Speech perception after cochlear implantation in 53 patients with otosclerosis: multicentre results.

OBJECTIVES: To analyse the speech perception performance of 53 cochlear implant recipients with otosclerosis and to evaluate which factors influenced patient performance in this group. The factors included disease-related data such as demographics, pre-operative audiological characteristics, the results of CT scanning and device-related factors. METHODS: Data were reviewed on 53 patients with otosclerosis from 4 cochlear implant centres in the United Kingdom and the Netherlands. Comparison of demographics, pre-operative CT scans and audiological data revealed that the patients from the 4 different centres could be considered as one group. Speech perception scores had been obtained with the English AB monosyllable tests and Dutch NVA monosyllable tests. Based on the speech perception scores, the patients were classified as poor or good performers. The characteristics of these subgroups were compared. RESULTS: There was wide variability in the speech perception results. Similar patterns were seen in the phoneme scores and BKB sentence scores between the poor and good performers. The two groups did not differ in age at onset of hearing loss, duration of hearing loss, progression, age at onset of deafness, or duration of deafness. CONCLUSIONS: The clinical presentation of the otosclerosis (rapid or slow progression) did not influence speech perception. Better performance was related to less severe signs of otosclerosis on CT scan, full insertion of the electrode array, little or no facial nerve stimulation and little or no need to switch off electrodes.

Imaging of electrode position in relation to electrode functioning after cochlear implantation.

This study assessed the electrode position in cochlear implant patients and evaluated the extent to which the electrode position is determinative in the electrophysiological functioning of the cochlear implant system. Five consecutively implanted adult patients received a multichannel cochlear implant. In all patients, the electrical impedance and the electrically evoked compound action potentials were recorded immediately after implantation. Multislice computer tomography was performed 6 weeks postoperatively before switch-on of the cochlear implant. The electrode position relative to the modiolus was assessed and correlated to the electrophysiological measurements. All electrodes were fully inserted; this was confirmed by computer tomography. The individual electrode distance toward the modiolus could be most precisely analyzed for the basal part of the electrode array. It was thus decided to study the data of electrodes one, four, and seven. No correlation was found between electrical impedance and electrode distance. A significant correlation was found between electrode distance and the electrically evoked compound action potentials, with a 96% probability using Kendall's rank correlation. We conclude that the electrode-modiolus distance is of importance to the stimulation of auditory nerve fibers. Future developments in imaging will further improve and refine our insight in the relation between electrode positioning.

Intracochlear assessment of electrode position after cochlear implant surgery by means of multislice computer tomography.

The development of electrode arrays, the past years, has focused on modiolus-hugging cochlear implant electrodes. Besides, atraumatic implantation of electrodes is of importance for the use in hearing preservation, in cases of combined electric and acoustic stimulation. Intracochlear positioning of the individual electrodes by means of multislice computer tomography (CT) has not yet been shown. In this study we formulated and tested a CT imaging protocol for postoperative scanning of the temporal bone in cochlear implant subjects. Both a fresh human temporal bone and a fresh human cadaver head were implanted with a cochlear implant. Multislice CT was performed for adequate depiction of the cochlear implant. All scans were analyzed on a viewing workstation. After mid-modiolar reconstruction we were able to identify the intracochlear electrode position relative to the scala tympani and scala vestibuli. This was possible in both the implanted isolated temporal bone and the fresh human cadaver head. The feasibility of imaging the electrode position of the cochlear implant within the intracochlear spaces is shown with multislice CT. An imaging protocol is suggested.

Audiological performance after cochlear implantation: a 2-year follow-up in children with inner ear malformations.

CONCLUSIONS: Open-set speech perception in children with an inner ear malformation is equal to that of other congenitally deaf children after an average of 2 years follow-up. OBJECTIVE: To analyze audiological performance after cochlear implantation in a sample of children with radiographically detectable malformations of the inner ear compared to performance in prelingually deafened children at large. MATERIALS AND METHODS: Nine children with osseous inner ear malformations were compared to 22 congenitally deaf children, all of whom underwent cochlear implantation. All subjects were tested on their electrical evoked compound action potential. Speech perception tests were performed using the monosyllabic trochee polysyllabic test without visual support and the open-set monosyllabic wordlist. RESULTS: In all, 20% of the congenitally deaf children in our center study have inner ear abnormalities. Inner ear malformations were limited to incomplete partition of the cochlea; none of the subjects had common cavity malformations. Electrical compound action potentials were successfully recorded in both groups intraoperatively. Speech perception tests on open-set speech yielded an average of 48.8% (SD 21.2%) in the group of children with inner ear malformations vs 54.5% (SD 21.1%) in congenitally deaf children. In four of nine cases with an inner ear malformation we encountered a minor CSF leak.

Intra- and postoperative electrode impedance of the straight and Contour arrays of the Nucleus 24 cochlear implant: relation to T and C levels.

The objective of this study was to investigate electrode impedance in cochlear implant recipients in relation to electrically evoked stapedius reflex measurements during surgery, and to electrode design, stimulation mode, and T and C levels over a nine month period after surgery. Seventy-five implant recipients, implanted with a Nucleus straight electrode array or a Contour array, were included. The results show that: (1) during surgery electrode impedance decreases markedly after electrically evoked stapedius reflex measurements, (2) after surgery, during the period without stimulation until speech processor switch-on, impedance increases, (3) after processor switch-on impedance decreases. The lower impedance values after a period of stimulation are found at the higher T and C levels. Impedances of the straight array electrodes are lower than those of the Contour array. The difference corresponds mainly to their respective surface areas. In addition, the straight array shows a larger increase of impedance in the apical direction than the Contour array, probably because of the larger fluid environment around the basal electrodes of the straight array.

Cochlear implantation in 53 patients with otosclerosis: demographics, computed tomographic scanning, surgery, and complications.

OBJECTIVES: To collect data from a large number of cochlear implant recipients with otosclerosis and to make an assessment of these patients' clinical characteristics, computed tomographic scans, surgical findings, and complications, and to quantify the occurrence of postoperative facial nerve stimulation. STUDY DESIGN: Retrospective multicenter study. PATIENTS: Fifty-three patients with otosclerosis from four cochlear implant centers in the United Kingdom and The Netherlands were reviewed. Sixty surgical procedures were performed in these patients: 57 devices were placed in 56 ears. RESULTS: The computed tomographic imaging demonstrated retrofenestral (cochlear) otosclerotic lesions in the majority of patients. Although not statistically significant, the extent of otosclerotic lesions on the computed tomographic scan as categorized in three types tends to be greater in patients with rapidly progressive hearing loss, in patients in whom there is surgically problematic insertion of the electrode array, and in patients with facial nerve stimulation. In four patients, revision surgery had to be performed. Twenty of 53 (38%) patients experienced facial nerve stimulation at various periods postoperatively. CONCLUSION: Cochlear implant surgery in patients with otosclerosis can be challenging, with a relatively high number of partial insertions and misplacements of the electrode array demanding revision surgery. A very high proportion of patients experienced facial nerve stimulation mainly caused by the distal electrodes. This must be discussed with patients preoperatively.

Semilongitudinal and axial CT planes in assessing cochlear patency in cochlear implant candidates.

OBJECTIVE: To investigate how cochlear patency as seen on computed tomography (CT), using axial plus semilongitudinal planes, is correlated with findings at surgery in cochlear implant patients. METHODS: Pre-operative CT scans of 45 patients were reviewed by three, independent observers. They classified the cochlear patency and recorded the location of any suspected decreased patency. The results were compared with the findings noted during surgery. RESULTS: In nine patients a decreased cochlear patency was found at surgery. The sensitivity and specificity of CT assessment were, respectively, 56-33-11% and 100-86-94%. The interobserver reproducibility is reflected in a mean kappa of 0.46. The sensitivity increased when only patients suffering from post-meningitic deafness were considered. CONCLUSION: Our study suggests that CT scans can be useful in assessing cochlear patency, especially in patients with post-meningitic deafness. This good performance might be explained by the combined use of scans in semilongitudinal and axial planes.

Electrode insertion depth in cochlear implantees estimated during surgery, on plain film radiographs and with electrode function testing.

Three methods of determining electrode insertion depth in cochlear implantees are studied: intraoperative counting of inserted electrodes, plain film radiography using Stenvers projection and postoperative electrode function testing. In 16 cases the number of electrodes inserted in the cochlea were counted both by the surgeon at surgery and by two independent observers on plain film radiographs using Stenvers projections. The electrode function was tested postoperatively. The differences between the three methods in estimation of the number of intracochlear electrodes were analyzed with t-tests, and 95% confidence intervals (95% CI) of the mean differences were calculated. The mean difference between the radiograph observers was 0.25 electrode (95% CI, -0.69 to 1.19 electrodes.) The mean difference between radiography observations and the surgical counts was 0.60 electrode (95% CI, -0.71 to 1.91 electrodes.) The mean difference between surgical counting and electrode function testing was 0.40 electrode (95% CI, -0.66 to 1.46 electrodes.) The mean difference between radiograph observations and electrode function testing was 0.50 electrode (95% CI, -0.51 to 1.51 electrodes.) No significant differences existed between the three methods. Our findings showed similar results in estimating electrode array insertion depth with the three methods. Plain film radiography using Stenvers projection is satisfactory if imaging is indicated for determining the number of inserted electrodes.

Cochlear orientation and dimensions of the facial recess in cochlear implantation.

OBJECTIVE: To study the dimensions of the facial recess and the spatial relationship between the facial recess and the cochlea, using CT scanning in cochlear implantees. METHOD: In 29 cochlear implantees, preoperative CT scans of the temporal bone were compared with findings done at surgery. The dimensions of the facial recess and the relationship between the facial recess and the cochlea were both measured on a viewing station and classified on printed films by 3 blinded and independent reviewers. RESULTS: No significant relations could be found between either intuitive classification of facial recess width or electrode array insertion feasibility and the measurements with the viewing station. The 3 reviewers had large interobserver variability. In 5 cases, neither intuitive review of the CT scans nor viewing station measurements could predict any of the problems encountered during surgery. CONCLUSION: Our findings show that intuitive review was not reliable in classifying facial recess width. Viewing station measurements, in classifying the spatial relation between the facial recess and the cochlear basal turn, need a more detailed review in terms of the relationship with the operation direction and the orientation of the basal turn of the cochlea. Advanced imaging techniques, specifically multislice CT, might improve the diagnostic capabilities.