Intraoperative assessment of cochlear nerve functionality in various vestibular schwannoma scenarios: Lessons learned.

The use of cochlear implants (CIs) is on the rise for patients with vestibular schwannoma (VS). Besides CI following tumor resection, new scenarios such as implantation in observed and/or irradiated tumors are becoming increasingly common. A significant emerging trend is the need of intraoperative evaluation of the functionality of the cochlear nerve in order to decide if a CI would be placed. The purpose of this paper is to explore the experience of a tertiary center with the application of the Auditory Nerve Test System (ANTS) in various scenarios regarding VS patients. The results are compared to that of the studies that have previously used the ANTS in this condition. Patients with unilateral or bilateral VS (NF2) who were evaluated with the ANTS prior to considering CI in a tertiary center between 2021 and 2023 were analyzed. The presence of a robust wave V was chosen to define a positive electrical auditory brainstem response (EABR). Two patients underwent promontory stimulation (PromStim) EABR previous to ANTS evaluation. Seven patients, 2 NF-2 and 5 with sporadic VS were included. The initial scenario was simultaneous translabyrinthine (TL) tumor resection and CI in 3 cases while a CI placement without tumor resection was planned in 4 cases. The ANTS was positive in 4 cases, negative in 2 cases, and uncertain in one case. Two patients underwent simultaneous TL and CI, 1 patient simultaneous TL and auditory brainstem implant, 3 patients posterior tympanotomy with CI, and 1 patient had no implant placement. In the 5 patients undergoing CI, sound detection was present. There was a good correlation between the PromStim and ANTS EABR. The literature research yielded 35 patients with complete information about EABR response. There was one false negative and one false positive case; that is, the 28 implanted cases with a present wave V following tumor resection had some degree of auditory perception in all but one case. The ANTS is a useful intraoperative tool to asses CI candidacy in VS patients undergoing observation, irradiation or surgery. A positive strongly predicts at least sound detection with the CI.

A Retrospective Cohort Study of Longitudinal Audiologic Assessment in Single and Fractionated Stereotactic Radiosurgery for Vestibular Schwannoma.

BACKGROUND: Fractionated stereotactic radiosurgery (SRS) for vestibular schwannomas (VS) has been theorized to allow for tumor control with higher rates of hearing preservation in selected patients with useful hearing. However, there is a paucity of literature with formal audiologic measures of hearing preservation to support the standard use of fractionated SRS in VS. We hypothesized that fractionation would diminish the amount of hearing damage. OBJECTIVE: To evaluate the relationship between audiologic performance and SRS fractionation scheme. METHODS: We performed an IRB-approved retrospective review of patients treated with 1, 3, or 5 fraction SRS for VS at our institution from 1998 to 2016. Pre- and post-SRS audiograms with speech awareness threshold (SAT) in treated and contralateral ears were obtained. Contralateral ear measurements were used for hearing normalization to account for presbycusis. RESULTS: Fifty-six patients with median audiologic follow-up 2.0 yr (mean 2.66 yr, min-max 0.50-9.45 yr) were included. Patients treated with single fractionation had a significantly worsened SAT (dB) compared to patients treated with 5 fractions (P = .008) and compared to all multifraction patients (P = .009) at 12 to 24 mo follow-up. CONCLUSION: This retrospective analysis supports the use of fractionated SRS to preserve hearing in patients with VS. SAT can be used as an objective metric of hearing response to radiosurgery.

Chronic balance disorders after acoustic neuroma surgery: assessment of gravitational vertical perception.

CONCLUSION: The head tilt response (HTR) test performed in a group of patients with chronic dizziness after acoustic neuroma surgery showed alterations in the gravitational vertical perception (GV). OBJECTIVE: The assessment of the accuracy in the GV through the HTR test in patients with long-term balance disorders after acoustic neuroma surgery. METHODS: The HTR was performed in two groups of patients that had undergone acoustic neuroma surgery: six uncompensated patients (UPs) who maintained vestibular symptoms 1 year after surgery and two compensated patients (CPs) without vestibular symptoms. Twelve healthy control adults were also tested (control group, CG). Three parameters were measured in the HTR test: steady-state error (SSE), rise time (TRS), and mean energy of the error signal per step (MEE). RESULTS: The UP group showed higher values for the TRS and MEE parameters compared with the CG (p < 0.05) when performing the HTR test to the side of the lesion and to the contralateral side, while the SSE only showed significant higher values when the patient estimated the GV towards the side of the lesion. The two patients in the CP group did not have differences in the three parameters assessed when compared with the CG.

Head movements in patients with vestibular lesion: a novel approach to functional assessment in daily life setting.

OBJECTIVES: (1) To determine if head movements in patients with vestibular deficiency differ from those in normal subjects during daily life activities. (2) To assess if these differences can be correlated with patients' perception of dizziness-induced handicap. STUDY DESIGN: Prospective matched-pairs study SETTING: Tertiary referral center PATIENTS: Thirty-one vestibular schwannoma patients with documented postoperative unilateral vestibular loss and their age-, gender-, and physical activity level-matched controls with symmetric vestibulo-ocular reflexes. INTERVENTIONS: Head movements during 10 tasks from daily life were recorded using body-worn movement sensors. MAIN OUTCOME MEASURES: The time to complete the task, the average head velocity and acceleration during each task, and the number of head turns performed were compared between cases and controls. These measures were then correlated with the self-reported Dizziness Handicap Inventory (DHI) scores of the patients. RESULTS: Patients with a unilateral vestibular deficit took significantly longer to perform most daily life activities compared to controls. Their head movements, however, were not always slower. They adopted a different movement strategy, in certain instances less efficient and more disorganized. Dimensions of movement are not all affected equally after a unilateral vestibular loss with evidence of clear clustering of the differences within dimensions across tasks. There was no correlation between the DHI and patients' performance in those tasks. CONCLUSION: Vestibular loss, even when compensated, affects patients' movements, which can be measured in an ambulatory setting of daily life activities. The differences in movements associated with vestibular loss do not correlate with the degree of self-reported handicap.

The role of cervical and ocular vestibular evoked myogenic potentials in the assessment of patients with vestibular schwannomas.

OBJECTIVES: To investigate the clinical utility of VEMPs in patients suffering from unilateral vestibular schwannoma (VS) and to determine the optimal stimulation parameter (air conducted sound, bone conducted vibration) for evaluating the function of the vestibular nerve. METHODS: Data were obtained in 63 patients with non-operated VS, and 20 patients operated on VS. Vestibular function was assessed by caloric, cervical and ocular VEMP testing. 37/63 patients with conclusive ACS ocular VEMPs responses were studied separately. RESULTS: In the 63 non-operated VS patients, cVEMPs were abnormal in 65.1% of patients in response to AC STB and in 49.2% of patients to AC clicks. In the 37/63 patients with positive responses from the unaffected side, oVEMPs were abnormal in 75.7% of patients with ACS, in 67.6% with AFz and in 56.8% with mastoid BCV stimulation. In 16% of the patients, VEMPs were the only abnormal test (normal caloric and normal hearing). Among the 26 patients who did not show oVEMP responses on either side with ACS, oVEMPs responses could be obtained with AFz (50%) and with mastoid stimulation (89%). CONCLUSIONS: The VEMP test demonstrated significant clinical value as it yielded the only abnormal test results in some patients suffering from a unilateral vestibular schwannoma. For oVEMPs, we suggest that ACS stimulation should be the initial test. In patients who responded to ACS and who had normal responses, BCV was not required. In patients with abnormal responses on the affected side using ACS, BCV at AFz should be used to confirm abnormal function of the superior vestibular nerve. In patients who exhibited no responses on either side to ACS, BCV was the only approach allowing assessment of the function of the superior vestibular nerve. We favor using AFz stimulation first because it is easier to perform in clinical practice than mastoid stimulation.

Vestibular assessment in patients with vestibular schwannomas: what really matters?

Vestibular function is often underdiagnosed in vestibular schwannomas (VS). To evaluate it in a selected group of patients harbouring vestibular schwannomas, 64 patients were included in this study, recruited between March 2008 and June 2011 at our institution. All patients underwent Gd-enhanced MRI and complete neurotological evaluation before gamma knife surgery. Morphological measurements included Koos Classification and quantification of internal acoustic canal filling in length and diameter. Cochlear and vestibular functions were assessed considering pure tone and speech audiometry, bedside examination and caloric test by videonystagmography. A statistical analysis was performed to find possible correlations between morphological and cochleovestibular data. Patients with a higher intracanalicular length (ICL, mean value 8.59 and median 8.8 mm) of the tumour presented a higher value of UW than the subgroup with a lower length (51.9 ± 24.3% and 38.8 ± 18.1% respectively, p = 0.04), while no difference was detected for pure tone audiometry (PTA) values (50.9 ± 22.3 db and 51.1 ± 28.9 db respectively). Patients with a higher ICL also presented a higher rate of positive HIT (88% and 60% respectively, p = 0.006). Patients with a higher value of intracanalicular diameter (ICD, mean value 5.22 and median 5.15 mm) demonstrated higher values of UW (50.2 ± 29.1% and 39.3 ± 21% respectively, p = 0.03), but not different PTA (50.2 ± 29.1 db and 51.9 ± 29.9 db respectively). Finally, patients with a positive head impulse test (HIT) demonstrated significantly higher values of unilateral weakness (UW) (p = 0.001). Vestibular disorders are probably underdiagnosed in patients with VS. ICL and ICD seem to be the main parameters that correlate with vestibular function. Also, in case of small intracanalar T1 VS a slight increase of these variables can result in significant vestibular impairment. The data reported in the present study are not inconsistent with the possibility of proactive treatment of patients with VS.

Incidental vestibular schwannomas: a review of prevalence, growth rate, and management challenges.

With the relatively recent increase in the use of MRI techniques, there has been a concurrent rise in the number of vestibular schwannomas (VSs) detected as incidental findings. These incidental VSs may be prevalent in up to 0.02%-0.07% of individuals undergoing MRI and represent a significant portion of all diagnosed VSs. The management of these lesions poses a significant challenge for practitioners. Most incidental VSs tend to be small and associated with minimal symptoms, permitting them to be managed conservatively at the time of diagnosis. However, relatively few indicators consistently predict tumor growth and patient outcomes. Furthermore, growth rates have been shown to vary significantly over time with a large variety of long-term growth patterns. Thus, early MRI screening for continued tumor growth followed by repeated MRI studies and clinical assessments throughout the patient's life is an essential component in a conservative management strategy. Note that tumor growth is typically associated with a worsening of symptoms in patients who undergo conservative management, and many of these symptoms have been shown to significantly impact the patient's quality of life. Specific indications for the termination of conservative management vary across studies, but secondary intervention has been shown to be a relatively safe option in most patients with progressive disease. Patients with incidental VSs will probably qualify for a course of conservative management at diagnosis, and regular imaging combined with the expectation that the tumor and symptoms may change at any interval is crucial to ensuring positive long-term outcomes in these patients. In this report, the authors discuss the current literature pertaining to the prevalence of incidental VSs and various considerations in the management of these lesions. It is hoped that by incorporating an understanding of tumor growth, patient outcomes, and management strategies, practitioners will be able to effectively address this challenging disease entity.

Longitudinal assessment of quality of life and audiometric test outcomes in vestibular schwannoma patients treated with gamma knife surgery.

OBJECTIVE: To prospectively assess the quality of life (QOL) and hearing acuity in vestibular schwannoma (VS) patients after gamma knife surgery (GKS). PATIENTS: Fifty-nine VS patients. INTERVENTION: GKS. MAIN OUTCOME MEASURES: Prospective follow-up algorithm included 36-item Short Form Health Survey (SF-36), Hearing Handicap Inventory (HHI), Dizziness Handicap Inventory (DHI), Tinnitus Handicap Inventory (THI), pure-tone average, and speech discrimination hearing scores (Gardner-Robertson and American Academy of Otolaryngology), performed before and after GKS at 1-, 3-, 6-, 12-, and 18-month posttreatment intervals. RESULTS: From December 2006 to November 2008, 59 VS patients were treated with a median follow-up of 15 months. At baseline, mean scores for SF-36, HHI, DHI, and THI were 73, 37, 17, and 23, respectively. Median baseline Gardner-Robertson and American Academy of Otolaryngology hearing acuity scores were 2 and B, respectively. No significant decline in SF-36 health survey was noted after GKS. Mean SF-36 score at baseline was 73, compared with a range of 70 to 77 at predetermined posttreatment intervals. Similarly, no significant changes in DHI, HHI, and THI were noted. Approximately 47% of patients with baseline serviceable hearing maintained serviceable hearing at 12 months. Significant acute and chronic worsening in hearing acuity were noted at 1 and 18 months, respectively. No correlative decline in QOL was noted as assessed by SF-36 or HHI. CONCLUSION: No significant decline in global QOL occurred after GKS with relatively short follow-up and approximately 50% survey completion. When discussing therapy options with VS patients, anticipated treatment-related QOL outcomes should be considered.

Management of patients with acoustic neuromas: a Markov decision analysis.

OBJECTIVES/HYPOTHESIS: The management of patients with small (<1.5 cm) acoustic neuromas is controversial. Immediate treatment via microsurgical resection or radiosurgery is often advocated. A period of observation is sometimes advised followed by microsurgery or radiosurgery for tumors that demonstrate growth during the observation period. The purpose of this study is to calculate quality-adjusted life expectancy for the most commonly applied management strategies in hypothetical cohorts of patients of various ages. STUDY DESIGN: Markov decision analysis; societal perspective. METHODS: Assumptions used in creating this model and event probabilities were obtained from a thorough literature review. Key parameters were identified and defined by the best available evidence. The main outcome measure is the benefit derived from each management strategy in quality-adjusted life years (QALYs). Sensitivity analysis was used to define benchmark performance information for these parameters. RESULTS: The benefit of a period of observation followed by radiosurgery, if needed, for significant tumor growth is greater then all other strategies for all age groups and both sexes. When compared to observation followed by microsurgery, the additional benefit is small. QALY totals for the two immediate treatment groups were significantly lower than that for the observation groups. CONCLUSIONS: For patients of all ages, a period of observation during which tumor growth and hearing thresholds are closely monitored is the superior strategy. For tumors that grow substantially or when hearing deteriorates, definitive management via radiosurgery is recommended.

The role of magnetic resonance imaging in the identification of suspected acoustic neuroma: a systematic review of clinical and cost effectiveness and natural history.

OBJECTIVE(S): To evaluate the clinical effectiveness and cost-effectiveness of a range of diagnostic strategies for investigating patients with unilateral hearing loss and/or tinnitus, with a view to confirming or eliminating a diagnosis of acoustic neuroma, and to describe the natural history of acoustic neuroma. DATA SOURCES: Major electronic databases were searched from January 1980 to August 2008. REVIEW METHODS: Selected studies were assessed and subjected to data extraction and quality assessment using standard methods. RESULTS: Studies comparing auditory brainstem response (ABR) with magnetic resonance (MR) imaging were highly heterogeneous. ABR has high sensitivity compared with MR imaging for acoustic neuromas greater than 1 cm in size but not for smaller neuromas. The sensitivities of T2-weighted (T2W) and T2-star-weighted (T2*W) imaging strategies compared with gadolinium-enhanced T1-weighted (GdT1W) MR imaging (gold standard) were high and relatively homogeneous. The specificity of T2W and T2*W studies ranged from 90% to 100% and from 86% to 99% respectively. The review of cost-effectiveness showed that GdT1W MR imaging immediately or in conjunction with ABR appears to be more cost-effective than 'traditional' protocols; ABR/GdT1W MR imaging protocols were more cost-effective than going directly to GdT1W MR imaging. Non-contrast-enhanced MR imaging was found to be a more cost-effective test for acoustic neuroma than GdT1W MR imaging. The incidence of acoustic neuroma has increased over the last 30 years, with the median age at diagnosis remaining at 55 years. Most patients present with insidious symptoms of unilateral hearing impairment, tinnitus and/or vertigo. The pattern and rate of growth of acoustic neuroma are highly variable and currently unpredictable. At least 50% of tumours do not grow, at least for some years after diagnosis. Some studies have found large initial size to be a determinant of later growth, with the opposite also being reported. The mean growth rate for all tumours varies between 1 and 2 mm/year, with a rate of 2-4 mm/year for only those that grow; however, there are cases with significant regression (5%) or exceptional growth (which may exceed 18 mm/year). CONCLUSIONS: The majority of the evidence reviewed was poorly reported and there is therefore an inherent risk of bias. Given the recent improvement in resolution and reduction in cost of MR imaging, ABR can no longer be considered appropriate as the primary test used to screen for acoustic neuroma. T2W or T2*W sequences enable accurate evaluation of the VIIIth and VIIth cranial nerves within the cerebellopontine angle and internal auditory canal as well as evaluation of the cochlea and labyrinth, and inclusion of GdT1W sequences is unlikely to contribute information that would alter patient management in the screening population. The quality of the imaging chain and experience of the reporting radiologist are key factors determining the efficacy of a non-contrast screening strategy. Based on a cost-effectiveness model developed to reflect UK practice it was concluded that a diagnostic algorithm that deploys non-contrast MR imaging as an initial imaging screen in the investigation of acoustic neuroma is less costly than and likely to be as effective as available contrast MR imaging.

Mechanisms of intraoperative brainstem auditory evoked potential changes.

Brainstem auditory evoked potential (BAEP) changes during intraoperative monitoring may reflect damage to or potentially reversible dysfunction of the ear, the eighth nerve, or the brainstem auditory pathways up to the level of the mesencephalon. They may also be caused by other physiologic mechanisms such as anesthesia, hypothermia, and acoustic masking from drilling noise, or they may result from technical factors that prevent proper stimulus delivery or recording of an evoked potential that is actually present. Cochlear ischemia or infarction resulting from compromise of the internal auditory artery and inner ear damage during temporal bone drilling will affect all BAEP components, including wave I. Direct mechanical or thermal trauma to the eighth nerve will delay, attenuate, and possibly eliminate waves III and V, but wave I, which is generated at the cochlear end of the eighth nerve, may be preserved. During scraping of tumor off the eighth nerve, force applied in an ear-toward-brainstem direction can avulse the fragile fibers of the distal eighth nerve at the area cribrosa. Prolonging the I-to-III interpeak interval during retraction of the cerebellum and brainstem reflects stretching of the eighth nerve, and is often reversible. Vasospasm within the eighth nerve can cause similar, potentially reversible BAEP changes. Damage to the brainstem auditory pathways at or below the level of the mesencephalon will delay and attenuate or eliminate wave V. Wave III is affected similarly if the damage is at or caudal to the region of the superior olivary complex. These BAEP changes may reflect direct mechanical or thermal damage to the brainstem, brainstem compression, or ischemia or infarction resulting from vascular compromise. During BAEP monitoring, examination of the pattern of BAEP changes, analysis of their correlation with surgical maneuvers, and investigation for possible contributory technical factors can help to determine the cause of the BAEP changes and provide the appropriate information to the rest of the surgical team.

[Contribution and Cost-Effectiveness of ABR and MRI in Acoustic Neuroma screening. Retrospective Study of 151 Cases]. / Intérêt et rapport coût efficacité des PEA et de l'IRM dans le dépistage du neurinome de l'acoustique.

The aim of this study was to retrospectively assess during two periods (1991-1995 and 1996-2000) if MRI spreading had changed: (1) private ENT physicians screening habits; (2) the average tumor size at the time of diagnosis and the diagnostic delay of acoustic neuroma; and (3) the cost of acoustic neuroma diagnosis. In addition, the sensibility of each diagnostic test was calculated on 151 tumors. Our results show no significant change neither in the screening strategy (except a mild decrease in CT-scan utilization) nor in the tumor size, diagnostic delay or diagnostic cost between the two periods. Even if MRI is the gold standard for acoustic neuroma diagnosis, our 86%-sensibility of ABR, increased to 99% if combined with stapedial reflex and caloric test may still incline to use ABR in selected cases.

Assessment of real-time clinical facial function during vestibular schwannoma resection.

OBJECTIVES: To describe a technique for quantifying residual facial function after vestibular schwannoma surgery. The intraoperative electrophysiological results are correlated with immediate postoperative clinical facial function to assess technique validity. STUDY DESIGN: Prospective blinded study. METHODS: Thirty-two patients undergoing translabyrinthine resection of vestibular schwannoma were included. Compound muscle action potential (CMAP) amplitude was calculated to supramaximal stimulation of the facial nerve, proximal to vestibular schwannoma compression, at the brain stem. The procedure was repeated after tumor removal. Comparison of the two CMAP amplitudes enabled estimation of change in facial function during surgery. The data were correlated with intracranial tumor diameter and immediate postoperative clinical facial function. RESULTS: CMAP amplitude recorded after tumor resection correlated with immediate postoperative clinical facial function (0.879, P < .01). Correlation was improved when residual facial function was calculated (0.944, P < .01). In contrast, preoperative tumor size had relatively poor correlation with immediate postoperative facial function (0.688, P < .01). CONCLUSIONS: Comparison of electrophysiological data before and after tumor removal reduces intersubject variability resulting from intersubject variation in facial muscle morphology. Residual facial function closely correlates with immediate postoperative clinical facial function, assessed using the House-Brackmann grading system. From the data presented, the technique can inform the surgeon of current clinical facial function at any point during the dissection process.

Assessment of facial nerve function in acoustic tumor disease by nasal muscle F waves and transcranial magnetic stimulation.

Standard transcranial magnetic stimulation and nasal muscle F-wave recordings were used to assess proximal facial nerve function in 27 patients with unilateral acoustic tumors (mean diameter, 29 mm) and clinically intact facial nerve function. Latency measurements for F waves and cortical magnetic stimulation were abnormal. Moreover, F ratios, central motor conduction time, and the ratio of response latency to cortical and cisternal magnetic stimulation were significantly increased. Amplitudes were unchanged. Correlation analysis with tumor diameter as dependent variable yielded maximum r values for F-wave latencies (0.57) and F ratios (0.41), whereas for magnetic stimulation, a significant correlation could be found (0.4) only for cortical stimulation. Nasal muscle F-wave recording can reveal clinically inapparent facial nerve dysfunction. Its efficacy in predicting tumor diameter seems to be superior to that of standard magnetic stimulation.

Audiological assessment before and after fractionated stereotactic irradiation for vestibular schwannoma.

PURPOSE: To find the audiological outcome after LINAC-based fractionated stereotactic irradiation (STI). MATERIALS AND METHODS: Twenty-four patients with vestibular schwannoma treated by fractionated STI between 1991 and 1997 had measurable hearing before STI and were followed audiologically for more than 6 months. The pure tone average (PTA) was measured by averaging the air-conduction threshold for five main frequencies (250-4000 Hz) before and periodically after STI in the 24 patients. Several possible prognostic factors for hearing preservation (defined as a PTA change at the last follow-up of less than 10 dB) were investigated. The median follow-up time was 22 months, ranging from 5 to 69 months. The irradiation schedule was 36 Gy in 20 fractions in 5 weeks to 44 Gy in 22 fractions in 6 weeks followed by 4 Gy/1 fraction boost. RESULTS: The pure tone average before STI was distributed from 7 to 73 dB. Fifty percent of patients showed a change in PTA of less than 10 dB, 79.2% of patients showed a change in PTA of less than 20 dB and 20.8% of patients showed a change in PTA of more than 21 dB at the last follow-up. Only one patient (4%) became deaf. Cases with a sudden loss of hearing were more likely to experience hearing preservation than those with gradual loss of hearing (P<0.05). The mean age was younger in patients whose hearing was preserved (P<0.05). Poor pretreatment PTA appeared to linearly correspond to the changes in PTA (regression coefficient 0.78). The size of the tumor was not related to the change in PTA. No relationship was observed between the maximum or peripheral dose and the PTA change. The real benefit of stereotactic boost after small-field fractionated irradiation was not certain. CONCLUSION: Fractionated STI produced a hearing preservation rate compatible with meticulously collimated multi-spots single fraction irradiation. Further follow-up is required to confirm the long-term benefits of fractionation.

[Assessment of cochlear function with distortion products of otoacoustic emissions in acoustic neuroma]. / Nachweis kochleärer Funktionszustände mittels Distorsionsprodukten otoakustischer Emissionen bei Akustikusneurinomen.

Unilateral hearing loss (HL) caused by an acoustic neuroma (AN) is regarded to be neural ("non-cochlear"). By using otoacoustic emissions it is possible to prove concurrent sensory (cochlear) HL. We prefer distortion-product otoacoustic emissions (DPOAE) because these are more frequency-specific and stable. From April 1994 to May 1996, we examined preoperatively 24 patients with radiologically proven AN. Pure-tone audiometry, DP-grams, brainstem-evoked response audiometry (BERA) and vestibular studies were performed in all cases, while special auditory tests (Fowler, Carhart) and short increment sensitivity indices were also performed in 12 cases. BERA was pathological in 23 cases and latencies were borderline in one case. After comparing audiograms and DP-grams we found 13 patients with sensory HL, 4 patients with combined sensorineural HL and 7 patients with neural HL. There was a strong correlation between the results of DPOAE and the results of special auditory test (phi = 0.63) whereas there was no correlation between tumor size and cochlear function. The result showed that the typical HL caused by AN was a combined sensorineural loss. DPOAE were not suited for the detection of AN but were able to give exact information about any remaining cochlear function.

[Assessment of cochlear functions of patients with acoustic neuromas].

Electrocochleographic cochlear microphonics (ECochG-CM) and Evoked Otoacoustic Emissions (EOAE) were recorded for 17 patients with acoustic neuromas to assess their cochlear functions. ECochG-CM was recorded by a transtympanic needle electrode technique. The acoustic stimuli of EOAE were short tone bursts and thresholds of detection of the slow components were determined. In 13 of the 17 patients, elevated detection thresholds of ECochG-CM and/or abnormal interaural differences in detection thresholds of the slow components of EOAE were observed. The patients with hearing loss and an elevated thresholds of CM were believed to have cochlear impairments. Those with hearing loss and a relatively low detection threshold of CM were thought to have cochlear nerve damage and a smaller degree of cochlear impairment. The correlation of ECochG-CM and EAOE was 0.799. Both ECochG-CM and EOAE were useful in evaluating the cochlear functions of patients with acoustic neuromas. Although EOAE was easier to apply clinically, ECochG was indispensable when detailed examinations of cochlear functions were necessary.

Acoustic neuroma: clinical aspects, audiovestibular assessment, diagnostic delay, and growth rate.

The diagnostic findings in 300 patients with acoustic neuromas are reported. Because of a centralized treatment of acoustic neuromas, we have a uniform diagnostic work-up of all patients, which enables us to make a nonselected comparison of the diagnostic efficiency of the various tests. In patients with hearing better than 80 dB, a normal auditory brainstem response, the presence of recruitment, and normal caloric reaction, the presence of a tumor can be excluded. In patients with poor hearing, tomography is necessary if one does not prefer to perform CT directly. If CT, even with contrast enhancement, is negative, we continue to perform air CT. Only then do we know whether or not the patient has a tumor. Magnetic resonance imaging has not been available to us, but with this diagnostic modality even intrameatal tumors are visualized. However, with the present economy involved with magnetic resonance imaging it is not realistic at the present time to use this way of imaging as a screening procedure. In spite of an intensive campaign for making early diagnosis of acoustic neuromas, our attempts have not been successful, since we have even more tumors measuring over 40 mm in diameter among the latest 100 patients than among the first one hundred. Both patients and physicians (otologists) to some extent are still ignoring the possible significance of a unilateral, progressive, sensorineural hearing impairment. Guidelines for improving this situation are given. Twenty-one patients were followed for an average of 4 years, repeated CT scans were performed, and the tumor appeared to be progressing to a size requiring surgical intervention in only three of these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Limits of ABR and contribution of transtympanic electrocochleography in the assessment of cerebellopontine angle tumours.

Auditory brainstem responses (ABR) and transtympanic electrocochleography (ECochG) were analysed for 63 patients with tumours of the cerebellopontine angle (CPA) and/or internal auditory meatus (IAM). ABR recordings indicated a clearly prolonged wave I-V interval (above 4.3 ms) in half of the patients, hence suggesting a retrocochlear disorder. For the remaining patients ABR alone was not sufficient for clear diagnosis and ECochG was therefore used in addition. When the latency of wave V was uncertain due to the absence of wave I, the latency of wave N1 was always measurable by ECochG. The NI-V interval evaluated in this way was always significantly prolonged (above 4.5 ms) relative to a control group of patients with a sensorineural hearing loss. In 9 of the 13 subjects without any discernible ABR, an ECochG response could be recorded and its threshold was often better than the mean pure tone audiogram. This study confirms the validity of transtympanic ECochG in the diagnosis of retrocochlear disorders. The time difference observed between wave N1 (ECochG) and wave I (ABR) in CPA tumours is discussed and a possible explanation is proposed.

Electrophysiologic assessment of the lower portion of the auditory pathway in the human subject. A preliminary report on auditory evoked eighth nerve and brain stem potentials including their relation to the electrocochleogram.

The electrophysiologic approaches to the assessment of electrical activity of the various portions of the human auditory pathway are reviewed. A method of detection of click evoked eighth nerve and brain stem responses with the use of surface electrodes is described. Preliminary observations in the normal subject with different stimulus parameters and in patients with unilateral deafness are presented. Simultaneous recordings of the eighth nerve and brain stem responses with the cortical evoked response and with the extratympanic electrocochleogram are described. The technique of click evoked eighth nerve and brain stem potentials offers us an additional method of objective assessment of auditory function in a human subject.