Multicentre evaluation of the temporal bones obtained from a patient with suspected Menière's disease

Microanatomy of the human tunnel of Corti structures and cochlear partition-tonotopic variations and transcellular signaling

Auditory sensitivity and frequency resolution depend on the optimal transfer of sound-induced vibrations from the basilar membrane (BM) to the inner hair cells (IHCs), the principal auditory receptors. There remains a paucity of information on how this is accomplished along the frequency range in the human cochlea. Most of the current knowledge is derived either from animal experiments or human tissue processed after death, offering limited structural preservation and optical resolution. In our study, we analyzed the cytoarchitecture of the human cochlear partition at different frequency locations using high-resolution microscopy of uniquely preserved normal human tissue. The results may have clinical implications and increase our understanding of how frequency-dependent acoustic vibrations are carried to human IHCs. A 1-micron-thick plastic-embedded section (mid-modiolar) from a normal human cochlea uniquely preserved at lateral skull base surgery was analyzed using light and transmission electron microscopy (LM, TEM). Frequency locations were estimated using synchrotron radiation phase-contrast imaging (SR-PCI). Archival human tissue prepared for scanning electron microscopy (SEM) and super-resolution structured illumination microscopy (SR-SIM) were also used and compared in this study. Microscopy demonstrated great variations in the dimension and architecture of the human cochlear partition along the frequency range. Pillar cell geometry was closely regulated and depended on the reticular lamina slope and tympanic lip angle. A type II collagen-expressing lamina extended medially from the tympanic lip under the inner sulcus, here named "accessory basilar membrane." It was linked to the tympanic lip and inner pillar foot, and it may contribute to the overall compliance of the cochlear partition. Based on the findings, we speculate on the remarkable microanatomic inflections and geometric relationships which relay different sound-induced vibrations to the IHCs, including their relevance for the evolution of human speech reception and electric stimulation with auditory implants. The inner pillar transcellular microtubule/actin system's role of directly converting vibration energy to the IHC cuticular plate and ciliary bundle is highlighted.

Systematic review of magnetic resonance imaging for diagnosis of Meniere disease

The diagnostic criteria for Meniere Disease (MD) are clinical and include two categories: definite MD and probable MD, based on clinical examination and without the necessity of advanced vestibular or audiological testing. The condition is a heterogeneous disorder and it is associated with endolymphatic hydrops (EH), an accumulation of endolymph in the inner ear that causes damage to the ganglion cells. Patients with suspected EH can be examined by Magnetic Resonance Imaging (MRI), offering new insights into these inner ear disorders. Results of imaging studies using the hydrops protocols show conflicting results in MD patients. These discrepancies can be dependent either on the MRI sequence parameters or on the method of hydrops grading or the inclusion criteria to select patients. The visualization of EH can be classified based on a semi-quantitative ratio between endolymph and perilymph liquids, or on the distinction between the saccule and the utricle structures. In addition, MRI can also be used to evaluate whether cochleovestibular nerves can present with imaging signs of axonal loss.In this systematic review, we have selected case-controlled studies to better characterize the potential added value in the diagnosis and management of patients with MD. Using different techniques, studies have identified the saccule as the most specifically involved structure in MD, and saccular hydrops seems to be associated with low to medium-tone sensorineural hearing loss degree. However, early symptoms still appear too subtle for identification using MRI and the reproducibility of the hydrops protocols with various MRI scan manufacturers is debatable, thus limiting expansion of these techniques into clinical practice for the diagnosis of MD at this time.Further research is needed. The future inclusion of semicircular canal hydrops location in the imaging signs and the application of MRI in patients with atypical presentations hold promise.

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.

Clinical value of tone burst vestibular evoked myogenic potentials at threshold in acute and stable Ménière's disease

Introduction:

The objectives of this preliminary, prospective, cohort study were to ascertain the characteristics of vestibular evoked myogenic potentials at threshold levels in two groups of Ménière's disease patients – acute and stable – and to identify whether vestibular evoked myogenic potentials can provide any specific, objective information to distinguish acute from stable Ménière's disease.

Subjects and methods:

The study was based at a tertiary neuro-otology centre. Twenty adult patients who fulfilled the American Academy of Otolaryngology–Head and Neck Surgery1 criteria for Ménière's disease were divided into two groups: 11 patients with acute Ménière's disease and nine patients with stable Ménière's disease. Eighteen healthy adult volunteers served as controls. All subjects underwent vestibular evoked myogenic potential testing with ipsilateral, short tone burst stimuli at 500 Hz, as well as pure tone audiometry. The patients also underwent caloric testing.

Results:

Vestibular evoked myogenic potentials were present in all controls, and were present in 65 per cent of patients but absent in 35 per cent. The mean absolute threshold (Tvestibular evoked myogenic potential) ± standard deviation in normal controls was 116 ± 7.7 dBSPL; this did not differ statistically from that in patients, nor did it differ between acute and stable Ménière's disease. The p13/n23 latencies at the threshold levels in the normal, acute and stable groups (mean ± standard deviation) were respectively: 15 ± 2.2 ms/23.0 ± 2.5 ms; 15.7 ± 0.9 ms/23.7 ± 0.9 ms; and 15.3 ± 2.0 ms/24.2 ± 1.9 ms. The mean interaural amplitude difference ratio (IAD) ± standard deviation was significantly higher in the stable group compared with the acute group (0.54 ± 0.33 vs −0.15 ± 0.22; p = 0.007) and with the controls (0.54 ± 0.33 vs 0.1 ± 0.22; p = 0.05).

Conclusions:

The parameter that best differentiated acute from stable Ménière's disease at threshold was the interaural amplitude difference ratio. Therefore, this parameter may be used to monitor the clinical course of Ménière's disease.

Demyelination of Vestibular Nerve Axons in Unilateral Ménière's Disease

We conducted a study to determine whether vestibular nerves inpatients with unilateral Ménière's disease whose symptoms are refractory to medical management exhibit neuropathologic changes. We also endeavored to determine whether retrocochlear abnormalities are primary or secondary factors in the disease process. To these ends, we obtained vestibular nerve segments from five patients during retrosigmoid (posteriorfossa) neurectomy, immediately fixed them, and processed them for light and electron microscopy. We found that all five segments exhibited moderate to severe demyelination with axonal sparing. Moreover, we noted that reactive astrocytes produced an extensive proliferation of fibrous processes and that the microglia assumed a phagocytic role. We conclude that the possible etiologies of demyelination include viral and/or immune-mediated factors similar to those seen in other demyelinating diseases, such as multiple sclerosis and Guillain-Barré syndrome. Our findings suggest that some forms of Ménière's disease that are refractory to traditional medical management might be the result of retrocochlear pathology that affects the neuroglial portion of the vestibular nerve.

History of Meniere's disease and its clinical presentation

The term Meniere's disease is used to define either the classic triad of vestibular and cochlear symptoms and aural pressure from known or unknown causes or its clinical variants, vestibular and cochlear Meniere's disease. Some variants evolve after years into typical forms, whereas others do not. Some symptoms (positional vertigo) have been long underestimated in previous reports. The more we study our patients and correlate clinical findings and the natural history with pathologic studies on temporal bones and laboratory research, the more we will understand Meniere's disease and its causes. Some causes have already been identified as most probable. Extrinsic factors (inflammation, trauma, otosclerosis, autoimmunity, endocrine disorders, and such) interact with congenital (genetic) and developmental intrinsic factors (primary or secondary, acquired) into a multifactorial inheritance that is, to date, the best explanation for the basis of Meniere's disease. Endolymphatic hydrops is widely accepted as the pathologic substrate, but not all hydrops seems to be progressive or becomes clinically manifest. Endolymphatic hydrops is the result of a dysfunction in the mechanism of production/absorption of endolymph, which is mainly due to defective absorptive activity of the endolymphatic duct and sac. Hyperproduction of endolymph cannot be excluded in some cases. Ruptures of the labyrinthine membranes do not satisfactorily substantiate the multiform duration, recurrence, and repetitiveness of attacks of Meniere's disease, nor do they explain the entire complex of symptoms. It seems reasonable to explain symptoms of Meniere's disease on the basis of mechanical factors (as observed in temporal bone studies) associated with biologic and biochemical factors.

A morphological and morphometric study of the peripheral process of the human vestibular nerve following posterior cranial fossa neurectomy

Three vestibular nerve specimens removed at transmeatal neurectomy were studied in order to understand better retrograde degeneration and regeneration after vestibular neurectomy in the posterior cranial fossa. In two cases this procedure followed retrolabyrinthine retrosigmoid posterior fossa vestibular neurectomy. The subjects, three patients with Menière's disease, were compared with one another and two autopsy controls with no known otological problem. The specimens were obtained at the distal end of the internal auditory canal and transversely sectioned. Many collapsed Schwann cell basement membranes were observed. The ratio of small-diameter nerve fibres increased significantly after neurectomy. Onion bulb formation around myelinated nerve fibres with small diameters and Schwann cell proliferation around the soma of vestibular ganglion cells reflected remyelination. We conclude that peripheral processes of vestibular nerve fibres can undergo retrograde degeneration and subsequent regeneration after transection of the central process.

Ultrastructural analysis of the vestibular nerve in Ménière's disease

Numerical analysis of the vestibular nerve in Méniè's disease was performed. Vestibular nerve specimens were obtained from three patients with classical clinical findings of Ménière's disease during retrosigmoid vestibular neurectomy. For each patient, an ultrathin section, including an entire cross-section of the nerve specimen, was examined. Fiber counts of nerve specimens with definite pathologic findings were compared with caloric testing results. A significant correlation was found between reduced vestibular response and the incidence of abnormal nerve fibers and also the density of the abnormal nerve fibers. However, the number of nerve fibers with pathologic findings was small. Results of the present study demonstrate no general degeneration of nerve fibers caused by the disease process of Ménière's disease.

Ménière's disease

There now exists a vast literature on Ménière's disease. In this review, we examine closely the foundations of some of the current concepts regarding various aspects of the disorder, including definitions, clinical features, natural history, pathology, pathogenesis, pathophysiology, diagnosis and treatment. We will highlight areas where the current state of knowledge is incomplete and also suggest some avenues for further research.

Cochlear vascular pathology and hydrops in otosclerosis

Three ears with otosclerosis were found incidentally in a series of human temporal bones examined to evaluate cochlear sensorineural degeneration. Otosclerosis was identified with microdissection, surface preparation technique and transmission electron microscopy. Vascular abnormalities were present in all ears, and otosclerosis involved the cochlear endosteum extensively, mainly in the scala tympani of the basal turn. In the scala tympani of the lower half of the basal turn, shunts had formed so that venules deviated abruptly from their normal radiating course towards the spiral vein, left the scala and entered into otosclerotic foci. There was a marked loss of radiating venules in areas where otosclerosis affected the endosteum of the scala. In the pair of bones capillaries in the stria vascularis were extremely dilated, the widest being 80 microns in diameter. The third single bone from a patient with Meniere's disease had severe cochleo-saccular hydrops. Ten serially sectioned temporal bones with known otosclerosis were reviewed. Two of the bones, one of which had cochleo-saccular hydrops, displayed vascular shunts in the scala tympani and enormously dilated strial capillaries with a maximum diameter of 139 microns.