耳外科手术中电钻产生噪声的评估

目的 探讨耳显微外科中电钻产生噪声的大小及其影响因素,以及耳蜗开窗术时噪声的特点.方法 采用ER-7c型声级计,对耳显微手术中不同种类和不同规格的电钻在9具尸头的12侧颞骨中产生的噪声进行测量,并分别对噪声的等效声压级的峰值(MAX)和RMS(均方根)值进行统计学分析.结果 在9具尸头的12侧颞骨中测量噪声值如下:(1)不同直径的切割钻在乳突骨皮质产生噪声峰值的均值为120.4 dB SPL～121.7 dB SPL,RMS值为108.3 dB SPL～110.6 dB SPL;(2)在乳突腔,不同直径的切割钻和金刚钻产生噪声峰值为116.8 dB SPL～121.5 dB SPL,RMS为105.4 dB SPL～110.1 dB SPL,其差别无统计学意义;(3)耳蜗开窗术记录噪声峰值在116.0dB SPL～131.5 dB SPL,噪声RMS值为108.6 dB SPL～124.9 dB SPL,并且在3具尸头的3侧颞骨中记录到转动的金刚钻接触鼓阶内骨膜时噪声值超过130 dB SPL.结论 耳显微手术中电钻转动所产生的噪声值较大,尤其在耳蜗开窗时转动的金刚钻接触鼓阶内骨膜时噪声值更大,足以引起噪声性耳聋.因此改进耳显微手术的技术、缩短内耳受噪声暴露的时间对降低噪声性耳聋的发生率至关重要.     

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.     

Evaluation of an electrode design for the combined electric-acoustic stimulation

BACKGROUND: The objective of this study was to assess the intracochlear position and the extent of trauma to cochlear structures using the C40(+) M electrode (MED-EL, Innsbruck, Austria), which was especially designed for the combined electric acoustic stimulation. METHODS: Five human temporal bones were implanted using a standard cochlear implant procedure featuring mastoidectomy, posterior tympanotomy, and promontory cochleostomy. For the cochleostomy, an inferior approach with preservation of the endosteum of the cochlea was used to contribute to hearing preservation in the in vivo condition. RESULTS: All insertions of the new electrode array were performed into the scala tympani of the cochlea. The average insertion depth was 288 degrees. Apically, 4 of the 5 implantations were completely atraumatic. One bone showed a rupture of the basilar membrane only at the tip of the electrode. However, 4 of the 5 arrays produced severe trauma to basal cochlear structures. Two pathomechanisms, the direct traumatization through drilling of the cochleostomy or the indirect traumatization via buckling of the array could be distinguished. CONCLUSIONS: Due to the reduced contact spacing and its flexible body, the C40(+) M electrode is suitable for cochlear implantations with hearing preservation and combined electric and acoustic stimulation of the auditory system. Modifications of the surgical pathway to the cochlea should help to minimize the risk of basal cochlear trauma.     

Concept and anatomical feasibility study of an "endosteal electrode" for bimodal stimulation in severely deaf ears

BACKGROUND: Many patients with severe hearing loss could benefit from a bimodal stimulation unilaterally: acoustically in the apical region of the cochlea with some residual low frequency hearing and electrically via a cochlear implant in the basal turn with lost high hearing in the high frequency range. As a new concept we introduce the idea of an "endosteal electrode" - to be inserted between spiral ligament and endosteum of the bony wall without opening the fluid-filled inner ear. In this paper the feasibility from the anatomical point of view is to be proven. MATERIALS AND METHODS: In 10 human temporal bone specimens the bone covering the membraneous inner ear is carefully removed in the site of a typical cochleostomy. It should by proven whether or not the soft tissue layer covering the inner ear could be left intact and, furthermore, whether a "dummy-electrode array" could be inserted "endosteally". RESULTS: In 10 of the 10 specimen the preparation could be carried out in the desired way, leaving the spiral ligament intact. The regular site of the "electrode" was morphologically proven after embedding the specimens for histological evaluation. CONCLUSIONS: From the anatomical point of view, an "endosteal cochlear implantation" seems feasible. Further experiments including animal studies must show, whether this concept might succeed functionally.     

Optical coherence tomography imaging of the inner ear: a feasibility study with implications for cochlear implantation

Cochlear implantation is now being performed in ears with residual hearing. Those implant recipients who keep residual hearing may benefit from improved pitch resolution through both electrical and acoustic hearing. Preservation of cochlear function after implantation is a challenging task for the surgeon. Current topics of hearing preservation research include electrode design and surgical technique. To maintain hearing, surgeons strive to create a cochleostomy and place the electrode in a minimally traumatic fashion. In this study, we examine a novel catheter-based real-time imaging modality with 10- to 15-microm resolution, optical coherence tomography (OCT), on the inner ear. We demonstrate the capability of OCT to allow visualization of inner ear structures through bone in live mice. We additionally used OCT to image the inner ear in a human temporal bone. Optical coherence tomography was able to delineate soft tissue structures within the cochlea and may be useful as an adjunct to cochlear implantation. Other potential otologic applications of OCT are discussed.     

Promontorial cochleostomy in nonhuman primates. Is it atraumatic?

The purpose of this study is to determine if surgical approach to the inner ear is feasible without generating a hearing loss in an animal model. Five Macaca fascicularis were used as experimental animals and followed up for 27 months. Mastoidectomy, posterior tympanotomy and promontorial cochleostomy were performed on four specimens and one specimen was kept as control animal. Before and after drilling and exposing the endosteal layer and the membranous labyrinth, otoacustic emissions (dPOAE) and auditory brainstem responses (ABR) were used to test hearing. In vivo experimental studies prove it is reliable to expose the membranous labyrinth without causing hearing loss. dPOAE were present after 3, 6, 12, 24 and 26 months of follow-up. Regarding the ABR results from the four M. fascicularis in which a cochleostomy has been carried out, auditory thresholds are within the 20–30 dB interval at 27 months of follow-up. Experimental studies support clinical experiences indicating it is feasible to surgically approach the membranous labyrinth of the cochlea without damaging its hearing function.     

Application of carbon dioxide and erbium:yttrium-aluminum-garnet lasers in inner ear surgery: an experimental study.

BACKGROUND: Surgery of the inner ear requires atraumatic techniques to preserve the sensory structures of the inner ear. With modern laser technology, surgery can be performed without mechanical contact, reducing the risk of direct mechanical trauma. However, energy transfer by laser light has the potential to induce damage by heating, pressure waves, or direct irradiation, depending on the properties of the laser and parameters of application. HYPOTHESIS: The application of laser systems in inner ear surgery may have an advantage over traditional techniques; the carbon dioxide laser in continuous mode with an automated scanning procedure and the erbium:yttrium-aluminum-garnet laser were compared with a mechanical technique, using a diamond drill. METHODS: A cochleostomy in the basal cochlear turn of guinea pigs was created. Thresholds in response to frequency-specific stimuli and clicks were established by recording compound action potentials, both before and after the procedure. RESULTS: The best results in terms of preservation of cochlear function were obtained with the diamond drill. However, a single ear had a complete loss after fracture of the cochlear wall. Mean threshold shifts observed with the carbon dioxide laser were slightly greater, showing mild high-frequency losses, although differences to the group of drilling were not statistically significant. Results with the erbium:yttrium-aluminum-garnet laser showed significantly higher degrees of hearing loss than the other two groups, predominantly in the high-frequency region. CONCLUSIONS: Mechanical opening of the inner ear using a microdrill can be performed with minimal hearing loss; however, it carries the risk of direct trauma to the inner ear. The carbon dioxide laser with a new scanning technology as a noncontact procedure is shown to be effective and safe. It can be regarded as a useful tool in inner ear surgery. The erbium:yttrium-aluminum-garnet laser has a greater potential to cause damage.     

Application of a corticosteroid (Triamcinolon) protects inner ear function after surgical intervention

HYPOTHESIS: Opening of the inner ear during stapes surgery or cochlear implantation may result in trauma to inner ear structures and possible hearing loss. The dual aim of the present study was to evaluate the effectiveness of locally applied Triamcinolon* to protect the inner ear against surgically induced trauma and to exclude possible ototoxic effects. METHODS: In an animal model (guinea pig), a corticosteroid (Triamcinolon) was topically applied to the inner ear, either by extracochlear application and diffusion through the round window membrane or by direct intracochlear application via a cochleostomy. Physiological effects of the steroid were investigated by monitoring the hearing of steroid treated animals in comparison to control animals treated with Ringer solution instead of Triamcinolon. Thresholds as well as input/output functions (I/O function) of compound action potentials (CAPs) in response to auditory stimuli were determined before the cochleostomy and at specific intervals up to 4 weeks after application of Triamcinolon. RESULTS: Extracochlear application of Triamcinolon induced only minor shifts of mean CAP thresholds but significantly increased mean maximal amplitudes of I/O function 14 d after application. No detrimental effects on cochlear function were noted; thus, indicating absence of ototoxicity for extracochlear application in the concentrations used. After the surgical trauma of cochleostomy, CAP thresholds increased by 12.5 dB directly after surgery and by 15.8 dB at day 3. Amplitudes of CAPs diminished. Intracochlear application of Triamcinolon resulted in significantly enhanced recovery of CAP thresholds and amplitudes of I/O function from initial loss over a period of 4 weeks. CONCLUSIONS: From these results, we conclude that extracochlear topical application of Triamcinolon has no ototoxic effect in the concentrations that were used and that intracochlear application supports an increased recovery of cochlear functions after surgical trauma. Furthermore, the results indicate a protective effect of corticosteroids, partially preventing progressive loss of hearing after cochleostomy over a period of 4 weeks. Intracochlear application of Triamcinolon may be useful to prevent hearing loss after surgical intervention on the inner ear; however, clinical safety and efficacy remain to be proven in clinical studies.     

Equivalent noise level generated by drilling onto the ossicular chain as measured by laser Doppler vibrometry: a temporal bone study

BACKGROUND: Inadvertent drilling on the ossicular chain is one of the causes of sensorineural hearing loss (HL) that may follow tympanomastoid surgery. A high-frequency HL is most frequently observed. It is speculated that the HL is a result of vibration of the ossicular chain resembling acoustic noise trauma. It is generally considered that using a large cutting burr is more likely to cause damage than a small diamond burr. AIM: The aim was to investigate the equivalent noise level and its frequency characteristics generated by drilling onto the short process of the incus in fresh human temporal bones. METHODS AND MATERIALS: Five fresh cadaveric temporal bones were used. Stapes displacement was measured using laser Doppler vibrometry during short drilling episodes. Diamond and cutting burrs of different diameters were used. The effect of the drilling on stapes footplate displacement was compared with that generated by an acoustic signal. The equivalent noise level (dB sound pressure level equivalent [SPL eq]) was thus calculated. RESULTS: The equivalent noise levels generated ranged from 93 to 125 dB SPL eq. For a 1-mm cutting burr, the highest equivalent noise level was 108 dB SPL eq, whereas a 2.3-mm cutting burr produced a maximal level of 125 dB SPL eq. Diamond burrs generated less noise than their cutting counterparts, with a 2.3-mm diamond burr producing a highest equivalent noise level of 102 dB SPL eq. The energy of the noise increased at the higher end of the frequency spectrum, with a 2.3-mm cutting burr producing a noise level of 105 dB SPL eq at 1 kHz and 125 dB SPL eq at 8 kHz. In contrast, the same sized diamond burr produced 96 dB SPL eq at 1 kHz and 99 dB at 8 kHz. CONCLUSION: This study suggests that drilling on the ossicular chain can produce vibratory force that is analogous with noise levels known to produce acoustic trauma. For the same type of burr, the larger the diameter, the greater the vibratory force, and for the same size of burr, the cutting burr creates more vibratory force than the diamond burr. The cutting burr produces greater high-frequency than lower-frequency vibratory energy.     

"井喷"在内耳畸形人工耳蜗植入术中的发生率

目的：探讨“井喷”在内耳畸形人工耳蜗植入术中的发生率，为有“井喷”现象的人工耳蜗植入术积累临床经验。方法：对680例行人工耳蜗植入术患者行术前高分辨CT检查，显示80例双耳有内耳畸形，其中20例并发内耳道底骨性缺损与内耳相通，行人工耳蜗植入术。结果：20例（25％）并发内耳道底骨性缺损与内耳相通者，术中发生了“井喷”，其中大前庭导水管畸形者5例，Mondini畸形者11例，耳蜗前庭与内耳道共同腔畸形者4例；耳蜗、前庭、外半规管共同腔和前庭、外半规管共同腔畸形者无“井喷”发生。结论：①80例内耳畸形人工耳蜗植入术患者“井喷”的发生率为25％；②内耳畸形人工耳蜗植入术中“井喷”的发生率依次为：耳蜗、前庭与内耳道共同腔畸形，Mondini畸形，大前庭导水管畸形；③单纯前庭、耳蜗、外半规管共同腔畸形及半规管畸形者，人工耳蜗植入术中未发生“井喷”；④80例内耳畸形人工耳蜗植入术中，发生“井喷”者均存在内耳道底骨缺损，与内耳形成共同开放的通道。     

An autonomous surgical robot for drilling a cochleostomy: preliminary porcine trial

Objective: To produce an autonomous drilling robot capable of performing a bony cochleostomy whilst minimising the damage to the underlying cochlear endosteum. Design: In this laboratory based study, a robotic drill was designed to measure the changes in force and torque experienced by the tool point during the drilling process. This information is used to predict the point of breakthrough and stop the drill prior to damaging the underlying endosteal membrane. Setting: Aston University. Participants: Five porcine cochleas. Main outcomes measures: An assessment was made of whether a successful bony cochleostomy was performed, the integrity of endosteal membrane was then assessed. Results: The autonomous surgical robotic drill successfully performed a bony cochleostomy and stopped without damaging the endosteal membrane in all five cases. Conclusions: The autonomous surgical robotic drill can perform a cochleostomy whilst minimising the trauma to the endosteal membrane. The system allows information about the state of the drilling process to be derived using force and torque data from the tool point. This information can be used to effectively predict drill breakthrough and implement a control strategy to minimise drill penetration beyond the far surface.     

Prevention of cochlear implant electrode damage

PURPOSE OF REVIEW: As the current trend in cochlear implantation is to prescribe cochlear implants for patients with residual hearing and to use electroacoustic stimulation, cochlear implant damage must be prevented. This article summarizes current research endeavors to prevent electrode insertion trauma and resulting hearing loss. RECENT FINDINGS: Alteration in surgical technique is necessary with each new electrode design. Nontraumatic surgical technique also requires minimizing acoustic trauma due to drilling the cochleostomy, mechanical damage from electrode insertion, potential infection, and fibrosis of the cochlea. The pattern of hearing loss following electrode insertion trauma is an immediate loss that results from direct trauma to the macroscopic elements of the cochlea and a delayed loss that may reflect the activation of inflammatory and cell death pathways. Therapies under investigation include glucocorticoids, inhibitors of cell death pathways, and hypothermia. SUMMARY: Electrode insertion trauma-induced hearing loss involves multiple mechanisms ranging from mechanical insertion trauma to activation of inflammatory and cell death pathways. The macroscopic mechanical damage to the cochlea may be prevented by improvement of electrode design and surgical technique. The molecular damage needs further studies to assess the efficacy of novel therapeutic strategies in preserving functional residual hearing.     

Preservation of residual hearing following cochlear implantation: comparison between three surgical techniques

The preservation of residual hearing is becoming a high priority in cochlear implant surgery. It allows better speech understanding and ensures long-lasting and stable performance; it also allows the possibility, in selected cases, of combining electro-acoustic stimulation in the same ear. We present the results of a retrospective study of the conservation of residual hearing in three different groups of patients who had undergone cochlear implantation using three different cochlear implant electrode arrays, combined with three different surgical techniques for the cochleostomy. The study aimed to evaluate which approach allowed greater preservation of residual hearing. The best residual hearing preservation results (i.e. preservation in 81.8 per cent of patients) were achieved with the Contour Advance electrode array, using the Advance Off-Stylet technique and performing a modified anterior inferior cochleostomy; this combination enabled reduced trauma to the lateral wall of the cochlea during electrode insertion.     

In vivo imaging of mammalian cochlear blood flow using fluorescence microendoscopy.

AIMS: We sought to develop techniques for visualizing cochlear blood flow in live mammalian subjects using fluorescence microendoscopy. BACKGROUND: Inner ear microcirculation appears to be intimately involved in cochlear function. Blood velocity measurements suggest that intense sounds can alter cochlear blood flow. Disruption of cochlear blood flow may be a significant cause of hearing impairment, including sudden sensorineural hearing loss. However, inability to image cochlear blood flow in a nondestructive manner has limited investigation of the role of inner ear microcirculation in hearing function. Present techniques for imaging cochlear microcirculation using intravital light microscopy involve extensive perturbations to cochlear structure, precluding application in human patients. The few previous endoscopy studies of the cochlea have suffered from optical resolution insufficient for visualizing cochlear microvasculature. Fluorescence microendoscopy is an emerging minimally invasive imaging modality that provides micron-scale resolution in tissues inaccessible to light microscopy. In this article, we describe the use of fluorescence microendoscopy in live guinea pigs to image capillary blood flow and movements of individual red blood cells within the basal turn of the cochlea. METHODS: We anesthetized eight adult guinea pigs and accessed the inner ear through the mastoid bulla. After intravenous injection of fluorescein dye, we made a limited cochleostomy and introduced a compound doublet gradient refractive index endoscope probe 1 mm in diameter into the inner ear. We then imaged cochlear blood flow within individual vessels in an epifluorescence configuration using one-photon fluorescence microendoscopy. RESULTS: We observed single red blood cells passing through individual capillaries in several cochlear structures, including the round window membrane, spiral ligament, osseous spiral lamina, and basilar membrane. Blood flow velocities within inner ear capillaries varied widely, with observed speeds reaching up to approximately 500 microm/s. CONCLUSION: Fluorescence microendoscopy permits visualization of cochlear microcirculation with micron-scale optical resolution and determination of blood flow velocities through analysis of video sequences.     

Imaging of Cochlear Structures by Optical Coherence Tomography (OCT). Temporal bone experiments for an OCT-guided cochleostomy technique

BACKGROUND: Optical Coherence Tomography (OCT) is a relatively new imaging technique, which provides scans similar to sonography on an optical base. We questioned whether OCT may be helpful in optimizing anatomical orientation in cochlear implant (CI) surgery. In a study on temporal bone specimens we tested, whether OCT provides information about the cochlear topography, particularly in situations, when for cochleostomy the bony otic capsule is already opened but the membranous endosteal layer is still intact. MATERIAL AND METHODS: OCT was performed on five human temporal bone preparations, in which the cochleostomy was carried out still leaving the endosteum covering the fluid-filled inner ear intact. A prototype of operating microscope was used, in which a spectral-domain OCT (SD-OCT) with a central wavelength of 840 nm was integrated. RESULTS: On all scans, OCT supplies information about inner ear structures, such as the lateral attachment of the basilar membrane dividing the scalae. Even delicate structures like the Reissner's membrane could be identified in one case. CONCLUSIONS: This pilot study clearly documents the possibility to identify inner ear structures, especially the site of the scala tympani while its enveloping membranes are still intact. These findings may have an impact on cochlear implant surgery, especially as an orientation guide to localize the scala tympani precisely before opening the fluid-filled inner ear.     

Sensorineural hearing loss following the decompression of the facial nerve

This study aims to ascertain whether sensorineural hearing loss occurs after the decompression of the facial nerve. Nine patients have undergone decompression of the facial nerve (limited to the vertical segment) by the transmastoid approach were selected as the subjects of this study because the influence of disinfectants and surgical trauma on the inner ear seems to be less severe in this operation than in tympanoplasty. Additionally, this approach seems to be more suitable for judgement of the effect of the drilling noise induced acoustic trauma on the inner ear than tympanoplasty. Though high tone abrupt sensorineural hearing loss was occurred in the operated ear in seven patients, no changes in hearing level were found in the contralateral side ear. Bekesy audiometry performed in only one case revealed Jerger II which suggested some disorder in the cochlea. Not only acoustic trauma induced by the drilling noise but also labyrinthitis occurred via the opened facial canal and the internal ear canal seemed to be the cause of sensorineural hearing loss following the decompression of the facial nerve.     

New window for cochlear implant insertion.

Nine patients with profound bilateral hearing loss received a cochlear implant via the middle fossa. Subjects presented with a bilateral radical mastoidectomy cavity, fibroadhesive otitis media, otosclerosis, autoimmune inner ear disease, previous cranial trauma and genetic prelingual deafness. A classic middle fossa approach was adopted. A small cochleostomy was performed on the most superficial part of the basal turn. A Nucleus CI24M cochlear implant system (Cochlear Corporation) was inserted in four patients, a Lauraflex implant (Philips Hearing Implants) in three patients and a Combi 40 + (Med-el) with double electrode array in two. The receiver-stimulator was positioned in a bone well drilled in the temporal squama and the electrode carrier was inserted in the fenestrated cochlea. Speech perception tests, performed over a period of time ranging from 1 to 6 months after cochlear implant activation, yielded better results than those obtained in postlingually deaf patients operated on via the traditional transmastoid route. Cochlear implant insertion via the middle fossa approach is a technique which is suitable for auditory rehabilitation of subjects with a bilateral radical mastoidectomy cavity, chronic middle ear disease, patients suffering from middle ear malformations, and patients with partial obliteration of the cochlea in the basal turn. However, the main advantage of middle fossa cochleostomy consists in the possibility of stimulating areas of the cochlea, i.e. middle and apical turns, where a greater survival rate of spiral ganglion cells is known to occur. This new approach led to major improvements in speech perception in all patients compared with patients operated on with the transmastoid approach and thus, given the present state of the art, it is the only approach which allows stimulation of the entire cochlea and enables the best auditory outcomes to be achieved in patients with a cochlear implant.     

Positional vertigo and cochlear implantation.

OBJECTIVE: To identify patients developing positional vertigo after cochlear implantation. STUDY DESIGN: Prospective study on a cohort of patients undergoing cochlear implantation. SETTING: Academic tertiary referral center. PATIENTS: The study included 70 consecutive patients who underwent vestibular evaluation before and after cochlear implantation. INTERVENTION: Medical record review. MAIN OUTCOME MEASURE: Recorded vestibular symptoms after cochlear implantation. Patients with positional vertigo were considered case subjects, whereas those without vestibular symptoms were considered case controls. RESULTS: Benign paroxysmal positional vertigo (BPPV) occurred in 8 patients (on the cochlear implant [CI] side in 7 patients, and in the other ear in 1). One patient had BPPV of the lateral semicircular canal on the implanted side, and 7 patients had BPPV of the posterior semicircular canal (on the same CI side in 6 patients, and on the opposite side in 1), which were detected and presented during the last examination. In 5 patients, the onset of symptoms varied from 7 to 130 days after implant activation; in 2 patients, the onset occurred before activation. CONCLUSION: Three different mechanisms are proposed for the occurrence of BPPV in patients with CI. The first focuses on the fall of bone dust particles into the cochlea during cochleostomy. In the second, the vibration caused by drilling the cochlea would be sufficient to dislodge otoconia into the labyrinth. The third hypothesis suggests dislodging of an otolith because of the electric stimulation. In our patients, conservative approaches have been used with a minimal invasive cochleostomy and without perilymph suction. Thus, the vibratory trauma affecting the cochlea during cochleostomy seems to play a fundamental role in the development of paroxysmal vertigo in patients with implant.     

Effects of inner ear trauma on the risk of pneumococcal meningitis

OBJECTIVE: To examine the risk of pneumococcal meningitis in healthy rats that received a severe surgical trauma to the modiolus and osseous spiral lamina or the standard insertion technique for acute cochlear implantation. DESIGN: Interventional animal studies. SUBJECTS: Fifty-four otologically normal adult Hooded-Wistar rats. INTERVENTIONS: Fifty-four rats (18 of which received a cochleostomy alone; 18, a cochleostomy and acute cochlear implantation using standard surgical techniques; and 18, a cochleostomy followed by severe inner ear trauma) were infected 4 weeks after surgery with Streptococcus pneumoniae via 3 different routes (hematogenous, middle ear, and inner ear) to represent all potential routes of bacterial infection from the upper respiratory tract to the meninges in cochlear implant recipients with meningitis. RESULTS: Severe trauma to the osseous spiral lamina and modiolus increased the risk of pneumococcal meningitis when the bacteria were given via the middle or inner ear (Fisher exact test, P<.05). However, the risk of meningitis did not change when the bacteria were given via the hematogenous route. Acute electrode insertion did not alter the risk of subsequent pneumococcal meningitis for any route of infection. CONCLUSIONS: Severe inner ear surgical trauma to the osseous spiral lamina and modiolus can increase the risk of pneumococcal meningitis. Therefore, every effort should be made to ensure that cochlear implant design and insertion technique cause minimal trauma to the bony structures of the inner ear to reduce the risk of pneumococcal meningitis.     

Representation of acoustic signals in the human cochlea in presence of a cochlear implant electrode

BACKGROUND: In subjects with remaining low frequency hearing, combined electric-acoustic stimulation (EAS) of the auditory system is a new therapeutic perspective. Intracochlear introduction of a cochlear implant electrode, however, may alter the biomechanical properties of the inner ear and thus affect perception of acoustic stimuli. STUDY DESIGN: Based on histological observations of morphologic changes after cochlear implantation in cadaveric and post mortem studies the effects of basilar membrane (BM) stiffening in the ascending basal and middle turns of the cochlea due to close contact of the BM with the electrode were simulated in a 3D-computational finite element model of the inner ear. To verify our simulated results, pre- and postoperative pure-tone audiograms of 13 subjects with substantial residual hearing, who underwent cochlear implantation, were evaluated. RESULTS: In the scenario of partial BM-fixation, acoustic energy of middle (2 kHz) and high (6 kHz) frequency was focused basally and apically to the fixed section, increasing BM displacement amplitudes up to 6 dB at a stimulation level of 94 dB (SPL). Lower frequencies were not affected by fixation in the basal and middle turn of the cochlea. In implanted subjects, a small but significant decrease of thresholds was observed at 1.5 kHz, a place in tonotopy adjacent to the tip region of the implanted electrode. CONCLUSION: Our model suggests that stiffening of the basilar membrane adjacent to an implanted electrode into the basal and middle cochlear turn did not affect BM movement in the low frequency area. Focussing of acoustic energy may increase perception in regions adjacent to the fixed section. Observations in implanted subjects were concordant with our model predictions. High frequencies, however, should not be amplified in patients using EAS to avoid disturbances in discrimination due to tonotopically incorrect frequency representation.