The sensitivity of auditory brainstem response testing in small acoustic neuromas.

Auditory brainstem response (ABR) testing is a reliable and sensitive test for retrocochlear pathology in neurotologic diagnosis. Several investigators have reported the sensitivity of ABR testing as 95% or greater. Fifty-one consecutive patients with surgically confirmed acoustic neuromas were examined. Forty patients had sufficient hearing preoperatively for assessment with ABR. In addition, all had been evaluated with gadolinium-enhanced magnetic resonance imaging and conventional electronystagmography. Overall, 34 of 40 patients (85%) had abnormal ABRs. One of 25 patients with extracanalicular tumors had a normal ABR for a false-negative rate of 4%; however, 5 of 15 patients with intracanalicular tumors had normal ABRs for a false-negative rate of 33%. Tumor size and nerve of origin were important factors affecting the ABR sensitivity. The ABR was less sensitive in detecting intracanalicular tumors than in detecting extracanalicular tumors.     

Contralateral auditory brainstem response abnormalities in acoustic neuroma

Contralateral Auditory Brainstem Response (ABR) findings in a series of 79 patients with unilateral acoustic neuroma are presented. Sixty-four patients (81 per cent) had a normal contralateral ABR, thirteen (16.4 per cent) had latency abnormalities contralaterally and in two patients (2.6 per cent) no consistent responses could be recorded despite good hearing. Abnormalities in the contralateral ABR were analysed and five patients had abnormal III-V interwave intervals, in seven patients the I-III intervals were abnormal and in one patient, only the fifth wave was present and of abnormal latency. The tumour size was assessed by computed axial tomography (CT) and the relationship between tumour size and contralateral ABR findings established. Large tumours (greater than 2.5 cm.) were associated with contralateral ABR abnormalities in 25.6 per cent of the patients, medium tumours (1.0-2.5 cm.) with ABR abnormalities in 14 per cent and there were no abnormalities in the small group (intracanalicular). The implications for interpretation of ABR recordings contralateral to an acoustic neuroma are discussed in relation to brainstem compression and its effect on the wave generator sites.     

Auditory brainstem response and magnetic resonance imaging for acoustic neuromas: costs by prevalence

OBJECTIVE: To compare hypothetical costs for identification of acoustic tumors when using magnetic resonance imaging with gadolinium Gd 64 (MRI-(64)Gd) as a sole diagnostic test and when using auditory brainstem response (ABR) testing followed by MRI-( 64)Gd (ABR + MRI-(64)Gd) for those with positive ABR findings. PATIENTS AND METHODS: Retrospective review of the medical records of 75 patients having surgically confirmed acoustic neuromas to categorize them into 3 subgroups relative to their risk of having a cerebellopontine angle tumor based on history, symptoms, and routine pure-tone and speech audiometric findings. Hypothetical costs associated with identification of patients with acoustic neuroma in each subgroup were calculated for MRI-(64)Gd alone and ABR + MRI-( 64)Gd. Auditory brainstem response sensitivity and specificity data for the 75 patients with acoustic neuroma and 75 patients without a tumor matched for hearing loss were applied to the hypothetical subgroups. Tumor size was considered also. SETTING: Tertiary care center. MAIN OUTCOME MEASURE: Comparison of costs for MRI-(64)Gd and ABR + MRI-(64)Gd. RESULTS: Fouteen patients with acoustic neuroma were assigned to the high-risk category (30% probability); 45 were in the intermediate-risk category (5% probability); and 16 were in the low-risk category (1% probability). Auditory brainstem response testing correctly identified 100% of the large tumors (>2.0 cm), 93% of the medium-sized tumors (1.1-2.0 cm), and 82% of the small tumors (<1.0 cm). The hypothetical costs for identifying 14 patients with acoustic neuroma among 47 patients in the high-risk category using MRI-(64)Gd would be $70,500; ABR + MRI-(64)Gd costs for the 13 patients identified by ABR would be $39,600. Hypothetically 900 patients would be tested to identify the 45 acoustic neuromas in the intermediate-risk category. Magnetic resonance imaging with (64)Gd screening would reach $1.35 million for this sample. Auditory brainstem response testing and MRI-(64)Gd would be $486,000, but 4 acoustic neuromas would be missed. For the low-risk subgroup MRI-6(4)Gd screening of 1600 patients to identify 16 acoustic neuromas would total $2.4 million; ABR + MRI-(64)Gd to identify 15 of them would be $787,500. In this sample of 75 acoustic neuromas, large tumors were more prevalent in the low-risk subgroup than in the high- or intermediate-risk subgroups. CONCLUSIONS: Decisions regarding assessment of patients at risk for acoustic neuromas must be made on a case-by-case basis. Use of ABR + MRI-( 64)Gd allows considerable savings when patients are in the intermediate- or low-risk subgroups. New MRI and ABR testing techniques offer promise for reducing costs.     

Normal auditory brainstem response in patients with acoustic neuroma

Auditory brainstem response testing has been a major breakthrough in audiologic screening for acoustic neuroma because of its high degree of sensitivity. Although it is not uncommon for other cerebellopontine angle masses to present with normal ABR findings, reports of eighth nerve tumors with false-negative auditory brainstem response tests are quite rare. A series of 120 acoustic neuromas resected at the University of Michigan was reviewed and revealed two such patients. These two patients presented with asymmetric sensorineural hearing loss and unilateral tinnitus and were found to have completely normal auditory brainstem response. The diagnosis of acoustic neuroma would have been delayed if a comprehensive evaluation had not been pursued.     

Interaural stacked auditory brainstem response measures for detecting small unilateral acoustic tumors

The Stacked auditory brainstem response (SABR) was developed and investigated as a screening tool for small (≤1 cm) unilateral acoustic tumors (vestibular schwannomas) that were missed by standard clinical auditory brainstem response (ABR) measures [Don et al.: Am J Otol 1997;18:608-621; Audiol Neurotol 2005;10:274-290]. While the SABR measure provided much greater sensitivity than the standard ABR measures for small tumor detection, we believed that the large intersubject variability of the SABR measure compromised both the sensitivity and specificity of the measure. However, as we demonstrate in this paper, the variability between ears of a given individual is small. Thus, we introduced an interaural SABR (ISABR) amplitude difference measure to improve the sensitivity and specificity of the SABR amplitude measure to detect small unilateral acoustic tumors. Its main advantages are two-fold. First, it is somewhat immune to variables that affect the absolute SABR amplitudes because it is a relative measure. Second, it is better at assessing tumor patients with very large and non-tumor patients with very small absolute SABR amplitudes. We believe that the ISABR is a useful addition to ABR measures aimed at detecting the presence of unilateral acoustic tumors.     

The auditory steady-state response: comparisons with the auditory brainstem response

Two studies are reported in which the threshold estimates from auditory steady-state response (ASSR) tests are compared to those of click- or toneburst-evoked auditory brainstem responses (ABRs). The first, a retrospective review of 51 cases, demonstrated that both the click-evoked ABR and the ASSR threshold estimates in infants and children could be used to predict the pure-tone threshold. The second, a prospective study of normal-hearing adults, provided evidence that the toneburst-evoked ABR and the modulated tone-evoked ASSR thresholds were similar when both were detected with an automatic detection algorithm and that threshold estimates varied with frequency, stimulus rate, and detection method. The lowest thresholds were obtained with visual detection of the ABR. The studies illustrate that ASSRs can be used to estimate pure-tone threshold in infants and children at risk for hearing loss and also in normal-hearing adults.     

听觉脑干置入用于双侧听神经瘤全聋患者的听力康复(附1例报告)

目的：探讨听觉脑干置入（ABI）用于双侧听神经瘤全聋患者的听力康复。方法：对1例双侧听神经瘤全聋患者，在经乙状窦枕下径路切除第2侧听神经瘤时，同期将12道听觉脑干装置的电极阵置入第4脑室的侧隐窝内，术中行第Ⅶ、Ⅸ脑神经监测，并且记录电刺激脑干诱发电位，以确定和校正电极位置。术后2个月开通电极并作调试。结果：术后头颅X线侧位片示电极位置正确，术后开通调试发现电刺激12个电极均能引起听觉反应，无一电极引起非听觉反应。结论：多道ABI能让双侧听神经瘤全聋患者产生有意义的听觉。术中电极阵准确地置入到脑干耳蜗核是手术成功的关键。     

Threshold sensitivity and frequency specificity in auditory brainstem response audiometry

Frequency-specific electric response audiometry can be performed on difficult to test young children if the child is sedated and proper choices are made of acoustic stimuli and recording parameters, although certain compromises are necessary. A very satisfactory sedative is secobarbital, administered intramuscularly in doses related to the weight of the child. As stimuli we recommend '2-1-2' tone bursts at 500, 1 000, 2 000, and 4 000 Hz: i.e., with a rise and fall of two periods and a plateau of one period of the modulated tone. A very robust and sensitive response that is not significantly modified by the sedation and is effective for all four frequencies is the P6-SN10 of the early brainstem sequence. To record this complex favorably requires a bandpass input filter of the Butterworth type with pass-band (at -3 dB) from 50 to 1 700 Hz and rejection rates of 24 dB/octave. With this combination, polarity of stimulus is unimportant and sweep time, rate of stimulation and number of responses averaged may be selected for convenience and simplicity. A routine that requires about an hour of testing time is described and the necessary correction factors are given for estimating a child's behavioral pure-tone thresholds. We believe that our threshold estimates are generally correct within 10 dB, and are sufficiently frequency-specific for proper selection of a hearing aid.     

A modified screening protocol for the diagnosis of acoustic neuromas

In many centres the diagnosis of acoustic neuromas relies on a preliminary screening protocol. The current method is a combination of caloric tests, tomography of the internal auditory meati and brain stem evoked response audiometry (BSERA) with 2 positive results indicating the need for further investigation. This protocol, although sensitive lacks specificity and results in a high incidence of normal CT air meatograms. As this procedure is associated with a significant morbidity, we have devised a 'weighted' system of scoring to avoid subjecting large numbers of normal patients to CT air meatography. The proposed system has been derived from screening 61 patients with unilateral sensorineural hearing loss, 24 of whom had an acoustic neuroma. This method reduced the false positive rate of CT air meatography from 68%, using the 2 out of 3 criteria, to 18%, whilst the false negative incidence remained at 8%.     

Use of disposable ear canal electrodes in auditory brainstem response testing

In this study a disposable ear canal electrode and stimulus delivery system (the Enhancer l) was evaluated for its clinical utility and the observed enhancement of the auditory brainstem response Wave I with its use. Data were collected from normally and abnormally hearing subjects, with both the conventional forehead-to-mastoid electrode array and the forehead-to-ear canal electrode arrangement provided by the Enhancer I ear canal electrode setup. For the normally hearing group, simultaneous acquisition of forehead-to-ipsilateral ear canal and forehead-to-ipsilateral mastoid electrode linkages was obtained. For the abnormally hearing subjects, a comparison was made between the Enhancer I system and the conventional forehead-to-mastoid electrode configuration used with a TDH-49 transducer for click delivery. Our findings indicate that Wave I was enhanced substantially when using the disposable ear canal electrode compared with the more conventional forehead-to-mastoid electrode configuration for both normally and abnormally hearing subjects. The Enhancer I electrode evaluated in this study proved to be painless for the subjects and extremely easy to use, requiring no more time in subject preparation than the more common surface recording electrode application.     

Detection functions for the human auditory brainstem response

Previously obtained data characterizing the auditory brainstem response near the threshold for detection in 10 normal-hearing subjects are used to evaluate the detection method applied. The basic detection formula is described in terms of rates of true positive and false positive ABR detection and in combination with the normative ABR values used to calculate the ABR detection functions as well as the corresponding receiver operating characteristics (ROC curves). The observed distribution of the ABR-threshold levels is similar to that derived from the detection function, and therefore verifies the present results which are based partly on theoretical considerations.     

听性脑干反应与畸变产物耳声发射检测在听神经病诊断中的表现和意义

目的分析听神经病患者的听性脑干反应与畸变产物耳声发射特征,探讨该类听力学检测方法在听神经病诊断中的意义。方法回顾性研究本科确诊为听神经病的患者37例,比较分析其听性脑干反应与畸变产物耳声发射检测结果,探索其诊断意义。结果本组患者中,3例5耳（双耳病变2例,单耳病变1例）可引出V波,阈值70～90dB SPL,其余患耳ABR各波均未引出（刺激声强〉100dB SPL）。无论纯音听阈损失程度轻重如何,所有患者的DPOAE均全部引出。在各个频率点上,DPOAE的DP—gram幅值左、右耳间的差异均无统计学意义（P〉0．10）。结论听神经病的主要病变部位可能位于听神经传入通路,或伴有脑干内侧橄榄耳蜗系统的传出神经通路病变。