Three-dimensional cultured ampullae from rats as a screening tool for vestibulotoxicity: Proof of concept using styrene.

Numerous ototoxic drugs, such as some antibiotics and chemotherapeutics, are both cochleotoxic and vestibulotoxic (causing hearing loss and vestibular disorders). However, the impact of some industrial cochleotoxic compounds on the vestibular receptor, if any, remains unknown. As in vivo studies are long and expensive, there is considerable need for predictive and cost-effective in vitro models to test ototoxicity. Here, we present an organotypic model of cultured ampullae harvested from rat neonates. When cultured in a gelatinous matrix, ampulla explants form an enclosed compartment that progressively fills with a high-potassium (K+) endolymph-like fluid. Morphological analyses confirmed the presence of a number of cell types, sensory epithelium, secretory cells, and canalar cells. Treatments with inhibitors of potassium transporters demonstrated that the potassium homeostasis mechanisms were functional. To assess the potential of this model to reveal the toxic effects of chemicals, explants were exposed for either 2 or 72 h to styrene at a range of concentrations (0.5-1 mM). In the 2-h exposure condition, K+ concentration was significantly reduced, but ATP levels remained stable, and no histological damage was visible. After 72 h exposure, variations in K+ concentration were associated with histological damage and decreased ATP levels. This in vitro 3D neonatal rat ampulla model therefore represents a reliable and rapid means to assess the toxic properties of industrial compounds on this vestibular tissue, and can be used to investigate the specific underlying mechanisms.

Signal and morphological changes in the endolymph of patients with vestibular schwannoma on non-contrast 3D FLAIR at 3 Tesla.

BACKGROUND: Non-contrast FLAIR revealed increased signal within the inner ear in patients with vestibular schwannoma, which is generally assumed to occur in the perilymph; however, the majority of previous studies did not differentiate between the endolymph and perilymph. Therefore, endolymph signal changes have not yet been investigated in detail. The purpose of the present study was three-fold: (1) to assess perilymph signal changes in patients with vestibular schwannoma on heavily T2-weighted (T2W) 3D FLAIR, also termed positive perilymphatic images (PPI), (2) to evaluate signal and morphological changes in the endolymph on PPI, and (3) to establish whether vertigo correlates with the signal intensity ratios (SIR) of the vestibular perilymph or vestibular endolymphatic hydrops. METHODS: Forty-two patients with unilateral vestibular schwannoma were retrospectively recruited. We semi-quantitatively and qualitatively evaluated the perilymph signal intensity on the affected and unaffected sides. We also quantitatively examined the signal intensity of the vestibular perilymph and assessed the relationship between vertigo and the SIR of the vestibular perilymph on the affected side. We semi-quantitatively or qualitatively evaluated the endolymph, and investigated whether vestibular hydrops correlated with vertigo. RESULTS: The perilymph on the affected side showed abnormal signal more frequently (signal intensity grade: overall mean 1.45 vs. 0.02; comparison of signal intensity: overall mean 36 vs. 0 cases) and in more parts (the entire inner ear vs. the basal turn of the cochlea and vestibule) than that on the unaffected side. No significant difference was observed in the SIR of the vestibular perilymph with and without vertigo (5.54 vs. 5.51, p = 0.18). The endolymph of the vestibule and semicircular canals showed the following characteristic features: no visualization (n = 4), signal change (n = 1), or vestibular hydrops (n = 10). A correlation was not observed between vestibular hydrops and vertigo (p = 1.000). CONCLUSIONS: PPI may provide useful information on signal and morphological changes in the endolymph of patients with vestibular schwannoma. Further research is warranted to clarify the relationship between vertigo and the MR features of the inner ear.

The proteome of the human endolymphatic sac endolymph.

The endolymphatic sac (ES) is the third part of the inner ear, along with the cochlea and vestibular apparatus. A refined sampling technique was developed to analyse the proteomics of ES endolymph. With a tailored solid phase micro-extraction probe, five ES endolymph samples were collected, and six sac tissue biopsies were obtained in patients undergoing trans-labyrinthine surgery for sporadic vestibular schwannoma. The samples were analysed using nano-liquid chromatography-tandem mass spectrometry (nLC-MS/MS) to identify the total number of proteins. Pathway identification regarding molecular function and protein class was presented. A total of 1656 non-redundant proteins were identified, with 1211 proteins detected in the ES endolymph. A total of 110 proteins were unique to the ES endolymph. The results from the study both validate a strategy for in vivo and in situ human sampling during surgery and may also form a platform for further investigations to better understand the function of this intriguing part of the inner ear.

Immunohistochemical location of Na+, K+-ATPase α1 subunit in the human inner ear.

Na+, K+-ATPase (Na,K-ATPase) is an ubiquitous enzyme in the inner ear and a key factor in the maintenance of the osmotic gradient of the endolymph. This study uses Na,K-ATPase α1 subunit immunoreactivity (IR) to identify cellular structures in the normal and disease human cochlea. Formalin-fixed celloidin-embedded (FFCE) human temporal bone sections were immunoreacted with mouse monoclonal antibodies against Na,K-ATPase α1 subunit. Na,K-ATPase α1 IR was examined in the cochlea of 30 patients: four with normal hearing, 5 with Meniere's disease, and 21 with other inner ear diseases: 11 male, 19 female; ages 42 to 96 years-old (yo), average age of 77 yo. Na,K-ATPase α1 IR area was quantified using the ImageJ software program. Na,K-ATPase α1 IR was located in the stria vascularis, and in type I, II and IV fibrocytes of the spiral ligament in the cochlea from patients with normal hearing. Na,K-ATPase α1 IR was seen in Deiters's cells and inner phalangeal cells of the organ of Corti. Na,K-ATPase α1 IR was present in satellite cells that surround the neurons of the spiral ganglia. In the inner ear of pathological specimens, Na,K-ATPase IR area was decreased (compared to the normal) in the stria vascularis, supporting cells in the organ of Corti and satellite cells of the spiral ganglia. These results show that Na,K-ATPase α1 IR is a good marker to identify cellular structures of the human inner ear and may be used to study cellular changes in the cochlea associated with aging and disease. The ubiquitous localization of Na,K-ATPase α1 in the human cochlea is consistent with the Na,K-ATPase role in ionic homeostasis and osmolarity, similar to that seen in animal models.

Styrene alters potassium endolymphatic concentration in a model of cultured utricle explants.

Despite well-documented neurotoxic and ototoxic properties, styrene remains commonly used in industry. Its effects on the cochlea have been extensively studied in animals, and epidemiological and animal evidence indicates an impact on balance. However, its influence on the peripheral vestibular receptor has yet to be investigated. Here, we assessed the vestibulotoxicity of styrene using an in vitro model, consisting of three-dimensional cultured newborn rat utricles filled with a high­potassium (K+) endolymph-like fluid, called "cysts". K+ entry in the cyst ("influx") and its exit ("efflux") are controlled by secretory cells and hair cells, respectively. The vestibular epithelium's functionality is thus linked to K+ concentration, measured using a microelectrode. Known inhibitors of K+ efflux and influx validated the model. Cysts were subsequently exposed to styrene (0.25; 0.5; 0.75 and 1 mM) for 2 h or 72 h. The decrease in K+ concentration measured after both exposure durations was dose-dependent, and significant from 0.75 mM styrene. Vacuoles were visible in the cytoplasm of epithelial cells from 0.5 mM after 2 h and from 0.25 mM after 72 h. The results presented here are the first evidence that styrene may deregulate K+ homeostasis in the endolymphatic space, thereby altering the functionality of the vestibular receptor.

[In vivo dynamic changes of inner ear guinea pigs with 9.4 T esla MRI].

Objective: To observe the imaging characteristics of guinea pig cochlear structure using 9.4 Tesla magnetic resonance imaging system at different time intervals of contrast agent distribution in the inner ear. Methods: Form May 2015 to October 2015, five albino guinea pigs were injected with Gd-DTPA via the right internal jugular vein (3 ml/kg). Inner ears were scanned with 9.4T MRI. At the 10 th, 30 th, 60 th, 90 th and 120 th minutes post-Gd-DTPA, we took inner ear images to detect changes of endolymph and perilymph. Using Image J software, we acquired MRI gray value through the first, second, third and apical turn of cochlear at different time points. Analysis by one-way ANOVA was taken to analyze the resultsusing GraphPad Prism 5 software. Results: Only outlines of the cochlea and vestibule were visible before Gd-DTPA injection and there was no clear distinction between endolymph and perilymph. Cochlea vestibule on T1 weighted images was enhanced at the 10 th (the first turn of cochlear 8 203±819) after injection, and then imaging of each part of cochlea, including cochlea, vestibule, semicircular canal and even endolymph and perilymph, can be distinguished clearly, because they enhanced gradually at the 30 th(10 489±819), 60 th(13 965±591), and at 90 th(18 050±1 250) after injection. While at the 120 th(18 952±1 185) minute, imaging was not significantly enhanced than at the 90 th minute. The speed and volume of contrast agent spreaded into the various parts of the inner ear were different, and changes with distribution of contrast agent in each part of the inner ear showed a rising process in a certain period of time. The distribution of contrast agent in the inner ear had concentration gradient via basal turn higher and apical turn lower. Conclusions: Endolymph of inner ear can be distinguished from the perilymph using a 9.4T MRI system with Gd-DTPA, and the best observation timer was 90 minutes after intravenous injection of contrast agent. In summary, our study provides the clearly visualized imaging evidence of the changes of the lymphatic fluid, which may be useful for diagnosis of inner ear diseases such as Meniere's Disease.

Endolymph magnetic resonance imaging: Contribution of saccule and utricle analysis in the management of patients with sensorineural ear disorders.

Endolymphatic hydrops features excess endolymph in the membranous labyrinth, and is a marker of Menière's disease. Between the early 1980s and late 2000s, MRI in Menière's disease aimed purely to rule out tumor or malformation as differential diagnoses for the pressure disorder. Progress in high-resolution MRI, however, now enables excess endolymph to be visualized in the membranous labyrinth, differentiating saccule and utricle in Menière's disease and in other clinical presentations such as cochleovestibular schwannoma. More recently, non-visibility of the saccule was demonstrated in a subgroup of Menière's disease patients, and utricle atelectasis in case of uni- or bilateral vestibular areflexia. Endolymph quantification remains highly controversial in terms of grading approach, but a simple semiology based on excess or deficient visualization of endolymph according to the compartment sheds light on the pathophysiological mechanisms of cochleovestibular disorder and may in future allow effective monitoring of medical and surgical treatment.

Evolution of Endolymph Secretion and Endolymphatic Potential Generation in the Vertebrate Inner Ear.

The ear of extant vertebrates reflects multiple independent evolutionary trajectories. Examples include the middle ear or the unique specializations of the mammalian cochlea. Another striking difference between vertebrate inner ears concerns the differences in the magnitude of the endolymphatic potential. This differs both between the vestibular and auditory part of the inner ear as well as between the auditory periphery in different vertebrates. Here we provide a comparison of the cellular and molecular mechanisms in different endorgans across vertebrates. We begin with the lateral line and vestibular systems, as they likely represent plesiomorphic conditions, then review the situation in different vertebrate auditory endorgans. All three systems harbor hair cells bathed in a high (K+) environment. Superficial lateral line neuromasts are bathed in an electrogenically maintained high (K+) microenvironment provided by the complex gelatinous cupula. This is associated with a positive endocupular potential. Whether this is a special or a universal feature of lateral line and possibly vestibular cupulae remains to be discovered. The vestibular system represents a closed system with an endolymph that is characterized by an enhanced (K+) relative to the perilymph. Yet only in land vertebrates does (K+) exceed (Na+). The endolymphatic potential ranges from +1 to +11 mV, albeit we note intriguing reports of substantially higher potentials of up to +70 mV in the cupula of ampullae of the semicircular canals. Similarly, in the auditory system, a high (K+) is observed. However, in contrast to the vestibular system, the positive endolymphatic potential varies more substantially between vertebrates, ranging from near zero mV to approximately +100 mV. The tissues generating endolymph in the inner ear show considerable differences in cell types and location. So-called dark cells and the possibly homologous ionocytes in fish appear to be the common elements, but there is always at least one additional cell type present. To inspire research in this field, we propose a classification for these cell types and discuss potential evolutionary relationships. Their molecular repertoire is largely unknown and provides further fertile ground for future investigation. Finally, we propose that the ultimate selective pressure for an increased endolymphatic potential, as observed in mammals and to a lesser extent in birds, is specifically to maintain the AC component of the hair-cell receptor potential at high frequencies. In summary, we identify intriguing questions for future directions of research into the molecular and cellular basis of the endolymph in the different compartments of the inner ear. The answers will provide important insights into evolutionary and developmental processes in a sensory organ essential to many species, including humans.

In Vitro Survival of Human Mesenchymal Stem Cells is Enhanced in Artificial Endolymph with Moderately High Concentrations of Potassium.

While mesenchymal stem cells (MSCs) are promising candidates for inner ear hair cell regeneration, to date, there have been no convincing reports indicating whether MSCs can survive in the cochlea for more than a few weeks, as the high levels of potassium (K+) in the endolymph (EL) are thought to be toxic to transplanted stem cells. For conditioning the EL for MSC transplantation, we conducted this in vitro study to examine the effects of artificial EL with altered K+ concentration levels, in the range of 5-153.8 mM, on proliferation, apoptosis, and morphological changes in MSCs derived from various human tissues. Our findings demonstrate that altering the K+ concentration in artificial EL could significantly influence the survival of MSCs in vitro. We discovered that K+ concentrations of 55-130 mM in artificial EL could enhance the survival of MSCs in vitro. However, MSCs exhibited reduced proliferation regardless of K+ concentration.

The human endolymphatic sac expresses natriuretic peptides.

OBJECTIVES/HYPOTHESIS: The function of the human endolymphatic sac (ES) has been enigmatic for decades. Hypotheses include controlling endolymphatic fluid homeostasis and inner ear immunological defense. Additionally, several studies indicate a possible endocrine capacity and a yet undefined role in intracranial pressure homeostasis. However, no direct evidence of such capacity exists. This study aims to explore and identify the hypothesized endocrine capacity of the human ES. STUDY DESIGN: DNA microarrays and immunohistochemistry were used for analyses of fresh human ES tissue samples. METHODS: Twelve tissue samples from the human ES were obtained during translabyrinthine surgery for vestibular schwannoma. Microarray technology was used to investigate tissue sample gene expression. Genes specific for an endocrine function were determined, and results were verified by immunohistochemistry. RESULTS: Several natriuretic peptides were found expressed significantly in the ES, including uroguanylin and brain natriuretic peptide, but also peptides regulating vascular tone, including adrenomedullin 2. In addition, both neurophysin and oxytocin (OXT) were found significantly expressed. All peptides were verified by immunohistochemistry. CONCLUSION: The present data support the hypothesis that the human ES may have an endocrine/paracrine capacity through expression of several peptides with potent natriuretic activity. Furthermore, the ES may influence the hypothalamo-pituitary-adrenal axis and may regulate vasopressin receptors and aquaporin-2 channels in the inner ear via OXT expression. We hypothesize that the ES is likely to regulate inner ear endolymphatic homeostasis, possibly through secretion of several peptides, but it may also influence systemic and/or intracranial blood pressure through direct and indirect action on the vascular system and the kidney. LEVEL OF EVIDENCE: NA. Laryngoscope, 127:E201-E208, 2017.

Herpes simplex virus-1 and cytomegalovirus DNAs detection in the inner ear of implanted patients with non-congenital infection.

CONCLUSIONS: The detection of cytomegalovirus (CMV) and herpes simplex virus-1 (HSV-1) genome in perilymph of patients with negative serology or clinical history for congenital infections supports the hypothesis that Herpesviridae, even after acquired postnatal infections, could remain in latent phase in the spiral ganglion and damage the cochlea by a possible subsequent reactivation. Further studies are needed to identify the markers of such reactivation. OBJECTIVE: To identify the presence of certain viral species in the endolabyrinthic fluid of deaf patients with non-congenital infection. The research of viral DNA within the inner ear is the only direct way to increase our knowledge about the viral role in postnatal damage to the cochlea. METHODS: Thirty-six patients (1-69 years) suffering from bilateral sensorineural hearing loss (SNHL) were subjected, during cochlear implant (CI) surgery, to a sample taking of inner ear fluid. Several types of viral genome (HSV, VZV, CMV, EBV and Enterovirus) were investigated in each sample through multiplex polymerase chain reaction (PCR) and reverse transcriptase-polymerase chain reaction (RT-PCR). Radiological exams, serology (specific IgG and IgM) and PCR of peripheral blood were also performed. RESULTS: While the research of the viral genome in peripheral blood was negative in all patients, multiplex PCR on endolabyrinthic fluid samples was positive in three patients (two cases of CMV-DNA and one case of HSV-1 DNA).

Ion transport its regulation in the endolymphatic sac: suggestions for clinical aspects of Meniere's disease.

Ion transport and its regulation in the endolymphatic sac (ES) are reviewed on the basis of recent lines of evidence. The morphological and physiological findings demonstrate that epithelial cells in the intermediate portion of the ES are more functional in ion transport than those in the other portions. Several ion channels, ion transporters, ion exchangers, and so on have been reported to be present in epithelial cells of ES intermediate portion. An imaging study has shown that mitochondria-rich cells in the ES intermediate portion have a higher activity of Na+, K+-ATPase and a higher Na+ permeability than other type of cells, implying that molecules related to Na+ transport, such as epithelial sodium channel (ENaC), Na+-K+-2Cl- cotransporter 2 (NKCC2) and thiazide-sensitive Na+-Cl- cotransporter (NCC), may be present in mitochondria-rich cells. Accumulated lines of evidence suggests that Na+ transport is most important in the ES, and that mitochondria-rich cells play crucial roles in Na+ transport in the ES. Several lines of evidence support the hypothesis that aldosterone may regulate Na+ transport in ES, resulting in endolymph volume regulation. The presence of molecules related to acid/base transport, such as H+-ATPase, Na+-H+ exchanger (NHE), pendrin (SLC26A4), Cl--HCO3- exchanger (SLC4A2), and carbonic anhydrase in ES epithelial cells, suggests that acid/base transport is another important one in the ES. Recent basic and clinical studies suggest that aldosterone may be involved in the effect of salt-reduced diet treatment in Meniere's disease.

[The correlation analysis of the cochlear hydrops degree found by MRI angiography with Meiniere's disease classification].

Objective:To investigate the correlation between the levels of cochlear hydrops with the clinic classification of Meniere's disease(MD).Method:3D-FlAIR MRI was performed 24 hours after intratympanic injection of 8-fold diluted Gadopentetate Dimeglumine in 31 patients with unilateral MD. We evaluated the levels of cochlear hydrops and further analyzed the correlation between the levels of cochlear hydrops and thresholds of pure tone audiometry and clinic classification of MD. Result:MRI image clearly distinguished perilymph from endolymph in the labyrinth. The images showed different levels of enhancement of perilymphatic fluid spaces. In the 31 patients, obvious signs of endolymphatic hydrops were found, including 4 cases of level 0, 6 cases of level 1, 11 cases of level 2 and 10 cases of level 3. Their average hearing threshold was(54.37±3.88)dB HL. The levels of cochlear hydrops were significantly correlated with pure tone audiometry thresholds （r=0.636，P<0.01） and MD classification(r=0.516,P<0.01). None of the patients after intratympanic injection complained about discomfort or happened with any complications such as eardrum perforation, infection, and so on. Conclusion:The degree of endolymphatic hydrops based on MRI in MD patient has significant correlation with the pure tone audiometry and classification of disease. The examination can act as an objective index for MD diagnosis.

The gastric H,K-ATPase in stria vascularis contributes to pH regulation of cochlear endolymph but not to K secretion.

BACKGROUND: Disturbance of acid-base balance in the inner ear is known to be associated with hearing loss in a number of conditions including genetic mutations and pharmacologic interventions. Several previous physiologic and immunohistochemical observations lead to proposals of the involvement of acid-base transporters in stria vascularis. RESULTS: We directly measured acid flux in vitro from the apical side of isolated stria vascularis from adult C57Bl/6 mice with a novel constant-perfusion pH-selective self-referencing probe. Acid efflux that depended on metabolism and ion transport was observed from the apical side of stria vascularis. The acid flux was decreased to about 40 % of control by removal of the metabolic substrate (glucose-free) and by inhibition of the sodium pump (ouabain). The flux was also decreased a) by inhibition of Na,H-exchangers by amiloride, dimethylamiloride (DMA), S3226 and Hoe694, b) by inhibition of Na,2Cl,K-cotransporter (NKCC1) by bumetanide, and c) by the likely inhibition of HCO3/anion exchange by DIDS. By contrast, the acid flux was increased by inhibition of gastric H,K-ATPase (SCH28080) but was not affected by an inhibitor of vH-ATPase (bafilomycin).  K flux from stria vascularis was reduced less than 5 % by SCH28080. CONCLUSIONS: These observations suggest that stria vascularis may be an important site of control of cochlear acid-base balance and demonstrate a functional role of several acid-base transporters in stria vascularis, including basolateral H,K-ATPase and apical Na,H-exchange. Previous suggestions that H secretion is mediated by an apical vH-ATPase and that basolateral H,K-ATPase contributes importantly to K secretion in stria vascularis are not supported. These results advance our understanding of inner ear acid-base balance and provide a stronger basis to interpret the etiology of genetic and pharmacologic cochlear dysfunctions that are influenced by endolymphatic pH.

Meniere's disease.

Meniere's disease (MD) is a disorder of the inner ear that causes vertigo attacks, fluctuating hearing loss, tinnitus and aural fullness. The aetiology of MD is multifactorial. A characteristic sign of MD is endolymphatic hydrops (EH), a disorder in which excessive endolymph accumulates in the inner ear and causes damage to the ganglion cells. In most patients, the clinical symptoms of MD present after considerable accumulation of endolymph has occurred. However, some patients develop symptoms in the early stages of EH. The reason for the variability in the symptomatology is unknown and the relationship between EH and the clinical symptoms of MD requires further study. The diagnosis of MD is based on clinical symptoms but can be complemented with functional inner ear tests, including audiometry, vestibular-evoked myogenic potential testing, caloric testing, electrocochleography or head impulse tests. MRI has been optimized to directly visualize EH in the cochlea, vestibule and semicircular canals, and its use is shifting from the research setting to the clinic. The management of MD is mainly aimed at the relief of acute attacks of vertigo and the prevention of recurrent attacks. Therapeutic options are based on empirical evidence and include the management of risk factors and a conservative approach as the first line of treatment. When medical treatment is unable to suppress vertigo attacks, intratympanic gentamicin therapy or endolymphatic sac decompression surgery is usually considered. This Primer covers the pathophysiology, symptomatology, diagnosis, management, quality of life and prevention of MD.

[Long-term efficacy of triple semicircular canal occlusion in the treatment of intractable Meniere's disease].

OBJECTIVE: To explore the long-term efficacy and safety of triple semicircular canal occlusion (TSCO) in the treatment of intractable Meniere's disease (MD) so as to provide an alternative surgical procedure for treating this disorder. METHODS: Data from Forty-nine patients, who were referred to our hospital and diagnosed with unilateral MD strictly meeting the criteria issued by Chinese Academy of Otolaryngology-Head and Neck Surgery Committee (2006) from Dec. 2010 to Jul. 2012, were retrospectively analyzed in this work. Forty-nine patients, in whom the standardized conservative treatment was given at least one year and frequent vertigo still occurred, received TSCO. Vertigo control and auditory function were measured. Pure tone audiometry, caloric test, and cervical vestibular evoked myogenic potential (cVEMP) were performed for evaluation of audiological and vestibular function. Magnetic resonance hydrograph of inner ear was performed in patients received TSCO after 2 years for the observation of morphology of membranous labyrinth. Postoperative follow-up period was more than 2 years. RESULTS: According to the preoperative staging of hearing, among these 49 patients, there were 2 cases in stage II (with an average hearing threshold of 25-40 dBHL), 40 in stage III (41-70 dBHL) and 7 in stage IV (over 70 dBHL). Vertigo was controlled effectively in all 49 cases in two-year follow-up, of which 40 cases (81.6%) were completely controlled and 9 cases (18.4%) were substantially controlled after surgery. The rate of hearing preservation was 69.4% and the rate of hearing loss was 30.6%. Post-operatively, all patients suffered from temporary vertigo and balance disorders. Vertigo was disappeared in all patients within 3-5 days, while averagely recovered after 13.5 days. Two years afer treatment, loss of semicircular canal function by caloric test was found in the operation side of all patients and no change in cVEMP test was noted. All patients had no facial paralysis, cerebrospinal fluid leakage, and other complications. Magnetic resonance hydrograph of inner ear showed that endolymph fluid in the position of plugging had no water after 2-years of TSCO. CONCLUSIONS: TSCO, which can reduce vertiginous symptoms effectively in patients with intractable MD in long-term follow-up, represents an effective and safe therapy for this disorder. TSCO is expected to be used as an alternative procedure for the treatment of MD in selected patients suffering from severe hearing loss or recurrence after endolymphatic sac surgery.

Gadolinium contrast-enhanced MRI reveals cystic lateral semicircular canal contents.

CONCLUSION: Contrast-enhanced magnetic resonance imaging (MRI) reveals variations in the endolymphatic morphology of the cystic lateral semicircular canal (CLSC) that correlate with inner ear function. This report is the first to suggest a relationship between the morphology and function of this common inner ear malformation in clinical cases. OBJECTIVES: This study investigated the radiological and functional findings of a common inner ear malformation using computed tomography (CT), gadolinium contrast-enhanced magnetic resonance imaging (MRI), caloric testing, and cervical and ocular vestibular evoked myogenic potential (VEMP) testing. METHOD: Four ears in three patients who were radiologically diagnosed with a CLSC and a normal cochlea on high-resolution CT and contrast-enhanced MRI were included. Semicircular canal and vestibular functions were analyzed using the caloric test and cervical and ocular VEMP testing. RESULTS: Unilateral and bilateral cystic canals were found in two and one patients, respectively. In the first patient, the malformed vestibule and cystic space were separate on imaging, and perilymph filled the cystic space. The functional test results were normal. In the second patient, endolymph filled both cystic spaces, and the functional responses were poor. In the third patient, endolymph filled the cystic space, and the ear did not respond during functional testing.

Ratio of Vestibular Endolymph in Patients with Isolated Lateral Semicircular Canal Dysplasia.

PURPOSE: Isolated vestibular-lateral semicircular canal dysplasia (LSCCD) is one of the most common anomalies of the inner ear. However, endolymphatic size in LSCCD is unknown. We measured the size of the endolymph in the vestibule of patients with LSCCD and compared it with that measured in patients without LSCCD. METHODS: We extracted 1102 magnetic resonance (MR) studies for the evaluation of endolymphatic hydrops (EH) from our database of radiology reports. Among these, we found 15 ears from 11 patients with LSCCD; 4 patients had bilateral abnormalities. Seven of the 15 ears demonstrated aplasia and 8 ears, hypoplasia of the lateral semicircular canal (LSCC). The control group consisted of 26 ears from 13 randomly selected patients without LSCCD. We measured the area of endolymph in the vestibule (ELA), total area of vestibular lymph fluid (TLA), and area of the central bony island (CBI) of the LSCC from axial MR images obtained after intratympanic or intravenous administration of gadolinium-based contrast material. The ratio of endolymphatic area to total lymphatic area (%EL) was defined as %EL = ELA/TLA × 100.We evaluated the correlation between %EL and the area of the CBI and compared age, %EL, degree of cochlear EH, hearing level, and presence of rotating vertigo among the 3 groups (aplasia, hypoplasia, control). RESULTS: The mean %EL was 76.7% in the aplasia group, 50.0% in the hypoplasia group, and 27.8% in the control group (P < 0.001). There was a relatively strong linear correlation between the area of the CBI and %EL (r = -0.767). Patient age, mean hearing level, degree of cochlear EH, or presence of vertigo attacks did not differ significantly among the groups (P > 0.05). CONCLUSION: The size of vestibular endolymph was larger in the groups with aplasia or hypoplasia than the control group. Thus, the current diagnostic cut-off value for significant vestibular EH (>50%) might not be appropriate for ears with LSCCD.

[Visualization of endolymphatic hydrops in 3D-FLAIR MRI after intratympanic Gd-DTPA administration in Meniere's disease patients].

OBJECTIVE: To study the feasibility of endolymphatic visualization and the diagnosis of Meniere's disease by applying intratympanic gadolinium administration through the tympanic membrance and three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging (3D-FLAIR MRI). To study the relationship between the endolymphatic hydrops visualized by MRI and audio-vestibular functional tests, such as pure tone audiometry (PTA), electrocochleography (EcoG), caloric test and vestibular evoked myogenic potential (VEMP). METHODS: With a three Tesla magnetic resonance imaging (MRI) unit, 3D-FLAIR imaging was performed 24 hours after intratympanic gadolinium through the tympanic membrance in 32 patients with clinically diagnosed unilateral Meniere's Disease. We visualized the enhanced imaging of perilymphatic space in bilateral cochlea, vestibular and (or) canal, scoring scala tympani and scala vestibule of bilateral cochlear basal turn respectively and measuring the developing area of bilateral vestibule and the signal intensity ratio (SIR) between the vestibule and the brain stem subjectively. PTA, EcoG, caloric test and VEMP were performed. The relationship between the endolymphatic hydrops visualized by MRI and audio-vestibular functional tests were studied. RESULTS: The gadolinium appeared in almost all parts of the perilymph in cochlea, vestibular and (or) canals in all 32 patients' inner ears, so the endolymphatic space was clearly shown on 3D-FLAIR imaging. The scala vestibuli score value between the affected side and the healthy side were statistically significant (Z = 4.309, P < 0.05) . The developing vestibular area between the affected side and the healthy side [(6.04 ± 2.89) mm(2), (8.28 ± 3.04)mm(2)] were statistically significant (t = 3.322, P < 0.05) . Abnormal vestibular evoked myogenic potentials were significantly correlated with the developing vestibular area of the affected side (F = 11.96, P < 0.05) . Abnormal electrocochleography were significantly correlated with scala vestibuli score value of cochlear basal turn in the affected side (Z = 3.17, P < 0.05) . No significant correlation was found between the scala vestibuli score value or the developing vestibular area and caloric test or PTA findings. CONCLUSIONS: 3D-FLAIR MRI with intratympanic gadolinium injection through the tympanic membrance can discriminate the border between the perilymph and the endolymph and show endolymphatic hydrops. This method may provide radiographic reference for the diagnosis of Meniere's disease. The results of VEMP and electrocochleography might have appropriate correlation with degree of vestibular and cochlear hydrops.

Endolymphatic Na⁺ and K⁺ concentrations during cochlear growth and enlargement in mice lacking Slc26a4/pendrin.

Slc26a4 (Δ/Δ) mice are deaf, develop an enlarged membranous labyrinth, and thereby largely resemble the human phenotype where mutations of SLC26A4 cause an enlarged vestibular aqueduct and sensorineural hearing loss. The enlargement is likely caused by abnormal ion and fluid transport during the time of embryonic development, however, neither the mechanisms of ion transport nor the ionic composition of the luminal fluid during this time of development are known. Here we determine the ionic composition of inner ear fluids at the time at which the enlargement develops and the onset of expression of selected ion transporters. Concentrations of Na(+) and K(+) were measured with double-barreled ion-selective electrodes in the cochlea and the endolymphatic sac of Slc26a4 (Δ/+), which develop normal hearing, and of Slc26a4 (Δ/Δ) mice, which fail to develop hearing. The expression of specific ion transporters was examined by quantitative RT-PCR and immunohistochemistry. High Na(+) (∼141 mM) and low K(+) concentrations (∼11 mM) were found at embryonic day (E) 16.5 in cochlear endolymph of Slc26a4 (Δ/+) and Slc26a4 (Δ/Δ) mice. Shortly before birth the K(+) concentration began to rise. Immediately after birth (postnatal day 0), the Na(+) and K(+) concentrations in cochlear endolymph were each ∼80 mM. In Slc26a4 (Δ/Δ) mice, the rise in the K(+) concentration occurred with a ∼3 day delay. K(+) concentrations were also found to be low (∼15 mM) in the embryonic endolymphatic sac. The onset of expression of the K(+) channel KCNQ1 and the Na(+)/2Cl(-)/K(+) cotransporter SLC12A2 occurred in the cochlea at E19.5 in Slc26a4 (Δ/+) and Slc26a4 (Δ/Δ) mice. These data demonstrate that endolymph, at the time at which the enlargement develops, is a Na(+)-rich fluid, which transitions into a K(+)-rich fluid before birth. The data suggest that the endolymphatic enlargement caused by a loss of Slc26a4 is a consequence of disrupted Na(+) transport.