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At least 127 records · Page 7Linked to original sources
PubMed2001

Electrical stimulation of the auditory nerve: single neuron strength-duration functions in deafened animals.

Destruction of cochlear hair cells initiates degenerative changes within auditory nerve fibres (ANFs), including loss of peripheral processes and demyelination of the cell body. These changes are likely to affect the biophysical processes involved in action potential generation to an electrical stimulus. We measured the strength-duration relationship in acutely deafened (100% ANF survival) versus long-term deafened cochleae (approximately 15% ANF survival) by recording from single neurons in the central nucleus of the inferior colliculus (ICC). Input/output functions were constructed for 22 ICC neurons in response to stimulation of the auditory nerve using biphasic current pulses of 20-1000 micros/phase. Strength-duration curves were derived and found to be of the same general form for both acute and long-term deafened cochleae. While there was an increase in rheobase for neurons from long-term versus acute deafened cochleae, this increase was not statistically significant (p=0.097). In contrast, chronaxie--which is related to the membrane time constant--was significantly shorter in the long-term deafened cochleae (p = 0.004). This presumably reflects a shift in the site of action potential initiation to the larger diameter, heavily myelinated central axon as a result of the pathology. These changes in the site of action potential generation have implications for the delivery of charge to ANFs via cochlear implants.

Animals↗
PubMed1993

The perception of temporal modulations by cochlear implant patients.

The perception of temporal modulations of pulsatile electric stimuli was measured in seven cochlear implant patients using the Cochlear Pty. Limited prosthesis. Four patients were postlingually deafened adults and three patients were young adults who were deafened very early in life. The first study measured detection thresholds for modulated pulse duration for a series of modulation frequencies and pulse rates. The shape of the detection thresholds as a function of modulation frequency, the temporal modulation transfer function, often resembled a low-pass filter with a 50-100-Hz cut-off frequency. Thresholds did not markedly vary across the different pulse rates for most patients. Thresholds were less than 10%-20% of the range of usable hearing for most patients. The second study compared detection thresholds for modulated pulse durations around different reference pulse durations: 50, 100, and 300 microseconds. Detection thresholds were generally proportional to the different reference pulse durations. The third study measured difference limens for the discrimination of modulation depth. The difference limens were similar to the detection thresholds for the same reference pulse duration and pulse rate. The three patients deafened very early in life showed more within-group variation in performance, and their overall levels of performance were poorer than those of the postlingually deafened adults.

Acoustic Stimulation↗
PubMedDate not supplied

Scala vestibuli insertion in cochlear implantation: a valuable alternative for cases with obstructed scala tympani.

Insertion of a sufficient number of electrodes is important for a successful use of cochlear implants. We investigated the results of scala vestibuli insertion for cochlear implantation in cases of obstructed scala tympani. In a series of 200 cochlear implantations, scala vestibuli insertion was successfully performed in 4 cases with obstruction of the scala tympani. Etiologies included a temporal bone fracture, severe otosclerosis and malformations of the cochlea. The maximum insertion depth obtained via the scala vestibuli was 30 mm. Postoperative results were comparable to patients in whom conventional scala tympani insertion was performed. No adverse effects related to the site of insertion were observed. Scala vestibuli insertion offers a valuable alternative in cases of obstructed scala tympani that can be employed for a variety of etiologies.

Adult↗
PubMed2005

Effect of cochlear implantation on residual spiral ganglion cell count as determined by comparison with the contralateral nonimplanted inner ear in humans.

It is generally assumed that at least a minimal number of spiral ganglion cells is essential for successful speech perception with a cochlear implant. Although the insertion of a multichannel cochlear implant frequently results in loss of residual hearing in the implanted ear, this outcome does not imply that significant damage to residual populations of spiral ganglion cells has occurred. The purpose of the current study was to compare spiral ganglion cell counts in implanted and nonimplanted cochleas in 11 patients for whom both temporal bones were available and in whom a multichannel cochlear implant had been placed unilaterally. The temporal bones were processed for light microscopy by standard techniques. The cochleas were reconstructed by 2-dimensional methods. Spiral ganglion cell counts of the implanted and nonimplanted sides were compared by a paired t-test (2-tailed). The mean spiral ganglion cell counts for implanted and nonimplanted ears were not statistically different in the most basal three segments of the cochlea. However, the mean spiral ganglion cell count in segment 4 (apical segment) and the mean total spiral ganglion cell count were lower in the implanted cochleas than in the nonimplanted cochleas (p < .01). The results of this study suggest a modest decrease in the total spiral ganglion cell count in the implanted ears as compared to the nonimplanted ears, principally in the apical segment. Possible interpretations of this finding are discussed.

Aged↗
PubMed1999

Implantation of the CLARION cochlear implant in an ossified cochlea.

This report describes the successful implantation of the CLARION Multi-Strategy Cochlear Implant electrode in the totally ossified cochlea of a 5-year-old child via a radical mastoidectomy approach. Postoperatively, the child demonstrated responses to auditory stimuli, even though the electrode array contacted only bone and muscle graft tissue with no visible evidence of nerve fibers or cochlear lumen. Responses to sound did not begin to emerge until 10 weeks following initial stimulation and improved slowly over time. Although the child's postoperative auditory performance is more limited than that of most implanted children, she derives substantially more benefit from her implant than she did from conventional hearing aids.

Cochlear Diseases↗
PubMed1990

The prognostic value of round window electrical stimulation in cochlear implant patients.

The use of preoperative round window stimulation has been advocated for its possible predictive value in cochlear implant patients. We have attempted to correlate cause of deafness, preoperative radiologic study, and postoperative stimulability and performance with preoperative stimulation. Round window stimulation procedures consisted of measurements of electrical thresholds and comfort levels, gap detection, and temporal difference limen. Radiologic studies were performed using high-resolution computerized semi-axial and coronal tomography with 1.5-millimeter overlapping cuts. Patient performance was measured using a standard audiologic test battery. Sixteen postlingually, profoundly deaf adults who received the Nucleus multichannel cochlear implant were studied. All 16 patients who responded to preoperative stimulation had acceptable CT scans for the ear operated on and stimulated postoperatively with the prosthesis. The lowest level at which a patient could reliably detect a gap between two signals ranged from 10 to 150 milliseconds, which was not predictive. For the temporal difference limen task, the patients who could reliably identify the longer of two pulses when the difference was less than 100 milliseconds did achieve varying amounts of open-set speech discrimination postoperatively. In summary, results indicate that the preoperative psychoacoustic electrical stimulation test battery provides useful information in predicting postoperative performance.

Cochlea↗
PubMed1992

Cochlear implants in children: reliability of computed tomography.

Preoperative temporal bone computed tomography (CT) can demonstrate anatomic details relevant to surgical management and is therefore essential in the presurgical evaluation of patients receiving cochlear implants. The purpose of this study was to evaluate preoperative CT studies and compare them to surgical findings in 34 children who received the Nucleus multichannel cochlear implant. The focus of this report is to discuss the dependability of CT scans in predicting surgical findings at the time of cochlear implantation. Results indicate that agreement of CT interpretations with surgical findings is partially related to the etiology of hearing loss and the experience of the surgeon and neuroradiologist. Advantages and limitations of the CT scans in predicting surgical findings are discussed.

Adolescent↗
PubMed2003

High resolution computed tomography and magnetic resonance imaging in the pre-operative assessment of cochlear implant patients.

Optimal imaging protocols for cochlear implantation have yet to be determined. Pre-operative computed tomography (CT) and magnetic resonance image (MRI) scans are used to assess cochlear anatomy and patency, to delineate surgical access, and to aid in choice of side for implantation. However, opinion still differs as to which modality provides more information in pre-operative assessment, or if, indeed, a combination of the two is superior. The first 88 patients on the Irish National Cochlear Implant Programme (NCIP) were retrospectively studied to determine the accuracy of pre-operative CT and MRI in predicting abnormalities at the time of surgery. Correlation with surgical findings was determined in three separate groups of patients (those who had CT only, those who had MRI only, and those who had both CT and MRI performed). Of the 24 patients that had both CT and MRI performed, both modalities had a 79 per cent correlation with surgical findings. CT and MRI reports concurred in 75 per cent of cases. Specificity and negative predictive value were high (86 per cent and 90 per cent, respectively). CT alone (47 cases) correlated with surgery in 39 cases (83 per cent); MRI alone (17 cases) correlated in 15 cases (88 per cent). The findings of this study suggest that CT and MRI are effective at predicting normal inner ear anatomy, and thus at predicting the patient and the cochlea most suitable for implantation. Both modalities are useful in determining the side of implantation, thus avoiding potential surgical difficulties in cases of unilateral abnormalities. There was no significant difference between the ability of MRI and CT to detect abnormalities at the time of surgery. In this series the combination of CT and MRI has not been shown to be superior to either modality used alone, although anecdotal evidence to the contrary was noted.

Adult↗
PubMed1992

The basal turn of the cochlea.

The coils of the cochlea are now readily demonstrated by thin-section high-resolution computed tomography (CT) in the axial plane. This assessment has become important in severely deaf patients who are candidates for cochlear implant surgery. The commonest abnormality shown in these cases is post-meningitic or tympanogenic labyrinthitis ossificans, which can obstruct the passage of the electrode. Severe otosclerosis can cause a similar problem. Congenital deformities of the labyrinth are rarely suitable for implantation, but the procedure may be indicated for the true Mondini deformity. Implantation is contraindicated for severe dysplasia of the cochlea and for the recently described variety of x-linked deafness with deficient bone at the fundus of the internal auditory meatus.

Calcinosis↗
PubMed1991

Multichannel cochlear implant and electrically evoked auditory brainstem responses in a child with labyrinthitis ossificans.

Ossification of the cochlea following meningitis presents a surgical challenge. Electrode mapping, especially in the young child, is difficult given the uncertainty of electrode contact with viable neural elements. This paper reviews surgical technique and the use of auditory brainstem responses to map the electrodes. A 4-year-old child deafened by meningitis at age 20 months had bilateral cochlear ossification by computed tomography. At surgery, a canal wall-down mastoidectomy and closure of the ear canal were performed. A trough around the modiolus was drilled, and the electrode array was placed in it. Post-operatively, the patient gave aversive or no responses to electrode stimulation. To assess electrode function, auditory brainstem responses to individual electrode activation were obtained under general anesthesia. Functioning electrodes could thus be selected for mapping. The patient now responds well to sound.

Child, Preschool↗
PubMed1992

Auditory performance of children with cochlear ossification and partial implant insertion.

The management of the profoundly deaf child with a cochlear implant poses a special challenge, particularly when total ossification of the cochlea is present. In this setting, insertion of an electrode array into a child's cochlea is often difficult. Our experience supports the feasibility of partial insertion of a multichannel implant into the basal turn of an ossified cochlea. Five children with ossified cochleae who had undergone partial implantation of a multichannel electrode were compared with the performance of matched controls who had full insertion of multichannel implants. No dramatic differences were detected during a 6- to 18-month follow-up period on selected test measures. These preliminary results suggest that active electrode number may exert a limited effect on performance with a cochlear implant. Drilling out the basal turn of an ossified cochlea in conjunction with partial insertion of a multichannel implant appears to be an acceptable surgical and rehabilitational alternative for placement of a cochlear implant prosthesis in children with complete cochlear ossification.

Adolescent↗
PubMed1993

Bony dehiscence between singular canal and round window niche.

The incidence of bony dehiscence of the human singular canal was studied by examining 409 human temporal bones obtained from 300 individuals. Such a dehiscence was noted in three (0.7%) of the bones from three (1%) of the individuals, all male, aged 2, 6, and 76 years. All of these bony dehiscences were located between the round window niche and the cribrose area of the singular canal. The finding of a microfissure in the vicinity of the bony dehiscence in two of the three cases indicates that such dehiscences occur independently of microfissures. Although the incidence of bony dehiscences of the singular canal is small, these dehiscences appear to have considerable clinical significance in that they form a communication between the middle and inner ears or possibly between the middle ear and the cerebrospinal fluid space.

Adolescent↗
PubMed1994

The Vienna Cochlear Implant in patients with obliteration of the cochlea.

Twelve deaf patients with obliterated or ossified cochleas received the extracochlear version of the Vienna Cochlear Implant. Four patients, 1 of them a child, developed open speech comprehension. Obliteration of the cochlea could not always be predicted by conventional tomography of the temporal bone. Short duration of deafness, wide dynamic range, and good ability of time resolution (small temporal difference limen [TDL]) are predictors for good postoperative results. Obliteration or ossification of the cochlea per se is no contraindication to cochlear implantation.

Adult↗
PubMed1994

Multichannel cochlear implantation in obliterated cochleas using the Gantz procedure.

Gantz, et al, reported two patients with extensive cochlear ossification in which cochlear implantation was done with a Nucleus 22-Channel Cochlear Implant after extensive cochlear drill-out. One of the patients did well with 20 functioning electrode pairs. We report an additional three patients with extensive cochlear ossification who received Nucleus 22-Channel Cochlear Implants. All three patients had extensive cochlear drill-out as described by Gantz, et al. All three patients have use of all 21 electrode pairs with amperages typical of conventional implantation in two of the three and slightly increased levels in the third. Extensive bilateral cochlear ossification does not seem to be an absolute contraindication for multi-channel cochlear implantation.

Adult↗
PubMed2003

Ossified versus patent cochlea: objective and subjective results of partial drill-out of the basal turn.

OBJECTIVE: To compare the objective benefits and subjective impact of surgery on the quality of life (QOL) of implanted patients with a totally ossified or patent cochlea. DESIGN: Prospective, observational, pre- versus postsurgery study. SETTING: Academic otolaryngology department. PATIENTS: Five consecutive patients (3 women and 2 men with a mean age of 43.6 years; range 15-62 years) with a totally ossified cochlea treated with Cohen's partial drill-out technique were selected from a series of 78 patients who underwent cochlear implantation. Five implanted patients (three women and two men with a mean age of 43.8; range 26-60 years) with a patent cochlea were used as a control group. The mean age, gender distribution, and causes of deafness were the same in the two groups. MAIN OUTCOME MEASURES: Recognition test of open and closed sets of two-syllable words; sentence test; subjective QOL test for auditory, social, and emotional impairment. RESULTS: The patients with an ossified cochlea showed a gradual improvement in all objective speech modalities during the 24-month follow-up period, whereas those with a patent cochlea reached their best score at the first follow-up evaluation. At the subjective QOL test, auditory impairment in the patients with an ossified cochlea was 91% before and 34% after surgery; the social impairment scores at the same times were, respectively, 52% and 18%. The presurgery emotional impairment score of 56% decreased over the following months, but this trend was more striking in the earlier postoperative period. CONCLUSIONS: The benefits of cochlear implants should be considered not only in terms of objective evaluation by means of traditional clinical tests but also in terms of the patients' subjective evaluation of auditory and communicative performances. Together with the improvement in auditory and communicative skills, a better QOL (psychological and social comfort) is undoubtedly one of the more appreciated aspects for implanted patients.

Adolescent↗
PubMed1991

Cochlear pathology following chronic electrical stimulation using non charge balanced stimuli.

During the course of a chronic intracochlear electrical stimulation study using charge balanced biphasic current pulses, one animal inadvertently received a short period of direct current (DC) stimulation at a level of approximately 1 microA. Subsequent, the animal was chronically stimulated using a poorly charge balanced waveform that produced a DC level of approximately 2 microA. Extensive pathological changes were observed within the cochlea. These changes included widespread spiral ganglion cell loss and new bone growth that extended throughout all turns of the cochlea. Significant changes in the morphology of the electrically evoked auditory brainstem response (EABR) were associated with these pathological changes. EABRs recorded prior to the DC stimulation exhibited a normal waveform morphology. However, responses recorded during the course of the DC stimulation were dominated by a short latency response believed to be vestibular in origin. The response thresholds were also significantly higher than levels recorded before the DC stimulation. In contrast, the contralateral cochlea, stimulated using charge balanced stimuli, showed no evidence of adverse pathological changes. Furthermore, EABRs evoked from this cochlea remained stable throughout the chronic stimulation period. Although preliminary, the present results illustrate the adverse nature of poorly charge balanced electrical stimuli. These results have important implications for both the design of neural prostheses and the use of DC stimuli to suppress tinnitus in patients.

Animals↗