan (CS) NPs, investigated the NP distribution within cochlear and vestibular organs, and assessed the availability of RWM and OW pathways to NP transport. Intriguingly, there were high levels of CS NPs in vestibular hair cells, dark cells and supporting cells, but negligible ones in cochlear hair cells and epithelial cells after intratympanic administration. However, the NPs were visualized in two cell models, L929 and HEI-OC1 cell lines, and in the hair cells of cochlear explants after co-incubation in vitro. These combined studies implied that CS NPs might enter the vestibule directly through the OW and then preferentially accumulated in the cells of vestibular organs. Thus, in vivo studies were carried out and clearly revealed that CS NPs entered the inner ear through both the RWM and OW, but the latter played a governing role in delivering NPs to the vestibule with vivid fluorescence signals in the thin bone of the stapes footplate. Overall, these findings firstly suggested that the OW, as a royal gate, afforded a convenient access to facilitate CS NPs transport into inner ear, casting a new light on future clinical applications of NPs in the effective treatment of vestibular disorders by minimizing the risk of hearing loss associated with cochlear hair cell pathology.

Clinical features of delayed endolymphatic hydrops and intralabyrinthine schwannoma : An imaging-confirmed comparative case series. English version

BACKGROUND

The aim of this study was to compare the clinical history and audiovestibular function test results of patients suffering from intralabyrinthine schwannoma or delayed endolymphatic hydrops (DEH).

PATIENTS AND METHODS

Five patients diagnosed with intralabyrinthine schwannoma by magnetic resonance imaging (MRI) and five patients diagnosed with DEH by locally enhanced inner ear MRI (LEIM) were retrospectively studied.

RESULTS

All patients with intralabyrinthine schwannoma or DEH initially presented with hearing loss. Vertigo occurred in two patients with intralabyrinthine schwannoma and in all patients with DEH. While audiometry achieved poorer results for patients with intralabyrinthine schwannomas, vestibular function tests revealed normal results in about half of the patients in both groups.

CONCLUSION

Patients with intralabyrinthine schwannomas may present with clinical symptoms similar to patients suffering from other inner ear disorders such as delayed endolymphatic hydrops and they may obtain similar findings in audiovestibular function tests. High-resolution magnetic resonance imaging with locally applied contrast agent may provide evidence of both underlying pathologies.

Gentamicin Applied to the Oval Window Suppresses Vestibular Function in Guinea Pigs

Intratympanic gentamicin therapy is widely used clinically to treat the debilitating symptoms of Ménière's disease. Cochleotoxicity is an undesirable potential side effect of the treatment and the risk of hearing loss increases proportionately with gentamicin concentration in the cochlea. It has recently been shown that gentamicin is readily absorbed through the oval window in guinea pigs. The present study uses quantitative functional measures of vestibular and cochlea function to investigate the efficacy of treating the vestibule by applying a small volume of gentamicin onto the stapes footplate in guinea pigs. Vestibular and cochlea function were assessed by recording short latency vestibular evoked potentials in response to linear head acceleration and changes in hearing threshold, respectively, 1 and 2 weeks following treatment. Histopathology was analyzed in the crista ampullaris of the posterior semi-circular canal and utricular macula in the vestibule, and in the basal and second turns of the cochlea. In animals receiving gentamicin on the stapes footplate, vestibular responses were significantly suppressed by 72.7 % 2 weeks after treatment with no significant loss of hearing. This suggests that the vestibule can be treated directly by applying gentamicin onto the stapes footplate.

Magnetic resonance volumetric measurement of endolymphatic space in patients without vertiginous or cochlear symptoms

CONCLUSION

Magnetic resonance volumetric measurement of inner ear endolymphatic space (ELS) was performed in patients without vertiginous or cochlear symptoms. The existence of the ELS in patients with chronic rhinosinusitis (CRS) was shown. The ELS in the cochlea and vestibule was classified into four categories. These findings could be useful as a standard reference for further research.

OBJECTIVES

To identify normal values of the ELS in the cochlea and vestibule.

METHODS

Twenty-four patients with CRS were enrolled. Inner ear fluid space images and positive perilymph/positive endolymph images were acquired using a 3.0-tesla unit. Three-dimensional (3-D) images were constructed semi-automatically using both anatomical and tissue information by fusing the 3-D images of the inner ear fluid space and the ELS.

RESULTS

Among all patients, the mean ELS/the total fluid space (TFS) ratio in the cochlea was 8.8% and that in the vestibule was 16.2%. The ELS in the cochlea and vestibule was classified into four categories. Age-related differences were found in the TFS, ELS, and ELS/TFS ratio in the inner ear and the ELS and ELS/TFS ratio in the vestibule.

Inner ear barriers to nanomedicine-augmented drug delivery and imaging

There are several challenges to inner ear drug delivery and imaging due to the existence of tight biological barriers to the target structure and the dense bone surrounding it. Advances in imaging and nanomedicine may provide knowledge for overcoming the existing limitations to both the diagnosis and treatment of inner ear diseases. Novel techniques have improved the efficacy of drug delivery and targeting to the inner ear, as well as the quality and accuracy of imaging this structure. In this review, we will describe the pathways and biological barriers of the inner ear regarding drug delivery, the beneficial applications and limitations of the imaging techniques available for inner ear research, the behavior of engineered nanomaterials in inner ear applications, and future perspectives for nanomedicine-based inner ear imaging.

Perilymph pharmacokinetics of locally-applied gentamicin in the guinea pig

Intratympanic gentamicin therapy is widely used clinically to suppress the vestibular symptoms of Meniere's disease. Dosing in humans was empirically established and we still know remarkably little about where gentamicin enters the inner ear, where it reaches in the inner ear and what time course it follows after local applications. In this study, gentamicin was applied to the round window niche as a 20 μL bolus of 40 mg/ml solution. Ten 2 μL samples of perilymph were collected sequentially from the lateral semi-circular canal (LSCC) at times from 1 to 4 h after application. Gentamicin concentration was typically highest in samples originating from the vestibule and was lower in samples originating from scala tympani. To interpret these results, perilymph elimination kinetics for gentamicin was quantified by loading the entire perilymph space by injection at the LSCC with a 500 μg/ml gentamicin solution followed by sequential perilymph sampling from the LSCC after different delay times. This allowed concentration decline in perilymph to be followed with time. Gentamicin was retained well in scala vestibuli and the vestibule but declined rapidly at the base of scala tympani, dominated by interactions of perilymph with CSF, as reported for other substances. Quantitative analysis, taking into account perilymph kinetics for gentamicin, showed that more gentamicin entered at the round window membrane (57%) than at the stapes (35%) but the lower concentrations found in scala tympani were due to greater losses there. The gentamicin levels found in perilymph of the vestibule, which are higher than would be expected from round window entry alone, undoubtedly contribute to the vestibulotoxic effects of the drug. Furthermore, calculations of gentamicin distribution following targeted applications to the RW or stapes are more consistent with cochleotoxicity depending on the gentamicin concentration in scala vestibuli rather than that in scala tympani.

Intracochlear Drug Delivery Through the Oval Window in Fresh Cadaveric Human Temporal Bones

HYPOTHESIS

Drug delivered to the oval window can diffuse to the apex of the human cochlea.

BACKGROUND

We have previously demonstrated that zoledronate, a nitrogen-containing bisphosphonate, can arrest the sensorineural hearing loss in cochlear otosclerosis. We have also shown that, in animals, delivery of bisphosphonate into the cochlea can dramatically increase delivery efficiency. Intracochlear drug delivery has the potential to increase local concentration of drug while decreasing the risk of systemic toxicity. In the present study, a fluorescently labeled bisphosphonate compound (6-FAM-ZOL) was introduced into the human cochlea through the oval window and its distribution within the temporal bone was quantified.

METHODS

In three fresh human temporal bones, we introduced 6-FAM-ZOL via the oval window. We compared these specimens to control specimens treated with artificial perilymph alone. Specimens were then processed, embedded into methyl methacrylate, and ground to the mid-modiolar axis. We quantified the fluorescence in confocal images.

RESULTS

We found 6-FAM-ZOL to be distributed up to the apical cochlear turn. In specimens treated with 6-FAM-ZOL, we identified a strong baso-apical gradient of fluorescent signal along the lateral cochlear wall and the modiolus both in the scala vestibuli and in the scala tympani.

CONCLUSION

Bisphosphonate introduced via the oval window in the human cochlea can be delivered up to the apical cochlear turn. Interscalar communication is likely to play an important role in determining patterns of drug delivery in the inner ear.

What is Menière's disease? A contemporary re-evaluation of endolymphatic hydrops

Menière's disease is a chronic condition with a prevalence of 200-500 per 100,000 and characterized by episodic attacks of vertigo, fluctuating hearing loss, tinnitus, aural pressure and a progressive loss of audiovestibular functions. Over 150 years ago, Prosper Menière was the first to recognize the inner ear as the site of lesion for this clinical syndrome. Over 75 years ago, endolymphatic hydrops was discovered as the pathologic correlate of Menière's disease. However, this pathologic finding could be ascertained only in post-mortem histologic studies. Due to this diagnostic dilemma and the variable manifestation of the various audiovestibular symptoms, diagnostic classification systems based on clinical findings have been repeatedly modified and have not been uniformly used in scientific publications on Menière's disease. Furthermore, the higher level measures of impact on quality of life such as vitality and social participation have been neglected hitherto. Recent developments of high-resolution MR imaging of the inner ear have now enabled us to visualize in vivo endolymphatic hydrops in patients with suspected Menière's disease. In this review, we summarize the existing knowledge from temporal bone histologic studies and from the emerging evidence on imaging-based evaluation of patients with suspected Menière's disease. These indicate that endolymphatic hydrops is responsible not only for the full-blown clinical triad of simultaneous attacks of auditory and vestibular dysfunction, but also for other clinical presentations such as "vestibular" and "cochlear Menière's disease". As a consequence, we propose a new terminology which is based on symptomatic and imaging characteristics of these clinical entities to clarify and simplify their diagnostic classification.

Postaurical injection is a systemic delivery supported by symmetric distribution of Gd-DOTA in both the ipsilateral and contralateral ears

Postaurical injection of therapeutics was recently applied in clinical practice to treat inner ear diseases based on supposed existence of a direct channel from the postaurical area to the inner ear. Doubting on the associated reports and aiming to provide evidence on the inner ear uptake mechanism, the present study tracked the dynamic distribution of gadolinium-tetra-azacyclo-dodecane-tetra-acetic acid (Gd-DOTA) in rat inner ears after postaurical injection using MRI. A targeted tympanic medial wall delivery was utilized as control. The results showed that, at the early time points after postaurical injection, Gd-DOTA distributed mainly in tissues surrounding the bulla, temporal bone and skull and neck space. In the inner ear, there was gradual uptake of Gd-DOTA on both the ipsilateral and contralateral sides with equal signal intensities. There was no sign of direct channel carrying the agent from the postaurical area to the inner ear. Targeted tympanic medial wall delivery induced significantly greater uptake of Gd-DOTA in the inner ear than did postaurical injection. At 30 min post-administration, targeted tympanic medial wall delivery yielded 4.6-folds higher signal intensity than did postaurical injection. The total dose of Gd-DOTA delivered by the targeted tympanic medial wall approach was only 0.1% of that delivered by postaurical injection. In conclusion, postaurical injection is a systemic administration, which is similar to hypodermic injection, rather than a focal delivery method. By contraries, targeted tympanic medial wall delivery induces fast and abundant uptake of Gd-DOTA in the ipsilateral inner ear without significant distribution in unwanted areas.

Calcium Metabolism Profile in Rat Inner Ear Indicated by MRI After Tympanic Medial Wall Administration of Manganese Chloride

Objectives:

To evaluate the efficacy of the novel method for the targeted delivery of Mn++ to the inner ear and monitor calcium metabolism activity in the inner ear.

Materials and Methods:

Dynamic signal changes of Mn++ in the rat inner ear were followed using T1-weighted magnetic resonance imaging (MRI) after administration of 2.5 µl MnCl2 (500 mM) to the medial wall of the middle ear cavity.

Results:

Mn++ passed through both the oval and round windows and distributed in the perilymphatic compartments, where it formed bright sharp lines along the fluid-cellular borders 12 minutes post administration and entered the endolymph sufficiently after 45 minutes. After 6 hours, the distribution of Mn++ shifted from a fluid-dominant pattern to a cell-dominant pattern. Mn++ concentrated in the area of the basilar membrane, periphery process, and soma of the spiral ganglion on day 2; became more distinguishable on day 4; declined on day 8; and remained detectable for 16 days post administration.

Conclusions:

The novel targeted delivery method efficiently introduced Mn++ into the inner ear. The dynamic distribution pattern of Mn++ in the inner ear shown by MRI indicates that this method can be used to monitor calcium metabolism activity in the inner ear.

Intratympanic Contrast in the Evaluation of Menière Disease: Understanding the Limits

BACKGROUND AND PURPOSE

Studies describing endolymphatic hydrops in Menière disease after off-label intratympanic gadolinium-based contrast have been limited by long acquisition times. We aimed to demonstrate the feasibility of post-intratympanic imaging on a 3T MR imaging system within a clinically tolerable acquisition time and to address potential pitfalls in acquisition or interpretation.

MATERIALS AND METHODS

FDA Investigational New Drug 115,342 and institutional review board approval were obtained for intratympanic injection of 8-fold diluted Gd-DTPA into the more symptomatic ear of 6 adults with Menière disease. 3T MR imaging was performed using a 3-inch surface coil before and up to 28 hours after injection using FLAIR to define the nonenhancing endolymphatic space within the enhancing perilymph. Variable FLAIR TI images were used to determine the impact of fluid-suppression on interpretation. Image quality was assessed for perilymphatic and extralabyrinthine contrast enhancement, definition of endolymphatic anatomy, and other anatomic variants or pathologic findings.

RESULTS

The surface coil afforded 0.375 × 0.375 mm in-plane FLAIR resolution in <4 minutes 30 seconds, sufficient to perceive the nonenhancing spiral lamina, interscalar septa, and endolymphatic structures. Coronal views highlighted a potential interpretation pitfall of vestibular endolymphatic distention overestimation due to partial volume averaging. Varying FLAIR TI resulted in visible changes in the perception of the cochlear endolymphatic space. CSF enhancement was detectable at the internal auditory canal fundus on the injected side in half of the patients, which may confound interpretation.

CONCLUSIONS

Using a surface coil preserves high resolution within a clinically acceptable acquisition time. Pitfalls remain regarding the interpretation of these images and optimizing protocols across platforms in the absence of a clear internal reference for standardization.

MR volumetric assessment of endolymphatic hydrops

OBJECTIVES

We aimed to volumetrically quantify endolymph and perilymph spaces of the inner ear in order to establish a methodological basis for further investigations into the pathophysiology and therapeutic monitoring of Menière's disease.

METHODS

Sixteen patients (eight females, aged 38-71 years) with definite unilateral Menière's disease were included in this study. Magnetic resonance (MR) cisternography with a T2-SPACE sequence was combined with a Real reconstruction inversion recovery (Real-IR) sequence for delineation of inner ear fluid spaces. Machine learning and automated local thresholding segmentation algorithms were applied for three-dimensional (3D) reconstruction and volumetric quantification of endolymphatic hydrops. Test-retest reliability was assessed by the intra-class coefficient; correlation of cochlear endolymph volume ratio with hearing function was assessed by the Pearson correlation coefficient.

RESULTS

Endolymph volume ratios could be reliably measured in all patients, with a mean (range) value of 15% (2-25) for the cochlea and 28% (12-40) for the vestibulum. Test-retest reliability was excellent, with an intra-class coefficient of 0.99. Cochlear endolymphatic hydrops was significantly correlated with hearing loss (r = 0.747, p = 0.001).

CONCLUSIONS

MR imaging after local contrast application and image processing, including machine learning and automated local thresholding, enable the volumetric quantification of endolymphatic hydrops. This allows for a quantitative assessment of the effect of therapeutic interventions on endolymphatic hydrops.

KEY POINTS

• Endolymphatic hydrops is the pathological hallmark of Menière's disease. • Endolymphatic hydrops can be visualized by locally enhanced ultra-high-resolution MR imaging. • Computer-aided image processing enables quantification of endolymphatic hydrops. • Endolymphatic hydrops correlates with hearing loss in patients with Menière's disease. • Therapeutic trials in Menière's disease can be monitored with this quantitative approach.

Magnetic resonance imaging of the middle and inner ear after intratympanic injection of a gadolinium-containing gel

OBJECTIVE

To investigate the distribution and elimination of a gadolinium containing high viscosity formulation of sodium hyaluronan (HYA gel) after injection to the middle ear.

MATERIALS AND METHODS

The T1 contrast agent gadolinium-diethylenetriamine pentaacetic acid-bis methylamine (Gd-DTPA-BMA) was added to HYA gel and delivered to the middle ear of 13 albino guinea pigs by 3 different ways of injection. Magnetic resonance imaging was performed with a 4.7 T MRI system using a T1-weighted 3-dimentional rapid acquisition with relaxation enhancement sequence.

RESULTS

An injection technique where the Gd-DTPA-BMA-containing HYA gel was delivered to the middle ear through a percutaneous injection through the auditory bulla after a small incision had been made in the tympanic membrane gave the best filling of the middle ear, covering the cochlea and the region of the round window niche for 24 hours in a majority of the ears studied. Ears injected without an incision in the tympanic membrane showed an immediate uptake of Gd-DTPA-BMA in the inner ear as a sign of rupture of the round window membrane.

CONCLUSION

A percutaneous injection of a HYA gel into the tympanic bulla is distributed in a predictable way and gives a good filling of the middle ear cavity. The HYA gel remains in close vicinity to the RWM for more than 24 hours. Injection should be performed after an incision of the tympanic membrane has been made to prevent rupture of the round window membrane.

The predominant vestibular uptake of gadolinium through the oval window pathway is compromised by endolymphatic hydrops in Ménière's disease

OBJECTIVE

Intratympanic administration of gentamicin is becoming a common therapy to control vertigo in Ménière's disease (MD). Drug entry through an oval window pathway was recently demonstrated in rats. The present study aimed to evaluate the permeability of the oval window to gadolinium in MD patients.

METHODS

Eight patients with MD and other inner ear diseases received a transtympanic injection of 5-fold diluted gadopentetate dimeglumine (Gd-DTPA). Three-dimensional fluid-attenuated inversion-recovery (3D-FLAIR) and 3D inversion recovery turbo spin echo with real reconstruction (3D-real IR) imaging was performed using a 3-Tesla MRI scanner at 3, 6, 12, and 24 h after injection. The extent of vestibular endolymphatic hydrops (EH) was determined, and the dynamics of the signal changes in the vestibule and the cochlear basal turn were evaluated.

RESULTS

Transtympanically injected Gd-DTPA entered the cochlea of all 8 of the patients and entered the vestibule of 7 of the 8 patients. EH was demonstrated in 2 patients with MD and the patient with idiopathic sensorineural hearing loss or idiopathic vertigo. In the patients lacking EH, the vestibules exhibited more efficient uptake of Gd-DTPA than did the cochleae. In the patients with vestibular EH, the Gd-DTPA signal in the vestibule was less intense than that in the cochlear basal turn.

CONCLUSION

In patients with inner ear diseases, the vestibular distribution of Gd-DTPA was compromised by vestibular EH, suggesting oval window passage of Gd-DTPA is reduced in the presence of EH.

Visualization of endolymphatic hydrops with MR imaging in patients with Ménière's disease and related pathologies: current status of its methods and clinical significance

Ménière's disease is an inner ear disorder characterized by vertigo attacks, fluctuating low-frequency hearing loss, ear fullness, and tinnitus. Endolymphatic hydrops has long been thought to be the pathological basis for Ménière's disease. Some patients have inner ear symptoms that do not match the diagnostic guidelines for Ménière's disease, and these are also thought to be related to endolymphatic hydrops. The diagnosis of endolymphatic hydrops is usually made based on clinical symptoms with some assistance from otological functional tests. Recently, the objective diagnosis of endolymphatic hydrops by MR imaging has become possible and many research results have been reported regarding the imaging methods, evaluation methods, the correlation between imaging results and functional otological tests and the correlation between imaging findings and clinical symptoms. In this article we summarize the development of current imaging methods, evaluation techniques and clinical reports based on a review of the literature. We also attempt to characterize the current significance and future directions of MR imaging of endolymphatic hydrops.

Nanoparticle based inner ear therapy

Synthetic nanoparticles can be used to carry drugs, genes, small interfering RNA (siRNA) and growth factors into the inner ear, to repair, restore and induce cellular regeneration. Nanoparticles (NPs) have been developed which are targetable to selected tissue, traceable in vivo, and equipped with controlled drug/gene release. The NPs are coated with a ‘stealth’ layer, and decorated with targeting ligands, markers, transfection agents and endosomal escape peptides. As payloads, genes such as the BDNF-gene, Math1-gene and Prestin-gene have been constructed and delivered in vitro. Short-hairpin RNA has been used in vitro to silence the negative regulator of Math1, the inhibitors of differentiation and DNA binding. In order to facilitate the passage of cargo from the middle ear to the inner ear, the oval window transports gadolinium chelate more efficiently than the round window and is the key element in introducing therapeutic agents into the vestibule and cochlea. Depending upon the type of NPs, different migration and cellular internalization pathways are employed, and optimal carriers should be designed depending on the cargo. The use of NPs as drug/gene/siRNA carriers is fascinating and can also be used as an intraoperative adjunct to cochlear implantation to attract the peripheral processes of the cochlear nerve.

Efficient siRNA transfection to the inner ear through the intact round window by a novel proteidic delivery technology in the chinchilla

The use of small-interfering RNA (siRNA) has great potential for the development of drugs designed to knock down the expression of damage- or disease-causing genes. However, because of the high molecular weight and negative charge of siRNA, it is restricted from crossing the blood-cochlear barrier, which limits the concentration and size of molecules that are able to gain access to cells of the inner ear. Intratympanic approaches, which deliver siRNA to the middle ear, rely on permeation through the round window for access to the structures of the inner ear. We developed an innovative siRNA delivery recombination protein, TAT double-stranded RNA-binding domains (TAT-DRBDs), which can transfect Cy3-labeled siRNA into cells of the inner ear, including the inner and outer hair cells, crista ampullaris, macula utriculi and macula sacculi, through intact round-window permeation in the chinchilla in vivo, and there were no apparent morphological damages for the time of observation. We also found that Cy3-labeled siRNA could directly enter spiral ganglion neurons and the epithelium of the stria vascularis independently; however, the mechanism is unknown. Therefore, as a non-viral vector, TAT-DRBD is a good candidate for the delivery of double-stranded siRNAs for treating various inner ear ailments and preservation of hearing function.

Influence of cochleostomy and cochlear implant insertion on drug gradients following intratympanic application in Guinea pigs

Locally applied drugs can protect residual hearing following cochlear implantation. The influence of cochlear implantation on drug levels in the scala tympani (ST) after round window application was investigated in guinea pigs using the marker trimethylphenylammonium (TMPA) measured in real time with TMPA-selective microelectrodes. TMPA concentration in the upper basal turn of the ST rapidly increased during implantation and then declined due to cerebrospinal fluid entering the ST at the cochlear aqueduct and exiting at the cochleostomy. The TMPA increase was found to be caused by the cochleostomy drilling if the burr tip partially entered the ST. TMPA distribution in the second turn was less affected by implantation procedures. These findings show that basal turn drug levels may be changed during implantation and the changes may need to be considered in the interpretation of therapeutic effects of drugs in conjunction with implantation.

Gentamicin administration on the stapes footplate causes greater hearing loss and vestibulotoxicity than round window administration in guinea pigs

Clinically, gentamicin has been used extensively to treat the debilitating symptoms of Mèniére's disease and is well known for its vestibulotoxic properties. Until recently, it was widely accepted that the round window membrane (RWM) was the primary entry route into the inner ear following intratympanic drug administration. In the current study, gentamicin was delivered to either the RWM or the stapes footplate of guinea pigs (GPs) to assess the associated hearing loss and histopathology associated with each procedure. Vestibulotoxicity of the utricular macula, saccular macula, and crista ampullaris in the posterior semicircular canal were assessed quantitatively with density counts of hair cells, supporting cells, and stereocilia in histological sections. Cochleotoxicity was assessed quantitatively by changes in threshold of auditory brainstem responses (ABR), along with hair cell and spiral ganglion cell counts in the basal and second turns of the cochlea. Animals receiving gentamicin applied to the stapes footplate exhibited markedly higher levels of hearing loss between 8 and 32 kHz, a greater reduction of outer hair cells in the basal turn of the cochlea and fewer normal type I cells in the utricle in the vestibule than those receiving gentamicin on the RWM or saline controls. This suggests that gentamicin more readily enters the ear when applied to the stapes footplate compared with RWM application. These data provide a potential explanation for why gentamicin preferentially ablates vestibular function while preserving hearing following transtympanic administration in humans.