Electrochemical impedance spectroscopy of human cochleas for modeling cochlear implant electrical stimulus spread.

Cochlear implants (CIs) have tremendously helped people with severe to profound hearing loss to gain access to sound and oral-verbal communication. However, the electrical stimulus in the cochlea spreads easily and widely, since the perilymph and endolymph (i.e., intracochlear fluids) are essentially electrolytes, leading to an inability to focus stimulation to discrete portions of the auditory nerve, which blurs the neural signal. Here, we characterize the complex transimpedances of human cadaveric cochleas to investigate how electrical stimulus spread is distributed from 10 Hz to 100 kHz. By using electrochemical impedance spectroscopy (EIS), both the resistive and capacitive elements of human cochleas are measured and modeled with an electrical circuit model, identifying spread-induced and spread-independent impedance components. Based on this electrical circuit model, we implement a Laplace transform to simulate the theoretical shapes of the spread signals. The model is validated by experimentally applying the simulated stimulus as a real stimulus to the cochlea and measuring the shapes of the spread signals, with relative errors of <0.6% from the model. Based on this model, we show the relationship between stimulus pulse duration and electrical stimulus spread. This EIS technique to characterize the transimpedances of human cochleas provides a new way to predict the spread signal under an arbitrary electrical stimulus, thus providing preliminary guidance to the design of CI stimuli for different CI users and coding strategies.

Hearing outcomes of cochlear implant recipients with pre-operatively identified cochlear dead regions.

Objectives: To determine how patients who did not meet UK TA166 NICE criteria for cochlear implantation (CI) but were subsequently found to have cochlear dead regions (DRs) performed with CI.Methods: A retrospective review of medical records was performed on CI recipients: 152 controls and 40 in the DR group. Of these, 34 pairs were matched by pre-operative Bamford-Kowal-Bench (BKB) scores and compared.Results: The forty DR patients had a median age at implantation of 56 years. Their mean pre-operative BKB score of 23% increased to 78% after CI. Thirty-seven experienced improvements in BKB scores. In matched case-control analysis, the improvement in mean BKB score with CI was no different (p = 0.19) between the DR group and control group; a similar proportion of patients benefitted in each group.Discussion: This study is the largestreport to date of performance of patients with DRs, before and after CI. The DR group gain similar benefit as the controls.Conclusion: Patients with DRs, who did not meet TA166 NICE criteria, received the same benefit as those who did. TEN testing to detect DRs should be included in routine CI work-up where standard criteria are not met.

Conservative management of vestibular schwannomas: third review of a 10-year prospective study.

Seventy-two patients with a unilateral vestibular schwannoma have been treated conservatively for a median of 121 months. They have been followed prospectively by serial clinical examination, MRI scans and audiometry. Twenty-five patients (35%, 95% CI: 24-47) failed conservative management and required active intervention during the study. No factors predictive of tumour growth or failure of conservative management could be identified. Seventy-five per cent of failures occurred in the first half of the 10-year study. The median growth rate for all tumours at 10 years was 1 mm/year (range -0.53-7.84). Cerebellopontine angle tumours grew faster (1.4 mm/year) than intracanalicular tumours (0 mm/year, P < 0.01); 92% had growth rates under 2 mm/year. Hearing deteriorated substantially even in tumours that did not grow, but did so faster in tumours that grew significantly (mean deterioration in pure tone average at 0.5, 1, 2 and 3 kHz was 36 dB; speech discrimination scores deteriorated by 40%). Patients who failed conservative management had clinical outcomes that were not different from those who underwent primary treatment without a period of conservative management.

Conservative management of vestibular schwannomas - second review of a prospective longitudinal study.

Vestibular schwannomas have been traditionally managed with microsurgical removal and in recent years, stereotactic radiotherapy. However, there is a group of patients in whom a conservative management approach might represent a desirable alternative. The aim of this study was to determine the natural history and outcome following the conservative management of 72 patients with unilateral vestibular schwannomas. This is a prospective cohort review of a previously published group of patients [Clin. Otolaryngol. (2000) 25, 28-39] with unilateral vestibular schwannoma that were initially analysed at our institution in 1998 [Walsh R.M., Bath A.P., Bance M.L. et al., Clin. Otolaryngol. (2000) 25, 28]. The mean duration of follow-up was 80 months (range 52-242 months). All the patients in the study underwent serial magnetic resonance imaging (MRI) for assessment of tumour growth. Patients were deemed to have failed conservative management if there was evidence of rapid radiological tumour growth and/or increasing signs and symptoms, which necessitated active intervention. The mean tumour growth rate for the entire group at the second review was 1 mm/year (range -0.84-9.65 mm/year). The mean growth rate for cerebellopontine angle tumours (1.3 mm/year) was significantly greater than that of internal auditory canal (IAC) tumours (0 mm/year) (P = 0.005). The majority of tumours (87.14%) grew <2 mm/year. There was significant tumour growth seen in 38.9%, no or insignificant growth in 41.7%, and negative growth in 19.4%. Twenty-three patients (32%) failed conservative management at the second review. There was no difference in the outcome of these failed patients in comparison with patients who underwent primary treatment without a period of conservative management. The mean growth rate of tumours in patients that failed conservative management (3.1 mm/year) was significantly greater than that in patients who did not fail (0.2 mm/year) (P < 0.001). No factors predictive of tumour growth or failure of conservative management were identified. Hearing deterioration with pure tone averages (0.5, 1, 2, 3 kHz) and speech discrimination scores occurred irrespective of tumour growth. This prospective study further emphasizes the role of conservative management in selected cases of vestibular schwannomas. Tumours in this study confined to the IAC typically demonstrated minimal or no growth on serial MRI scanning. Regular follow-up with interval scanning is mandatory in all patients.

The AAO-HNS Committee on Hearing and Equilibrium guidelines for the diagnosis and evaluation of therapy in Menière's disease: have they been applied in the published literature of the last decade?

To assess how effectively the American Academy of Otolaryngology-Head and Neck Surgery Committee on Hearing and Equilibrium (AAO-HNS CHE) guidelines for the diagnosis and evaluation of therapy in Meniere's disease have been applied in the last 11 years of published literature. This was a MedLine-based review. Some 79.7% of papers attempted to use the AAO-HNS CHE guidelines. However, only 50% of these publications managed to use the AAO-HNS CHE criteria in the diagnosis and evaluation of therapy correctly. In order to advance our understanding of this condition, improved application of the AAO-HNS CHE guidelines by authors and editors alike is required in the reporting of results of the therapy of Meniere's disease.

Does high-frequency pseudo-random rotational chair testing increase the diagnostic yield of the eng caloric test in detecting bilateral vestibular loss in the dizzy patient?

OBJECTIVES: To assess the incremental diagnostic yield of testing vestibulo-ocular (VOR) gain with high-frequency pseudo-random rotational chair (PsRRC) over testing with bithermal electronystagmography caloric tests in the dizzy patient, particularly in detecting bilateral vestibular loss. PATIENTS AND METHODS: One hundred ninety-eight patients presenting with dizziness underwent PsRRC and caloric testing. The VOR gain on PsRRC was measured at 0.32 to 5.0 Hz, with gain categorized as normal or decreased. PsRRC results were compared with caloric responses, also categorized as normal, or into graded categories of unilateral or bilateral vestibular loss. RESULTS: Reduced PsRRC gain was found in 29 (15%) patients, and reduced caloric tests responses in 70 (35%), with 25 (13%) having bilateral loss. Of patients with reduced chair gain, 25 of 29 (86%) demonstrated bilateral caloric loss. PsRRC gain was normal in most patients with unilateral caloric weakness, but was decreased in all patients with bilateral caloric weakness. The probability of a patient with completely normal caloric responses having an abnormal rotation chair in this study group was under 1% (1 of 128). CONCLUSIONS: PsRRC testing does not offer much additional diagnostic benefit when caloric responses are normal. It is useful in specific conditions, such as unilateral caloric loss for which the patient is not compensating, borderline caloric loss when traditional water caloric tests cannot be used, or for monitoring progressive bilateral vestibular loss.

Does evidence-based medicine exist in the treatment of Menière's disease? A critical review of the last decade of publications.

Debate surrounding the need for evidence-based research in all fields of otolaryngology has recently emerged. A review of English language articles dealing with the treatment of Menière's disease published from 1989 to 1999 was performed. The papers were classified according to article type (observational studies, non-clinical studies, controlled trials, randomised controlled trials) and according to the grade of evidence that was offered. A total of 128 publications were reviewed, of which only three were randomised controlled trials and a further three were well-designed controlled studies without randomization. The majority of papers were non-experimental clinical descriptive studies or case series. Data from this review would suggest that more comprehensive evidence-based studies are required in order to settle areas of confusion surrounding treatment of this relapsing condition

Comparison of two radiologic methods for measuring the size and growth rate of extracanalicular vestibular schwannomas.

OBJECTIVE: To compare two methods for measuring the size and growth rate of extracanalicular vestibular schwannomas: the method recommended in 1995 by the American Academy of Otolaryngology--Head Neck Surgery (AAO-HNS) and the maximum cerebellopontine angle (CPA) tumor diameter, i.e., the method often used in radiologic reports. STUDY DESIGN: Retrospective clinical study. SETTING: Tertiary referral center. PATIENTS: Fifty-four patients with a radiologic diagnosis of unilateral extracanalicular vestibular schwannoma whose tumors were managed conservatively for a mean duration of 39.8 months (range 12-194 months). INTERVENTION: The extracanalicular component was measured by use of high-resolution magnetic resonance imaging (2- to 3-mm axial slices) at 6- to 12-month intervals. MAIN OUTCOME MEASURES: Tumor diameter was calculated by two methods. In the AAO-HNS method, the axial image with the largest extracanalicular tumor diameter was selected, and the maximum anteroposterior (A-P) and medial-lateral (M-L) tumor diameters were calculated. The A-P diameter was calculated parallel to the posterior surface of the petrous temporal bone, and the M-L diameter was calculated perpendicular to it. The size of the tumor was calculated as the square root of the product of these two diameters. In the maximum CPA method, the maximum CPA tumor diameter in any direction was also measured. RESULTS: There was no significant difference between the two methods for measuring the extracanalicular tumor size and growth rate, although the maximum CPA diameter method was consistently greater than the AAO-HNS method. There was a strong positive correlation between the two methods for assessing tumor size and growth. The A-P and M-L extracanalicular tumor diameters also showed a strong positive correlation, suggesting that the extracanalicular portion of vestibular schwannomas tends to enlarge equally in both these directions. CONCLUSION: There is a strong positive correlation between these two methods for assessing both the tumor size and the growth rate of extracanalicular vestibular schwannomas. However, because vestibular schwannomas tend to grow in both the A-P and the M-L directions, this suggests that the AAO-HNS method is preferable.

The natural history of untreated vestibular schwannomas. Is there a role for conservative management?

OBJECTIVE: The aim of this study was to investigate the natural history and outcome following the conservative management of a group of patients with unilateral vestibular schwannomas. METHODS: 72 patients with a radiological diagnosis of unilateral vestibular schwannoma were managed conservatively because of poor general health, advanced age, patient preference, small tumour size, minimal symptoms, or tumour in the only/better hearing ear. All patients underwent serial magnetic resonance imaging for assessment of tumour growth, according to American Academy of Otolaryngology-Head & Neck Surgery guidelines (1995). The mean duration of follow-up was 37.8 months (range 12-194 months). Patients were deemed to have failed conservative management if there was evidence of continuous or rapid radiological tumour growth, and/or increasing symptoms or signs. RESULTS: The mean tumour growth rate was 1.16 mm/year (range -0.75 to 9.65 mm/year). Approximately 83% of tumours grew at less than 2 mm/year. Significant tumour growth (total growth > 1 mm) was seen in 36.4%, no or insignificant growth (0-1 mm) in 50%, and negative growth (< 0 mm) in 13.6% of tumours. The growth rate of cerebellopontine angle (CPA) tumours (1.4 mm/year) was significantly greater than that of tumours limited to the internal auditory canal (IAC) (0.2 mm/year) (p = 0.001). Failure of conservative management, in which active treatment was required, occurred in 15.3%. The outcome of these patients appeared to be as favourable as those who underwent primary treatment, without a period of conservative management. The growth rate of tumours in patients who failed conservative management (4.2 mm/year) was significantly greater than that in patients who did not fail (0.5 mm/year) (p < 0.01). No factors predictive of tumour growth were identified. Deterioration of mean pure tone average (0.5, 1, 2, 3 kHz) and speech discrimination scores occurred regardless of whether radiological tumour growth was demonstrated or not. CONCLUSIONS: The majority of vestibular schwannomas are slow growing, although, CPA tumours appear to grow faster than IAC tumours. Deterioration of auditory function occurs even in the absence of tumour growth. Although most Otolaryngologists and Neurosurgeons would agree that the treatment of choice for the majority of vestibular schwannomas is microsurgery, there remains a small group of patients in whom a conservative management approach may be a desirable alternative.

The transmastoid partial labyrinthectomy approach to medial skull base lesions.

INTRODUCTION: It has long been thought that surgical disruption of the membranous labyrinth invariably results in sensorineural hearing loss and balance dysfunction. Recent evidence suggests that the inner ear can withstand such manipulation without loss of function. The technique of transmastoid partial labyrinthectomy has recently been described as a means of providing access to lesions of the medial skull base by removing part of the labyrinth and at the same time attempting to preserve hearing and vestibular function of the lateral semicircular canal (LSCC) and otolithic organs. PROCEDURE: An extended cortical mastoidectomy is performed and the posterior and middle cranial fossa dura are exposed widely. The posterior and superior semicircular canals are occluded at their ampullated ends and at the crus commune, and then resected. The LSCC and vestibule are left undisturbed. The petrous apex is removed and the medial end of the internal auditory canal is exposed. Posterior cranial fossa dural flaps are raised allowing access to the brainstem, petro-clival area and cerebellopontine angle. Temporal and suboccipital craniotomies can be performed, as required. RESULTS: Four patients underwent this procedure by a joint Otolaryngological-Neurosurgical team for access to the following lesions: three intra-axial pontine cavernomas and a basilar artery aneurysm. The preliminary hearing and balance results are discussed. CONCLUSIONS: The partial labyrinthectomy approach provides improved access to certain lesions of the medial skull base and requires less brain retraction compared with the retrolabyrinthine approach. It also has the potential to preserve serviceable hearing.

Reversible tobramycin-induced bilateral high-frequency vestibular toxicity.

We report an unusual case of tobramycin-induced bilateral high-frequency vestibular toxicity with subsequent clinical and objective evidence of functional recovery. In those patients with a clinical presentation suggestive of aminoglycoside-induced bilateral vestibular toxicity (ataxia and oscillopsia) and normal low-frequency (ENG-caloric) responses, high-frequency rotation chair testing should be performed to exclude a high-frequency vestibular deficit.

The role of conservative management of vestibular schwannomas.

Although microsurgery is generally regarded as the conventional treatment of choice for most vestibular schwannomas, there remains a group of patients in whom a conservative management approach may be a desirable alternative. The aim of this study was to determine the natural history and outcome following the conservative management of 72 patients with unilateral vestibular schwannomas. The reasons for conservative management included poor general health, age, patient preference, small tumour size, minimal or no symptoms, and tumour in the only/better hearing ear. The mean duration of follow-up was 39.8 months (range 12-194 months). All patients underwent serial magnetic resonance imaging (MRI) for assessment of tumour growth. Patients were deemed to have failed conservative management if there was evidence of continuous or rapid radiological tumour growth and/or increasing symptoms or signs. The mean tumour growth rate, according to the 1995 guidelines of the American Academy of Otolaryngology/Head and Neck Surgery, was 1.16 mm/year (range: 0.75 9.65 mm/year). Approximately 83% of tumours grew at < 2 mm/year. Significant tumour growth was seen in 36.4%, no or insignificant growth in 50%, and negative growth in 13.6% of tumours. The growth rate of CPA tumours (1.4 mm/year) was significantly greater than that of IAC tumours (0.2 mm/year) (P = 0.001). Failure of conservative management, in which active treatment was required, occurred in 15.3%. The outcome of these patients appeared to be as favourable to a comparable group who underwent primary treatment, without a period of conservative management. The mean growth rate of tumours in patients who failed conservative management (4.2 mm/year) was significantly greater than that in patients who did not fail (0.5 mm/year) (P < 0.01). No factors predictive of tumour growth or failure of conservative management were identified. Deterioration of mean pure tone average (0.5, 1, 2, 3 kHz) and speech discrimination scores occurred regardless of whether radiological tumour growth was demonstrated or not. This study suggests that in a select number of cases of vestibular schwannoma, a conservative management approach may be appropriate. Regular follow-up with serial MRI is mandatory. Deterioration of auditory function occurs even in the absence of tumour growth.

Consequences to hearing during the conservative management of vestibular schwannomas.

OBJECTIVE: To estimate the risk of loss of serviceable hearing during the conservative management of vestibular schwannomas. STUDY DESIGN: Retrospective case review. METHODS: Twenty-five patients with a radiological diagnosis of unilateral vestibular schwannoma were managed conservatively for a mean duration of 43.8 months (range, 12-194 mo). The pure-tone average (PTA) (0.5, 1, 2, and 3 kHz) and speech discrimination scores (SDS) were measured at regular intervals throughout the entire duration of follow-up. Serviceable hearing was defined using two criteria: 70% SDS/30 dB PTA (the 70/30 rule) and 50% SDS/50 dB PTA (the 50/50 rule). The size and growth rate of tumors were determined according to the American Academy of Otolaryngology-Head and Neck Surgery guidelines (1995). Intervention was recommended if there was evidence of continuous or rapid radiological tumor growth, and/or increasing symptoms or signs suggestive of tumor growth. RESULTS: The risk of loss of serviceable hearing for the total group was 43% using the 70/30 rule and 42% using the 50/50 rule. Tumor growth was considered significant (> 1 mm) in 8 tumors (32%) and nonsignificant in 17 (68%). The risk of loss of serviceable hearing for the tumor-growth group was 67% using the 70/30 rule and 80% using the 50/50 rule. In contrast, the risk of loss of serviceable hearing for the no tumor-growth group was 25% using the 70/30 rule and 14% using the 50/50 rule. No audiological factors predictive of tumor growth were identified. CONCLUSIONS: There is a significant risk of loss of serviceable hearing during the conservative management of vestibular schwannomas. This risk appears to be greater in tumors that demonstrate significant growth.

Experience from a multidisciplinary "dizzy" clinic.

OBJECTIVE: To describe the experience of a combined otolaryngology and neurology multidisciplinary clinic in the evaluation, investigation, and management of patients with dizziness. STUDY DESIGN: Prospective clinical study. SETTING: Patients were seen in a tertiary referral, multidisciplinary clinic at The Toronto Hospital, University of Toronto, Ontario, Canada. INTERVENTION: A thorough history, formal otoneurologic examination, and appropriate laboratory investigations were performed. After their assessment, the patient's diagnoses were classified as peripheral, central, psychogenic, or undiagnosed and were then subdivided into specific clinical diagnoses. RESULTS: The first 812 consecutive patients seen in the multidisciplinary clinic from January 1, 1993 to December 31, 1998 are reported. Five hundred twenty-five (64.7%) patients were found to have a peripheral vestibular cause for their dizziness, 66 (8.1%) had a central cause, 108 (13.3%) had a diagnosis unknown, and 73 (9.0%) were thought to be psychogenic. In 40 (4.9%) patients, a peripheral and central cause were found. More than one type of peripheral disorder was noted in 17.9% of patients with a peripheral vestibular cause for their dizziness, and 12.3% of patients with a central cause for their dizziness had more than one specific type of central nervous system disorder. CONCLUSIONS: Most patients that were seen in a multidisciplinary clinic had a peripheral vestibular disorder. Central causes of dizziness were relatively uncommon. Serious diseases such as tumor, multiple sclerosis, and encephalitis were rare and unlikely to present with dizziness only. It is important to realize that a patient may have more than one type of disorder accounting for the symptoms, which may represent a spectrum of disease affecting the inner ear.

Ototoxicity of topical gentamicin preparations.

OBJECTIVE: To document that commercially available topical gentamicin-containing eardrops carry a risk of ototoxicity if they reach the middle ear through a tympanic membrane defect. STUDY DESIGN: Clinical study, retrospective case-note review. SETTING: Department of Otolaryngology, The Toronto Hospital, University of Toronto. PATIENTS: Sixteen patients were identified with well-documented histories, physical findings and laboratory investigations consistent with topical gentamicin-induced ototoxicity. One patient with incapacitating unilateral Meniere's disease underwent successful intentional vestibular ablation using topical gentamicin/steroid drops. RESULTS: In all cases of inadvertent ototoxicity, patients had used the drops for longer than 7 days (average 20.7 d) prior to symptoms developing. All patients developed vestibulotoxicity that was confirmed on ENG testing. Only 1 patient had a noticeable worsening of cochlear reserve. Deliberate and successful therapeutic ablation of vestibular function in a patient with unilateral Meniere's disease confirms the vestibulotoxic nature of commercially available topical gentamicin preparations. CONCLUSIONS: Physicians should consider the potential for ototoxicity if gentamicin-containing eardrops (and by extrapolation all topical aminoglycoside drops) are used for longer than 7 days in patients with a tympanic membrane defect. These preparations should not be used in the presence of healthy middle ear mucosa and should be discontinued shortly after the discharge has stopped. It is important to recognize that toxicity is primarily vestibular rather than cochlear.

Presumed reduction of vestibular function in unilateral Menière's disease with aminoglycoside eardrops.

We report the first case in the world literature of deliberate ablation of vestibular function in unilateral Menière's disease with aminoglycoside eardrops (Garasone). These findings give conclusive proof that Garasone eardrops, and by implication, all topical aminoglycoside ear drops can be vestibulotoxic in the presence of a tympanic membrane defect. The lower concentration of gentamicin in Garasone, in comparison to the standard intratympanic preparations for chemical ablation of vestibular function, may also offer a reduction in the potential risk of cochleotoxocity.

Vestibular disease unmasked by hyperventilation.

Hyperventilation-induced dizziness is often thought to be psychogenic, but its effects in the presence of known vestibular disease have not been adequately examined. In this study hyperventilation was tested in two models of vestibular disease. These were, first, patients with profound unilateral vestibular deficit (prior translabyrinthine acoustic neuroma resection [postsurgery group]) and, second, patients with variable unilateral vestibular deficit (unoperated unilateral acoustic neuroma [presurgery group]). Patients were hyperventilated for 90 seconds. Using infrared videonystagmography, 100% of the 32 postsurgery patients and 82% of the 28 presurgery patients developed nystagmus with hyperventilation. Hyperventilation was more sensitive than head shake for eliciting nystagmus in these models. The false-positive rate for nystagmus in 29 normal volunteers was 3.5% for hyperventilation and 10% for head shake. Our results show that hyperventilation can unmask underlying vestibular disease.

Vestibular stimulation by multichannel cochlear implants.

The recipient of a Nucleus 22 multichannel cochlear implant began to experience severe vestibular stimulation related to the implant. This patient's experience initiated a study with the objective of determining the frequency of implant-related vestibulo-ocular stimulation. Subjects consisted of 17 randomly selected patients who use cochlear implants. Included in the study were 14 Nucleus 22 and three Med-El Combi 40-devices. Stimulation of the implants was performed both by individual channel and with sound field broad-band 80-dB noise using the users' normal device settings. Eye movements were monitored with infrared videonystagmography. Only one subject, who used a Med-El Combi 40, showed a consistent and strong ocular response to cochlear stimulation but had no subjective symptoms. The authors conclude that vestibulo-ocular activation is possible with multichannel cochlear implants but is infrequent and may not be clinically significant.

Decision and cost analysis in acoustic neuroma diagnosis.

Demonstrating improved outcomes and cost containment are current health care imperatives. For many diseases, competing diagnostic tests are available. Each has a direct economic cost and indirect costs based on missed disease. It is often difficult to determine the most efficient testing strategy for a given patient. Clinical Decision Analysis can optimise diagnostic strategies to maximise cost-effectiveness. Analytic techniques are developed to allow analysis of diagnostic strategies that include multi-test protocols. The test parameters required for modelling these strategies are derived from a literature analysis.

Interaction of saccadic and vestibular mechanisms in combined eye-head gaze shifts.

Saccades are the only purely volitional eye movements available to primates. They are used extensively to acquire new or interesting targets in the visual environment. Most patients with saccadic disorders are referred to neurologists. Patients complaining of disorientation, however, are often presumed to be suffering from a vestibular disorder. Vestibular and saccadic physiology has been studied mostly in isolation of each other. We examine the interaction of saccadic burst neurons and vestibular signals to achieve accurate gaze shifts.