Comparison of electrode position in the human cochlea using various perimodiolar electrode arrays.

OBJECTIVE: This study was conducted to evaluate the insertion properties and intracochlear trajectories of three perimodiolar electrode array designs and to compare these designs with the standard Cochlear/Melbourne array. BACKGROUND: Advantages to be expected of a perimodiolar electrode array include both a reduction in stimulus thresholds and an increase in dynamic range, resulting in a more localized stimulation pattern of the spiral ganglion cells, reduced power consumption, and, therefore, longer speech processor battery life. METHODS: The test arrays were implanted into human temporal bones. Image analysis was performed on a radiograph taken after the insertion. The cochleas were then histologically processed with the electrode array in situ, and the resulting sections were subsequently assessed for position of the electrode array as well as insertion-related intracochlear damage. RESULTS: All perimodiolar electrode arrays were inserted deeper and showed trajectories that were generally closer to the modiolus compared with the standard electrode array. However, although the precurved array designs did not show significant insertion trauma, the method of insertion needed improvement. After insertion of the straight electrode array with positioner, signs of severe insertion trauma in the majority of implanted cochleas were found. CONCLUSIONS: Although it was possible to position the electrode arrays close to the modiolus, none of the three perimodiolar designs investigated fulfilled satisfactorily all three criteria of being easy, safe, and atraumatic to implant.

Chronic middle ear disease and cochlear implantation.

We have presented three patients with bilateral CSOM who were otherwise suitable for cochlear implantation. These patients had conventional surgical management of CSOM and were implanted after a period of 6 months through apparently healthy middle ears. However, all three had a recurrence of middle ear disease requiring further surgery, and one had a potentially life-threatening complication necessitating removal of the implant. Before considering cochlear implantation in patients with bilateral CSOM, it is essential to eradicate all disease, and radical mastoidectomy with obliteration may be necessary. The use of a cochlear sealing device may further ensure prevention of infection spreading into the cochlea.

Cochlear pathology following reimplantation of a multichannel scala tympani electrode array in the macaque.

The histopathologic consequence of removing and reimplanting intracochlear electrode arrays on residual auditory nerve fibers is an important issue when evaluating the safety of cochlear prostheses. The authors have examined this issue by implanting multichannel intracochlear electrodes in macaque monkeys. Macaques were selected because of the similarity of the surgical technique used to insert electrodes into the cochlea compared to that in humans, in particular the ability to insert the arrays into the upper basal turn. Five macaques were bilaterally implanted with the Melbourne/Cochlear banded electrode array. Following a minimum implant period of 5 months, the electrode array on one side of each animal was removed and another immediately implanted. The animals were sacrificed a minimum of 5 months following the reinsertion procedure, and the cochleas prepared for histopathologic analysis. Long-term implantation of the electrode resulted in a relatively mild tissue response within the cochlea. Results also showed that inner and outer hair cell survival, although significantly reduced adjacent to the array, was normal in 8 of the 10 cochleas apicalward. Moreover, the electrode reinsertion procedure did not appear to adversely affect this apical hair cell population. Significant new bone formation was frequently observed in both control and reimplanted cochleas close to the electrode fenestration site and was associated with trauma to the endosteum and/or the introduction of bone chips into the cochlea at the time of surgery. Electrode insertion trauma, involving the osseous spiral lamina or basilar membrane, was more commonly observed in reimplanted cochleas. This damage was usually restricted to the lower basal turn and resulted in a more extensive ganglion cell loss. Finally, in a number of cochleas part of the electrode array was located within the scala media or scala vestibuli. These electrodes did not appear to evoke a more extensive tissue response or result in more extensive neural degeneration compared with electrodes located within the scala tympani. In conclusion, the present study has shown that the reimplantation of a multichannel scala, tympani electrode array can be achieved with minimal damage to the majority of cochlear structures. Increased insertion trauma, resulting in new bone formation and spiral ganglion cell loss, can occur in the lower basal turn in cases where the electrode entry point is difficult to identify due to proliferation of granulation and fibrous tissue.

Factors predicting postoperative sentence scores in postlinguistically deaf adult cochlear implant patients.

A sample of 64 postlinguistically profoundly to totally deaf adult cochlear implant patients were tested without lipreading by means of the Central Institute for the Deaf (CID) sentence test 3 months postoperatively. Preoperative promontory stimulation results (thresholds, gap detection, and frequency discrimination), age, duration of profound deafness, cause of deafness, lipreading ability, postoperative intracochlear thresholds and dynamic ranges for electrical stimulation, depth of insertion of the electrode array into the scala tympani, and number of electrodes in use were considered as possible factors that might be related to the postoperative sentence scores. A multiple regression analysis with stepwise inclusion of independent variables indicated that good gap detection and frequency discrimination during preoperative promontory testing, larger numbers of electrodes in use, and greater dynamic ranges for intracochlear electrical stimulation were associated with better CID scores. The CID scores tended to decrease with longer periods of profound deafness.

Surgical complications with the cochlear multiple-channel intracochlear implant: experience at Hannover and Melbourne.

The surgical complications for the first 153 multiple-channel cochlear implant operations carried out at the Medizinische Hochschule in Hannover and the first 100 operations at the University of Melbourne Clinic, The Royal Victorian Eye and Ear Hospital, are presented. In the Hannover experience the major complications were wound breakdown, wound infection, electrode tie erosion through the external auditory canal, electrode slippage, a persistent increase in tinnitus, and facial nerve stimulation. The incidence of wound breakdown requiring removal of the package was 0.6% in Hannover and 1.0% in Melbourne. The complications for the operation at both clinics were at acceptable levels. It was considered that wound breakdown requiring implant removal could be kept to a minimum by making a generous incision and suturing the flap without tension.

The biologic safety of the Cochlear Corporation multiple-electrode intracochlear implant.

Studies have been undertaken to confirm the biologic safety of the Cochlear Corporation multi-electrode intracochlear implant. The materials used are biocompatible. The electrode array is flexible: it can be inserted with minimal or no trauma, providing the insertion is stopped when resistance is first felt. An atraumatic insertion is facilitated if a good view is obtained along the scala tympani of the basal turn of the cochlea by drilling through the crista fenestrae. The passage of the electrode around the cochlea can be facilitated if the electrode is rotated during insertion (clockwise for the left and anticlockwise for the right cochlea). The electrode can be explanted and another one reinserted with minimal or no trauma. A seal established around the electrode after an implantation period of 2 weeks can prevent infection extending from the middle to the inner ear. The electrical stimulus parameters produced by the Nucleus receiver-stimulator cause no loss of spiral ganglion cells or corrosion of the platinum band electrodes. Long-term stimulation has been carried out for up to 8 years in patients without affecting their clinical performance.

A multiple-electrode intracochlear implant for children.

A multiple-electrode intracochlear implant that provides 21 stimulus channels has been designed for use in young children. It is smaller than the adult version and has magnets to facilitate the attachment of the headset. It has been implanted in two children aged 5 and 10 years. The two children both lost hearing in their third year, when they were still learning language. Following implantation, it was possible to determine threshold and comfortable listening levels for each electrode pair. This was facilitated in the younger child by prior training in scaling visual and electrotactile stimuli. Both children are regular users of the implant, and a training and assessment program has been commenced.

Preliminary results for the cochlear corporation multielectrode intracochlear implant in six prelingually deaf patients.

The preliminary results from this study indicate that some prelingually deaf patients may get worthwhile help from a multiple-electrode cochlear implant that uses a formant-based speech processing strategy. It is encouraging that these improvements can occur in young adults and teenagers. The results for two children are also encouraging. A 10-year-old child obtained significant improvement on some speech perception tests. It was easy to set thresholds and comfortable listening levels on a 5-year-old child, and he is now a regular user of the device. There are, however, considerable variations in performance among the prelingual patients, which may be related to the following factors: whether they have had some hearing after birth, the method of education used, the motivation of the patient, and age at implantation.

The University of Melbourne--nucleus multi-electrode cochlear implant.

To summarize, our preliminary results indicate that some prelingually deaf patients may get worthwhile help from a multiple-electrode cochlear implant which extracts formants. They can understand words and running speech better when using the cochlear implant with lip-reading compared to lip-reading alone. It has been encouraging that these improvements can occur in young adults and teenagers. It has also been encouraging that some can recognize place pitch as well as rate pitch. There are, however, considerable variations in performance and this may be due to the following factors: whether they have had some hearing after birth, the method of education used, the motivation of the patient and age at implantation. In conclusion it is important to emphasize that deaf children are severely disadvantaged however good their teacher of the deaf. Research on cochlear implants offers hope for profoundly-totally deaf children. These developments will not replace the caring, competent educators but complement their skills. There is also a greater need than ever for an interdisciplinary approach to these children.

Banded intracochlear electrode array: evaluation of insertion trauma in human temporal bones.

A banded free-fit scala tympani array was inserted into the basal turn of nine human cochleas to evaluate the trauma produced by the procedure. These nine cochleas, together with five nonimplanted controls, were serially sectioned and examined microscopically for damage to the membranous labyrinth, in particular the spiral ligament, the basilar and Reissner's membranes, the stria vascularis, and the osseous spiral lamina. The severity and location of any trauma along the cochlear spiral were recorded. The results indicate that the insertion of the banded scala tympani array resulted in minimal mechanical damage, occurring primarily to a localized region of the spiral ligament. This would not result in significant neural degeneration, and therefore would not compromise the efficacy of the multichannel cochlear prosthesis.

Clinical trial of a multi-channel cochlear prosthesis: results on 10 postlingually deaf patients.

The clinical trial of a multi-channel cochlear prosthesis has been carried out on 10 profoundly-totally deaf adult patients. Speech perception tests have shown that all the patients received significant benefit from the device. They obtained improvements in understanding running speech from 47% to 550% when using the device in conjunction with lipreading compared to lipreading alone. With an open-set CID sentence test, three patients obtained scores showing an ability to understand speech without the need to lipread, and a further three patients had scores indicating they could also receive useful information without lipreading. In two patients, very limited open-set scores for electrical stimulation alone were obtained. This was most probably due to the fact that only a few channels of stimulation were possible due to cochlear disease, and they were therefore receiving information more like a single-channel device. The prosthesis has also been found to provide considerable help in hearing and recognizing everyday sounds.

Surgery for an improved multiple-channel cochlear implant.

An improved multiple-channel cochlear implant has been developed. The titanium container with enclosed electronics, the receiver coil, and the connector are embedded in medical-grade Silastic. The upper half of the implant has a diameter of 35 mm and a height of 4.5 mm, and the lower half a diameter of 23 mm and a height of 5 mm. The electrode array has also been designed to reduce the possibility of breakage due to repeated movements over many years. The surgery involves drilling a bed in the mastoid bone for the receiver-stimulator, and fixing the proximal electrode under the mastoid cortex. Gentle insertion of the electrode array through the round window and along the scala tympani is achieved with a specially designed microclaw .