Hearing preservation following suboccipital removal of acoustic neuromas

Advances in the diagnosis and intraoperative management of acoustic neuromas have greatly reduced the incidence of neurologic deficits following their removal. Ninety-three patients underwent acoustic tumor removal during a 41/2-year period, and hearing preservation was attempted in 20 cases. Hearing was preserved in 65% of the entire series, and excellent results were obtained in tumors less than 1.5 cm. No patient with a tumor greater than 1.5 cm had serviceable hearing preserved when total tumor removal was performed. Two patients, one with neurofibromatosis and one with an acoustic neuroma in an only-hearing ear, had planned partial tumor removal with preservation of hearing. Preoperative auditory brainstem response results were not predictive of postoperative hearing preservation. Intraoperative auditory brainstem response monitoring demonstrated that loss of wave V consistently correlated with loss of hearing postoperatively, whereas persistence of wave V (with a latency prolongation not exceeding 3.00 ms) was predictive of successful hearing preservation regardless of latency increases.     

Confirmation of G. von Békésy's theory of paradoxical wave propagation along the cochlear partition by means of bone-conducted auditory brainstem responses

In order to investigate the propagation time of the traveling wave in the cochlea after bone-conduction stimulation of the inner ear, bone-conducted auditory brainstem responses (ABRs) were recorded in 6 normally hearing subjects after masking the basal cochlear region using high-pass filtered noise. As in air-conducted ABRs, Jewett V wave latency is delayed corresponding to the propagation time of the traveling wave front traversing the desynchronized hair cell region. These results support the theory of paradoxical wave propagation proposed by von Békésy in 1952, who postulated that wave motion always starts from the stiffest part of the basilar membrane, independent of the location of the vibrating force. In addition, we also found a latency delay of the Jewett V wave of bone-conducted ABRs in 8 patients with high-frequency hearing loss which corresponded to the severity of their hearing impairment.     

迟发性膜迷路积水的诊断与治疗

目的探讨迟发性膜迷路积水的诊断和治疗。方法回顾性分析37例（40耳）迟发性膜迷路积水患者的临床资料,包括纯音测听、前庭诱发的肌源性电位（vestibular evoked myogenic potentials,VEMP）、高刺激ABR、前庭双温试验等结果。主要予以利尿剂、血管扩张剂等药物治疗。结果37例患者均为中、重度以上感音神经性聋。膜迷路积水与听力下降同侧25例,对侧9例,双侧3例。水平半规管和球囊均有积水10例,水平半规管积水9例,球囊积水15例,VEMP和双温试验均正常3例。VEMP正常12例,异常者25例,其中6例患侧p13-n23振幅消失,5例p13潜伏期延长,14例患侧p13-n23低振幅。37例患者中一周内完全控制眩晕发作18例;眩晕明显减轻、二周后完全控制17例;2例行化学迷路切除后眩晕未再发作。结论迟发性膜迷路积水的诊断应依据纯音测听、耳蜗电图、前庭双温试验和前庭诱发肌源性电位等检查结果综合判定;治疗以药物治疗为主,利尿剂和血管扩张剂是主要治疗药物。     

Brainstem Auditory Evoked Potentials in Patients With Ischemic Heart Disease

The authors of this study used the method of increased stimulus rate on brainstem auditory evoked potentials (BAEPs) in 30 patients with ischemic heart disease (IHD) and in an equal number of healthy age-matched control subjects. The BAEPs were recorded using 100- to 3000-Hz alternating polarity clicks at a rate of 22.6 per second. Measurements included the absolute latencies of waves I through V, the interpeak latencies I-III, III-V, and I-V, and the peak amplitudes of peaks I, III, and V. The measured absolute latencies and interpeak latencies were found to be significantly increased, and the peak amplitudes were found to be diminished. The audiometric tests revealed no significant hearing loss in IHD patients. This study is the first to demonstrate prolongation of BAEPs in IHD patients. BAEP recording may become an additional noninvasive tool for detecting IHD patients with impaired microcirculation.     

Electrocochleography and brain-stem potentials in Ramsay Hunt syndrome

Audiometric investigations and electrophysiologic recordings of cochlear and brain-stem auditory evoked potentials (BAEPs) were performed in 13 patients to elucidate further the type of hearing disorders in Ramsay Hunt syndrome. Transtympanic electrocochleography showed no enhancement of summating potential and did not suggest secondary endolymphatic hydrops. The recording of BAEPs was clearly abnormal in several of the 13 patients. The striking feature of the abnormalities in these patients was the prolongation of the latencies of waves III and V with the preservation of wave I, which clearly suggests retrocochlear involvement. In all the patients tested, abnormalities of the BAEPs were present only on the affected side. It is possible, on the basis of BAEP findings, to suggest that in Ramsay Hunt syndrome both cochlear and retrocochlear involvement may occur.     

Influence of age and hearing loss on the latency shifts of the auditory brainstem response as a result of increased stimulus rate

Latency shifts of auditory brainstem response waves, I, III and V were studied as a function of increasing the stimulus repetition rate from 9 to 21, 42 and 63/s. There appears to be an accumulative retardation of the successive waves when faster click rates are administered that yield a prolongation of the interpeak intervals I-III and III-V. The effect on wave V and on the interpeak interval III-V seems to intensify with age (especially over 55 years). In ears with a flat sensorineural hearing loss, the adaptation of waves III and V is found to be somewhat smaller than in normal ears at the same intensity in dB SPL.     

The latency of auditory nerve-brainstem responses in sensorineural hearing loss

Summary The use of auditory nerve-brainstem responses in differential diagnosis of hearing loss is based on several properties of these responses including response latency. The auditory nerve response latency has been shown to be prolonged in conductive hearing loss. The latency of the brainstem responses is also often prolonged in retrocochlear hearing loss. However, the effect of sensorineural hearing losses on auditory nerve response latency is not clear. Several authors report that response latency is prolonged in sensorineural loss, whereas others claim that it is unchanged.To study this, auditory nerve-brainstem responses to 75 dB HL clicks were recorded in normal-hearing subjects and in those with various degrees of high-frequency sensorineural hearing loss. In the more extreme hearing losses, the auditory nerve response could not be seen in the response trace, so the latency of the earlobe positive wave from the region of the inferior colliculus was considered as mirroring auditory nerve response latency, since the time interval between these two waves has been shown to be constant.The average latency of the more severe hearing loss group (more than 40 dB hearing loss at 4 kHz) was found to be only 0.35 ms longer than that of the normal-hearing group. This value is smaller than that seen in most conductive and retrocochlear hearing losses.This result warrants continued use of prolonged auditory nerve response latency (greater than 0.35 ms) as an indicator of conductive hearing loss. Possible explanations for smaller latency prolongation than expected of the auditory nerve response in sensorineural hearing loss are discussed based on the properties of single auditory nerve fibers.Part of a PhD thesis to be submitted by R. Kinarti to the Senate of the Tel-Aviv Universtity     

Auditory threshold and inner ear pressure: measurements in experimental endolymphatic hydrops

HYPOTHESIS: Experimental endolymphatic hydrops leads to an endolymph-perilymph pressure imbalance that is responsible for the loss of auditory sensitivity in the ear. BACKGROUND: This study investigates whether intralabyrinthine pressure is a factor in the auditory dysfunction of experimental endolymphatic hydrops. METHODS: Auditory function was investigated in 10 guinea pigs 90 to 120 days after endolymphatic sac ablation by measuring compound action potentials in response to acoustic stimuli including alternating clicks and tone bursts of 0.5, 1, 2, 4, and 8 kHz. After auditory thresholds to the various stimuli were established, endolymphatic and perilymphatic pressures were measured with a no-flow micropressure measuring system. The cause of the hearing loss in Meniere's disease, especially in the early phases of this condition, remains an enigma. Histologic temporal bone preparations show a disproportion in the volume of endolymph to perilymph with an expanded and distorted membranous labyrinth. Speculation as to whether an endolymph-perilymph fluid pressure imbalance is responsible for these morphologic changes were raised by Hallpike and Cairns (1) in their initial report of the histopathology of Meniere's disease. Further speculation has questioned whether this pressure imbalance may be responsible for the symptoms and physical finding of this condition, including hearing loss. The ability to produce experimental endolymphatic hydrops in the guinea pig secondary to surgical occlusion of the endolymphatic sac and duct has been useful in studying various aspects of Meniere's disease (2). Investigators have been able to demonstrate auditory threshold shifts with hydrops. Elevated endolymph-perilymph pressure gradients have also been demonstrated (3). This RESULTS: Increased auditory thresholds were noted in the hydrops ears at all tested parameters (p < 0.03). A relative increase in endolymph over perilymph pressure was found in hydrops ears as previously reported. The increase in endolymph-perilymph pressure of hydrops could not be correlated directly to the elevated auditory threshold shift. CONCLUSION: Endolymphatic hydrops is a complex pathologic state with multiple inner ear alterations including abnormal intralabyrinthine pressure. Factors other than or in addition to pressure contribute to the auditory threshold shift of hydrops.     

听神经瘤术中连续听力监测的初步探讨

目的探讨听神经瘤外科术中连续听力监测的意义。方法采用乙状窦人路，在听性脑干反应（auditory brainstem response，ABR）和耳蜗电图（electrocochleogram，ECochG）监测下完成的听神经瘤切除术10例。对手术过程和术后听力结合术中监测进行分析。结果10例听神经瘤术前听力A级3耳，B级4耳，C级3耳（美国耳鼻咽喉头颈外科学会分级标准）。术前的ABR检查Ⅰ、Ⅲ、Ⅴ波存在者5耳（A级3耳，B级2耳），仅见Ⅰ波者5耳（B级2耳，C级3耳）。麻醉后手术前的监测显示：Ⅰ、Ⅲ、Ⅴ波存在者2耳，仅Ⅰ波存在者6耳，以复合动作电位（compound action potential，CAP）的N1波代替波Ⅰ；无波形者2耳。术后听力保留2耳，肿瘤均〈2cm，术前听力都为A级；连续听力监测显示1耳术中及术毕时Ⅰ、Ⅲ、Ⅴ持续存在，1耳Ⅰ、Ⅲ波存在，Ⅴ波消失；术后听力均为A级。听力未保留8耳，其中6耳术中监测时仅CAP的N1（波Ⅰ）存在，手术过程中夹内听动脉或处理内耳道处肿瘤时，4耳CAP波幅明显下降，甚至下降至0，术毕又恢复至术前的50％～60％或正常；1耳蜗神经与肿瘤一并切除，但CAP始终存在；1耳因牵拉脑干侧的耳蜗神经，CAP波幅降至0，手术结束亦未恢复。2耳为全身麻醉后术前监测中未引出任何波形者，其中1耳术中切除部分肿瘤后，出现CAP波，但波幅低，直至术毕；1耳始终未出现波形。结论联合应用ABR和ECochG术中监测，对提高听力保护率有积极意义，能及时反映术中与保留听力相关的敏感手术步骤，然而外科医师的熟练的解剖和精确的手术技巧是手术成功的最基本因素。     

Acute hearing loss in patients with hematological disorders

Objective: This study adopted an inner ear test battery to investigate the causes of acute sensorineural hearing loss in patients with hematological disorders. Methods: During the past 20 years, the authors have experienced 14 patients with hematological disorders, i.e. leukemia or aplastic anemia, having acute sensorineural hearing loss. An inner ear test battery comprising audiometry and cervical vestibular-evoked myogenic potential (cVEMP), ocular VEMP (oVEMP), and caloric tests was performed. Results: Diagnoses comprised of sudden sensorineural hearing loss in 12 patients and endolymphatic hydrops in four patients (two patients had one ear with sudden sensorineural hearing loss while the other ear had endolymphatic hydrops). Percentages of recruitment phenomenon showed a significant difference between endolymphatic hydrops and sudden sensorineural hearing loss. Abnormal percentages for mean hearing level (86%), cVEMP test (71%), oVEMP test (25%), and caloric test (14%) exhibited a significant sequential decline in these patients. Conclusion: Acute sensorineural hearing loss in a patient with leukemia or aplastic anemia may be related to either sudden sensorineural hearing loss or endolymphatic hydrops. A significant sequential decline in the function of the cochlea, saccule, utricle, and semicircular canals indicates that the pars inferior is more vulnerable to blood insult than the pars superior.     

Effects of sex, age and hearing asymmetry on the interaural differences of auditory brainstem responses

Healthy patients with asymmetric sensorineural hearing loss who had received examination of auditory brainstem responses (ABR) were gathered for retrospective analysis. The effects of sex, age and hearing asymmetry on the interaural differences of ipsilateral ABR were determined by multivariant linear regression. Our results showed that the interaural differences of ABR wave III and wave V latencies were significantly affected by hearing asymmetry but not by sex or age. However, in female subjects younger than 50 years, differences of III-V intervals could be negatively correlated with hearing asymmetry. We suggest that plasticity in the auditory brainstem in younger females might account for asymmetrical peripheral hearing in this group.     

Analysis of gender differences in the auditory brainstem response

This study examined the effects of hormones, head size, and oral temperatures on latencies and amplitudes of the auditory brainstem response in 10 young women, 10 young men, and 5 postmenopausal women. Significant gender differences between men's and women's auditory brainstem responses were confirmed. Men showed longer latencies and smaller amplitudes than women. Results showed that oral temperature has little effect on auditory brainstem response latencies and amplitudes. Head size affects waves III, V, and the amplitude of wave V, but is not entirely responsible for the gender latency difference. By examining young women with normal monthly hormonal cycles, significant changes in the absolute latencies of wave V were observed. These changes were correlated with hormonal changes as measured from venous blood samples. It was concluded that the etiology of the gender difference is a combination of hormonal and head-size differences.     

Auditory brainstem response and otoacoustic emissions in Duane retraction syndrome

OBJECTIVE: We aimed to investigate the origin of hearing loss with relevance to auditory brainstem responses and otoacoustic emissions in patients with Duane's retraction syndrome (DRS). MATERIALS AND METHODS: 17 patients with DRS were included in the study. 14 patients were diagnosed as DRS type 1 and the remaining three as type 3. The control group consisted of nine healthy subjects. Pure tone audiogram, auditory brainstem response, as well as distortion product otoacoustic emissions were recorded in all the patients and the controls. RESULTS: Among the 17 patients with DRS, 15 demonstrated normal hearing according to pure tone audiogram. One patient with DRS had profound sensorineural hearing loss with a pure tone average of 110 dB, and one patient had moderate sensorineural hearing loss with a pure tone average of 60 dB. Auditory brainstem response latencies of the waves I, III and V, and interwave latencies were calculated in 15 patients with DRS and were compared with the control group. There was statistically significant increase in wave I latency of left ear in the DRS group compared to the controls (P<0.05). Amplitudes of distortion product otoacoustic emissions were also recorded at frequencies of 2, 3, 4, 6, and 8 kHz in both groups and the comparison of the DRS patients and controls revealed no statistically significant difference. CONCLUSIONS: We recommend auditory examinations be undertaken in patients with DRS by auditory brainstem response tests, as well as distortion product otoacoustic emissions, whereas all patients with normal results should be followed-up for future hearing loss.     

The development of endolymphatic hydrops following CMV inoculation of the endolymphatic sac

The effect of inoculation of cytomegalovirus (CMV) into the endolymphatic sac was examined in CMV-seronegative and seropositive animals. Seronegative animals developed hearing loss, infection in the epithelial cells of the endolymphatic sac and perisaccular connective tissue, and endolymphatic hydrops. Control animals inoculated with inactivated CMV showed no hearing loss, viral infection, or endolymphatic hydrops. Seropositive animals showed complete protection from hearing loss and viral infection, yet a monocytic infiltrate was seen surrounding the endolymphatic sac. Associated with this localized immune response was mild evidence of endolymphatic hydrops in 40% (2/5) of the animals. Control seropositive animals inoculated with inactivated CMV showed no hearing loss or morphological changes. CMV then, can infect cells of the endolymphatic sac resulting in hearing loss and endolymphatic hydrops. The immune response to CMV in seropositive animals is protective, but is associated with endolymphatic sac inflammation.     

Delayed vertigo and profound sensorineural hearing loss

Episodic vertigo, similar to that of Meniere's disease, can occasionally develop years to decades after an ear has suffered a profound sensorineural hearing loss. Although the pathogenesis of this process is unknown, it is theorized that delayed endolymphatic hydrops develops. An inflammatory reaction could cause obstruction of the endolymphatic duct or interfere with venous drainage from the region of the endolymphatic sac, leading to hydrops. This condition is reviewed, and two adult patients with severe episodic vertigo and a unilateral profound sensorineural hearing loss which occurred in childhood are presented. Their evaluation and management are discussed.     

Axonal injury in auditory nerve observed in reversible latency changes of brainstem auditory evoked potentials (BAEP) during cerebellopontine angle manipulations in rats

Intraoperative monitoring of brainstem auditory evoked potentials (BAEP) has been widely utilized to reduce the incidence of postoperative hearing disturbance due to cerebellopontine angle manipulations. The prolongation of wave V of BAEP is usually used as a criterion to warn the surgeons to modify their surgical maneuvers. However, it is not known whether all neuropathological changes are avoided if BAEP latency intraoperatively returns to the baseline level or some neuropathological changes 'silently' occur even if BAEP normalizes. The aim of this study was to experimentally clarify this point that would be important for the long-term prognosis of patients' hearing. The cerebellopontine angle portion of the auditory nerve was quantitatively compressed in the rats and reversible prolongation of BAEP latency was reproduced just as it occurs during surgery in humans. Twenty-four hours after the compression, the auditory nerve was removed for beta-APP immunostaining to investigate the degree of axonal injury. The results of the present study disclosed that axonal injury occurred even in the cases where the intraoperative normalization of prolonged wave IV (equivalent to wave V in humans) latency had been obtained. Therefore, the interpretation of BAEP changes based only on the prolongation of the latency of BAEP was not enough to prevent the auditory nerve from developing morphological changes. Changes in the amplitude of wave V of BAEP appears to be more sensitive than its latency change as an intraoperative indicator for axonal injury in the auditory nerve.     

Travelling wave velocity test and Ménière’s disease revisited

Transtympanic Electrocochleography (TT-ECoG) and the glycerol test can aid in the diagnostic process of Ménière’s disease (MD). Measurement of travelling wave velocity (TWV) has been proposed as an alternative to TT-ECoG to detect endolymphatic hydrops. We assessed the feasibility and obtained normative data of the TWV test in the diagnosis of MD, and compared the test results in MD patients with their symptoms and their TT-ECoG results. The TWV test records two runs of auditory brainstem responses to clicks that are ipsilaterally masked with two different high pass filtered noise bands. The resulting latency difference of peak V was used as a measure of the TWV. The 95% confidence interval of this latency difference was defined in a group of 28 normals. Subsequently, the test was performed in nine MD patients. After the TWV test, seven of these patients underwent a TT-ECoG. The symptoms of MD patients at the time of testing and their TT-ECoG results were compared with TWV test results. The 95% confidence interval of the latency difference of peak V in the control group was 0.190–0.668 ms. A latency difference <0.190 ms indicates an increase in TWV, and thus reflects a positive test. In nine MD patients, we found a clear correlation between the result of the TWV test and TT-ECoG. The TWV test result did not significantly correlate with a single symptom. Our findings suggest that the TWV test can be useful to detect endolymphatic hydrops, but further experiments with larger patient groups are needed to confirm the diagnostic value of the TWV test.     

Effects of hyperbaric therapy on function and morphology of Guinea pig cochlea with endolymphatic hydrops.

OBJECTIVE: The objective of this study was to investigate the effect on experimental endolymphatic hydrops in guinea pigs after hyperbaric therapy. BACKGROUND: The histopathologic character of Ménière's disease is the presence of endolymphatic hydrops. Endolymphatic hypertension could be one of the factors resulting from endolymphatic hydrops. Some treatments of Ménière's disease are aimed toward preventing the endolymphatic hypertension. Exposure to pressure change has risen in recent years. METHODS: Thirty-two guinea pigs were operated on the right ears to induce endolymphatic hydrops by obliterating the endolymphatic sac through an extradural posterior cranial fossa approach. After 5 weeks' survival, 12 guinea pigs were put into a chamber with an absolute atmospheric pressure of 2.2 for 3 weeks (90 minutes once a day 5 times a week). We observed the morphologic and functional changes in guinea pig cochleae of the pressure group, 4-week hydrops group (n = 10), 8-week hydrops group (n = 10), and the normal group (n = 10). We measured the hearing threshold of the auditory brainstem response, the 70-dB SPL action potential (AP) latency, the ratio of 70-dB SPL summating potential magnitude to action potential magnitude (-SP/AP) of the electrocochleogram, and the maximum scala media area (SMA) ratio, respectively. RESULTS: The average 70-dB SPL-SP/AP magnitude of right ears (0.29 +/- 0.09) and the average maximum SMA ratio (2.23 +/- 0.20) in the pressure group were significantly less than that in the 8-week hydrops group (0.69 +/- 0.15 and 4.04 +/- 0.52, respectively) with the same survival time (p < 0.05). The results in the pressure group were almost as similar as that in the 4-week hydrops group (0.29 +/- 0.13 and 2.22 +/- 0.20, respectively) (p > 0.05). The average hearing threshold of ABR of right ears in the pressure group (36.67 +/- 14.30-dB SPL) was lower than that of the 8-week hydrops group (44 +/-1 4.30-dB SPL), but the difference was insignificant (p > 0.05). The average 70-dB SPL AP latency of right ears in the pressure group was not significantly different from those of the 8-week hydrops group, the 4-week hydrops group, or the normal group (p > 0.05). CONCLUSIONS: Our findings suggest hyperbaric therapy can significantly suppress the development of endolymphatic hydrops and improve cochlear function in guinea pigs. This study provided strong evidence for the development of pressure treatment of Ménière's disease without destroying the inner ear.     

Auditory brainstem responses in young children with Down's syndrome

Auditory brainstem evoked responses (ABRs) were studied in 37 Japanese infants and children with Down's syndrome to determine the level of the lesion causing their unresponsiveness to sound stimuli. ABR thresholds, peak latencies of waves I and the peak interval latency of wave I-V were measured. For comparison with ABR thresholds, behavioral audiometry was performed. Thirty-two percent of the patients (12 cases) with Down's syndrome showed no responses by ABR as well as behavioral audiometry. The other ABR abnormalities with respect to age-matched controls were classified into 6 types: shorter wave I latencies (2 cases, 5%), shorter wave V latencies (7 cases, 19%), shorter wave I-V intervals (8 cases, 22%), wave I prolongation (13 cases, 35%), wave V prolongation (5 cases, 14%) and prolongation of wave I-V peak interval (no case, 0%). Our results demonstrate a high incidence of hearing loss at middle and inner ear levels, and suggest some anomaly within the auditory brainstem in Japanese cases of Down's syndrome.