Intraoperative recordings of electromyogenic responses from the human stapedius muscle.

Following surgical implantation of a cochlear implant, the external processor must be programmed individually, which is typically achieved by behavioral measurements, with the user indicating the perceived loudness between the threshold and the maximum comfort levels (MCLs). However, the stapedius reflex measurement could be used instead, as the basis for programming the fitting maps. The electrically evoked stapedius reflex threshold is known to have a high correlation with the MCLs and thus is used as an objective tool to determine the MCL, especially in children and non-cooperative patients. Previous studies demonstrated that the electromyogenic (EMG) activity of the stapedius muscle could be measured to determine stapedius reflex responses. The objective of this study was to demonstrate that intraoperative EMG recordings from the stapedius muscle could be performed with an EMG recording electrode designed for chronical implantation. Ten adult subjects with single sided deafness (SSD) participated in this study. The study was split up into a pre-, intra- and postoperative phase. In the preoperative phase the subjects were screened for the presence of the acoustic stapedius reflex by using a standard tympanometer in the ear to be implanted, while the contralateral ear was stimulated acoustically. During the intraoperative phase an EMG recording electrode was placed in the stapedius muscle and EMG responses were recorded during acoustical and electrical stimulation. The surgical procedure consisted of two interconnected procedures: A classical surgical approach for cochlear implantation with two additional surgical steps, and the temporary placement of an EMG recording electrode in the stapedius muscle made through an opening in the pyramidal eminence, allowing EMG recordings. The postoperative phase was used to evaluate the preservation of the stapedius reflex postoperatively at 1- and 6-months with contralateral acoustic and ipsilateral electrical stimulation. The EMG recording electrode could successfully be placed in the stapedius muscle in all subjects and was able to reliably record EMG signals from the stapedius muscle elicited by acoustic and electrical stimulation. Overall, EMG recordings were obtained intraoperatively in all subjects tested (8 out of 8 subjects). Contralateral acoustic stapedius reflexes were obtained in 6 out of 8 subjects and ipsilateral electrical stapedius reflex in 7 out of 8 subjects. In the postoperative phase, the preservation of the postoperative reflex was observed in 6 out of 10 subjects 1-month after surgery and in 8 out of 10 subjects 6-months after surgery. The study showed that intraoperative EMG recordings from the stapedius muscle can be performed with an EMG recording electrode designed for chronical implantation. The minimally invasive procedure is promising; in particular with regard to the future perspective of measurements in the long-term with an integrated closed-loop self-fitting system.

Comparison of electrophysiological parameters between perimodiolar and lateral wall electrodes in paediatric cochlear implant users.

PURPOSE: (1) To compare the in vivo impedances of electrical contacts of the Nucleus Contour Advance (CA) perimodiolar electrodes and the Nucleus Slim Straight (SS) lateral wall electrodes. (2) To compare the relation between the electrode contact impedances and the behavioural T-/C-levels for both types of electrodes. METHODS: Retrospective case review in two quaternary otologic referral centres was performed. Data on the impedance of the electrode contacts and the T-/C-levels have been collected from 70 consecutive paediatric CI patients. RESULTS: (1) SS electrodes show significantly higher impedance values of the contacts compared to the CA electrodes. This can be explained by differences in the active surface of the electrode contacts and is true for the whole electrode arrays. (2) There are significant negative correlations observed between the impedances of the electrode contacts and the behaviourally measured T-/C-levels. (3) The strength correlation between the electrode impedances and the behavioural T-/C-levels is significantly higher and the T-/C-level variability is lower for the perimodiolar CA electrodes than for the lateral wall SS electrodes. CONCLUSIONS: There exist significant differences in the contact impedance between different cochlear implant electrode arrays. These differences could influence the implant programming parameters and should be considered in any protocols related to automatic implant programming based on objective measures. The predictive value of the electrode impedances for the behavioural T-/C-levels is higher for the perimodiolar CA electrodes than for the lateral wall SS electrodes.

Influence of the pre- or postlingual status of cochlear implant recipients on behavioural T/C-levels.

INTRODUCTION: Previous auditory experience modifies the sensitivity of the auditory cortex to the afferent activity of the auditory pathways and may influence the threshold (T) and comfort (C) levels in patients receiving a cochlear implant (CI). Literature data on this particular topic is very scarce. OBJECTIVE: This study aimed to evaluate the differences in T/C-levels between pre- and postlingually implanted cochlear implant patients. METHODS: Retrospective case review in a quaternary otologic referral centre was performed. Data on the T/C-levels have been collected in 90 consecutive CI patients divided into 2 groups. Group 1 comprised 16 prelingually deaf children implanted between 8 months and 10 years of age. Group 2 comprised 74 postlingually deaf adults (average age of 62 years). All patients were users of the Nucleus 24RECA (Freedom, Contour Advance-of-Stylet electrode) cochlear implant. All measurements were performed at the fifth implant programming session at 4-6 months after surgery, when stable T/C thresholds have already been obtained. RESULTS: The behavioural C-levels present important and statistically significant differences between the pre- and postlingually implanted patients for all electrode contacts that could reach 30 CL. For the T-levels the observed differences were smaller and statistically insignificant for most electrode contacts. CONCLUSIONS: The previous auditory experience (pre- or postlingual deafness) seems to be an independent parameter influencing the T/C-levels in patients receiving a CI. Together with the electrode contact impedance and the contact position in the electrode array it can explain up to 37% of the variability in the definition of the C-levels. The fact that the stabilised C-levels measured 4-6 months postoperatively can be up to 30 CL higher in the prelingually deaf patients than in the postlingual ones results also in a much higher dynamic range observed in prelingual subjects. Therefore implant programming of the prelingual patients should be very cautious in order to avoid the risk of overstimulation.

Prediction of Behavioral T/C Levels in Cochlear Implant Patients Based Upon Analysis of Electrode Impedances.

BACKGROUND: Fitting cochlear implants in babies and noncooperative patients is cumbersome and time consuming. Therefore, objective parameters have been sought in order to predict the subjective threshold (T) and maximum comfort (C) levels. Measurements of the electrically evoked compound action potentials (ECAPs) have been widely used for this purpose, yet the correlation between these objective measures and the subjective T/C levels is weak to moderate. PURPOSE: This article aims (1) to evaluate correlations between the subjective parameters of the fitting maps such as thresholds (T level) and maximum comfort levels (C level), the impedance of the electrode contacts, and the ECAP thresholds, and (2) to compare the value of the electrode impedances and the ECAP measures for prediction of the T/C levels. RESEARCH DESIGN: Case review study in a quaternary otologic referral center. STUDY SAMPLE: Ninety-eight consecutive CI patients were enrolled. The average age of the patients was 49 years. All patients were users of the Nucleus 24RECA (Freedom, Contour Advance-of-Stylet electrode) cochlear implant. DATA COLLECTION AND ANALYSIS: Data on impedance of the electrode contacts and the behavioral T/C levels at the first fitting session (2-5 weeks after surgery) and at the 5th fitting session (4-6 months after surgery) have been retrospectively collected in 98 consecutive CI patients. Additionally, the intraoperative impedance values and the ECAP thresholds (tNRT) have been recorded. RESULTS: Impedances of electrode contacts show significant strong negative correlations with the stabilized T/C levels at 4 to 6 months after implantation and are an important predictor for the behavioral T/C levels. They can explain R 2 = 28 to 41% of the variability of the behavioral T/C levels. In multiple regression analysis electrode contact impedances can explain twice as much of the variability of the stabilized T/C levels than the tNRT values. The electrode impedances together with the tNRT values are able to explain R 2 = 37 to 40% of the global variability of the T/C levels while the tNRT thresholds solely are able to explain only R 2 = 5 to 14% of the T/C levels variability. CONCLUSION: Impedances of electrode contacts correlate strongly with the stabilized behavioral T/C levels and may be used as an objective measure for fitting of cochlear implants.

Prognostic significance of electrophysiological tests for facial nerve outcome in vestibular schwannoma surgery.

OBJECTIVE: To assess the prognostic significance of pre-operative electrophysiological tests for facial nerve outcome in vestibular schwannoma surgery. METHODOLOGY: Retrospective study design in a tertiary referral neurology unit. We studied a total of 123 patients with unilateral vestibular schwannoma who underwent microsurgical removal of the lesion. Nine patients were excluded because they had clinically abnormal pre-operative facial function. Pre-operative electrophysiological facial nerve function testing (EPhT) was performed. Short-term (1 month) and long-term (1 year) post-operative clinical facial nerve function were assessed. RESULTS: When pre-operative facial nerve function, evaluated by EPhT, was normal, the outcome from clinical follow-up at 1-month post-operatively was excellent in 78% (i.e. HB I-II) of patients, moderate in 11% (i.e. HB III-IV), and bad in 11% (i.e. HB V-VI). After 1 year, 86% had excellent outcomes, 13% had moderate outcomes, and 1% had bad outcomes. Of all patients with normal clinical facial nerve function, 22% had an abnormal EPhT result and 78% had a normal result. No statistically significant differences could be observed in short-term and long-term post-operative facial function between the groups. CONCLUSION: In this study, electrophysiological tests were not able to predict facial nerve outcome after vestibular schwannoma surgery. Tumour size remains the best pre-operative prognostic indicator of facial nerve function outcome, i.e. a better outcome in smaller lesions.

Magnetic resonance imaging in patients with meningitis induced hearing loss.

The aim of this multicentre study was to compare T1 with T2 weighted MRI scans of the labyrinth after meningitis and to investigate whether waiting with scanning improved the reliability of diagnosing an ongoing process such as cochlear osteogenesis. Forty-five patients were included who suffered from meningitis induced hearing loss (radiological imaging <1 year after meningitis). Twenty-one gadolinium enhanced T1 and 45 T2 weighted MRI scans were scored by two radiologists regarding the condition of the labyrinth. These radiological observations were compared with the condition of the cochlea as described during cochlear implantation. A higher percentage of agreement with surgery was found for T2 (both radiologists 73%) than for T1 weighted MRI scans (radiologist 1: 62%, radiologist 2: 67%), but this difference is not significant. There was no significant difference between early (0-3 months) and late (>3 months) scanning, showing that radiological imaging soon after meningitis allows early diagnosis without suffering from a lower agreement with surgical findings.

Transient depression of inner ear function after stapedotomy: skeeter versus CO(2) laser technique.

Performing stapes surgery for otosclerosis is known to be potentially irreversibly harmful to the inner ear function in about 1% of the cases. An early postoperative transient depression of the bone conduction thresholds is frequently detected after stapes surgery. The purpose of this study was to compare the evolution of bone conduction thresholds after primary stapedotomy with two different techniques: skeeter versus CO(2) laser stapedotomy. Audiological data of 336 otosclerosis operations performed by 2 surgeons between 1997 and 2003 were subjected to analysis. The calibrated hole in the footplate was performed randomly either with the skeeter drill or with the CO(2) laser. Preoperative bone conduction thresholds were compared with the postoperative levels (day 2-3, week 2, week 6 and month 6) in all patients. Evolution of the bone conduction was compared for the two studied subgroups (laser versus skeeter).

High resolution micro-CT scanning as an innovative tool for evaluation of the surgical positioning of cochlear implant electrodes.

X-ray microtomography (micro-CT) is a new technique allowing for visualization of the internal structure of opaque specimens with a quasi-histological quality. Among multiple potential applications, the use of this technique in otology is very promising. Micro-CT appears to be ideally suited for in vitro visualization of the inner ear tissues as well as for evaluation of the electrode damage and/or surgical insertion trauma during implantation of the cochlear implant electrodes. This technique can greatly aid in design and development of new cochlear implant electrodes and is applicable for temporal bone studies. The main advantage of micro-CT is the practically artefact-free preparation of the samples and the possibility of evaluation of the interesting parameters along the whole insertion depth of the electrode. This paper presents the results of the first application of micro-CT for visualization of the inner ear structures in human temporal bones and for evaluation of the surgical positioning of the cochlear implant electrodes relative to the intracochlear soft tissues.

Overview of safety imaging methods for newly designed cochlear implant electrodes.

Different individual test methods and protocols have been reported for the in-vitro evaluation of temporal bones implanted with newly designed cochlear implant electrodes, prior to human implantation. In practice, however, these methods may not always give the required information. In this study, a large battery of tests has been evaluated using the electrode as a fixed parameter. Standard clinical x-ray gave the best information to evaluate the electrode's position. Light microscopic evaluation and polishing technique studies proved to be the most valuable techniques to evaluate endocochlear damage.

The LAURA Pediatric Cochlear Implant Program in Antwerp: what have we learnt in 5 years?

The LAURA Cochlear Implant Program at the University of Antwerp was initiated 5 years ago. Up to now 50 children have received the LAURA cochlear implant (Philips Hearing Implants). Our accumulated experience in selecting the patients, counselling their parents, implanting and fitting the device allowed us to gradually modify the inclusion/exclusion criteria for cochlear implantation and achieve very rewarding results. The most important change was the gradual shift towards a younger age at implantation, our youngest implantee being 11 months old. In this paper we describe the rationale for this change, as well as the prerequisites for a successful pediatric cochlear implant program.

New developments in cochlear implants.

Essential to improve the performance with cochlear implants is a better control of the electrode-nerve interface. The long-term stability of the electrode characteristics has to be guaranteed. Most important herein is to have a low and stable electrical impedance and to prevent fibrosis. Results of electrode coating and fibrosis-inhibiting products are described. To assess the properties of the electrode-nerve interface such as stimulation threshold, spatial selectivity and channel interaction, the electrically evoked compound action potential is measured. The measurement paradigm and the first results are described. Models of auditory nerve response to electrical stimulation can be used as a tool for cochlear implant fitting. A simple model is proposed and its predictions are compared with measured responses.