Recent advances in cochlear blood flow measurements

Changes in blood flow to the inner ear have been thought to influence or underlie a number of cochlear diseases, including some forms of noise-induced hearing loss, sudden hearing loss, and Meniere's disease. Recently, important advances have been made in two technologies for the study of cochlear blood flow. The first is in the area of vital microscopic studies of cochlear microcirculation, and the second is based on the introduction of laser technology in the form of laser Doppler flowmetry. In this report, measurements are given of changes in cochlear circulation caused by carbon dioxide breathing, intravenous phenylephrine injection, systemic hemodilution, positive end expiratory pressure, and direct electrical stimulation of the cochlea. From these changes, we observe that cochlear blood circulation responds to systemic blood pressure alterations and is subject to local flow control mechanisms. Linearity and speed of response of the laser Doppler instrumentation also are shown. These advances show promise for contributing to our knowledge of control mechanisms of inner ear blood flow and for revealing the influence of various pharmacologic agents of potential clinical value.     

Acoustic-mechanical trauma during cochleostomy: animal experimental studies

Introduction

When performing cochlear implant (CI) surgery in ears with residual hearing, cochlear function should be preserved as far as possible. Besides non-traumatic electrode insertion the acoustic-mechanical trauma of the cochleostomy should be minimized. According toexperiences from temporal bone preparations the hypothesis that thorough exposition of the endosteal membrane with the drill prior to opening the cochlea might constitute a bigger acoustic mechanical trauma than direct drilling of the inner ear was examined. These experiments were performed in an animal model.

Material and Method

In 12 guinea pigs the cochlear capsule was exposed by opening the bulla under general anesthesia. In 6 animals the fluid-filled cochlea was exposed by careful unilateral abrasion of the bone, whereas on the other ear cochleostomy was performed by direct penetration drilling into the perilymphatic spaces. Hearing tests were performed before and after drilling by measuring evoked brainstem potentials (brainstem electric response audiometry, BERA). In 8 other guinea pig ears abrasive exposition of the cochlea was performed again by only softly touching the otic capsule with the running burr for 10?s. After a hearing test the drilling maneuver was repeated 4 times collectively. Thereby the inner ear was gradually opened from the surface but not deeper into the cochlear lumen. A total of 4 guinea pig ears treated with a single abrasion of 10?s were used as controls. Brain stem measurements were performed accordingly.

Results

Hearing loss was lower after a quick direct and deep penetration of the cochlea in comparison to a longer, less invasive opening of the inner ear. Hearing thresholds ascended depending on the duration of the drilling procedure.

Conclusion

The results support the hypothesis that prolonged drilling of exposed inner ear structures causes more acoustical damage than a direct cochleostomy with the drill.     

Influence of carbon dioxide laser irradiation on the morphology and function of guinea pig cochlea

Both experimental and clinical studies have demonstrated that carbon dioxide laser is suitable for stapedotomy. The aim of this study was to investigate morphological, electrophysiological and functional changes in the inner ear after irradiation with CO(2) laser set with different energy parameters. A cochleostomy in the basal cochlear turn of guinea pig cochleae was performed with CO(2) laser of 1, 2 and 3 w, respectively. The cochleae were removed three weeks after laser irradiation. The auditory evoked brainstem response (ABR) was measured before and after laser application and immediately before removal of the cochlea. Immunohistochemical methods were used to examine inducible nitric oxide synthase (iNOS/NOSII) and heat-shock protein 70 (Hsp70) concentrations in the cochlea after laser application. The organ of Corti was studied by scanning electron microscopy. Worse hearing loss was observed in animals receiving higher-power CO(2) laser. These findings correlated with more intense injury of the cochlear ultrastructure and with positive expression of iNOS and Hsp70 in spiral ganglion cells, nerve fibres, supporting cells of the organ of Corti and cells of the spiral ligament. The CO(2) laser as a noncontact procedure is shown to be effective and safe if the total amount of energy is kept within the limits applied in this study. Nitric oxide and stress proteins play important roles in the traumatic mechanism of the inner ear, which are related to hearing loss and injury of the ultrastructure of the inner ear.     

Frequency of cochlear enhancement on magnetic resonance imaging in patients with autoimmune sensorineural hearing loss

OBJECTIVE: To evaluate magnetic resonance imaging (MRI) scans for enhancement of inner ear structures of patients with sensorineural hearing loss and documented antibodies to the 68-kd inner ear antigen. STUDY DESIGN: Retrospective case review with reexamination of MRI scans. SETTING: Outpatient office. PATIENTS: Thirty-five patients with autoimmune sensorineural hearing loss defined by audiograms documenting a sensorineural hearing deficit in one or both ears and the presence of an anti-inner ear antibody (68-kd band) in serum samples who underwent precontrast and postcontrast T1-weighted axial and coronal MRI scans of the inner ear, which were performed concurrently with the hearing loss. INTERVENTIONS: Diagnostic. MAIN OUTCOME MEASURES: Frequency and intensity of cochlear enhancement on MRI scans. RESULTS: One patient demonstrated +2 cochlear enhancement. However, that finding was thought to represent postoperative inflammatory change. CONCLUSION: No correlation was found between the presence of antibodies to inner ear antigen in patients with hearing loss and cochlear enhancement on MRI scans.     

Combining acoustic and electrical speech processing: Iowa/Nucleus hybrid implant

OBJECTIVES: In this paper we test the concept of combining electrical stimulation for high-frequency sound with acoustic hearing for low-frequency information in the same ear. In addition, we test whether residual hearing can be preserved when an electrode is placed up to 10 mm into the inner ear, and whether the site of electrical stimulation influences speech perception. MATERIAL AND METHODS: Nine post-lingual adults with severe high-frequency hearing impairment were recruited to participate in the study. A single-subject clinical trial design was employed. A unique six-channel cochlear implant was designed for this clinical trial. The intracochlear electrodes were either 6 or 10 mm in length based on a Nucleus CI-24 multichannel implant. Monosyllabic word understanding and consonant identification in a recorded sound-only condition were used to assess changes in speech perception. Follow-up was > 12 months. RESULTS: Acoustic hearing was preserved in all nine subjects. Preoperative monosyllabic word and sentence scores were unchanged in all subjects following implantation. A 30-40% improvement in consonant recognition occurred with the 10-mm electrode. The 10-mm electrode subjects were able to understand 83-90% of the monosyllabic words using the implant plus binaural hearing aids. Scores were more than doubled when compared to preoperative scores achieved with hearing aids only. CONCLUSIONS: The human ear has the capability to integrate both acoustic and high-frequency electrically processed speech information. Placement of a short 10-mm electrode does not appear to damage residual low-frequency inner ear hair cell function, interfere with the micro-mechanics of normal cochlear vibration or decrease residual speech perception. The improvement in speech recognition was due primarily to the increased perception of higher-frequency consonantal speech cues. Such a device can provide a substantial benefit in terms of speech understanding to those with severe high-frequency hearing loss, while still maintaining the benefits of the residual lower-frequency acoustic hearing. The position of the electrode and the site of frequency information within the cochlea are shown to be important factors in the success of such a device.     

Clinical results after stapedotomy: a comparison between the erbium: yttrium-aluminum-garnet laser and the conventional technique.

OBJECTIVE: The objective of this study was to assess whether the use of the erbium: yttrium-aluminum-garnet (Er:YAG) laser has negative effects on inner ear function and to compare the short- and long-term hearing outcome of patients undergoing conventional stapedotomy versus laser stapedotomy. STUDY DESIGN: Retrospective review of prospectively collected audiometric data of patients with otosclerosis operated on by one experienced surgeon. SETTING: Academic tertiary referral center. PATIENTS: A total of 266 stapes surgeries were evaluated for intraoperative findings, of which 209 patients were evaluated for preoperative and postoperative hearing thresholds after a 6- to 452-week (mean, 22 wk) audiological follow-up. INTERVENTION: One hundred fifteen (43%) of the operations were performed conventionally, using manual perforators for stapedotomy (Group A); in 115 (43%) surgeries, the perforators were used in combination with the Er:YAG laser (Group B), and in 36 (14%) operations, the Er:YAG was used exclusively for footplate perforation (Group C). MAIN OUTCOME MEASURES: Pure-tone audiometry was performed before surgery, 2 days postoperatively (bone conduction only) and at 5, 26, and 57 weeks postoperatively. RESULTS: A postoperative temporary threshold shift of the bone conduction could be found in all groups. In Group C, where the laser was used exclusively for footplate perforation, this threshold shift was not only the most significant, but also-in contrast to the other groups-not totally reversible. In all techniques, a satisfactory air-bone gap closure could be achieved. The best long-term results (96% of the patients had 相似文献   

Cochlear microperfusion: experimental evaluation of a potential new therapy for severe hearing loss caused by inflammation.

HYPOTHESIS: Cochlear microperfusion will be a useful treatment of severe sensorineural hearing loss caused by inflammation. BACKGROUND: Viruses, bacteria, and autoimmunity can initiate inflammation in the inner ear. The acute phase is associated with elevations in cytokines, nitrous oxide, and cellular infiltrates and the breakdown of the blood-labyrinthine barrier. The chronic phase leads to irreversible ossification of the labyrinth. METHODS: The authors developed cochlear microperfusion to facilitate removal of inflammatory cells and their byproducts during the acute phase of inflammation. Using a ventral approach to the guinea pig cochlea, the authors displaced resident perilymph by delivering perfusate into the scala vestibuli and collecting the effluent from the scala tympani. The authors evaluated the benefit of the procedure in an animal model of severe hearing loss caused by inflammation. RESULTS: Healthy controls undergoing cochlear microperfusion with phosphate-buffered saline incurred a mean hearing loss of 16 dB (n=4). This hearing loss was associated with the creation of two cochleostomies and not the perfusion itself. Sterile labyrinthitis (n=5) generated by perfusion of the cochlea with antigen consistently produced severe hearing loss over the initial 48 hours, and this hearing loss persisted for the subsequent 7 days. Therapeutic cochlear microperfusion, performed within the first 24 hours of developing severe hearing loss (n=9), immediately restored on average 24 dB (p <0.007) of hearing. CONCLUSION: Cochlear microperfusion is a promising new technique for treating severe deafness caused by inflammation. The benefit may be sustained when combined with local delivery of immunosuppressive agents to the inner ear.     

Autoimmune-mediated sympathetic hearing loss: a case report.

BACKGROUND: Damage to one inner ear is occasionally followed by contralateral sensorineural hearing loss. This has been defined as sympathetic hearing loss. HYPOTHESIS: It is hypothesized that autoimmunity can play a role in the pathogenesis of sympathetic hearing loss. METHODS: A male patient who developed right-sided sympathetic hearing loss at 20 years of age, 11 years after deafness of the left ear caused by a temporal bone fracture, is described. The patient's serum was analyzed for the presence of autoantibodies against inner ear tissues by immunocytochemistry and Western blotting using rat inner ear tissues. The patient's serum was tested specifically for antibodies against heat shock protein 70 by immunodot blot. The presence of autoantibodies known to play a role in systemic autoimmune disease was also examined. RESULTS: Immunocytochemistry on rat temporal bone sections demonstrated autoantibodies in the patient's serum specifically targeted against cochlear outer hair cells. No reactivity of the patient's serum was observed with control tissues including kidney, brain, and liver. Western blotting using homogenized rat cochlear tissues showed that the patient's serum reacted with a 25- and 27-kDa protein. No reactivity was observed with heat shock protein 70 in the immunodot blot analysis. The patient's serum did not contain autoantibodies against antinuclear antibodies, double-stranded DNA, antineutrophil cytoplasmic antibodies, basement membrane, reticulin, intestinal mucosa, muscle, collagen, or mitochondria. CONCLUSION: Observations indicate that this patient suffered sympathetic hearing loss caused by organospecific autoimmunity directed to cochlear outer hair cells.     

共同腔畸形人工耳蜗手术适应证及手术方法的探讨

目的：探讨共同腔畸形人工耳蜗手术适应证以及人工耳蜗电极植入人路的选择。方法：在对重度或全聋患者进行人工耳蜗植入术前影像掌检查中,发现了6例耳蜗、前庭、外半规管呈共同腔畸形,其中5例有残留听力,1例未查到残留听力。结果：6例影像学检查呈共同腔畸形患者中,对5例有残留听力患者进行了人工耳蜗植入,其中3例选择了常规入路植入电极,2例选择了经乳突侧入路植入电极,术后均建立了人工耳蜗的听觉反应。1例因未查到残留听力,放弃了人工耳蜗手术治疗。结论：有残留听力的共同腔畸形患者,如果能够接受术后听觉言语识别效果差的事实,可以进行人工耳蜗手术。无残留听力或无法了解到有听觉反应的共同腔畸形患者,在现有技术条件下应放弃人工耳蜗植入手术。     

不完全分隔内耳畸形患者人工耳蜗植入研究进展

不完全分隔内耳畸形作为内耳畸形的一种,是导致重度、极重度感音神经性聋的病因之一.其曾被认为是人工耳蜗植入手术的禁忌症.但是随着相关研究的进展,人工耳蜗植入已成为其主要治疗手段.本文就不完全分隔内耳畸形的概念、分类、及其所致的重度、极重度感音神经性聋患者人工耳蜗植入手术的相关研究进展作一综述.     

Autoimmune mouse antibodies recognize multiple antigens proposed in human immune-mediated hearing loss.

HYPOTHESIS: Autoimmune diseased mice with hearing loss will have autoantibodies against the various cochlear antigens proposed in clinical autoimmune inner ear disease. BACKGROUND: Serum antibodies of patients with hearing loss recognize several proteins that are proposed as possible antigenic targets in the ear. This often leads to a clinical diagnosis of autoimmune inner ear disease, although it is not clear how these antibodies cause inner ear disease. Therefore, to better understand the relationship of autoantibodies and ear disease, an examination was made of serum autoantibodies in the MRL/MpJ-Fas(lpr) autoimmune mouse with hearing loss. Similar antibody patterns in the mouse would provide an animal model in which to investigate potential autoimmune mechanisms of this clinical ear disorder. METHODS: Sera from MRL/MpJ-Fas(lpr) autoimmune mice and normal C3H mice were tested by the enzyme-linked immunosorbent assay technique for reactivity against various reported cochlear antigens: heat shock protein 70 (bovine, human, bacterial), laminin, heparan sulfate proteoglycan, cardiolipin, and collagen types II and IV. RESULTS: The autoimmune mouse sera showed significantly greater antibody reactivity against all of the antigens when compared with normal mouse sera. CONCLUSIONS: Serum antibodies from autoimmune mice recognized several putative autoantigens reported for patients with hearing loss, suggesting that comparable antigen-antibody mechanisms might be operating. However, the recognition of multiple antigens did not identify any one as being the specific target in autoimmune hearing loss. The correlation of antibodies in the MRL/MpJ-Fas(lpr) autoimmune mouse and human studies indicates this animal model should aid further investigations into potential cochlear antigens in autoimmune hearing loss.     

内耳结构异常的语前聋人工耳蜗植入儿童听觉语言康复效果评价

目的评价不同类型内耳结构异常的语前聋儿童人工耳蜗植入术后听觉语言康复效果。方法选取人工耳蜗植入儿童10例(12耳),其中内耳结构发育正常的3例,前庭导水管扩大3例,Mondini畸形1例,蜗孔狭窄1例,内听道狭窄听神经纤细2例,分别采用电刺激诱发听神经复合动作电位(electrically evoked compound action potential,eCAP)、助听听阈、听障儿童听觉能力、语言能力评估标准及方法,从听神经客观电生理水平、听察觉阈、听觉辨识与理解能力以及语言能力4方面评价患儿的康复效果。结果①客观电生理:单纯前庭导水管扩大患者听神经对电刺激敏感度与内耳发育正常者相似,Mondini畸形患者比内耳发育正常者略高,蜗孔狭窄及听神经纤细患者听神经敏感度较差;②听察觉阈:与内耳结构正常及轻度畸形(Mondini畸形)患者相比,蜗孔狭窄及听神经纤细患者听察觉阈偏高,高频比低频阈值低;③听觉辨识与理解能力:在安静环境近距离交谈情境下,单纯前庭导水管扩大、Mondini畸形及蜗孔狭窄患者对熟悉语词和短句的辨识与理解能力与内耳发育正常者无差别,听神经纤细患者得分较低;④语言能力:单纯前庭导水管扩大、Mondini畸形患者与内耳发育正常者无差别,蜗孔狭窄患者的语言交往与表达能力落后于内耳发育正常者,听神经纤细患者在语法、理解、交往、表达4个维度均落后于内耳发育正常者。结论语前聋儿童人工耳蜗植入术后听觉语言康复效果需要使用多种方法综合评价。Mondini畸形患者给予足够电刺激量后,其听觉语言能力可达到内耳发育正常者水平。蜗孔狭窄、听神经纤细等严重内耳畸形患者,人工耳蜗对其听觉语言能力发展有一定帮助,家长需要建立合理期望值并坚持长期康复。     

High-frequency hearing impairment assessed with cochlear microphonics

Abstract Conclusion: Cochlear microphonic (CM) measurements may potentially become a supplementary approach to otoacoustic emission (OAE) measurements for assessing low-frequency cochlear functions in the clinic. Objective: The objective of this study was to investigate the measurement of CMs in subjects with high-frequency hearing loss. Currently, CMs can be measured using electrocochleography (ECochG or ECoG) techniques. Both CMs and OAEs are cochlear responses, while auditory brainstem responses (ABRs) are not. However, there are inherent limitations associated with OAE measurements such as acoustic noise, which can conceal low-frequency OAEs measured in the clinic. However, CM measurements may not have these limitations. Methods: CMs were measured in human subjects using an ear canal electrode. The CMs were compared between the high-frequency hearing loss group and the normal-hearing control group. Distortion product OAEs (DPOAEs) and audiogram were also measured. Results: The DPOAE and audiogram measurements indicate that the subjects were correctly selected for the two groups. Low-frequency CM waveforms (CMWs) can be measured using ear canal electrodes in high-frequency hearing loss subjects. The difference in amplitudes of CMWs between the high-frequency hearing loss group and the normal-hearing group is insignificant at low frequencies but significant at high frequencies.     

Cochlear processes affecting wave V latency of the auditory evoked brain stem response. A study of patients with sensory hearing loss

The effects of inner ear pathologies on wave V latency of the auditory evoked brain stem response (BSR) were studied in 12 selected patients with flat, low-frequency, severe high-frequency, and gradual high-frequency sensory hearing loss. In patients with flat and low-frequency sensory hearing loss (Meniere's disease), the latencies of wave V at intensities 4--10 dB greater than their response thresholds were roughly the same as those in normal-hearing subjects. In patients with severe high-frequency sensory hearing loss (sharp cut-off at about 2 or 3 kHz), the latencies of wave V were always delayed, compared with those in normal-hearing subjects. In patients with gradual high-frequency sensory hearing loss, the latency of wave V was delayed according to the degree of hearing loss (as determined by pure tone audiometry) above 2 kHz. The data are interpreted as showing that the wave V latency is sensitive to a kind of recruiting phenomenon in the transduction process as well as being an index of the pressure wave travel time to the cochlear portion responsible for the elicitation of the BSR.     

Combining acoustic and electrical hearing

OBJECTIVES/HYPOTHESIS: The concept of combining electrical stimulation for high-frequency sound with acoustic hearing for low-frequency information was tested. In addition, whether residual hearing can be preserved when an electrode is placed into the inner ear up to 10 mm and whether place of electrical stimulation influences speech perception were tested. STUDY DESIGN: A single-subject clinical trial design was employed. METHODS: Six postlingual adults with severe high-frequency hearing impairment were recruited to participate in the study. A new six-channel cochlear implant was designed for the clinical trial. The intracochlear electrodes were either 6 or 10 mm in length based on a Nucleus CI-24 multichannel implant. Monosyllabic word understanding and consonant identification testing in a recorded sound-only condition were used to assess changes in speech perception. Follow-up was greater than 12 months. RESULTS: Acoustic hearing was preserved in all six subjects (n = 3, 6-mm electrodes; n = 3, 10-mm electrodes). Preoperative monosyllabic word and sentence scores were unchanged in all subjects following implantation. A 30% to 40% improvement in consonant recognition occurred with the 10-mm electrode. The subjects with 10-mm electrodes were able to understand 83% to 90% of the monosyllabic words using the implant plus binaural hearing aids. Scores were more than doubled when compared with preoperative scores with hearing aids only. CONCLUSION: The human ear has the capability to integrate both acoustic and high-frequency electrically processed speech information. Placement of a short, 10-mm electrode does not appear to damage residual low-frequency inner ear hair cell function, interfere with the micro mechanics of normal cochlear vibration, or decrease residual speech perception. The improvement in speech recognition was due primarily to the increased perception of higher-frequency consonantal speech cues, and this improvement took several months to become apparent. Such a device can provide a substantial benefit in speech understanding to individuals with severe high-frequency hearing loss, while still maintaining the benefits of the residual lower-frequency acoustic hearing. The position of the electrode and the place of frequency information within the cochlea were shown to be important factors in the success of such a device.     

Probational treatment of sudden deafness with prostacyclin: a pilot study.

Sudden idiopathic hearing loss has occasionally been supposed to be caused by a disturbed microcirculation in the inner ear of unknown origin. Little is known about the regulation of cochlear blood flow and the effectiveness of drugs in cochlear microcirculation. Because animal experiments gave evidence that prostacyclin (PGI2) might be one biochemical substratum of local regulators in the flow of blood in the stria vascularis, 11 patients with sudden idiopathic hearing loss were treated once for 6 h with prostacyclin (10 ng/kg body weight/min) in a first open clinical trial. In most cases prostacyclin increased hearing level (mean value: 7.4 dB/frequency/day) more than a standard therapy with pentoxifylline. The substitution of PGI2 could be another indication of a rheologic disorder--whether per se or within a larger context of inflammation-like interaction--in the inner ear of patients with sudden hearing impairment.     

Audiometry in fluctuant hearing loss.

Fluctuant hearing loss is a very complex matter, which involves not only neurological and physiological concepts but considerable acoustic factors as well. Fluctuant hearing loss is perhaps more visible with the use of pure tone audiometry because of the nature of its effect, the variation in the compliance properties of cochlear tissues. This visibility is due to impedance factors that bear on the inner ear as well as on the middle and external ear regions. It is suggested that changes in compliance of the cochlear tissues play a significant role in the existence of reduced sensitivity to low frequency pure tones. This indicates that sensorineural conditions with loss of hearing in the low frequency region may be a composite of conditions: sensory cell damage, which is only seen by high frequency response, and disturbance in the cochlear tissues, increasing their stiffness and resulting in loss of sensitivity for low frequency tones. When hearing damage is found in the inner ear exclusively because of permanent destruction of sensory cells, this theoretical model predicts that the fluctuating nature of certain types of hearing impairment ceases.     

Hearing in advanced age: critical view of so-called presbycusis

Presbycusis cannot be defined nosologically as an uniform disease. The computed threshold curves of the age dependent high-frequency hearing loss should not conceal the fact that the degree and form of the hearing loss vary greatly within the age groups. The pathological appearances also vary; degenerative changes vary in site and extent and are not limited to the cochlear structures, but are also found in all parts of the auditory system. The etiology of presbycusis can scarcely be attributed to the physiological senile degeneration of cochlear or central nervous structures alone because epidemiological studies suggest that without additional endogenous and exogenous noxious effects the hearing loss progresses more slowly than under the influence of these effects. Therefore, presbycusis, in the sense of a socially handicapping hearing loss, is not an invariable lesion of the auditory system (mainly of the inner ear) due to a combination of different etiological factors. There are only two possible treatments: (1) elimination of exogenous and endogenous noxious effects in the hope of delaying the progress of the hearing loss and (2) fitting of a hearing aid. The open high-tone CROS-aid seems to provide a sufficient discrimination gain which is especially valuable for the typical high tone hearing loss in aged people. The necessity for a careful follow-up is emphasised.     

Noise exposure of the inner ear during drilling a cochleostomy for cochlear implantation

OBJECTIVES: Inserting an electrode array into the cochlea may cause inner ear trauma, which has to be minimized, particularly in cochlear implant patients with substantial residual hearing. Another potential inner ear trauma has, to a large extent, been neglected so far: the acoustic trauma that can occur during cochleostomy using different techniques. In this study, the noise exposure of the inner ear during the drilling procedure was re-evaluated. In experiments on temporal bones, quantitative measurements of sound pressure level (SPL) were carried out while a cochleostomy for cochlear implantation was drilled. STUDY DESIGN: Experimental study. MATERIALS AND METHODS: Acoustic measurements during different drilling procedures were carried out on four human temporal bone preparations equipped with microphones attached to the round window. Special calibrations were carried out, which allowed determination of SPLs affecting the cochlea during the drilling procedure. RESULTS: The highest SPLs measured on the cochlea were recorded when a still-intact endosteal membrane was touched by the burr. The SPL exceeded 130 dB and reached a level almost comparable with the situation when the ossicular chain is touched by a running burr. CONCLUSIONS: In the drilling procedure for a cochleostomy, the inner ear may be affected by very high SPLs, particularly if the endosteal membrane is left intact and comes into contact with the running burr. Of course, the resulting SPLs depend on the drilling speed and the size and characteristics of the burr (larger burrs cause higher SPLs); however, we are of the opinion that the cochlear function is at risk, anyway, if special precaution is not exercised. Even when working with reduced drilling speed, the surgeon should be aware of the high risk in the form of an acoustic trauma, which may endanger residual hearing. Recommendations in terms of "soft surgery" are given in the paper (e.g., the use of microhooks instead of a drill to remove the very last shell of bone covering the cochlea).     

Temporal bone histopathology of noise-induced hearing loss

To examine the relationship between hearing and changes in the inner ear, we investigated human temporal bone specimens from 2 patients with noise-induced hearing loss and prepared audio-cytocochleograms as described by Schuknecht et al. Patient 1 was a 50-year-old male who died of thyroid cancer and had worked at a printing house for 38 years. Patient 2 was a 58-year old male who died of maxillary sinus cancer and had worked in construction for 22 years. A pure-tone audiogram showed high-tone sensorineural hearing loss with c5-dip-type hearing disorder in both ears in Patient 1, and a high-tone abrupt form of sensorineural hearing loss in Patient 2. Pathological examination of the temporal bone revealed degeneration and disappearance of the organ of Corti at the basal turn and disappearance of cochlear neurons in both patients. Audio-cytocochleograms revealed hearing disorder consistent with the changes in the inner ear in both patients. Marked degeneration and disappearance of the organ of Corti and stria vascularis were present in patient 1. It is generally known that disorders of the organ of Corti for a long period is involved in the etiology of noise-induced hearing loss. This degeneration of the organ of Corti is produced at a basilar membrane with the maximum amplitude related to exposure to noise according to a physical and mechanical factors. Moreover, animal experiments have shown that exposure to noise decrease cochlear blood flow. In Patient 1 both the organ of Corti and the stria vascularis exhibited degeneration, suggesting that not only physical and mechanical factors but a cochlear circulatory disorder related to exposure to noise was involved in the etiology of the pathological changes in the temporal bone related to noise-induced hearing loss.