Gamma knife surgery of vestibular schwannomas: volumetric dosimetry correlations to hearing loss suggest stria vascularis devascularization as the mechanism of early hearing loss.

OBJECTIVE: Determine which variables are correlated with early hearing changes after gamma knife surgery of vestibular schwannomas (VSs). STUDY DESIGN: Prospective clinical study of hearing outcomes, radiation dosimetry, conformity, and tumor size of all sporadic unilateral VS patients treated between June 2000 and July 2009. SETTING: Tertiary referral center. PATIENTS: : Fifty-nine VS patients with at least 6 months of follow-up data were studied. INTERVENTIONS: Audiometry and imaging were performed to determine auditory thresholds, speech discrimination, and tumor size. Radiation doses to 5 volumes were measured. MAIN OUTCOME MEASURES: Pretreatment and posttreatment comparisons were performed with regard to change in tumor size; radiation dose to specific volumes including the internal auditory canal, cochlea, basal turn of the cochlea, and modiolus; and conformity of the treatment. RESULTS: The mean follow-up was 63.76 months (standard deviation, ±29.02 mo; range, 9-109 mo). The median follow-up was 65.5 months. A statistically significant association between maximum radiation dose to the cochlea volume and 3-frequency pure-tone average in patients starting with 50 dB or lesser PTA3 was demonstrated using linear regression analysis. CONCLUSION: Longitudinal changes in hearing occur over time, with the largest changes seen in the first 12 months after treatment. With our study outcomes as basis, limiting the dose of radiation to the cochlea to no more than 4 Gy would likely reduce vascular injury to the stria vascularis and improve hearing outcomes. Shielding the cochlea during the treatment planning process would be one mechanism to accomplish this goal.

Association of hearing loss with PHACE syndrome.

BACKGROUND: PHACE syndrome describes a spectrum of anomalies associated with large facial infantile hemangiomas and characterized by posterior fossa malformations, hemangiomas, arterial anomalies, coarctation of the aorta and cardiac defects, and eye abnormalities. With improved recognition and imaging practices of infants with PHACE syndrome, additional associations have been identified. To our knowledge, the potential association of ipsilateral hearing loss and PHACE syndrome has not been previously emphasized. OBSERVATIONS: We describe 6 patients, 4 with definite and 2 with probable PHACE syndrome, according to the new diagnostic criteria, and associated auditory deficiencies. One patient had isolated conductive hearing loss; 2 patients had isolated sensorineural hearing loss; 1 patient had mixed hearing loss (both conductive and sensorineural components); and 1 patient had hearing loss that was inconclusive at the time. Also, 1 patient had conductive loss and auditory neuropathy and auditory dyssynchrony. Four of the 6 patients had magnetic resonance imaging features of lesions consistent with intracranial hemangiomas involving auditory structures. All 6 patients had facial hemangiomas in a nearly identical distribution ipsilateral to the ear with the hearing loss, with involvement of the proposed facial segments S1 and S3, the affected ear, the periauricular region, and the midoccipital area of the scalp. CONCLUSIONS: There is an underrecognized risk of hearing loss in patients with PHACE syndrome, although the exact nature of such deficiencies can vary. Patients with PHACE syndrome who have cutaneous hemangiomas involving the ear should be evaluated for intracranial hemangiomas and monitored for hearing loss. Early detection and therapy of intracranial hemangiomas may slow or stop tumor growth, resultant hearing loss, and structural damage.

Case-control analysis of cochlear implant performance in elderly patients.

OBJECTIVE: To characterize speech perception performance in elderly cochlear implant users compared with younger adult users. DESIGN: Case-control retrospective analysis from January 1, 1999, to January 28, 2008. SETTING: Tertiary care, academic practice cochlear implant program. PATIENTS: Medical records for 78 patients with age at implantation of 65 years or older were analyzed for ear-specific preimplantation speech perception performance, length of deafness, age at implantation, and 1-year postimplantation speech perception performance. A subset of 28 elderly patients with complete data was matched to 28 younger adult patients (age at implantation, 18-64 years) for preimplantation performance using the Hearing in Noise Test-Quiet scores (mean, 22% and 23%, respectively). MAIN OUTCOME MEASURE: One-year postimplantation performance on word and sentence testing. RESULTS: Within the elderly cohort, the Consonant-Nucleus-Consonant and Hearing in Noise Test-Quiet scores were not affected by age. The Hearing in Noise Test-Noise scores trended downward with increasing age but did not reach statistical significance (P = .052). Of the matched older and younger patients, 55 of 56 showed improvement in their 1-year postimplantation compared with preimplantation Hearing in Noise Test-Quiet scores, with better preimplantation performance predictive of better postimplantation performance, independent of age at implantation (P = .02). Group comparisons, however, revealed poorer postimplantation scores overall for the elderly patients compared with the younger ones for the Hearing in Noise Test-Quiet (70% vs 83%; P = .02) and the Consonant-Nucleus-Consonant test (38% vs 53%; P = .02). CONCLUSIONS: Elderly patients benefit significantly from cochlear implantation. Compared with a younger cohort matched for preimplantation performance, however, their postimplantation scores are significantly lower on some measures. These results may provide guidelines for candidacy and counseling regarding elderly patients with cochlear implants.

Effects of high-rate pulse trains on electrode discrimination in cochlear implant users.

Overcoming issues related to abnormally high neural synchrony in response to electrical stimulation is one aspect in improving hearing with a cochlear implant. Desynchronization of electrical stimuli have shown benefits in neural encoding of electrical signals and improvements in psychophysical tasks. In the present study, 10 participants with either CII or HiRes 90k Advanced Bionics devices were tested for the effects of desynchronizing constant-amplitude high-rate (5,000 Hz) pulse trains on electrode discrimination of sinusoidal stimuli (1,000 Hz). When averaged across the sinusoidal dynamic range, overall improvements in electrode discrimination with high-rate pulses were found for 8 of 10 participants. This effect was significant for the group (p = .003). Nonmonotonic patterns of electrode discrimination as a function of sinusoidal stimulation level were observed. By providing additional spectral channels, it is possible that clinical implementation of constant-amplitude high-rate pulse trains in a signal processing strategy may improve performance with the device.

Soft cochlear implantation: rationale for the surgical approach.

Recent advances in cochlear implant technology have focused renewed attention on the preservation of residual hearing. The focus on preservation of residual hearing is driven by the concept of electroacoustic stimulation. This option depends on the insertion of a short cochlear implant electrode into the basal region of the cochlea while preserving native function in the apical region. The desire to preserve residual hearing has led to the development of the soft-surgery cochlear implantation technique. Here, the authors evaluate its various components. Avoiding entry of blood into the cochlea and the use of hyaluronate seem to be reasonably supported, whereas the use of topical steroids is unlikely to be beneficial. The site of entry into the cochlea, the use of contoured or straight devices, and the depth of insertion are also evaluated. The authors highlight the importance of systematic recording of outcomes and surgical events.

Electrically evoked auditory brainstem responses in adults and children: effects of lateral to medial placement of the nucleus 24 contour electrode array.

OBJECTIVE: Previous electrophysiologic studies of electrode placement within the scala tympani in both animals and humans have shown effects on neural responses to electrical stimulation. The specific effects, however, may be dependent on electrode design, the location of an electrode along the array, and the method of perimodiolar positioning. The present study compares the effects of lateral and medial positioning of the Nucleus Contour electrode array on electrophysiologic responses in adult and pediatric subjects. STUDY DESIGN: Prospective clinical study. SETTING: Comprehensive Cochlear Implant Program/Tertiary Referral Center. PATIENTS: Subjects were adults (n = 15) and children (n = 20) who were consecutively implanted at our center with the Nucleus 24 Contour device. INTERVENTION: Rehabilitative. MAIN OUTCOME MEASURES: Intraoperative electrically evoked auditory brainstem responses (EABRs) were recorded within subjects for lateral and medial placement of the electrode array. Effects of electrode placement on EABR Wave V threshold and suprathreshold amplitude were measured. RESULTS: Group analyses showed significant decreases in EABR threshold and significant increases in EABR amplitude across all electrodes with medial electrode placement. The effects differed across electrode locations for the adult and pediatric subjects. No significant changes in Wave V input/output function slope were found. CONCLUSION: Medial electrode placement from stylet removal with the Nucleus 24 Contour array results in an increased neural response compared with the lateral condition as demonstrated by lower threshold and larger suprathreshold amplitude of the EABR. Possible clinical implications of these findings are lower psychophysical threshold and comfortable levels with medial cochlear electrode position.

Gamma Knife surgery of vestibular schwannomas: longitudinal changes in vestibular function and measurement of the Dizziness Handicap Inventory.

OBJECT: Gamma Knife surgery (GKS) is one of the methods available to treat vestibular schwannomas (VSs), in addition to microsurgical resection; however, clear information regarding balance function outcomes and the impact of treatment on patients' quality of life over time remains an important clinical need. The purpose of this study was to assess the longitudinal balance outcomes and Dizziness Handicap Inventory (DHI) following GKS for VSs. METHODS: This was a prospective clinical study of balance outcomes in all patients with VSs treated in the Acoustic Neuroma and Skull Base Surgery Program at a tertiary referral center by the senior author and the Gamma Knife team between June 2000 and May 2008. The main outcome measures included preoperative vestibular testing and postoperative caloric testing performed at 6-month intervals to determine vestibular function. The DHI questionnaires were administered retrospectively to assess the impact of GKS on self-perceived disability. RESULTS: Between June 2000 and May 2008, 55 sporadic VSs were treated. There was a >or= 60-month follow-up available in 27 of these patients, >or= 48 months in 32, >or= 36 months in 38, >or= 24 months in 43, >or= 12 months in 51, and >or= 6 months in 54 (1 patient was excluded from the analysis because the follow-up was < 6 months). Various patterns of changes in vestibular function were observed in either positive or negative directions. A significant difference in total DHI score was seen only in the elderly (> 65 years old) patients pre-GKS compared with post-GKS (t = 1.34, p = 0.05). CONCLUSIONS: Longitudinal changes in vestibular function occur over time, with the largest changes seen in the first 6 months after treatment. Potential for clinical intervention, such as vestibular rehabilitation therapy, exists during this interval; however, larger cohorts must be studied to determine the timing and efficacy of this intervention. The statistically significant improvement in the DHI score in the patient cohort > 65 years old treated with GKS suggests that this group may benefit from this option when considering the symptom of dizziness.

Quantitative analysis of electrically evoked auditory brainstem responses in implanted children with auditory neuropathy/dyssynchrony.

OBJECTIVE: Cochlear implantation is a common treatment approach for children with auditory neuropathy/dyssynchrony (AN/AD) who do not benefit from hearing aids. The auditory brainstem response (ABR) is a measure of neural synchrony along the auditory pathway up through the brainstem. By definition, acoustically evoked ABR is absent in AN/AD, however, ABR can be elicited by electrical stimulation through the cochlear implant (electrically evoked ABR [EABR]). Reports of EABR with AN/AD to date have been primarily descriptive in nature. The objective of this study was to quantify EABR wave V measures in implanted children with and without AN/AD. STUDY DESIGN: Retrospective analysis of EABR waveforms from March 2000 through February 2005. SETTING: Comprehensive Cochlear Implant Program/Tertiary Referral Center. PATIENTS: Pediatric cochlear implant users of two etiologic groups: congenital AN/AD (n = 5) and other congenital profound sensorineural hearing loss (n = 27). INTERVENTION: Diagnostic. MAIN OUTCOME MEASURES: Intraoperative EABR wave V threshold, suprathreshold amplitude, and latency measures were compared between groups. RESULTS: The EABR threshold and suprathreshold amplitude measures across the population were variable regardless of etiology. With some exceptions, a trend was observed for the AN/AD group that included average or below-average thresholds and below-average suprathreshold response amplitudes. CONCLUSION: Cochlear implantation can provide synchronous neural responses to auditory stimulation in AN/AD, as previously known. The quantification of EABR measures in this study indicates that subjects with AN/AD have sufficient neural sensitivity to electrical stimulation, however, they may experience less robust neural responses at suprathreshold levels. Given the heterogeneity of potential causes of AN/AD, however, caution needs to be applied when grouping this population for analyses.

Feasibility of auditory cortical stimulation for the treatment of tinnitus.

OBJECTIVES: To investigate the feasibility and safety of an implantable epidural cortical stimulator for the treatment of severe tinnitus. STUDY DESIGN: Prospective, controlled, single-blinded study of cortical stimulation for 4 weeks, and then an open-label stimulation period. SETTING: Tertiary care referral center. PATIENTS: Adults (n = 8) with constant tinnitus of at least 1 year with a tinnitus reaction questionnaire score greater than 33. Tinnitus was predominantly unilateral with a frequency less than 8,000 Hz. INTERVENTIONS: Surgical implantation of an investigational epidural electrode over the posterior superior temporal gyrus using functional magnetic resonance imaging targeting. A 2-week stimulation period alternated with a 2-week sham period in random order to which subjects were blinded. This was followed by continuous stimulation with parameter adjustments to maximize tinnitus suppression. MAIN OUTCOME MEASURE: Subjective rating of tinnitus severity, loudness, and device efficacy. Objective measures of hearing thresholds, tinnitus frequency, loudness, and minimum masking levels. Outcome measures using the Tinnitus Handicap Questionnaire, Tinnitus Reaction Questionnaire, and Beck Depression Inventory. RESULTS: There were no effects of stimulation during the 4-week blinded period. With continuous chronic stimulation, 2 patients had persistent reduction of pure-tone tinnitus, and 6 patients had short periods of total tinnitus suppression. Significant improvements in the Beck Depression Inventory and tinnitus questionnaires were found, although objective measures of tinnitus loudness remained fairly stable. No surgical or stimulation-related complications were noted. CONCLUSION: Chronic electrical stimulation of the secondary auditory cortex seems safe and warrants further investigation as a potential therapeutic intervention for the suppression of tinnitus.

More challenging speech-perception tasks demonstrate binaural benefit in bilateral cochlear implant users.

OBJECTIVE: Preliminary studies show that bilateral cochlear implantation improves speech-recognition ability in many subjects; however, the magnitude of this improvement has been variable. The objective of our research was to explore means to better differentiate the binaural benefit that many patients who receive bilateral cochlear implants (CIs) describe. HYPOTHESIS: Binaural improvements in speech-perception performance will be consistently evident across patients when they are tested in more challenging listening situations. DESIGN: This was a prospective clinical study. Speech-perception performance was compared between the unilateral and bilateral cochlear implant conditions. Because the purpose was to investigate testing parameters that would demonstrate binaural benefit, word- and sentence-recognition tests were administered under several stimulation conditions: with and without noise and at three presentation levels. In addition, all subjects completed the Abbreviated Profile of Hearing Aid Benefit as a measure of subjective benefit. Subjects were adult cochlear implant recipients. Three device manufacturers were represented (Advanced Bionics Corporation, Cochlear Americas, and the Med-El Corporation); three patients received simultaneous implantation, and the other four patients received sequential CIs. The setting was a comprehensive cochlear implant program/tertiary referral center. The main outcomes measures were speech-recognition scores in percent correct, mean score difference for unilateral versus bilateral conditions, and subjective benefit scores. RESULTS: The most significant improvements in binaural cochlear implant use were found when subjects were tested with sentence material presented at 60 dB SPL with a +8 dB signal-to-noise ratio. Six of seven subjects showed significant binaural improvement, with a mean improvement score of 12.43% (SD = 5.32). All subjects preferred the binaural listening condition. Measured improvements in quality of life were seen. CONCLUSIONS: Preliminary study findings suggest that significant cochlear implant binaural benefit in speech perception may be observed when testing in more difficult listening situations (i.e., lower presentation levels and in noise). According to the outcome of our study, testing the binaural benefit of CIs requires consideration of suitable test materials and stimulation parameters.

Biomechanical strength of reconstruction plates when used for medial support of MED-El cochlear implants: implications for diagnostic MRI.

PURPOSE: It is hypothesized that a mesh reconstruction plate designed to fit a cochlear implant (CI) internal device will provide immediate structural support to the site of the implant and that this strength far exceeds the forces induced by a 1.5-tesla MRI. PROCEDURES: Human calvarial specimens were drilled and plated with reconstruction mesh. Force was applied until failure was reached. RESULTS: Mean maximum force, mean force to first failure and mean displacement measures for group 1 (resorbable mesh, n = 10) were 302.9 N, 283.0 N and 3.05 mm, respectively. The mean maximum force for group 2 (0.4-mm titanium mesh, n = 10) and group 3 (0.6-mm titanium mesh, n = 8), were 121.3 and 234.0 N, respectively. Mean force of first failure was 92.0 N for group 2 and 164.8 N for group 3. CONCLUSIONS: The force required for failure of the mesh is significantly greater than the 0.17 N exerted on a CI magnet by a 1.5-tesla MRI scan.

Distortion of magnetic resonance images used in gamma knife radiosurgery treatment planning: implications for acoustic neuroma outcomes.

OBJECTIVE: To quantify the image distortion of our series of acoustic neuromas treated with gamma knife radiosurgery. STUDY DESIGN: Retrospective chart and digital radiographic file review with quantitative assessment of gamma knife treatment plans. SETTING: Tertiary referral center. PATIENTS: Patients undergoing gamma knife radiosurgery for the treatment of acoustic neuromas. INTERVENTION: Gamma knife radiosurgery. MAIN OUTCOME MEASURES: Gamma knife treatment plans containing magnetic resonance images were reviewed at each axial, sagittal, and coronal slice. The length of the greatest displacement of the treatment plan was measured and the volume of the treatment plan that fell outside of the internal auditory canal calculated. Known clinical measurements of audiometric, vestibular, facial, and trigeminal nerve functions were then compared with current measurements of tumor size. RESULTS: Twenty-two of the 23 patients had measurable image shifts on the axial images. The range of the image shift was 0 to 5.8 mm, with a mean shift of 1.92 +/- 1.29 mm (+/- standard deviation). Tumor volumes of the treatment plan that fell outside of the internal auditory canal ranged from 0 to 414 mm, with a mean of 90.5 mm. The mean percentage that fell outside of the internal auditory canal was 16.7% of total tumor volume (range, 2.4-77.6%). We could not draw any consistent correlations between degree of image shift and continued tumor growth or objective examination values. CONCLUSION: We have demonstrated a small but potentially significant shift in the treatment plan of gamma knife radiosurgery when based on magnetic resonance images. Although the image shift does not seem to affect the growth of the acoustic neuromas or auditory or facial nerve function, longer term follow-up is required to fully appreciate the true impact of this image shift.

Electrosurgery after cochlear implantation: eighth nerve electrophysiology.

HYPOTHESIS: Monopolar electrosurgery below the neck in cochlear implant recipients can be performed without damage to the internal cochlear stimulator, electrode array, and the cochlear nerve. STUDY DESIGN: Prospective pre- and postintervention electrically evoked compound action potential (ECAP) study of cochlear nerve function and behavioral sound perception assessment. METHODS: Neural response telemetry (NRT) was used to measure ECAPs before and after the use of monopolar electrosurgery during coronary artery bypass surgery to assess prosthetic device function and electrophysiologic function of the cochlear nerve. In addition, electrode voltage impedances and behavioral sound perception was measured at the same time intervals. RESULTS: ECAPs, behavioral sound perception, and electrode voltage impedances were within the normal range, within compliance, and similar preoperatively and on postoperative day 6. CONCLUSION: The studies reported herein were a series of measurements designed to test neural integrity and prosthetic device function before and after the use of monopolar electrosurgery. With appropriate precautions, use of monopolar electrosurgery below the neck in cochlear implant recipients can be performed safely.

Gamma knife radiosurgery for acoustic neuromas performed by a neurotologist: early experiences and outcomes.

OBJECTIVE: To assess early outcomes after Gamma knife radiosurgery of acoustic neuromas and other skull base tumors. BACKGROUND: Gamma knife radiosurgery is one of the available methods to treat acoustic neuromas, in addition to micro-surgical resection. Neuro-otologists have long been associated with microsurgical resection of these tumors; however, the application of Gamma knife radiosurgery to the treatment of these tumors by neuro-otologists has not been previously described. SETTING: Acoustic Neuroma and Skull Base Surgery Program / Tertiary Referral Center. STUDY DESIGN/PATIENTS/INTERVENTION: Prospective clinical study of all patients treated by the senior author and our gamma knife team beginning in June 2000. MAIN OUTCOME MEASURES: Preoperative MRI, audiometry, vestibular testing and facial nerve electromyography were completed. At six-month intervals postoperatively, audiometry, caloric testing and MRI were performed to determine thresholds and speech discrimination ability, vestibular function, and the size of the tumor. RESULTS: From June 2000 until March 2004, 38 patients were treated, and these included 33 acoustic neuromas, two meningiomas, one glomus jugulare tumor, and two facial neuromas. Greater than 36 month follow-up was available in 7 patients, > 24 months in 24, > 12 months in 31, and > 6 months in 34 patients. Statistically significant reduction in tumor size was seen over time, and tumor control was achieved in all but two patients. Various patterns of changes in auditory function, both in threshold and speech discrimination were observed in either positive or negative directions. CONCLUSIONS: Preliminary experience with Gamma knife radiosurgery indicates that this treatment method represents another option for neuro-otologists to use in managing patients with skull base tumors.

Fungal biofilm formation on cochlear implant hardware after antibiotic-induced fungal overgrowth within the middle ear.

Cochlear implantation in patients with chronic suppurative otitis media is managed with perioperative antibiotics; however, fungal overgrowth can occur. We present a child who received oral cefdinir and topical ofloxacin (Floxin). After 6 weeks, a fungal (Candida) biofilm was demonstrated on the implant surface. In this clinical setting, an antimicrobial strategy using an oral antifungal to prevent fungal overgrowth is a possibility.

Recognition of speech presented at soft to loud levels by adult cochlear implant recipients of three cochlear implant systems.

OBJECTIVE: The purpose of this study was to conduct a large-scale investigation with adult recipients of the Clarion, Med-El, and Nucleus cochlear implant systems to (1) determine average scores and ranges of performance for word and sentence stimuli presented at three intensity levels (70, 60, and 50 dB SPL); (2) provide information on the variability of scores for each subject by obtaining test-retest measures for all test conditions; and (3) further evaluate the potential use of lower speech presentation levels (i.e., 60 and/or 50 dB SPL) in cochlear implant candidacy assessment. DESIGN: Seventy-eight adult cochlear implant recipients, 26 with each of the three cochlear implant systems, participated in the study. To ensure that the data collected reflect the range of performance of adult recipients using recent technology for the three implant systems (Clarion HiFocus I or II, Med-El Combi 40+, Nucleus 24M or 24R), a composite range and distribution of consonant-nucleus-consonant (CNC) monosyllabic word scores was determined. Subjects using each device were selected to closely represent this range and distribution of CNC performance. During test sessions, subjects were administered the Hearing in Noise Test (HINT) sentence test and the CNC word test at three presentation levels (70, 60, and 50 dB SPL). HINT sentences also were administered at 60 dB SPL with a signal-to-noise ratio (SNR) of +8 dB. Warble tones were used to determine sound-field threshold levels from 250 to 4000 Hz. Test-retest measures were obtained for each of the speech recognition tests as well as for warble-tone sound-field thresholds. RESULTS: Cochlear implant recipients using the Clarion, Med-El, or Nucleus devices performed on average equally as well at 60 compared with 70 dB SPL when listening for words and sentences. Additionally, subjects had substantial open-set speech perception performance at the softer level of 50 dB SPL for the same stimuli; however, subjects' ability to understand speech was poorer when listening in noise to signals of greater intensity (60 dB SPL + 8 SNR) than when listening to signals presented at a soft presentation level (50 dB SPL) in quiet. A significant correlation was found between sound-field thresholds and speech recognition scores for presentation levels below 70 dB SPL. The results demonstrated a high test-retest reliability with cochlear implant users for these presentation levels and stimuli. Average sound-field thresholds were between 24 and 29 dB HL for frequencies of 250 to 4000 Hz, and results across sessions were essentially the same. CONCLUSIONS: Speech perception measures used with cochlear implant candidates and recipients should reflect the listening challenges that individuals encounter in natural communication situations. These data provide the basis for recommending new candidacy criteria based on speech recognition tests presented at 60 and/or 50 dB SPL, intensity levels that reflect real-life listening, rather than 70 dB SPL.

Response of the auditory nerve to sinusoidal electrical stimulation: effects of high-rate pulse trains.

Electrical stimulation of the auditory nerve produces highly synchronized responses. As a consequence, electrical stimulation may result in a narrow dynamic range of hearing and poor temporal representation of an input signal. The electrically evoked compound action potential (ECAP) is an electrophysiologic response used for neural assessment in individuals with auditory prostheses. Because the ECAP arises from the activity of a population of auditory nerve fibers, within- and across-fiber synchrony should be evident in the responses. Due to its clinical relevance and reflection of neural response properties, the ECAP is used in the present study to examine changes in neural synchrony. Empirical and modeled single-fiber data indicate that stimulation with electrical pulses of a sufficiently high rate may induce stochastic neural response behaviors. This study investigated the effects of adding high-rate conditioning pulses (5000 pps) on the ECAP in response to 100 Hz electrical sinusoids. The results showed that high-rate conditioning pulses increased response amplitudes at low sinusoidal levels and decreased the amplitudes at high sinusoidal levels, indicating a decrease in the slope of the ECAP growth functions to sinusoidal stimuli. The results are consistent with a hypothesis that high-rate conditioning pulses increase single-fiber relative spread (RS) in response to sinusoidal stimuli, and the effect is highly dependent on the level of the high-rate conditioning pulses.

Effect of magnetic resonance imaging on internal magnet strength in Med-El Combi 40+ cochlear implants.

OBJECTIVE: Magnetic resonance imaging (MRI) has been contraindicated when cochlear implants containing an internal magnet are in place because of concerns regarding torque, force, demagnetization, artifacts, induced voltages, and heating. The objective was to determine the magnetic field strength of Med-El Combi 40+ cochlear implant internal magnets after MRI studies. STUDY DESIGN/METHODS: Two fresh cadavers were used to study demagnetization using a repeated measures design and a magnetometer. Pre- and postMRI measurement of magnetic field strength was completed. Five sets of sagittal T1-weighted, axial T1-weighted, and axial T2-weighted sequences were performed on a cadaver at 0.2 Tesla in the device-up and device-down positions. In the other cadaver, 15 sets of sagittal T1-weighted, axial T1-weighted, and axial T2-weighted sequences were performed on a cadaver at 1.5 Tesla were conducted, 5 each with the head oriented at 80, 90, and 100 degrees rotated around the yaw plane (rotated around the z-axis). Subsequently, three cochlear implant patients completed 0.2 Tesla MRIs. For these patients, subjective and objective assessment of cochlear implant performance was performed. SETTING: Academic medical center. RESULTS: In the cadaver studies, analysis of variance showed no significant difference in the magnetic field strength after the 0.2 or 1.5 Tesla scans. There was no significant difference in the magnetic field strength for the three patients undergoing 0.2 Tesla MRIs and no adverse consequences, including no changes in telemetry, auditory sensations, nonauditory sensations, and sound quality. CONCLUSIONS: No significant demagnetization of the internal magnet occurred during repeated 1.5 Tesla MRI scans with the head orientations used in this study. In the cochlear implant patients, no significant demagnetization of the internal magnet occurred after a 0.2 Tesla MRI.

Auditory sensitivity in children using the auditory steady-state response.

OBJECTIVE: To determine the effectiveness of auditory steady-state response (ASSR) as a measure of hearing sensitivity in young children suspect for significant hearing loss. DESIGN: Within-subject comparisons of click auditory brainstem response (ABR) thresholds and ASSR thresholds. SUBJECTS: The study population comprised 42 children suspect for hearing loss and subsequently referred for hearing assessment using electrophysiologic techniques. MAIN OUTCOME MEASURES: Electrophysiologic threshold responses for click ABR and ASSR stimuli (0.5, 1, 2, and 4 kHz) for right and left ears. RESULTS: Based on ABR and ASSR thresholds, 50% of the subjects demonstrated significant hearing loss in the severe to profound range. In some subjects, ASSRs were present at higher stimulus levels when click ABRs were absent. Significant correlations (P<.05) were found between high-frequency ASSR and click ABR thresholds for this study sample. For some subjects, ASSR findings suggested differences between ears that were not observable from the no-response click ABR results. CONCLUSIONS: Auditory steady-state response testing may provide additional information for children who demonstrate hearing levels in the severe to profound range. This information may be helpful when selecting the ear for cochlear implantation for a young hearing-impaired child. Multiple objective methods, such as ABR and ASSR testing, may be needed to determine accurate hearing sensitivity for young children being considered for sensory devices, and in particular, cochlear implants.