Histologic evaluation of temporal bones with cochlear implants

Endoscopic-Assisted Cochlear Implantation in Far Advanced Otosclerosis

OBJECTIVES

To evaluate the effectiveness of cochlear implantation (CI) in case of far advanced otosclerosis and to evaluate the value of using intraoperative otoendoscopy to facilitate the identification of the round window membrane and the scala tympani without the need to remove the posterior canal wall or to perform a subtotal petrosectomy.

STUDY DESIGN

Retrospective case-series study.

SETTING

Tertiary academic CI center.

PATIENTS AND METHODS

This study was conducted on patients with far advanced otosclerosis who underwent endoscopic-assisted CI between January 2010 and June 2020 at the same CI center. The minimum follow-up period was 2 years after surgery.

RESULTS

Fourteen patients were included in the study. Ten patients had undergone a previous stapedotomy. Electrode insertion in the scala tympani was successfully accomplished in all cases included in the study. There was a statistically significant improvement in pure-tone average and speech discrimination scores in all cases of the study group (p < 0.0001). There were no statistically significant differences in postoperative pure-tone average or speech discrimination scores between cases with and without cochlear ossification or between cases with and without a previous stapedotomy (p > 0.05).

CONCLUSION

Endoscopic-assisted CI is an effective option for hearing restoration in patients with far advanced otosclerosis. Otoendoscopy can facilitate visualization and access to the scala tympani without the need to remove the posterior canal wall or to perform a subtotal petrosectomy.

Cochlear Implant Users with Otosclerosis: Are Hearing and Quality of Life Outcomes Worse than in Cochlear Implant Users without Otosclerosis?

Background: The otosclerotic process may influence the performance of the cochlear implant (CI). Difficulty in inserting the electrode array due to potential ossification of the cochlea, facial nerve stimulation, and instability of the results are potential challenges for the CI team. Objectives: To evaluate hearing results and subjective outcomes of CI users with otosclerosis and to compare them with those of CI users without otosclerosis. Method: Retrospective review of 239 adults with bilateral profound postlingual deafness who underwent unilateral cochlear implantation between 1992 and 2017. Hearing and speech understanding were assessed via pure-tone audiometry and speech perception tests. Subjective outcomes were assessed via the Nijmegen Cochlear Implant Questionnaire (NCIQ), the Glasgow Benefit Inventory (GBI), and the Hearing Implant Sound Quality Index (HISQUI19) at 6 months, 12 months, and at the last follow-up. Results: Subjects were 22 CI users with otosclerosis and 217 without otosclerosis. Both groups had a similar duration of deafness and age at CI implantation. Results did not significantly differ according to group: no significant intergroup difference was found regarding the frequency of complete electrode insertion, facial stimulation, reimplantation, or PTA4 scores at the last follow-up. Regarding speech perception, no significant intergroup difference was found on any test or at any interval. Further, subjective outcomes, as measured by the GBI, NCIQ, and HISQUI19, did not significantly differ between groups. Conclusions: Adults with otosclerosis and profound hearing loss derive significant benefit from CI use. Audiological and self-reported outcomes are not significantly different from that of other CI users with postlingual deafness.

Intracochlear Bleeding Enhances Cochlear Fibrosis and Ossification: An Animal Study

The aim of this study was to investigate the effects of intracochlear bleeding during cochleostomy on cochlear inflammatory response and residual hearing in a guinea pig animal model. Auditory brainstem response threshold shifts were greater in blood injected ears (p<0.05). Interleukin-1β, interleukin-10, tumor necrosis factor-α and nitric oxide synthase 2, cytokines that are related to early stage inflammation, were significantly increased in blood injected ears compared to normal and cochleostomy only ears at 1 day after surgery; with the increased IL-1β being sustained until 3 days after the surgery (p<0.05). Hair cells were more severely damaged in blood injected ears than in cochleostomy only ears. Histopathologic examination revealed more extensive fibrosis and ossification in blood injected ears than cochleostomy only ears. These results show that intracochlear bleeding enhanced cochlear inflammation resulting in increased fibrosis and ossification in an experimental animal model.

Surgical findings and auditory performance after cochlear implant revision surgery

The objective of this study was to review cochlear reimplantation outcomes in the tertiary hospital and analyze whether facts such as type of failure, surgical findings, or etiology of deafness have an influence. A retrospective study including 38 patients who underwent cochlear implant revision surgery in a tertiary center is performed. Auditory outcomes (pure tone audiometry, % disyllabic words) along with etiology of deafness, type of complication, issues with insertion, and cochlear findings are included. Complication rate is 2.7 %. Technical failure rate is 57.9 % (50 % hard failure and 50 % soft failure), and medical failure (device infection or extrusion, migration, wound, or flap complication) is seen in 42.1 % of the cases. Management of cochlear implant complications and revision surgery is increasing due to a growing number of implantees. Cases that require explantation and reimplantation of the cochlear implant are safe procedures, where the depth of insertion and speech perception results are equal or higher in most cases. Nevertheless, there must be an increasing effort on using minimally traumatic electrode arrays and surgical techniques to improve currently obtained results.

Cochlear implantation outcomes in advanced otosclerosis

INTRODUCTION

Several studies support the use of cochlear implants (CI) in far-advanced otosclerosis (FAO).

MATERIAL AND METHODS

We compared our results of CI in patients with FAO and unknown origin hearing loss (UOHL) and our incidence of facial electrical stimulation and difficult insertion of the electrode bundle up to 3 to 5 years from surgery.

RESULTS

We found 17 patients with CI in FAO and UOHL. FAO patients achieved better results on the pure tone average (PTA) and recognition of monosyllables by GEE test (p=0.022; p=0.006), and particularly at 1 year on the PTA (p=0.002), at 6 months and a year in monosyllables (p=0.002; p=0.001), and at 6 months in disyllables (p=0.004). There were no differences toward complications.

CONCLUSION

In our experience, placement of CI in FAO has proven successful, with results comparable to other similar cohorts, and with low complications.

Endocochlear inflammation in cochlear implant users: case report and literature review

OBJECTIVES

Cochlear implantation is a relatively safe procedure with a low complication rate. The overall rate of complications among cochlear implant patients ranges from 6% to 20%. Major complications are those that are life-threatening or require surgery, whereas minor complications are those that can be medically treated. Nonetheless, certain complications, even if highly rare, may require specific investigations and treatments. Among these rare complications are those with endocochlear involvement, such as cochleitis or labyrinthitis, with fibrosis or ossification that could lead to explantation. The aims of the present study were to report a particular case of post-operative cochleitis and to review the rate of complications after cochlear implantation, emphasising those conditions with proven endocochlear involvement.

METHODS

We refer to the case of an eight-year-old Italian boy affected by the sudden onset of headache, ipsilateral otalgia and facial paresis, who presented to our clinic for inexplicable worsening of the performance of his implant and his residual hearing, six years after surgery. A complete investigation including (clinical history, routine, autoimmune and serological blood tests, electrophysiological measurements from the cochlear implant and neuroimaging) was performed and is herein described. Additionally, a comprehensive review of the literature was conducted using internet search engines; 274 papers were selected, 88 of which were best suited to our purposes.

RESULTS

In our case, the progression of the symptoms and the performance decrement required explantation, followed by a complete recovery. Reviewing the literature revealed only three reports concerning cases of proven endocochlear phlogosis that required revision surgery. Wound swelling/infection and vertigo remain the two most common complications of cochlear implantation. Failure of the device is the third most frequent complication (10.06% of all complications and 1.53% of cochlear implantations). Other rare conditions (such as granulating labyrinthitis with cochlear fibrosis, ossification and erosion, silicone allergy and the formation of a biofilm around the internal device) are possible and unpredictable. Although rare (approximately 1%), such cases may require explantation.

CONCLUSIONS

Despite efforts by both surgeons and manufacturers, device-related and surgical complications still occur. These and other rare conditions demand specific management, and their frequency may be underestimated. Further studies are needed to assess more realistic rates of complications and devise more efficient strategies for early diagnosis and treatment.

Human cochlea: anatomical characteristics and their relevance for cochlear implantation

This is a review of the anatomical characteristics of human cochlea and the importance of variations in this anatomy to the process of cochlear implantation (CI). Studies of the human cochlea are essential to better comprehend the physiology and pathology of man's hearing. The human cochlea is difficult to explore due to its vulnerability and bordering capsule. Inner ear tissue undergoes quick autolytic changes making investigations of autopsy material difficult, even though excellent results have been presented over time. Important issues today are novel inner ear therapies including CI and new approaches for inner ear pharmacological treatments. Inner ear surgery is now a reality, and technical advancements in the design of electrode arrays and surgical approaches allow preservation of remaining structure/function in most cases. Surgeons should aim to conserve cochlear structures for future potential stem cell and gene therapies. Renewal interest of round window approaches necessitates further acquaintance of this complex anatomy and its variations. Rough cochleostomy drilling at the intricate "hook" region can generate intracochlear bone-dust-inducing fibrosis and new bone formation, which could negatively influence auditory nerve responses at a later time point. Here, we present macro- and microanatomic investigations of the human cochlea viewing the extensive anatomic variations that influence electrode insertion. In addition, electron microscopic (TEM and SEM) and immunohistochemical results, based on specimens removed at surgeries for life-threatening petroclival meningioma and some well-preserved postmortal tissues, are displayed. These give us new information about structure as well as protein and molecular expression in man. Our aim was not to formulate a complete description of the complex human anatomy but to focus on aspects clinically relevant for electric stimulation, predominantly, the sensory targets, and how surgical atraumaticity best could be reached.

Surgical implications of perimodiolar cochlear implant electrode design: avoiding intracochlear damage and scala vestibuli insertion

OBJECTIVE

To review the mechanisms and nature of intracochlear damage associated with cochlear implant electrode array insertion, in particular, the various perimodiolar electrode designs. Make recommendations regarding surgical techniques for the Nucleus Contour electrode to ensure correct position and minimal insertion trauma.

BACKGROUND

The potential advantages of increased modiolar proximity of intracochlear multichannel electrode arrays are a reduction in stimulation thresholds, an increase in dynamic range and more localized neural excitation. This may improve speech perception and reduce power consumption. These advantages may be negated if increased intracochlear damage results from the method used to position the electrodes close to the modiolus.

METHOD

A review of the University of Melbourne Department of Otolaryngology experience with temporal bone safety studies using the Nucleus standard straight electrode array and a variety of perimodiolar electrode array designs; comparison with temporal bone insertion studies from other centres and postmortem histopathology studies reported in the literature. Review of our initial clinical experience using the Nucleus Contour electrode array.

RESULTS

The nature of intracochlear damage resulting from electrode insertion trauma ranges from minor, localized, spiral ligament tear to diffuse organ of Corti disruption and osseous spiral lamina fracture. The type of damage depends on the mechanical characteristics of the electrode array, the stiffness, curvature and size of the electrode in relation to the scala, and the surgical technique. The narrow, flexible, straight arrays are the least traumatic. Pre-curved or stiffer arrays are associated with an incidence of basilar membrane perforation. The cochleostomy must be correctly sited in relation to the round window to ensure scala tympani insertion. A cochleostomy anterior to the round window rather than inferior may lead to scala media or scala vestibuli insertion.

CONCLUSION

Proximity of electrodes to the modiolus can be achieved without intracochlear damage provided the electrode array is a free fit within the scala, of appropriate size and shape, and accurate scala tympani insertion is performed.

Ganglion cell and 'dendrite' populations in electric acoustic stimulation ears

BACKGROUND/AIMS

The electric acoustic stimulation (EAS) technique combines electric and acoustic stimulation in the same ear and utilizes both low-frequency acoustic hearing and electric stimulation of preserved neurons. We present data of ganglion cell and dendrite populations in ears from normal individuals and those suffering from adult-onset hereditary progressive hearing loss with various degrees of residual low-frequency hearing. Some of these were potential candidates for EAS surgery. The data may give us information about the neuroanatomic situation in EAS ears.

METHODS

Dendrites and ganglion cells were calculated and audiocytocochleograms constructed. The temporal bones were from the collection at the House Ear Institute in Los Angeles, Calif., USA. Normal human anatomy, based on surgical specimens, is presented.

RESULTS

Inner and outer hair cells, supporting cells, ganglion cells and dendrites were preserved in the apical region. In the mid-frequency region, around 1 kHz, the organ of Corti with inner and outer hair cells was often conserved while in the lower basal turn, representing frequencies above 3 kHz, the organ of Corti was atrophic and replaced by thin cells. Despite loss of hair cells and lamina fibers ganglion cells were present even after 28 years of deafness.

CONCLUSIONS

Conditions with profound sensorineural hearing loss and preserved low-frequency hearing may have several causes and the pathology may vary accordingly. In our patients with progressive adult-onset sensorineural hearing loss (amalgamated into 'presbyacusis'), neurons were conserved even after long duration of deafness. These spiral ganglion cells may be excellent targets for electric stimulation using the EAS technique.

Role of electrode placement as a contributor to variability in cochlear implant outcomes

HYPOTHESIS

Suboptimal cochlear implant (CI) electrode array placement may reduce presentation of coded information to the central nervous system and, consequently, limit speech recognition.

BACKGROUND

Generally, mean speech reception scores for CI recipients are similar across different CI systems, yet large outcome variation is observed among recipients implanted with the same device. These observations suggest significant recipient-dependent factors influence speech reception performance. This study examines electrode array insertion depth and scalar placement as recipient-dependent factors affecting outcome.

METHODS

Scalar location and depth of insertion of intracochlear electrodes were measured in 14 patients implanted with Advanced Bionics electrode arrays and whose word recognition scores varied broadly. Electrode position was measured using computed tomographic images of the cochlea and correlated with stable monosyllabic word recognition scores.

RESULTS

Electrode placement, primarily in terms of depth of insertion and scala tympani versus scala vestibuli location, varies widely across subjects. Lower outcome scores are associated with greater insertion depth and greater number of contacts being located in scala vestibuli. Three patterns of scalar placement are observed suggesting variability in insertion dynamics arising from surgical technique.

CONCLUSION

A significant portion of variability in word recognition scores across a broad range of performance levels of CI subjects is explained by variability in scalar location and insertion depth of the electrode array. We suggest that this variability in electrode placement can be reduced and average speech reception improved by better selection of cochleostomy sites, revised insertion approaches, and control of insertion depth during surgical placement of the array.

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.

Histopathology of human cochlear implants: correlation of psychophysical and anatomical measures

The cadavaric temporal bones of five subjects who underwent cochlear implantation during life (2 Nucleus and 3 Ineraid) were analyzed using two-dimensional (2D) reconstruction of serial sections to determine the number of surviving spiral ganglion cells (SGCs) in the region of each electrode of the implanted arrays. The last psychophysical threshold and maximum-comfortable sensation level measured for each electrode were compared to their respective SGC count to determine the across-electrode psychophysical variance accounted for by the SGC counts. Significant correlations between psychophysical measures and SGC counts were found in only two of the five subjects: one Nucleus implantee (e.g., r=-0.71; p<0.001 for threshold vs. count) and one Ineraid implantee (e.g., r=-0.86; p<0.05 for threshold vs. count). A three-dimensional (3D) model of the implanted cochlea was formulated using the temporal-bone anatomy of the Nucleus subject for whom the 2D analysis did not result in significant correlations between counts and psychophysical measures. Predictions of the threshold vs. electrode profile were closer to the measured profile for the 3D model than for the 2D analysis. These results lead us to hypothesize that 3D techniques will be required to asses the impact of peripheral anatomy on the benefit patients derive from cochlear implantation.

Pattern Of Hearing Loss In A Rat Model Of Cochlear Implantation Trauma

HYPOTHESIS

Trauma caused by cochlear implant electrode insertion is attributable to the combination of direct physical trauma and the delayed cell death of oxidative stress-injured auditory sensory cells.

BACKGROUND

Histologic evaluation of cochlear implant electrode trauma has demonstrated that the extent of sensory cell losses is proportional to the degree of injury. However, the impact of delayed oxidative stress within injured cochlear tissues and the progressive loss of injured hair cells by way of apoptosis are at present unknown.

METHODS

Laboratory rats were evaluated for hearing acuity before and after electrode insertion, before and after round window membrane incision only. Hearing was measured before trauma or incision and over the next 7 days. Objective measurements of hearing function were distortion products of otoacoustic emissions (DPOAEs) in the frequency range of 2 to 32 kHz and tone-burst (i.e., 4-32 kHz) evoked auditory brain stem responses (ABRs).

RESULTS

For the experimental cochleae, there were progressive increases in ABR thresholds and decreases in ABR amplitudes. The amplitude of the DPOAEs in the experimental cochleae also showed progressive decreases. For the contralateral control and round window membrane surgical control ears, there were no significant changes in either DPOAE or ABR thresholds.

CONCLUSION

These results document a progressive loss of hearing acuity postimplantation and strongly suggest that electrode insertion trauma generated oxidative stress within injured cochlear tissues.

Arrest of apoptosis in auditory neurons: implications for sensorineural preservation in cochlear implantation

HYPOTHESIS

The JNK/c-Jun cell death pathway is a major pathway responsible for the loss of oxidative stress-damaged auditory neurons.

BACKGROUND

Implantation of patients with residual hearing accentuates the need to preserve functioning sensorineural elements. Although some auditory function may survive electrode insertion, the probability of initiating an ongoing loss of auditory neurons and hair cells is unknown. Cochlear implantation can potentially generate oxidative stress, which can initiate the cell death of both auditory neurons and hair cells.

METHODS

Dissociated cell cultures of P4 rat auditory neurons identified the apoptotic pathway initiated by oxidative stress insults (e.g., loss of trophic factor support) and characterized this pathway by arresting translation of pathway-specific mRNA with antisense oligonucleotide treatment and with the use of pathway specific inhibitors. The presence or absence of apoptosis-specific protein and changes in the level of neuronal survival measured the efficacy of these interventional strategies.

RESULTS

These in vitro studies identified the JNK/c-Jun cascade as a major initiator of apoptosis of auditory neurons in response to oxidative stress. Neurons pretreated with c-jun antisense oligonucleotide and exposed to high levels of oxidative stress were rescued from apoptosis, whereas neurons in treatment control cultures died. Treatment of oxidative-stressed cultures with either curcumin, a MAPKKK pathway inhibitor, or PD-098059, a MEK1 inhibitor, blocked loss of neurons via the JNK/c-Jun apoptotic pathway.

CONCLUSION

Blocking the JNK/c-Jun cell death pathway is a feasible approach to treating oxidative stress-induced apoptosis within the cochlea and may have application as an otoprotective strategy during cochlear implantation.

Comparative study of cochlear damage with three perimodiolar electrode designs

OBJECTIVE

To describe intracochlear insertion trauma caused by three perimodiolar cochlear implant electrodes.

STUDY DESIGN

Descriptive histological study of 15 human cadaver temporal bones.

METHODS

Fifteen cadaver temporal bones underwent surface preparation and were implanted with one of the following perimodiolar electrode arrays: Combi 40+PM (MedEl Corporation), HiFocus II (Advanced Bionics Corporation), or Contour (Cochlear Corporation). A cryosectioning technique was used to study horizontal sections at 200 microm intervals with the electrode in place. Image-enhanced videofluoroscopy and computer-assisted morphometrics were used to assess the mechanism of insertion trauma and to determine electrode position within the modiolus.

RESULTS

Histological examination revealed varying degrees of damage to the spiral ligament, basilar membrane, and osseous spiral lamina. Using a novel grading system for electrode trauma, there was no statistically significant difference among the three electrodes. A literature search of histological studies of a commonly used "standard" electrode showed damage equal to or greater than that seen in the current study.

CONCLUSIONS

Insertion trauma caused by periomodiolar electrodes occurs to an acceptable degree. Refinement of electrodes based on mechanisms of trauma may be able to further reduce damage.

Cochlear Implants in the Geriatric Population: Benefits Outweigh Risks

Cochlear implantation has become widely accepted as an effective means of hearing rehabilitation in severely and profoundly deaf individuals. In the elderly, cochlear implantation involves a number of unique issues that can affect patient outcomes. These factors include age-related changes in the auditory system, prolonged durations of deafness, diminished communication abilities, and coexisting medical and psychosocial problems.

In general, the results of cochlear implantation in the elderly have been comparable with those of younger adults. Perioperative attention to medical and surgical details allows for safe insertion and a minimum of postoperative complications. Patients older than 65 have obtained excellent results by both audiologic and quality-of-life measures.

Systematic Approach to Electrode Insertion in the Ossified Cochlea

Ossification of the fluid spaces of the cochlea occurs often in candidates for cochlear implantation, especially children. When noted before surgery on computerized tomography, ossification previously was thought to contraindicate cochlear implantation because of possible mechanical obstruction and uncertainty about the level of function that could be achieved by stimulating an ossified cochlea. However, during the preceding 6 years, techniques have been developed that permit implantation in ossified cochleas. We present a systematic approach that has been developed to treat the three clinically important categories of cochlear ossification: round window niche obliteration, inferior segment obstruction, and upper segment obstruction. Case reports are presented for each of these three drill-out procedures, demonstrating results often similar to those expected for implantation of the nonossified cochlea.

Triple fluorochrome labeling of cochlear bone growth

A new technique is described which measures the extent and time course of intracochlear bone formation after cochlear implantation in an experimental animal model. A series of fluorescent histochemical markers is used to delineate the amount of intracochlear bone deposition during specified time periods.

Evaluation of the temporal bones of a multichannel cochlear implant patient

In this report we detail the temporal bone findings of a 57-year-old patient who underwent placement of a Nucleus 22-channel electrode 7 months prior to his death. Audiometric testing postoperatively demonstrated suprasegmental speech cue discrimination only. Histologic evaluation of the cochleas revealed significant sensorineural survival except in the region of the basal turn of the implanted cochlea adjacent to the implant. There was no significant pathologic condition attributable to the operation or the electrode in areas remote from the basal turn of the cochlea.

Cochlear implants: histopathologic findings related to performance in 16 human temporal bones

This paper presents results of a histologic study of 16 temporal bones with cochlear implants from 13 subjects. Damage caused by electrode insertion in the basal turn of the cochlea was evaluated. Dendrite and spiral ganglion cell populations were compared to clinical performance scores to determine structures necessary for stimulation and the minimum number needed for electrical stimulation. Results show that damage from insertion of long electrodes was located mainly at the most anterior part of the basal turn; that despite total degeneration of dendrites in the area near the electrode, some spiral ganglion cells remained; and that spiral ganglion cells or possibly axons are the stimulated structures and that fewer of them than previously thought are necessary to achieve a hearing sensation from electrical stimulation.

Cochlear implantation of totally deaf ears. Histologic evaluation of candidacy

Successful cochlear implantation depends on the presence of stimulatable neural elements, which are believed to be the spiral ganglion, neurons, or their axons. We examined the 1,152 temporal bones in our laboratory to determine how many with a total sensorineural hearing loss would be implantable. We defined implantable as having 3,500 neurons or more, as determined by successful implant stimulation in two ears from our collection with less than 3,500 neurons. Of 46 bones with deafness, 37 had 3,500 neurons or more and would be considered implant candidates. The types of deafness in the potentially implantable ears and in ears with sufficient neural elements will be discussed.

Cochlear implantation: strategies to protect the implanted cochlea from middle ear infection

A cochlear implant for use in children must take into account the high incidence of middle ear infection in this age group. A scala tympani electrode that traverses the middle ear and round window will likely act as a conduit by which infection can spread to the inner ear and potentially to the CNS. In this study an attempt was made to reestablish a separation of the cochlea from the middle ear by developing a seal around the implant at the level of the round window. A series of cats were implanted with simulated cochlear prostheses consisting of either a plain Silastic cylinder, a Silastic cylinder wrapped with autogenous fascia, or a Silastic cylinder with a cuff of bioactive ceramic. Middle ear infection was induced, followed by histologic examination. Bioactive ceramic appears to have some merit as a round window sealing material, while fascia was shown to be of no value. Intracochlear infection, when it did occur, was limited to the basal regions of the cochlea.