Electrical stimulation of the auditory pathway in deaf patients following acoustic neurinoma surgery and initial results with a new auditory brainstem implant system.
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Auditory Pathways↗
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Distribution of beta-tubulin in guinea pig inner ear.
Our previous research had suggested that beta-tubulin might be an autoantigen for autoimmune inner ear disease. In this study, the expression of beta-tubulin in inner ears of normal and tubulin-immunized guinea pigs was examined by immunohistochemical staining. Strong immunoreactivity to beta-tubulin monoclonal antibody was found in stria vascularis, neurons of the spiral ganglion, cochlear nerve fibers and spiral ligament. Diffuse staining was found in the stria vascularis and the neurons of the spiral ganglion, while dense network staining was found in the spiral ligament, the nerve fibers and the vestibular end organs. The semicircular canals, endolymphatic duct and sac were also positively stained. In inner ears of guinea pigs challenged with beta-tubulin, staining intensity was diminished in the stria vascularis, the spiral ligament, and the neurons of the spiral ganglion. The results suggest that beta-tubulin is distributed to most structures of guinea pig inner ear. A challenge to the inner ear by tubulin could change the beta-tubulin distribution and cause degeneration in the spiral ganglion. The results support the hypothesis that beta-tubulin might be an autoantigen for autoimmune inner ear disease.
Animals↗
Neurovascular decompression in trigeminal neuralgia: role of intraoperative neurophysiological monitoring in the learning period.
This paper deals with the first 45 consecutive patients undergoing microvascular decompression (MVD) surgery for trigeminal neuralgia, studied with perioperative brainstem auditory evoked potentials (BAEPs) and electromyography (EMG). We observed a good correlation between the intraoperative BAEP modifications and postoperative hearing function. BAEP monitoring was useful in identifying the manoeuvres that may compromise cochlear nerve function. This improved the surgical technique in the subsequent cases and reduced the incidence of iatrogenic hearing deficits after the learning period. There were no correlations between the entity of the intraoperative EMG discharges and the postoperative facial and trigeminal function. Intraoperative EMG monitoring can be useful during the period of learning as a means of identifying the different nerves in the cisternal tract.
Adult↗
Evaluation of the results of endoscope-assisted acoustic neuroma surgery through posterior fossa approach.
The objective of this study was to evaluate the results of endoscope-assisted acoustic neuroma surgery in posterior fossa approach. Between 1996 and 2002, 60 consecutive patients with acoustic neuroma were operated via the retrosigmoid suboccipital approach. Standard 4-mm sinus endoscopes at different angles were used during the surgeries either for inspection or tumor endoscopic dissection. Clinical parameters and treatment outcome were evaluated retrospectively. Tumor sizes were small, medium and large in 46.6, 45 and 8.3% of the patients, respectively. The hearing preservation rate, which did not correlate with tumor size (p > 0.05), was 24.4%. The need for facial reanimation surgery, which was needed in 5% of patients, was significantly higher in the large tumors than in the small and medium tumors (p < 0.001). Cerebrospinal fluid fistula rate, which was not related to tumor size (p > 0.05), was 13.3%. Tumor recurrence or residual tumor was not encountered at all. In conclusion, endoscopes give accurate information about the relationship between the tumor and the adjacent structures and help control the fundus of the internal auditory canal to ensure complete tumor removal. It is also helpful in visually verifying the continuity of the facial and cochlear nerves. The use of endoscopes does not appear to increase the hearing preservation rate, but is very helpful in complete tumor removal in the posterior fossa approach.
Adult↗
Loss and recovery of sound-evoked otoacoustic emissions in young chicks following acoustic trauma.
Young and adult chickens exhibit substantial inner-ear damage and post-exposure deterioration in cochlear nerve activity following exposure to intense sound. Both the structural and functional losses largely recover in both age groups within 2-4 weeks after exposure. However, some aspects of acoustic trauma differ between the young and adult chicken ear. Overstimulation in the young chick causes considerable post-exposure loss and then recovery of the steady-state endocochlear potential, while in the adult animal there is little post-exposure effect on this potential. Moreover, in adults there is post-exposure loss but little recovery in the distortion product otoacoustic emission (DPOAE). The present study explores the possibility of an age difference in the effects of overstimulation on the DPOAE by examining these emissions in young chicks following exposure to an intense pure tone. Chicks exposed to intense sound were formed into groups at 0 and 12 days of recovery, and these were complemented by two additional groups of age-matched controls. The cubic difference tone emission (the 2f(1)-f(2) DPOAE component) was measured at 9 levels for 13 frequencies in all groups. Shortly after the exposure, the DPOAE reliably declined with the maximum loss at or above the exposure tone frequency. The exposed chicks examined 12 days after exposure showed complete recovery of the DPOAE. It would appear that 12 days of recovery sufficiently repaired inner ear damage to completely restore DPOAE production. This result is different from that in adult chicken and may be related to the greater severity of acoustic damage in the adult ear, a reduced susceptibility of the young ear to acoustic trauma, or the ability of the young animal to more successfully repair the inner ear.
Acoustic Stimulation↗
Stability of efferent-mediated protection against acoustic overexposure with long maintenance under barbiturate anaesthesia.
When anaesthetized animals are maintained over a long period, crossed-cochlear suppressive and enhancement-in-noise effects mediated by the olivocochlear bundle (OCB), as well as some OCB neuronal responses, show time-dependent variations. The present study determined if there were any such changes in OCB-mediated crossed-cochlear protection against compound action potential (CAP) threshold losses caused by a standard loud sound exposure at 11 kHz, presented under conditions either not evoking OCB-mediated protection (i.e. monaural exposure) or evoking protection (binaural exposure). Maintaining animals for periods up to approximately 30 h from initial anaesthetization resulted in non-significant changes in pre-exposure CAP thresholds. There were also only small changes over select frequency ranges in threshold losses caused by the monaural or binaural loud sound, after a single exposure as well as when the testing of OCB function was extended to examine effects after dual successive exposures, the latter result being determined by application of a previously described additivity model. The features of OCB-mediated protection also showed good stability over the long maintenance. These results are discussed as providing further circumstantial evidence that protection is mediated by a different OCB subcomponent to that/those responsible for other OCB-mediated crossed-cochlear effects. In general, the results show that the barbiturate anaesthetic used here does not significantly modulate the crossed-cochlear OCB effect of protection, even though it has been shown elsewhere to significantly depress other crossed-cochlear OCB effects.
Anesthesia, General↗
Study of a simultaneous lobe-vertex and membrane-vertex recording technique in auditory brainstem response.
The study of a simultaneous lobe-vertex and membrane-vertex recording in auditory brainstem response was performed in normal adults and in patients suffering from brainstem disorders. It was demonstrated that in normal subjects the detectability of waves I and V depends on the site of the recording electrodes and there is no statistical difference between the two recording methods in the latencies of the two waves. We reported 3 typical cases that illustrate the value of this recording method in the detection of the cochlear nerve or the brainstem disorders.
Acoustic Stimulation↗
Response properties of an integrate-and-fire model that receives subthreshold inputs.
A computational technique is described for calculation of the interspike interval and poststimulus time histograms for the responses of an integrate-and-fire model to arbitrary inputs. The effects of the model parameters on the response statistics were studied systematically. Specifically, the probability distribution of the membrane potential was calculated as a function of time, and the mean interspike interval and PST histogram were calculated for arbitrary inputs. For stationary inputs, the regularity of the output was studied in detail for various model parameters. For nonstationary inputs, the effects of the model parameters on the output synchronization index were explored. The results show that enhanced synchronization in response to low-frequency stimuli required a large number (n > 25) of weak inputs. Irregular responses and a linear input-output rate relationship required strong (but subthreshold) inputs with a small time constant. A model cell with mixed-amplitude synaptic inputs can respond to stationary inputs irregularly and have enhanced synchronization to nonstationary inputs that are phase-locked to low-frequency inputs. Both of these response properties have been reported for some cells in the ventral cochlear nucleus in the auditory brainstem.
Action Potentials↗
Sudden deafnfess of vascular origin: a human temporal bone study.
Temporal bone changes are described in a 57-year-old man who had sudden onset of dizziness and unilateral deafness two months before death. The patient suffered from hypertension, and congestive and renal failure. At autopsy, subarachnoid hemorrhage with punctate cortical hemorrhages and arteriolar thickening involved the right superior cerebellar hemisphere. The pathological changes involved primarily the right cochlea, saccule and posterior ampulla, and were consistent with vascular embarrassment of the temporal bone of two months duration. The cochlea demonstrated total loss of the organ of Corti and severe degenerative changes of the stria vascularis, spiral ligament, outer sulcus cells and distal cochlear nerve fibers. The saccule demonstrated loss of its macula and nerve fibers. The posterior ampulla showed evidence of previous rupture of its membranous wall with fibrosis and beginning bone formation. Fresh hemorrhage, present in some areas of both temporal bones, was related to the patient's terminal subarachnoid hemorrhage.
Deafness↗
Noise-induced hearing loss. A human temporal bone case report.
The histopathology of a case of profound hearing loss which seemed to be induced by noise exposure (explosions and drillings in a gold mine) is reported. The patient's only residual hearing was 250 Hz at 90 dB SPL in the right ear. The major histopathological findings were as follows: Bilateral absence or collapse of Corti's organ was observed in the middle and basal turns of the cochlea; however, in the remaining area (approximately 6.0 mm in range in the apical portion of the cochlea) Corti's organ was well-preserved with a moderate loss in number or atrophy of the hair cells. Bilateral marked decrease of the cochlear nerve was noted in the middle and basal turns; however, the nerve was well-preserved in the remaining apical portion (approximately 6.0 mm in range) of the cochlea. These pathological findings were somewhat less severe in the right cochlea than in the left. In general, there was good correlation between the profound hearing loss and the extensive pathological findings in Corti's organ. The residual hearing in the right ear would seem to be explained by the less severe pathological changes found in the apical portion of the right cochlea than in the left cochlea. In addition to noise exposure, other possible etiological factors contributing to this hearing loss are discussed. These include diabetes mellitus and presbycusis.
Aged↗
Auditory evoked potentials in audiometric assessment of compensation and medicolegal patients.
The clinical utility of auditory evoked potentials for validation of the pure tone audiogram in adult compensation claimants and medicolegal patients is examined. Large sample comparisons of evoked potential and conventional pure tone thresholds showed that the slow vertex response can estimate true hearing levels within 10 dB in almost all patients. Given adequate tester skills, it is the tool of choice, and it merits more widespread implementation. Properly used, it can improve and abbreviate the assessment battery for detection and quantification of nonorganic hearing loss. The 40-Hz middle latency response is useful as a secondary tool, but at present, cochlear nerve and brain stem potentials have limited audiometric value in this population.
Adult↗
Expression of intercellular adhesion molecule-1 during inner ear inflammation.
This study was designed to investigate the expression of intercellular adhesion molecule-1 (ICAM-1) on the spiral modiolar vein (SMV) with its collecting venules (CVs) and the venules of the endolymphatic sac during inner ear inflammation. These data will further elucidate the role of adhesion molecules in extravasation of inflammatory cells from blood vessels during an inner ear immune response. Labyrinthitis was induced in rats by inoculation of keyhole limpet hemocyanin into the scala tympani of animals who had been systemically sensitized to it. Expression of ICAM-1 was examined with a mouse monoclonal antibody to rat ICAM-1 by immunohistochemistry. ICAM-1 was found weakly on the epithelium of SMVs and CVs as early as 6 hours postchallenge, reaching a maximum by day 2 and then fading away gradually. The maximum influx of immunocompetent cells into the cochlea was seen between days 3 and 7. Staining for ICAM-1 was observed on the epithelium of the endolymphatic sac and perisaccular region at 12 and 24 hours, respectively, and this was associated with infiltration of cells into these areas 3 days postchallenge. By day 28, the inner ear had developed endolymphatic hydrops, but at this time it showed almost no significant staining with anti-ICAM-1. The molecule was also expressed in the mesothelium of perilymph, the perineurium of cochlear nerves, the spiral ligament, and the basal cells of the stria vascularis following immunization. Our data provide evidence that endothelial cells of the SMV and its CVs, as well as other inner sites, have the potential to express ICAM-1. This expression precedes the influx of immune cells; therefore, it is possible that this ligand plays a pivotal role in the onset of inflammation in the inner ear. This study also confirmed that the immune response results in endolymphatic hydrops as a long-term consequence.
Animals↗
Murine model of autoimmune hearing loss induced by myelin protein P0.
Myelin protein P0 has been identified as an autoantigen in inner ear diseases. In order to study autoimmune hearing loss, we performed brain stem auditory-evoked potential (BAEP) studies on P0-sensitized mice. Two P0-sensitized mice showed hunched posture, poor coat, loss of body weight, and abnormal walking with a waddling gait. About 25% of the P0-sensitized mice developed hearing loss. In the BAEP study, peak latencies of waves I, III, and V and the interpeak latency I-III were prolonged in the P0-sensitized hearing loss group of mice. Hearing thresholds were elevated in this group of mice in comparison with the control mice. Inflammatory cell infiltration was observed in the cochlear nerve region, and a reduced number of spiral ganglion cells was also detected. These results suggest that P0-sensitized mice are a useful model for studying autoimmune inflammation of the peripheral portion of the auditory system.
Animals↗
Electron microscopic temporal bone histopathology in experimental pneumococcal meningitis.
Bacterial meningitis is one of the most common causes of acquired profound sensorineural deafness in children. Measurement of hearing and examination of the cochlea is limited in patients suffering from acute meningitis. A rabbit model of pneumococcal meningitis was developed to identify the temporal bone histopathologic changes that occur in meningogenic labyrinthitis caused by Streptococcus pneumoniae. Light microscopy was previously performed on temporal bones from acutely meningitic rabbits with profound hearing loss as determined electrophysiologically. Extensive inflammation of the cochlea with endolymphatic hydrops was observed. The organ of Corti, however, showed preserved architecture in the majority of these animals. In order to further investigate these findings, a protocol was used to create meningitic rabbits with hearing loss ranging from early high-frequency loss to profound deafness. The temporal bones from 7 rabbits were examined by transmission electron microscopy. In cases of mild hearing loss, partial degeneration of the inner row of outer hair cells, as well as edema of efferent cochlear nerve endings and marginal cells of the stria vascularis, was seen. With increasing degrees of hearing loss, the remainder of the organ of Corti and intermediate cells of the stria showed ultrastructural abnormalities. Spiral ganglion cells and basal cells of the stria vascularis remained intact in all subjects. This study provides unique information regarding the histology and pathophysiology of meningogenic deafness. The clinical implications of these findings are discussed, with an emphasis on potentially reversible changes and therapeutic intervention.
Animals↗
Monitoring of intraoperative auditory brain stem responses.
We believe that our initial experience establishes the fact that ABRs can be routinely and reliably performed in an operating room environment. There was no added risk to the patient, and operative delays were minimal. We did note transient fluctuation in latency values up to 1.5 msec. These changes would revert to baseline levels within five to ten minutes. Changes noted during drilling were probably related to the random noise produced. Case 3 was worrisome in that hearing was lost after maintenance of the ABRs during the surgical procedure. Evidently the vestibule was damaged, and a labyrinthitis caused the hearing loss. We feel that this procedure will be most useful in those situations in which the cochlear nerve and blood vessels are at risk. Such procedures as acoustic tumor removal with attempts to preserve hearing, vestibular nerve sections, and facial nerve problems in the IAC should be routinely monitored. Further experience will, of course, be most helpful in explaining and recognizing these changes.
Adult↗
Auditory brain stem response abnormalities in patients with Bell's palsy.
To evaluate the hypothesis of CNS involvement in Bell's palsy, the auditory brain stem responses (ABR) of 31 patients were studied. In nine of these patients ABR abnormalities were found. None of these patients showed evidence of dysfunction of the cochlear nerve. Six of the patients who had abnormal ABR were retested after they recovered from the facial paresis. Five of these patients showed persistent ABR abnormality, and one showed a normalization of the ABR. These results may be consistent with an injury at the brain stem level in some patients with Bell's palsy. The possible causative agent of a reactivation of a herpes simplex virus infection is discussed.
Adolescent↗
Kanamycin inhibits cochlear-renal ODC in neonatal rats.
Ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis, is important in development and regeneration. We hypothesize that aminoglycoside inhibition of ODC mediates developmental hypersensitivity to aminoglycoside ototoxicity. Kanamycin effects on ODC activity (decarboxylation of ornithine) in vitro were determined in the postmitochondrial fraction of cochlear and renal homogenates from 11-day-old rats. Kanamycin inhibited cochlear and renal ODC by an uncompetitive mechanism. For the cochlear enzyme, the inhibitor constant (Ki) for kanamycin was 99 +/- 25 mumol/L; for the renal enzyme, the Ki = 1.5 +/- 0.1 mmol/L. In vivo effects of kanamycin on cochlear, renal, brain ODC activity were determined in rats treated with kanamycin (400 mg/kg/day, intramuscularly) or saline during postnatal days 11 through 20, the hypersensitive period for ototoxicity. Rats were killed on postnatal days 12, 14, 16, and 20 and ODC was assayed. Kanamycin significantly inhibited ODC in the lateral wall-organ of Corti and kidney (ANOVA alpha = 0.05), but had no effect on cochlear nerve and no consistent inhibitory effect in the brain. These results suggest that ODC is a potential target of kanamycin in susceptible tissues and may be a contributing factor in developmental sensitivity to the drug by inhibiting repair and developmental processes mediated by ODC.
Animals↗
Hearing improvement after conservative approach for large posterior fossa meningioma.
Hearing preservation during the posterior fossa surgery depends on many factors, including tumor size and site of origin. In many cases, regardless of the presumed tumor origin, the severity of the pure-tone loss or decline in speech discrimination on preoperative testing prompts the surgeon to choose a surgical approach (translabyrinthine or transcochlear) that negates the chance for postoperative functional hearing in the involved ear. We describe a 41-year-old woman with unilateral severe sensorineural hearing loss who experienced a remarkable recovery of hearing after combined retrolabyrinthine and retrosigmoid removal of a 4 cm petrous ridge meningioma using intraoperative cochlear monitoring. Despite the tumor size, early intraoperative loss of wave I and proximity of the tumor to the porus, complete tumor removal was accomplished with preservation of the cochleovestibular bundle. Three weeks postoperatively, the patient noted marked subjective improvement and speech audiometry demonstrated an improvement in word recognition, from 0% to 86%. This improvement has remained 1 year postoperatively, with no evidence of persistent tumor on repeat MRI scan. The case report illustrates the possibility of not just hearing preservation but improvement after removal of even large posterior fossa meningiomas that do not directly invade the cochlear nerve itself.
Adult↗