Stability of hearing preservation following acoustic neuroma surgery.

Identification of small acoustic neuromas has become commonplace. Frequently, affected individuals are identified prior to the development of significant hearing loss. Whereas many studies have focused on hearing preservation surgery, few have reported on stability of hearing results after resection of acoustic neuroma. Between 1985 and 1991, 36 patients underwent resection of an acoustic neuroma via a retrosigmoid, internal auditory canal approach with attempted hearing preservation. Hearing was preserved in 24 patients; 17 were available for testing for the present study. Follow-up ranged from 1.5 to 8 years. All patients underwent complete audiologic assessment; most patients also underwent auditory brainstem response testing. There was an average 6 dB increase in pure-tone average between early (1 month) postoperative and long-term postoperative test results. A binomial single subject statistic was used to assess for significant changes in speech recognition scores over time. In two subjects there was a significant decrease; however, speech recognition also improved significantly in two subjects. Five of the 17 subjects demonstrated either a significant (at least 15 dB) increase in pure-tone average or a significant decrease in speech recognition over the time-course of the study. All patients maintained usable hearing. We conclude that long-term hearing preservation is a realistic goal in selected acoustic neuroma operations.

Cochlear wall titanium implants for auditory nerve stimulation.

Genetically deaf dalmatian dogs and ototoxically deafened macaque monkeys were implanted with electrodes housed in cochlear wall titanium implants to assess long-term stability, tolerance, and performance. Short-term human implantation, followed by trials of stimulation, was performed in 4 unilaterally deaf patients. In the dog experiments, cochlear wall electrode stimulation produced consistent electrophysiologic thresholds that were higher, by approximately 6 dB, than those obtained with bipolar scala tympani stimulation. Clinical testing revealed electrically evoked middle latency response, auditory brain stem response, and/or behavioral detection responses in 3 of 4 patients, at levels below those for facial nerve activation and pain sensation. Electrode place discrimination studies, with controls for loudness cues, revealed near-perfect discrimination in a monkey subject. Eleven of the 12 animal implants were found to be rigidly fixed in the cochlear bone, with direct contract between bone and implant over 8% to 23% of the implant surface for the 6 implants examined in detail. These results suggest that long-term fixation of titanium cochlear wall implants occurs by virtue of intimate implant-bone contact in restricted areas. This approach to prosthetic stimulation demonstrates encouraging performance characteristics in achieving auditory activation.

Tinnitus suppression following cochlear implantation. A multifactorial investigation.

The effects of cochlear implant on loudness, annoyance, daily duration, location, and residual inhibition of tinnitus were evaluated by a closed-ended, quantifiable questionnaire in 33 postlingually deafened patients who had received implants at the University of Michigan, Ann Arbor, between 1986 and 1990. Preoperative tinnitus was present in 85% of patients. A statistical comparison of preoperative vs postoperative loudness and annoyance indicated a significant reduction in both of these complaints postoperatively. Loudness and annoyance were significantly correlated, both preoperatively and postoperatively. Fifteen patients (54%) with preoperative tinnitus demonstrated a loudness decrease of 30% or more; 43% demonstrated an annoyance decrease of 30% or more; and 48% demonstrated a decrease of 30% or more in daily tinnitus duration. Patients who experienced a loudness or annoyance decrease of 30% or more after implantation demonstrated significantly higher preoperative levels of these complaints, suggesting that degree of tinnitus reduction after implantation may be related to preoperative loudness and annoyance levels. Contralateral tinnitus suppression was reported by 42% of patients. Residual inhibition ranging from 60 seconds to several hours was reported by 50% of patients, predominantly in the ear with the implant. Age, gender, cause of hearing loss, duration of tinnitus, cochlear implant usage, and time after implantation were not predictive of tinnitus suppression. Overall, the majority of the patients (74%) thought that their cochlear implant was helpful in tinnitus suppression, especially in the ear with the implant. Contralateral residual inhibition and tinnitus suppression suggest a central mechanism contributing to these phenomena.

A comparison of round-window and transtympanic promontory electric stimulation in cochlear implant candidates.

We compared within-subjects electrical thresholds and dynamic ranges obtained with direct round-window and transtympanic promontory stimulation carried out preoperatively in 12 patients who were candidates for a cochlear implant. Square waves with frequencies of 50, 100, 200, and 400 Hz were delivered in a 50% duty cycle to both sites in each patient. With the exception of threshold at 50 Hz (promontory thresholds were lower than round-window thresholds), there were no statistically significant differences for either thresholds or dynamic ranges between the two sites of stimulation. There was a general trend for round-window thresholds to be lower and dynamic ranges larger, especially for the higher frequencies of stimulation. Mean threshold slopes for the two sites of stimulation were nearly identical.

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.

Effects of channel number and place of stimulation on performance with the Cochlear Corporation multichannel implant.

The effects of active channel number and place of stimulation on auditory-only performance with the Cochlear Corporation multichannel cochlear implant were investigated in seven subjects. A balanced crossover design was employed; subjects were initially programmed with either 10 basal or the full complement of 20 to 21 active electrodes. Following a 6-month period with the initial coding strategy, subjects were programmed with the alternate configuration, which they used for an additional 6 months. Auditory-only performance on suprasegmental, phoneme (vowel and consonant) open- and closed-set speech recognition was compared between the two electrode configurations. Additionally, performance with the first configuration and performance with the second configuration 3 days following programming were also compared. While a trend for increased scores was noted with 20 electrodes, especially with open-set speech recognition tasks, none of the differences between the two configurations reached statistical significance, as indicated by a Wilcoxon test. A comparison of performance at the end of the first 6-month period and 3 days following programming with the second configuration revealed a trend for reduced scores, especially on vowel tests. Overall, our results indicate that the feature extraction coding strategy associated with the Cochlear Corporation device allows patients to function well with only 10 basal electrodes and that speech recognition is only mildly affected initially when patients are programmed with a different encoding strategy.

Platform pressure test in identification of perilymphatic fistula.

In an effort to better define the effectiveness of the use of posturography in the preoperative diagnosis of perilymphatic fistula (PLF), a prospective investigation of the use of platform pressure posturography was performed. Six different protocols used atmospheric pressure change applied to the external auditory canal. Postural sway, monitored as the output parameter, was evaluated relative to its sensitivity and specificity in five different patient groups. Two independent surgeon groups were used to establish the final diagnosis of perilymphatic fistula. Results within a given surgeon group demonstrate varying sensitivity from 53 to 100 percent and specificity from 56 to 89 percent. Results across the two surgeon groups show nonstatistically significant changes in sensitivity and specificity, yet statistically significant differences exist between the surgeon groups for rate of surgery performed given a suspected patient group, and for rate of positive identification of PLF during surgery. We conclude that although the platform pressure test (PPT) shows promise as a test to raise preoperative suspicion for PLF, actual test performance figures cannot be calculated until a more definitive, objective, test is available to confirm the final diagnosis. The variability of selection criteria and diagnosis by surgical observation is too great to draw clear conclusions relative to test performance. Additionally, the use of vestibular rehabilitation techniques is suggested as a presurgical management strategy for a selected group of suspect patients.

Evaluation of the temporal bones of a multichannel cochlear implant patient.

In this report we detail the temporal bone findings of a 57-year-old patient who underwent placement of a Nucleus 22-channel electrode 7 months prior to his death. Audiometric testing postoperatively demonstrated suprasegmental speech cue discrimination only. Histologic evaluation of the cochleas revealed significant sensorineural survival except in the region of the basal turn of the implanted cochlea adjacent to the implant. There was no significant pathologic condition attributable to the operation or the electrode in areas remote from the basal turn of the cochlea.

The infratemporal fossa approach to skull base surgery.

The infratemporal fossa approach, in conjunction with the application of microsurgical technique and improved perioperative care, has permitted significant advances in lateral skull base surgery. The glomus jugulare tumor is the prototypical neoplasm resected by this approach, although this technique can be applied to a host of additional benign and malignant lesions of the skull base. This approach entails identification and control of the cranial nerves and great vessels in the neck, anterior transposition of the facial nerve, and infralabyrinthine petrosectomy. Intracranial tumor extension and petrous carotid artery involvement remain limiting factors. Significant morbidity, particularly neurologic deficit and hemorrhage, may occur due tot the nature and location of lateral skull base tumors. Recent advances in preoperative embolization and temporary carotid artery balloon occlusion have advanced the limits of resection via the infratemporal fossa approach.

Independent evaluation of the speech perception abilities of children with the Nucleus 22-channel cochlear implant system.

The performance of 28 children with the Nucleus multi-channel cochlear implant, who had used the device an average of 1.7 yr, was examined on a battery of speech perception measures. All children demonstrated better speech perception skills with the implant than they had in the preimplant condition with hearing aids. With the Nucleus implant, 61% of the children demonstrated some open-set speech recognition and another 14% demonstrated closed-set speech recognition. Scores on the tests were corrected for guessing and a hierarchy of test difficulty was developed. The results revealed systematic differences in performance as a function of perception task and test format. The results of regression analyses, which were performed to identify predictors of success, showed that communication mode made a significant unique contribution to the variance in performance among subjects on an open-set word recognition test. When the scores of the children who used oral or total communication were compared on the full battery of tests, however, there were few significant group differences.

Prognostic significance of hearing loss as a lateralizing indicator in the surgical treatment of vertigo.

In patients with peripheral vertigo the presence of an asymmetrical hearing loss is an important lateralizing sign, having both diagnostic and prognostic significance. In a consecutive series of 83 patients undergoing retro-labyrinthine vestibular nerve section for uncontrolled vertigo, asymmetrical hearing loss was associated with an 83 per cent incidence of complete control of vertigo and a 49 per cent incidence of complete relief from dysequilibrium. In the absence of a lateralizing hearing loss, the figures were 50 per cent and 24 per cent respectively (p less than 0.01 and p less than 0.05). The explanation for this finding may be that the presence of a hearing loss is more often associated with an exclusively peripheral disorder (controllable by peripheral surgical ablation), whereas in patients with symmetrical hearing there may be an unrecognized central or contralateral pathology resulting in less effective results from a unilateral peripheral surgical approach. The bithermal caloric test did not give such useful diagnostic or prognostic information.

Effects of preoperative electrical stimulability and historical factors on performance with multichannel cochlear implant.

We investigated the relationship between results of preoperative transtympanic electrical promontory stimulation, duration of deafness, postoperative implanted psychophysical results, and postoperative speech and speech sound recognition as indicated by a battery of five tests. Our subjects were 10 patients implanted with the Cochlear Corporation multielectrode implant, 1 year postimplantation, with a minimum of 17 active electrodes programmed in the bipolar + 1 mode. The results indicated that preoperative promontory thresholds, the slope of the threshold function, and the duration of auditory deprivation are excellent predictors of postoperative speech and speech sound recognition in the auditory (processor alone) mode. These results have significant implications for patient selection and counseling.

Retrolabyrinthine vestibular nerve section: efficacy in disorders other than Menière's disease.

The retrolabyrinthine vestibular nerve section has evolved as an effective treatment for intractable vertigo of peripheral vestibular origin when hearing preservation is desired. This report studies the efficacy of retrolabyrinthine vestibular nerve section for control of vertigo due to causes other than Meniere's disease. This report details our experience with 42 patients with a wide variety of diagnoses. The reduced success rate of retrolabyrinthine vestibular nerve section in these patients is difficult to evaluate, as very few patients have been analyzed with respect to their specific diagnoses. Of patients who underwent retrolabyrinthine vestibular nerve section for control of vertigo, 23 patients had uncompensated vestibular neuritis and 19 others had a wide range of other diagnoses. For patients with uncompensated vestibular neuritis (n = 23), the physician record noted that 39% of patients were cured and 30% improved. This compares to our series of patients with Meniere's disease (n = 48), where 94% were cured and 2% improved. The true vestibular abnormality may be less reliably identified in patients with uncompensated vestibular neuritis, contributing to the less effective results. Since the development of a vestibular rehabilitation program, retrolabyrinthine vestibular nerve section for uncompensated vestibular neuritis has been all but abandoned. Retrolabyrinthine vestibular nerve section appears to achieve a high cure rate in patients with sensorineural hearing loss associated with their vestibular abnormalities. While retrolabyrinthine vestibular nerve section is helpful for control of vertigo in some diagnoses, a substantial incidence of persistent postoperative dysequilibrium was noted.

Evaluation of acute vertigo: unusual lesions imitating vestibular neuritis.

The acute onset of vertigo is a common clinical problem presenting to primary care physicians or otologists for evaluation. Usually the underlying disease process is benign and self-limited in nature. In the absence of hearing loss or additional neurologic findings, a common initial diagnosis is vestibular neuritis. The patient is treated symptomatically and observed for spontaneous resolution. However, other more serious disease processes may mimic the presentation of vestibular neuritis and be misdiagnosed. Five cases of serious central nervous system disorders that were similar to vestibular neuritis in their initial presentation are reviewed to illustrate this point. Each patient presented with the acute onset of continuous vertigo without associated hearing loss. The correct diagnosis was established only after further evaluation was pursued. Recommendations for the initial and subsequent evaluation of these patients are discussed.

Cochlear implants in children.

The resources and areas of expertise necessary to establish and maintain a successful children's cochlear implant program is discussed. Insights based on experience with a pediatric patient population are presented.

Electrical stimulation of the auditory system after labyrinthectomy.

For many years labyrinthectomy has been used as a reliable surgical treatment for patients with unilateral nonserviceable hearing associated with episodic vertigo. In view of the rehabilitative potential of the cochlear implant, the role of labyrinthectomy has been questioned because of a concern to preserve structures of the auditory periphery. However, recent reports demonstrate substantial survival of spiral ganglion cells after labyrinthectomy, suggesting that such patients might be candidates for rehabilitation with cochlear implants if necessary. To address this question from a physiologic approach, we investigated the electrical stimulability of the operated ear in patients who underwent transmastoid labyrinthectomy for the management of vertigo. Ten patients were studied intraoperatively with electrically evoked middle latency response (MLR) potentials. Six of these patients were studied between 3 and 15 months postoperatively via transtympanic stimulation. Postoperatively all patients demonstrated an excitable auditory periphery and behavioral thresholds were similar to intraoperative electrophysiologic thresholds for the same stimuli. These results suggest the persistence of excitable auditory neural elements following labyrinthectomy.

Operative management of acoustic neuromas: the priority of neurologic function over complete resection.

The objective of surgical management of acoustic tumors is to remove them entirely and preserve facial nerve function and hearing when possible. A dilemma arises when it is not possible to remove the entire tumor without incurring additional neurologic deficits. Twenty patients who underwent intentional incomplete surgical removal of an acoustic neuroma to avoid further neurologic deficit were retrospectively reviewed. They were divided into a subtotal group (resection of less than 95% of tumor) and a near-total group (resection of 95% or more of tumor) and were followed yearly with either computed tomography or magnetic resonance imaging. The subtotal group was planned and consisted of elderly patients (mean age, 68.5 years) with large tumors (mean, 3.1 cm). The near-total group consisted of younger patients (mean age, 45.8 years) and smaller tumors (mean, 2.3 cm). The mean length of followup for all patients was 5.0 years. Ninety percent of patients had House grade I or II facial function post-operatively. Radiologically detectable tumor regrowth occurred in only one patient, who was in the subtotal resection group. Near-total resection of acoustic tumor was not associated with radiologic evidence of regrowth of tumor for the period of observation. Within the limits of the follow-up period of this study, subtotal resection of acoustic neuroma in elderly patients was not associated with clinically significant recurrence in most patients and produced highly satisfactory rates of facial preservation with low surgical morbidity.