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.     

Cost comparison of auditory brainstem response versus magnetic resonance imaging screening of acoustic neuroma

The cost-effectiveness of current diagnostic approaches employed in patients with suspected acoustic neuroma was evaluated. Currently, patients with signs and symptoms suggestive of acoustic neuroma, such as sudden unilateral hearing loss and/or tinnitus, undergo auditory brainstem response (ABR) screening tests to rule out this condition. If the ABR is normal, acoustic neuroma can be ruled out. However, if the ABR is abnormal, magnetic resonance imaging (MRI) or computed tomography is necessary to confirm the diagnosis. When one considers the total costs of this screening approach, one can ask whether straight MRI screening of all of these patients would be a more cost-effective approach to diagnosing this condition. A retrospective chart review of patient records obtained from the acoustic diagnostics laboratory at Hotel Dieu Hospital, Kingston, Ontario, was performed. A database of patients who have undergone ABR testing over the past 2 years was compiled and analyzed to assess how many of them went on to receive MRI. The total costs (based on Ontario Health Insurance Plan [OHIP] fee schedule rates) of this approach were compared with the estimated costs of straight MRI screening performed on the same patient population. By making such an analysis, decisions regarding the most cost-effective approach to screening for acoustic neuroma can be objectively assessed.     

Specificity of auditory brainstem response audiometry criteria in acoustic neuroma screening as a function of deviations of reference values in patients with cochlear hearing loss

Summary On the basis of 79 patients with cochlear hearing loss, the statistical distribution of two criteria commonly used in auditory brainstem response audiometry (ABR) was analyzed: the interaural V latency difference (ILD V) and the interaural difference of IN interpeak interval (ID I–V). The distribution of both criteria was Gaussian. By evaluating their standard deviations the percentages of statistical false-positives were estimated. The estimated results were 24% false-positive findings using the decision criterion ILD V > 0.2 ms and 5.4% false-positive findings using ID IN > 0.3 ms. This corresponds closely to the actual false-positive ABR rates obtained in this sample: 21.5% and 6.3%, respectively. In a separate series of 301 unselected cases with asymmetric sensorineural hearing loss, 29 ABRs were suspect for retrocochlear pathology. In 20 patients, ABRs were absent due to severe hearing loss. Retrocochlear pathology could be confirmed in only 2 cases (both from the group with ABR present). Thus, 47 ABRs (15.7% of 299) were false-positive.     

Short-latency auditory evoked potentials in patients with acoustic neuroma and relatively normal hearing

Out of 37 patients with verified neurinoma of the vestibulocochlear nerve 11 had essentially normal hearing and showed significant disorders of BERA (of the scissors type). This proved high sensitivity of computer audiometry (CA) applied to examine patients suspected for retrocochlear lesions. It is recommended to use CA when examining patients complaining of unilateral hearing impairment in order to rule out neurinoma of the 8th cranial nerve, especially at its early stage.     

Pure-tone audiometry of patients with auditory brainstem response abnormalities

To determine the pure-tone thresholds of patients with brainstem disorders, pure-tone audiometry was done on 22 patients with partial auditory brainstem response wave disappearance (including wave I response, wave I-III response, and wave I-IV response). This group of patients was selected since partial wave disappearance indicates pathology of the auditory nerve and/or the brainstem auditory pathway. The pure-tone threshold of these patients was essentially normal or very mildly impaired, except for patients with an acoustic tumor or an other cerebellopontine angle tumor.     

Intraoperative monitoring by transtympanic electrocochleography and brainstem electrical response audiometry in acoustic neuroma surgery

Summary The preservation of hearing is a major aim of contemporary temporal bone surgery. Our present findings demonstrate that intraoperative monitoring is a key method for attaining serviceable postoperative hearing after the removal of an acoustic neuroma. Both electrocochleography (ECoG) and brainstem electrical response audiometry were performed in 96 patients operated on for acoustic neuromas. The specificity of the different monitoring methods was affected by surgical manipulations in addition to such non-specific influences as CSF drainage, core body temperature and anesthesia. In the present study ECoG was found to be more reliable in assessing the intra- and postoperative course with respect to the preservation of cochlear function.     

Preoperative, intraoperative, and postoperative auditory evaluation of patients with acoustic neuroma

This article is a concise clinical review of preoperative, intraoperative, and postoperative auditory evaluation of patients with acoustic neuroma. The author describes behavioral audiometry, auditory brainstem response, and otoacoustic emissions for preoperative evaluation; auditory brainstem and direct eighth-nerve intraoperative monitoring for intraoperative evaluation; and touches on postoperative auditory assessment.     

Hearing preservation using combined monitoring of extra-tympanic electrocochleography and auditory brainstem responses during acoustic neuroma surgery

The aim of this study was to evaluate the efficacy of an intraoperative monitoring hearing preservation strategy that includes simultaneous recordings of an auditory brainstem response (ABR) and non-invasive electrocochleography (ECochG). The combined ABR and tympanic membrane (TM) ECochG testing was performed in 74 patients undergoing acoustic neuroma (AN) surgery. In addition, EMG recordings were conducted to monitor the facial nerve function. Hearing was preserved in 19 of the 30 patients with residual hearing prior to surgery (63%), and facial nerve function was maintained in 89% of the patients. In most cases, the presence of both auditory brainstem and TM-ECochG responses at the end of surgery was associated with preservation of postoperative functional hearing; however, eight patients had a TM-ECochG response with a complete loss of the ABR, pointing to deafferentation of the auditory nerve. Tumour size and preoperative hearing thresholds significantly affected the postoperative hearing. The TM-ECochG response yielded large reproducible responses, which, in some patients, was the only way to monitor the auditory function. This auditory monitoring approach offers a valuable auditory tool that helps to improve the hearing preservation during AN surgery.     

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.     

Vestibular evoked myogenic potentials in acoustic tumor patients with normal auditory brainstem responses

In order to clarify the utility of the vestibular evoked myogenic potential (VEMP) in detecting acoustic tumors, we report two patients who were found to have normal auditory brainstem responses (ABRs) and abnormal VEMPs. To record VEMPs, electromyographic responses to brief loud clicks (0.1 ms at 95 dBnHL) were amplified and averaged on the sternocleidomastoid muscle ipsilateral to the stimulated side. The stimulation rate was 5 Hz and the analysis time 50 ms. The first case was a 54-year-old woman in whom VEMPs were absent on the affected side while caloric tests and ABRs were normal. The second case was a 58-year-old woman whose VEMPs were absent on the affected side while caloric tests revealed a 22% canal paresis and normal ABRs. These results and previous studies suggested that the VEMP could reflect a function different from those evaluated by the ABR or the caloric test. We concluded that the VEMP can provide useful information in diagnosing acoustic tumors. Received: 17 March 1998 / Accepted: 29 July 1998     

Hearing preservation using combined monitoring of extra-tympanic electrocochleography and auditory brainstem responses during acoustic neuroma surgery

The aim of this study was to evaluate the efficacy of an intraoperative monitoring hearing preservation strategy that includes simultaneous recordings of an auditory brainstem response (ABR) and non-invasive electrocochleography (ECochG). The combined ABR and tympanic membrane (TM) ECochG testing was performed in 74 patients undergoing acoustic neuroma (AN) surgery. In addition, EMG recordings were conducted to monitor the facial nerve function. Hearing was preserved in 19 of the 30 patients with residual hearing prior to surgery (63%), and facial nerve function was maintained in 89% of the patients. In most cases, the presence of both auditory brainstem and TM-ECochG responses at the end of surgery was associated with preservation of postoperative functional hearing; however, eight patients had a TM-ECochG response with a complete loss of the ABR, pointing to deafferentation of the auditory nerve. Tumour size and preoperative hearing thresholds significantly affected the postoperative hearing. The TM-ECochG response yielded large reproducible responses, which, in some patients, was the only way to monitor the auditory function. This auditory monitoring approach offers a valuable auditory tool that helps to improve the hearing preservation during AN surgery.     

Frequency selectivity in patients with acoustic neuroma

Frequency selectivity was compared in subjects with hearing loss due to acoustic neuroma and cochlear pathology, and normal listeners. A particular interest was the role of probe tone parameters on the shape of the tuning curve. Psychophysical tuning curves (PTCs) were measured for each of two equal energy 2000-Hz probe tones (10 dB SL/300 msec and 17 dB SL/60 msec), using simultaneous 1/3-octave narrowband noise maskers centered at 1, 1.25, 1.6, 2.5, 3.15, and 4 kHz. The results showed that the critical masker levels obtained for impaired listeners were significantly greater than those from normal subjects. The slope of the low-frequency limb of the PTC was steeper for normal compared to hearing-impaired listeners but there was no difference due to site of lesion. In all three groups, the critical masker levels obtained with the short probe were significantly greater than those for the long probe, negating the hypothesis that equal energy probes would yield the same outcomes. Tuning in listeners with hearing loss was highly correlated with audiometric threshold but not with tumor size, width of the internal auditory canal, or tumor location within the cerebellopontine angle. The main conclusion was that cochlear and retrocochlear hearing loss are similar with respect to their effect on frequency selectivity.     

Gait instability in patients with acoustic neuroma

OBJECTIVE: To investigate pathological gait in patients with unilateral acoustic neuroma using tactile sensors placed under both feet. MATERIAL AND METHODS: Forty-three patients were enrolled in the study. They were categorized into two groups: the small tumor group had tumors < 2 cm from the porus acousticus without any brainstem compression and the large tumor group had tumors > 2 cm from the porus acousticus with brainstem compression. Eighteen healthy subjects served as controls. Subjects were asked to walk freely with eyes open or closed for a distance of nearly 8 m. The coefficients of variation (CVs) of stance, swing and double support were calculated. The stability of the trajectories of the center of force and the foot pressure difference were also studied. RESULTS: The CVs of stance, swing and double support were significantly greater with eyes closed and, with the exception of double support, these differences were greater in the tumor groups. The instability of the trajectories of the center of force was significantly greater in the tumor group, and in the large tumor group the horizontal component of sway movement of the trajectories of the center of force of the foot on the same side as the lesion was greater than that on the intact side with eyes closed. Regarding foot pressure differences between the two feet, the large tumor group had a greater foot pressure for the foot on the same side as the lesion than for the foot on the intact side, especially with eyes closed. No significant difference was found in the small tumor group. CONCLUSION: The presence of acoustic neuroma may cause unstable gait, and steady gait is considerably dependent on visual input. Larger tumors may produce shifts in the body's center of gravity to the lesioned side during gait, especially under conditions of visual deprivation. These abnormalities may reflect some influences on gait control systems such as phase and muscular tonus control systems.     

Tumor-associated hemorrhage in patients with acoustic neuroma

OBJECTIVE: To describe the clinical significance of tumor-associated hemorrhage in patients with acoustic neuromas. STUDY DESIGN: Retrospective chart review. SETTING: University-based, tertiary care teaching hospital. PATIENTS: Three patients with acoustic neuromas who experienced symptomatic tumoral bleeding. INTERVENTIONS: Radiographic imaging, surgical removal of tumors, and pathologic analysis. MAIN OUTCOME MEASURES: Patient histories, radiologic characteristics, surgical results, and pathologic findings. RESULTS: Tumoral hemorrhage can occur in patients with acoustic neuromas. These three cases and a review of the world literature suggest that tumor size may be the most important risk factor for tumor-related hemorrhage. CONCLUSION: These findings have implications for those patients with acoustic neuromas who choose not to have surgical removal.     

Audiometric findings in patients with acoustic neuroma

OBJECTIVE: Hearing loss remains the most common symptom associated with acoustic neuroma. This study documents the audiometric findings from 721 acoustic neuroma procedures. STUDY DESIGN: This was a retrospective study. The preoperative audiometric data were compiled and were analyzed by patient age, gender, tumor size, time of surgery, and neurofibromatosis Type 2 (NF 2). Postoperative audiometric data were arranged and compiled in the same way. The hearing classification proposed by the AAO-HNS was applied to all preoperative and postoperative cases. SETTING: Tertiary referral center. PATIENTS: Surgically confirmed acoustic neuroma patients who had not previously received surgical or radiosurgical therapy. Patients underwent surgery by the retrosigmoid approach. INTERVENTION: Surgical removal of an acoustic neuroma. MAIN OUTCOME RESULT: Provision of pure tone and speech data from a group of acoustic neuroma patients, including application of the recently introduced and accepted AAO-HNS hearing classification system. RESULTS: Preoperative audiometric data were obtained from 694 of 721 patients (96%), of whom 619 had measurable hearing. Postoperative audiometry was performed on 606 patients; 152 had usable data. The combined preoperative audiometric data revealed a high frequency sensorineural hearing loss. Word recognition was servicable. The postoperative pure tones and word recognition scores were worse than preoperative scores. Age, gender, tumor size, and time of surgery had some impact on the preoperative hearing and the postoperative result; NF 2 did not. CONCLUSIONS: The study confirms that hearing alteration is almost universal in acoustic neuroma patients. Hearing preservation is possible in a significant number of cases; however, the postoperative auditory function tends to be worse.     

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.     

Critical bandwidth in patients with acoustic neuroma

Eleven patients with verified acoustic neuroma had critical band estimation performed by the method of loudness summation using noise bands centered around 1 kHz. The normal loudness difference between broad band noise and narrow band noise was reduced at all levels except the highest. Judged as single individuals, 9 of the 11 patients had a normal critical band. The pooled data indicated a normal critical band, both in patients with hearing loss less than 50 dB HL and in patients with hearing loss greater than or equal to 50 dB HL. The results are similar to those obtained in patients with Ménière's disease (Bonding, 1978c) and thus CB-measurements cannot be utilized for differentiating between cochlear and retrocochlear lesions. However, at the highest test levels applied the loudness difference between broad band noise and narrow band noise appeared to have some correlation to the presence or absence of recruitment.     

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.     

Acoustic neuroma and the contralateral ear: recovery of auditory brainstem response abnormalities after surgery

Auditory brainstem responses are an established technique in the diagnosis of acoustic neuroma. In several reports abnormalities are shown to occur in the contralateral ear. That these abnormalities recover has been demonstrated, but only in terms of changes in inter-peak latency. In only one case has the waveform trace showing this been published. We present a case in which a highly abnormal wave form was obtained from the ear contralateral to a large acoustic neuroma. Following excision of the lesion, the waveform reverted to a normal pattern. The literature on the subject is reviewed.