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We report a patient who experienced a severe vertiginous episode with bilateral tinnitus and progressive right-sided hearing loss. She had Marfan's disease and was on anticoagulant treatment. The fluid in the labyrinth gave higher signal than cerebrospinal fluid on T1-weighted images, suggesting haemorrhage. The radiological follow-up is discussed.
We report on five patients with high signals in the labyrinth on unenhanced magnetic resonance imaging who developed sudden hearing loss and vertigo. Weissman et al. (1992) suggested the possibility that such high signals were caused by hemorrhage. We assessed these patients using audiograms, caloric tests, and auditory brainstem responses to investigate the possibility of inner ear hemorrhage. Most of the patients were found to have severe and irreversible impairment of both cochlear and vestibular function. These findings were consistent with the hypothesis that their symptoms were caused by inner ear hemorrhage.
Intra-axonal recordings were obtained from single afferent fibres of the posterior nerve in the isolated labyrinth of the frog (Rana esculenta). EPSPs and spike discharge were recorded both at rest and during rotatory stimulation of the canal. Electrical stimulation of either the distal end of the cut posterior nerve or of the central stumps of the anterior-horizontal nerves elicited a frequency-dependent inhibitory effect on the afferent discharge arising from the posterior canal. Denervation experiments revealed that inhibition is mediated by efferent fibres exhibiting a high degree of branching in the proximal part of the eighth nerve. The inhibitory effect was selectively cancelled by (1)D-tubocurarine 10(-6) M; (2) atropine 5 x 10(-5) M; (3) acetylcholine or carbachol 10(-4) M; (4) eserine 10(-5) M. Inhibition is thus most likely to be sustained by the release of acetylcholine from the efferent nerve terminals. Experiments in which the ionic composition of the external medium was modified suggest that the transmitter acts mainly by opening the chloride ion channels of the hair cell membrane. In some units the same stimulation pattern evoked a consistent increase in both EPSP and spike discharge, instead of inhibition. Such facilitation was unaffected by drugs for ionic modifications which block the efferent synapse, but disappeared after denervation. Inhibition and facilitation, therefore, act as two control mechanisms which are able to modify substantially, at the first stage of processing, the sensory information which is sent to the vestibular second order neurons.
Electron microscopy of the toadfish vestibular labyrinth demonstrated the usual cytoarchitectural efferent-hair cell organization with type II hair cells having efferent synaptic terminals directly onto the hair cell bodies. Additional, unexpected findings were: direct efferent-afferent synapses; and two types of synaptic vesicles either found both in the same efferent terminals or in two separate classes of efferent terminals.
To better understand the pathogenesis of cytomegalovirus labyrinthitis, a guinea pig model was created. Following inoculation at several sites (cardiac, perilymph, and endolymphatic sac) in both seronegative and seropositive animals, the immunologic, histologic, and electrophysiologic responses were measured. Seronegative animals uniformly showed progressive hearing loss with marked inflammation and degeneration of neural elements. In animals inoculated into the endolymphatic sac, an associated endolymphatic hydrops developed in addition to deafness. Seropositivity protected the hearing, but endolymphatic sac inoculations resulted in mild hydrops due to local inflammation that was devoid of evidence of viral replication. The question of whether hearing loss was attributable to local inflammatory responses rather than the cytopathic effects of the virus was then examined. To test this hypothesis, animals were immunosuppressed with cyclophosphamide prior to intracochlear inoculation of cytomegalovirus. The immunosuppressed animals showed significantly better hearing than the controls, and this correlated directly with the degree of cellular infiltration of the scala tympani. These studies confirm the importance of host immune responses in the pathogenesis of hearing loss due to cytomegalovirus.
The characteristics of the control exerted by macular and ampullar vestibular receptors on oculomotor neurons (OMN) have been investigated by submitting unanesthetized, encéphale isolé rabbits, with intact and canal-plugged labyrinths, to sinusoidal lateral tilts of varying frequencies (0.013-0.2 Hz). For frequencies of tilt above 0.025 Hz, corresponding to peak angular accelerations suprathreshold for canal related vestibular neurons, both phase and sensitivity of the OMN response differ significantly in the two types of preparation. At lower frequencies of tilt the characteristics of the OMN response are, on the contrary, very similar, thus indicating that also in the intact animals the control of the vertical vestibulo-ocular reflex, in this frequency range, is exerted almost exclusively by the otoliths.
Temporal bones were acquired four hours post mortem from a 67-year-old cancer patient. During dissection of the left vestibular labyrinth, a glistening white, spherical concretion was found in the posterior semicircular duct near the ampulla. The object was subsequently studied by light and scanning electron microscopy, x-ray diffraction, and x-ray energy dispersive elemental analysis. It was composed of four concentric layers: an outer zone of tabular vaterite crystals, a colorless intermediate zone of spherulitic octacalcium phosphate (OCP), and a cloudy core with inner and outer zones both composed of OCP. Examination of the vestibular receptor organs revealed severe loss of hair cells on all three cristae. Very few otoconia were present in the utricle, although the gelatinous layer of the otoconial membrane was intact on the macular surface. During the year preceding his death, the patient had received 800 mg of the potentially ototoxic drug cis-platinum. The concretion described in this report was, however, probably connected with age-related degeneration rather than with any effect of the drug.
Forty-eight patients with syphilitic labyrinthitis have been treated and followed up for periods of six months to 25 years; interpretation of the hearing results must be in the light of the natural history of this condition which is perceived to be progression of hearing loss to profound deafness. At the beginning of the series treatment was with ampicillin alone and on this treatment 11 ears with useful hearing were maintained at this level. The group with combined ampicillin and prednisone treatment, which included some failures from ampicillin alone, maintained useful hearing in 28 out of 29 ears. Those treated initially with ampicillin and prednisone and later also given regular injections of ACTH, maintained hearing in 16 out of 17 ears. At the outset, there were 29 profoundly deaf ears. One of these recovered some useful hearing but two ears with useful hearing at the outset became profoundly deaf so that at the end there were 30 profoundly deaf ears. However, all patients as opposed to ears, with useful hearing at the outset were left with some hearing; no patient became profoundly deaf.
A previous study on experimental autoimmune labyrinthitis (EAL) consistently demonstrated transient infiltration of lymphocytes only into the inner ear of mice. To clarify the profile of lymphocytes in the initiation of EAL, the present study investigated cell surface antigens, as well as cytokines, from Day 4 to Day 35, using immunohistochemical techniques. Many CD4+ cells mainly infiltrated the endolymphatic sac as early as Day 4 and gradually spread to the rest of the inner ear. Infiltration peaked on Day 12 and persisted in most animals until Day 35, although the number of cells gradually decreased. In contrast, very few CD8+ cells were found to have appeared in the inner ear of all animals on Day 10, and the number of cells rapidly decreased. Many cells positive for IFN-gamma and IL-2 were identified in the endolymphatic sac on Day 4. These results suggest that helper T1 lymphocytes, rather than cytotoxic T lymphocytes, may play a central role in the initiation of EAL.
Inflammatory reactions within the cochlea lead to the formation of fibrotic tissue and bone. To determine which cells are involved in the proliferation of the inflammatory response within the cochlea, sterile labyrinthitis was created by inoculating keyhole limpet hemocyanin (KLH) into the scala tympani of systemically sensitized animals. Cellular proliferation was assessed immunohistochemically using the monoclonal antibody Ki-67. Proliferating cells were identified among inflammatory cells and fibroblasts within the matrix, as well as in endosteal cells lining the scala tympani. Inflammatory and potential osteoprogenitor cells were labeled as late as 6 weeks after inoculation, suggesting the absence of a strong immunosuppressive mechanism. Endosteal cells may proliferate and secrete the extracellular matrix used by the inflammatory cells to move within the cochlear scalae. They may also participate in the ossification of the inflammatory matrix.
Sensorineural hearing loss is a common problem in the otolaryngologist's practice, with autoimmune disease of the inner ear being one possible cause. The restoration of auditory function in some patients following immunosuppressive therapy has created a desire to define and understand this disease better. Because of the lack of a well defined detection method to identify this entity clinically, this study was undertaken in order to provide an animal model for autoimmune disease of the inner ear. Previous studies with guinea pigs have demonstrated that sensitized lymphocytes from the systemic circulation migrate to the labyrinth during an immune response in the inner ear. The aim of this study was to prove the capacity of sensitized lymphocytes to transfer autoimmune inner ear disease, and to describe the resulting morphological and physiological changes. Therefore two groups of sensitized lymphocytes partially labelled with a radioactive marker from inbred guinea pigs with an immune response within the inner ear were injected into the bloodstream of naive recipient animals. Most of the labelled cells were observed in the apical turn of the experimental cochlea, while only few cells were detectable in the control cochleas. In addition, the absence of otoacoustic emissions and the loss of outer hair cells observed by electron microscopy were interpreted as a sign of damage caused by the provoked immunopathologic mechanism. The results are discussed as a possible model for a sympathetic cochleolabyrinthitis.
The effects of caloric stimulation of the labyrinth on the soleus motor pool have been investigated using the Achilles tendon reflex, the H reflex, and the vibratory inhibition of the H reflex. The excitability of the myotatic reflex are is augmented from the beginning of irrigation and remains so until the end of nystagmus. The effects are bilateral and roughly symmetrical. The observed effects are due to simultaneous activation of non-specific, probably reticular, and specific, doubtless vestibular, , mechanisms. The Achilles tendon reflex is more facilitated than the H reflex, and the vibratory inhibition of the H reflex is not modified following irrigation of the ear canal. These results indicate a simultaneous facilitation of alpha and gamma extensor motoneurones but gamma effects clearly predominate. This interpretation is in good agreement with the findings of the animal neurophysiology. The vibratory inhibition argues against a modification of presynaptic inhibition. Before interpreting this fact as different from animal mechanisms, one must take into account the particular experimental conditions realized in man: the stimulus is complex and interactions between various nervous structures are possible.
Inner ear melanocytes are mainly present in the cochlea, vestibular organ, and endolymphatic sac, but their exact biological function has not been determined. In this investigation, we study the pigment cells in the membranous labyrinth of the gerbil. The inner ear melanocytes of M. unguiculatus show an irregular dendritic shape with cytoplasmic processes. These cells are disposed following the distribution of strial marginal and vestibular dark cells that have an important metabolic activity. Gerbil inner ear melanocytes are characterized by the presence of melanosomes, which are homogeneously dense organelles, of variable size and shape, that are surrounded by a membrane. In these cells, the Golgi apparatus plays a important role in melanin synthesis. When melanocytes were incubated in L-DOPA solution, the vesicles and cisterns of the Golgi apparatus exhibited a positive tyrosinase reaction. An interesting observation is the relation between melanocytes and inner ear capillaries. Sometimes, near to sensory vestibular areas, the melanocytes were in contact with Schwann cells and with myelinated fibres of vestibular nerve. The ultrastructural findings of this investigation are consistent with the hypothesis that melanocytes may have functional significance in the inner ear.
Potassium (K(+)) plays a very important role in the cochlea. K(+) is the major cation in endolymph and the charge carrier for sensory transduction and the generation of the endocochlear potential. The importance of K(+) handling in the cochlea is marked by the discovery of several forms of hereditary deafness that are due to mutations of K(+) channels. Deafness results from mutations of KCNQ4, a K(+) channel in the sensory hair cells, as well as from mutations of the gap junction proteins GJB2, GJB3 and GJB6 that may facilitate cell-to-cell movements of K(+). Deafness results also from mutations of KCNQ1 or KCNE1, subunits of a K(+) channel that carries K(+) from strial marginal cells and vestibular dark cells into endolymph. Further, deafness results from mutations of KCNJ10, a K(+) channel that generates the endocochlear potential in conjunction with the high K(+) concentration in strial intermediate cells and the low K(+) concentration in the intrastrial fluid spaces. This review details recent advances in the understanding of K(+) transport and its regulation in the cochlea and the vestibular labyrinth.
Cyclophosphamide was used in this study to define the contribution of the inflammatory response relative to direct cytopathic effects of guinea pig cytomegalovirus (GPCMV) in inducing sensorineural hearing loss in the guinea pig. The eighth nerve compound action potential (CAP) threshold on day 7 after inoculation of GPCMV into the scala tympani was an average of 35 dB greater for control animals than for those that were immunosuppressed with daily intraperitoneal injections of cyclophosphamide (20 mg/kg body weight). The amount of GPCMV antigen in the cochlea, detected immunohistochemically did not correlate with the CAP threshold. However, the greater the inflammatory response to GPCMV in the cochlea, the higher the CAP threshold and thus the greater the hearing loss. This study demonstrates that the inflammatory response to GPCMV may be more important than direct cytopathic effects of the virus in producing sensorineural hearing loss in GPCMV-induced labyrinthitis.
We investigated the time course of hearing impairment and cellular infiltration into the inner ear after systemic sensitization of guinea pigs with a single intradermal injection of bovine inner ear antigen (IEAg) in complete Freund's adjuvant (CFA). Lymphocytes and polymorphonucleocytes appeared mainly in the scala tympani on days 7 to 14, and in addition there was thickening and cellular infiltration of the round window membrane at day 14. These cellular infiltrations resolved after day 28. The auditory brain stem response thresholds from IEAg-sensitized animals were significantly elevated after day 7. Some sensitized animals (n = 5) had spontaneous remissions after day 28; however, the hearing thresholds did not completely recover. These results demonstrate that experimental autoimmune labyrinthitis can be induced by a single inoculation of IEAg-CFA and that remission, as evidenced by clearing of the cochlear cellular infiltration and improved hearing thresholds, can occur spontaneously.
A report is presented of experiments on guinea pigs and pigeons concerning behavioural and electrophysiological responses of the labyrinth to sound. In the guinea pigs the cochlea was destroyed on both sides by CO2 laser radiation and fenestration of the lateral semicircular canal was done. In the pigeons the cochlea was removed before fenestration. On account of the results obtained, fenestration of the lateral canal in patients with bilateral total cochlear loss can be considered as an alternative to monopolar cochlear implants.
Abnormal mineral deposits from the membranous labyrinths of deaf Dalmatian puppies were examined microscopically. Most such deposits were located on the saccular otoconial membrane and were associated with collapse of the saccule and of Reissner's membrane. In both ears of one pup, crystals resembling otoconia were found on the surface of the stria vascularis. In two others, grossly abnormal crystals were seen on the utricular otoconial membrane, and in one of these crystals were also attached to the cupula of the left horizontal canal. In four animals the tectorial membrane was calcified. Most deposits consisted of apatite spherulites, but large multiple crystals (probably of calcite) were occasionally present. Some of the abnormal mineral deposits in the Dalmatian closely resemble those found in man, and they may originate in the same way.