Electrocochleography and auditory brainstem electric responses in patients with pontine angle tumors

Auditory Neural Responses and Communicative Functioning in Children With Microcephaly Related to Congenital Zika Syndrome

OBJECTIVES

Children with microcephaly exhibit neurodevelopmental delays and compromised communicative functioning, yielding challenges for clinical assessment and informed intervention. This study characterized auditory neural function and communication abilities in children with microcephaly due to congenital Zika syndrome (CZS).

DESIGN

Click-evoked auditory brainstem responses (ABR) at fast and slow stimulation rates and natural speech-evoked cortical auditory evoked potentials (CAEP) were recorded in 25 Brazilian children with microcephaly related to CZS ( M age: 5.93 ± 0.62 years) and a comparison group of 25 healthy children ( M age: 5.59 ± 0.80 years) matched on age, sex, ethnicity, and socioeconomic status. Communication abilities in daily life were evaluated using caregiver reports on Vineland Adaptive Behavior Scales-3.

RESULTS

Caregivers of children with microcephaly reported significantly lower than typical adaptive functioning in the communication and socialization domains. ABR wave I latency did not differ significantly between the groups, suggesting comparable peripheral auditory function. ABR wave V absolute latency and waves I-V interwave latency were significantly shorter in the microcephaly group for both ears and rates. CAEP analyses identified reduced N2 amplitudes in children with microcephaly as well as limited evidence of speech sound differentiation, evidenced mainly by the N2 response latency. Conversely, in the comparison group, speech sound differences were observed for both the P1 and N2 latencies. Exploratory analyses in the microcephaly group indicated that more adaptive communication was associated with greater speech sound differences in the P1 and N2 amplitudes. The trimester of virus exposure did not have an effect on the ABRs or CAEPs.

CONCLUSIONS

Microcephaly related to CZS is associated with alterations in subcortical and cortical auditory neural function. Reduced ABR latencies differ from previous reports, possibly due to the older age of this cohort and careful assessment of peripheral auditory function. Cortical speech sound detection and differentiation are present but reduced in children with microcephaly. Associations between communication performance in daily life and CAEPs highlight the value of auditory evoked potentials in assessing clinical populations with significant neurodevelopmental disabilities.

Auditory cortical generators of the Frequency Following Response are modulated by intermodal attention

The efferent auditory system suggests that brainstem auditory regions could also be sensitive to top-down processes. In electrophysiology, the Frequency Following Response (FFR) to speech stimuli has been used extensively to study brainstem areas. Despite seemingly straight-forward in addressing the issue of attentional modulations of brainstem regions by means of the FFR, the existing results are inconsistent. Moreover, the notion that the FFR exclusively represents subcortical generators has been challenged. We aimed to gain a more differentiated perspective on how the generators of the FFR are modulated by either attending to the visual or auditory input while neural activity was recorded using magnetoencephalography (MEG). In a first step our results confirm the strong contribution of also cortical regions to the FFR. Interestingly, of all regions exhibiting a measurable FFR response, only the right primary auditory cortex was significantly affected by intermodal attention. By showing a clear cortical contribution to the attentional FFR effect, our work significantly extends previous reports that focus on surface level recordings only. It underlines the importance of making a greater effort to disentangle the different contributing sources of the FFR and serves as a clear precaution of simplistically interpreting the FFR as brainstem response.

Audiological Evaluation of Vestibular Schwannoma Patients with Normal Hearing

Objective: To evaluate the audiological aspects of vestibular schwannoma (VS) patients with normal hearing. Study Design: Retrospective study. Setting: Quaternary referral center for skull base pathologies. Patients: The records on 4,000 patients who had been diagnosed with VS between 1986 and December 2017 were retrospectively reviewed. The patients included in the study were the ones who complied with the strict audiological normality criteria, as follows: a pure tone hearing threshold (at the 6-octave-spaced frequencies from 250 to 8,000 Hz) ≤25 dBHL; a word recognition score >90%; and interaural differences ≤10 dB at each frequency. Interventions: Auditory brainstem response (ABR) testing and radiological imaging. Main Outcome Measures: The incidence of normal objective hearing among VS patients, and the diagnostic utility of the ABR and the effect of tumor size and site on the response. Results: The incidence of normal hearing among VS patients was 4.2%. Tinnitus and vertigo were the most common symptoms across tumor grades; 5.6% of the tumors were large and giant tumors. The ABR yielded a sensitivity of 73.6%, with a false negative rate of 26.3% using a cutoff point of 0.2 ms for interaural latency differences. Conclusions: The diagnosis of VS should not be based on audiometric thresholds alone. Alarming signs of VS should be clear to the physician in order not to miss or delay the diagnosis of the disease. The ABR is useful in the diagnosis of VS, but normal results do not exclude the occurrence of the disease in patients with normal hearing.

Cochlea and auditory nerve

The transduction process in the cochlea requires patent hair cells. Population responses that reflect this patency are the cochlear microphonic (CM) and summating potential (SP). They can be measured using electrocochleography (ECochG). The CM reflects the sound waveform in the form of outer hair cell (OHC) depolarization and hyperpolarization, and the SP reflects the average voltage difference of the OHC membrane potential for depolarization and hyperpolarization. The CM can be measured using ECochG or via the so-called otoacoustic emissions, using a sensitive microphone in the ear canal. Neural population responses are called the compound action potentials (CAPs), which by frequency selective masking can be decomposed into narrow-band action potentials (NAPs) reflecting CAPs evoked by activity from small cochlear regions. Presence of CM and absence of CAPs are the diagnostic hallmarks of auditory neuropathy. Increased and prolonged SPs are often found in Ménière's disease but are too often in the normal range to be diagnostic. When including NAP waveforms, Ménière's disease can be differentiated from vestibular schwannomas, which often feature overlapping symptoms such as dizziness, hearing loss, and tinnitus. The patency of the efferent system, particularly the olivocochlear bundle, can be tested using the suppressive effect of contralateral stimulation on the otoacoustic emission amplitude.

Current audiological diagnostics

Today's audiological functional diagnostics is based on a variety of hearing tests, whose large number takes account of the variety of malfunctions of a complex sensory organ system and the necessity to examine it in a differentiated manner and at any age of life. The objective is to identify nature and origin of the hearing loss and to quantify its extent as far as necessary to dispose of the information needed to initiate the adequate medical (conservative or operational) treatment or the provision with technical hearing aids or prostheses. Moreover, audiometry provides the basis for the assessment of impairment and handicap as well as for the calculation of the degree of disability. In the present overview, the current state of the method inventory available for practical use is described, starting from basic diagnostics over to complex special techniques. The presentation is systematically grouped in subjective procedures, based on psychoacoustic exploration, and objective methods, based on physical measurements: preliminary hearing tests, pure tone threshold, suprathreshold processing of sound intensity, directional hearing, speech understanding in quiet and in noise, dichotic hearing, tympanogram, acoustic reflex, otoacoustic emissions and auditory evoked potentials. Apart from a few still existing gaps, this method inventory covers the whole spectrum of all clinically relevant functional deficits of the auditory system.

Ups and Downs in 75 Years of Electrocochleography

Before 1964, electrocochleography (ECochG) was a surgical procedure carried out in the operating theatre. Currently, the newest application is also an intra-operative one, often carried out in conjunction with cochlear implant surgery. Starting in 1967, the recording methods became either minimal- or not-invasive, i.e., trans-tympanic (TT) or extra tympanic (ET), and included extensive studies of the arguments pro and con. I will review several valuable applications of ECochG, from a historical point of view, but covering all 75 years if applicable. The main topics will be: (1) comparing human and animal cochlear electrophysiology; (2) the use in objective audiometry involving tone pip stimulation-currently mostly pre cochlear implantation but otherwise replaced by auditory brainstem response (ABR) recordings; (3) attempts to diagnose Ménière's disease and the role of the summating potential (SP); (4) early use in diagnosing vestibular schwannomas-now taken over by ABR screening and MRI confirmation; (5) relating human electrophysiology to the effects of genes as in auditory neuropathy; and (6) intracochlear recording using the cochlear implant electrodes. The last two applications are the most recently added ones. The "historical aspects" of this review article will highlight the founding years prior to 1980 when relevant. A survey of articles on Pubmed shows several ups and downs in the clinical interest as reflected in the publication counts over the last 75 years.

Role of cervical vestibular evoked myogenic potentials (cVEMP) and auditory brainstem response (ABR) in the evaluation of vestibular schwannoma

INTRODUCTION

Cervical vestibular evoked myogenic potentials (cVEMP) can assess the integrity of the inferior vestibular nerve thereby promising to be a useful tool in the audiological test battery to diagnose vestibular schwannoma.

OBJECTIVE

To ascertain the utility of cVEMP in diagnosis of vestibular schwannoma in conjunction with the ABR and to evaluate whether the size of lesion has any effect on the cVEMP measures.

METHODS

Case-files of 15 known cases of vestibular schwannoma whose pure tone audiometry, auditory brainstem response (ABR), cVEMP and radiological investigation findings were available, were included in the study. Patients were categorised as large or small tumours based on the size. The absolute and inter-peak latencies of ABR, amplitudes of waves V and I, and inter-aural latency difference of wave V of ABR; and latency of P1 and N1 of cVEMP and amplitude of P1-N1 complex were considered in the study.

RESULTS

There were eight large and nine small tumours. All the patients with large tumours showed significant severity of hearing loss whereas only three out of nine patients with small tumours showed severe to profound deafness in the affected ear. The rest showed hearing status ranging from normal hearing sensitivity to moderate hearing loss. Most of the patients with large tumours showed complete absence of ABR in the affected ears with no identifiable wave-peaks. ABR in small tumours exhibited delayed III-I and delayed V-I interpeak latency interval (IPL). Four out of five patients with large unilateral tumours revealed contralateral effects of reduced amplitude or absence of cVEMP. On the contrary, six out of eight unilateral small tumours showed a normal cVEMP response in the contralateral ear. Both the patients with NF2 in the present study demonstrated cVEMP abnormalities.

CONCLUSION

ABR and cVEMP, when used in combination, can be of immense use in identification of neuro-otologic conditions such as vestibular schwannoma and bilateral tumours in NF2. In the evaluation of unilateral vestibular schwannoma, abnormal contralateral findings of cVEMP and ABR are strongly indicative of the tumour size >2.5cm. In unilateral severe to profound loss wherein ABR in poorer ear cannot give information of site-of-lesion, cVEMP can help in the differentiation.

ABR in the diagnosis of vestibular schwannomas: a meta-analysis

PURPOSE

The aim of this study is to rigorously evaluate the role of auditory brainstem response (ABR) testing in the diagnosis of vestibular schwannomas (VS).

MATERIALS AND METHODS

Searches were conducted in multiple online databases, supplemented by hand searches. From the studies chosen for final inclusion, relevant data were extracted and meta-analysis of pooled data was performed.

RESULTS

623 studies were identified from which 43 met inclusion criteria for analysis (1978 to 2009) including 3314 patients. Pooled sensitivity for ABR detection of vestibular schwannomas was 93.4% (95% CI 92.6-94.3, P=0.0000). For tumors less than 1cm (8 studies, 176 patients) sensitivity was 85.8% (95% CI 80.6-90.1, P=0.0116). For tumors greater than 1cm (6 studies, 251 patients) pooled sensitivity was 95.6% (95% CI 93.1-98.2, P=0.0660). Sensitivity of ABR to detect extracanalicular tumors was higher than for intracanalicular tumors, though pooled data were not statistically valid. Pooled specificity (8 studies, 2432 patients) was 82.0% (95% CI 80.5-83.6, P=0.0000).

CONCLUSIONS

Although MRI remains the gold standard, emerging trends towards more conservative management coupled with limited financial resources may prompt many clinicians to review the role of ABR testing in screening for retrocochlear pathology. In light of the high sensitivity and specificity of ABR testing for VS, we strongly urge its reconsideration as a useful diagnostic tool for patients with clinically suspected VS.

Effects of Stimulus Intensity on Low-Frequency Toneburst Cochlear Microphonic Waveforms

This study investigates changes in amplitude and delays in low-frequency toneburst cochlear microphonic (CM) waveforms recorded at the ear canal in response to different stimulus intensities. Ten volunteers aged 20-30 were recruited. Low-frequency CM waveforms at 500 Hz in response to a 14-ms toneburst were recorded from an ear canal electrode using electrocochleography techniques. The data was statistically analyzed in order to confirm whether the differences were significant in the effects of stimulus intensity on the amplitudes and delays of the low-frequency CM waveforms. Electromagnetic interference artifacts can jeopardize CM measurements but such artifacts can be avoided. The CM waveforms can be recorded at the ear canal in response to a toneburst which is longer than that used in ABR measurements. The CM waveforms thus recorded are robust, and the amplitude of CM waveforms is intensity-dependent. In contrast, the delay of CM waveforms is intensity-independent, which is different from neural responses as their delay or latency is intensity-dependent. These findings may be useful for development of the application of CM measurement as a supplementary approach to otoacoustic emission (OAE) measurement in the clinic which is severely affected by background acoustic noise. The development of the application in the assessment of low-frequency cochlear function may become possible if a further series of studies can verify the feasibility, but it is not meant to be a substitute for audiometry or OAE measurements. The measurement of detection threshold of CM waveform responses using growth function approach may become possible in the clinic. The intensity-independent nature of CMs with regards to delay measurements may also become an impacting factor for differential diagnoses and for designing new research studies.

Hearing loss in vestibular schwannomas: analysis of cochlear function by means of distortion-product otoacoustic emissions

OBJECTIVE

We investigated cochlear function in a group of patients affected by vestibular schwannoma (VS), by means of recording distortion-product otoacoustic emissions (DPOAEs).

METHODS

Between January 1996 and January 2007, we observed 183 patients affected by unilateral VS. DPOAEs, compared to the corresponding hearing thresholds, were subjectively classified into three categories: "compatible" with hearing function, "cochlear" and "retro-cochlear". We also related the responses to some clinical variables (tumor size, intracanalicular tumor and radiologic appearance of the internal auditory canal). Statistical analysis was performed.

RESULTS

In 137 cases (74.9%), DPOAEs were as expected based on audiometry responses, while in 11 patients (6%) a "cochlear" DP-gram was recorded and in 35 patients (19.1%) DPOAEs evidenced a "retro-cochlear" pattern. In eight cases we detected acoustic responses despite a profound hearing loss. No statistically significant data merged from the comparison between "cochlear" and "retro-cochlear" responses and the clinical variables.

CONCLUSION

Our results confirm that sensorineural hearing loss due to VS can be of sensory and/or neural origin. DPOAEs still remain just a complementary auditory test; nevertheless, in case of severe or profound unilateral hearing loss, recorded acoustic responses may be suspicious for the presence of a vestibular schwannoma.

Auditory brainstem response findings in hypothyroid and hyperthyroid disease

OBJECTIVE

Retrocochlear sensorineural hearing loss, associated with hypothyroidism, has been reported. This study investigated that claim.

METHODS

Audiometric and auditory brainstem response (ABR) measures of patients with hyper- and hypothyroidism.

RESULTS

The hyperthyroid group (14 patients) gave no audiometric or ABR results that differed significantly from normal controls. The audiometric findings for the hypothyroid group (21 patients) showed that 36% of this group had a four frequency average threshold greater than 25dB. The statistically significant findings for ABR were a reduction in the amplitude of waves III and V and an abnormal increase in the I-V interval, appearing to confirm a retrocochlear disorder. However, as these patients have a low body temperature, the data were analysed by temperature and the results showed that the ABR abnormalities could be explained by body temperature.

CONCLUSIONS

Hyperthyroid patients did not differ significantly from the controls. The four frequency average threshold and ABR results in hypothyroid patients did differ from the controls. However there is no clear evidence that the retrocochlear involvement is a direct result of the hypothyroidism. The abnormalities in the ABR can be explained by the low body temperature seen in these patients.

SIGNIFICANCE

This corrects the impression that hypothyroid patients have retrocochlear problems (indicated by ABR); a conclusion confirmed by data from 7 patients after thyroxin treatment when body temperatures were close to normal values and ABR I-V intervals within or near normal limits.

Preoperative speech and pure-tone audiometry in four types of patients with acoustic neuroma

PURPOSE

The goal of this study was to compare pure-tone and speech audiometry in 4 groups of patients with confirmed unilateral acoustic neuroma in which auditory brainstem responses and transient-evoked otoacoustic emissions were either both normal, abnormal, or one of the tests was abnormal.

MATERIAL AND METHODS

This study was realized during a preoperative assessment of 65 patients (29 men, 36 women) from 25 to 78 years of age suffering from unilateral acoustic neuroma. The assessment, preceded by tympanometry, included recordings of auditory brainstem responses, transient-evoked otoacoustic emissions, pure-tone audiometry, speech recognition thresholds, and speech discrimination.

RESULTS

Some discrepancies between objective and behavioral test results were noticed. Subjects with no otoacoustic emissions but present auditory brainstem responses did not show any significant difference in their speech scores as compared with subjects with both auditory brainstem responses and otoacoustic emissions.

CONCLUSIONS

In summary, this study showed that comparable audiometric findings in acoustic neuroma patients can be found regardless of the presence of transient otoacoustic emissions (TEOAEs). TEOAEs are a good screening tool and have been used, like auditory brainstem-evoked responses, as a predictive measure before hearing preservation procedures but cannot predict the audiogram or give information about speech perception. The findings confirm that even if auditory brainstem responses are an extremely useful diagnostic tool for identifying acoustic neuroma, this test provides only giving pieces of information regarding auditory abilities. Also, the pure-tone audiogram gives useful information but has to be used in conjunction with speech audiometry to get an accurate picture of the patient's true auditory abilities.

Clinical picture of vestibular schwannoma

PURPOSE

To characterize the clinical picture with vestibular schwannoma, we retrieved 122 patients with vestibular schwannoma from the vestibular unit of the Helsinki University Central Hospital.

PROCEDURES

The patients filled out a questionnaire concerning their symptoms, earlier diseases, accidents, and the use of tobacco and alcohol. This information was then completed with results of audiometric, neurotologic and imaging studies. The data were prospectively stored to the database of neurotologic expert system called ONE.

RESULTS

The average tumor size was 21 mm. Most of the patients had hearing loss (94%) and tinnitus (83%) but only half of them (49%) had vertigo attacks. The most common initial symptom was hearing loss combined with tinnitus (34%, n=44). Vertigo only was the initial symptom for 12 patients. The mean duration of a vertigo attack was from 5 min to 4 h and the intensity of the attack was regularly mild (37%) or moderate (32%). The vertigo of the vestibular schwannoma patients differed from vertigo in other diseases by the absence (63%) or low intensity (18%) of nausea. Spontaneous nystagmus was present in 56 patients (46%), and caloric asymmetry (>25%) was observed in 66% (n=69). Caloric asymmetry increased with tumor size. The prevalence of headache was 18% (n=21). Sudden slips seldom (7%) occurred.

CONCLUSION

Hearing loss and tinnitus are the main symptoms of vestibular schwannoma. Only half of patients have vertigo. Screening to detect vestibular schwannoma is more yielding in sudden deafness patients rather than in patients with Meniere's disease.

Electrocochleographic study in patients with vestibular schwannomas and U-shaped audiograms

To determine the nature of sensorineural hearing loss in the middle-frequency range (U-shaped audiogram), we compared the differences in electrocochleographic findings for 15 ears with vestibular schwannomas and 10 ears without tumours. Short-tone bursts of 0.5, 1, 2, and 4 kHz were used to evoke cochlear microphonics (CM). Ears with tumours had normal or lower CM detection thresholds than ears without tumours. Input-output curves for 1-kHz frequency were normal in 10 ears with tumours and in 1 ear without tumours. These indicate that tumour ears have no or mild cochlear dysfunction. In addition, CM detection thresholds of ears with tumours were lower than audiometric thresholds, particularly at the 1- and 2-kHz region. These findings suggest that the loss seen by audiometry in ears with vestibular schwannomas was from a retrocochlear component.

Cochlear microphonics for hearing preservation in vestibular schwannoma surgery

OBJECTIVES

To determine whether cochlear function is beneficial in decision-making concerning the selection of hearing preservation surgery for vestibular schwannoma.

STUDY DESIGN

Retrospective review of 44 patients undergoing tumor resection with a middle fossa approach.

METHODS

Cochlear microphonics in electrocochleography together with tumor size, pure-tone average (PTA), speech discrimination score (SDS), auditory brainstem response (ABR), and compound action potentials were examined. As acoustic stimuli, short tone-bursts with frequencies of 0.5, 1, and 2 kHz were employed to measure cochlear microphonics and a click was used to obtain compound action potentials. We determined detection thresholds of cochlear microphonics and action potentials.

RESULTS

The overall rate of preservation of serviceable hearing was 59.1% (26/44). There were significant differences between patients with and without serviceable postoperative hearing in PTA, SDS, finding of ABR, compound action potential detection threshold, and mean cochlear microphonic detection threshold (at 0.5, 1, and 2 kHz). However, tumor size was unrelated to hearing outcome. Serviceable hearing was preserved in 23 (76.7%) of 30 patients, with a mean cochlear microphonic detection threshold of 40 dB nHL or less, suggesting normal or slightly impaired cochlear function. Hearing recovery was recognized in three patients, who also had a mean cochlear microphonic detection threshold of 40 dB nHL or less. Of the three patients, two had lower cochlear microphonic detection thresholds than audiometric thresholds, demonstrating the existence of a retrocochlear component in their hearing loss.

CONCLUSIONS

The cochlear microphonic detection threshold predicts not only hearing preservation but also hearing improvement in patients with vestibular schwannomas.

A study of the effects of cochlear loss on the auditory brainstem response (ABR) specificity and false positive rate in retrocochlear assessment

The auditory brainstem response (ABR) test is widely used as a screen for retrocochlear dysfunction in individuals suffering idiopathic auditory and vestibular disturbance. Although its sensitivity for lesions of the lower brainstem is well established, hearing loss is known to have significant effects upon the test's specificity and false positive rate. This study analysed the effects of aspects of cochlear hearing loss including level, slope and general audiogram shape on these properties of the ABR test in a large clinical group. The study comprised 306 patients (153 male, 153 female) referred for ABR screening to exclude retrocochlear dysfunction. Of 566 ears meeting the inclusion criteria, 85 (15 per cent) failed the test. On follow-up eight ears (3 per cent) were confirmed to have some form of retrocochlear abnormality, seven of which were pathological. All had abnormal ABR results. No cases of retrocochlear abnormality were found in the ABR pass group. In those patients diagnosed as free of retrocochlear problems, the importance of the I-V interval as a primary index of function was confirmed. It displayed a high specificity (>90 per cent) which was largely independent of the level or slope of high-frequency hearing loss. In contrast wave V specificity decreased with increasing loss and increasing slope. Its value as a functional index was limited with losses greater than 70 dB HL in whom specificity fell below 70 per cent. The study concluded that, despite reducing interval availability above 60 dB HL, wave V latency cannot be used as an alternative index because it displays weakening specificity over this range of loss. With the problems inherent in applying latency corrections, the author advocates the use of improved procedures for wave I identification in these cases.

Neurologic and otologic findings in Fisher's syndrome

We performed neurologic and otologic examinations in 14 patients with Fisher's syndrome to determine whether its manifestations inducing acute ophthaloplegia, ataxia and areflexia may involve the auditory and vestibular systems. Tests included pure tone audiometry, auditory brainstem response, observations of nystagmus, smooth pursuit test, saccade test, optokinetic nystagmus test, and the caloric test. One patient showed downbeat nystagmus and lateral gaze nystagmus without restriction of eye movement, two patients showed dysmetria on saccades without restriction of eye movement, and three patients showed superimposed saccadic eye movement on smooth pursuit without lateral gaze nystagmus. The abnormalities in those six cases could not be explained by solely muscular weakness, but also appeared to involve the central oculomotor system. In the other patients, nystagmus could be explained by muscular weakness alone. Additionally, three patients, including two patients with dysmetria on saccades, showed a unilateral diminished response to caloric testing with no severe restriction of eye movements. In evaluating the auditory brainstem response of these three patients, one patient, who showed abnormality on the saccade and caloric tests, showed an elongation of wave I latencies and of wave I-III interpeak latencies at both ears, and one other patient showed an elongation of wave III-V interpeak latencies at both ears. This disorder may involve the peripheral and central auditory systems as well as the peripheral vestibular system.

Temporal bone pathology of acoustic neuroma correlating with presence of electrocochleography and absence of auditory brainstem response

The temporal bone pathology of a 74-year-old female affected by vestibular schwannoma was compared with findings of auditory brainstem response and electrocochleography. At age 71, she complained of hearing loss in the left ear in which pure tone audiometry revealed threshold elevation in the middle- and high-frequency range. Temporal bone CT scanning revealed a medium-sized cerebellopontine angle tumour in the left ear. ABR showed no response in the left ear, but the electrocochleography showed clear compound action potentials. Three years later, at age 74, she died of metastatic lung cancer and sepsis. The left temporal bone pathology consisted primarily of a large vestibular schwannoma occupying the internal auditory meatus. The organ of Corti was well preserved in each turn. In the modiolus, the numbers of spiral ganglion cells and cochlear nerve fibres in each turn were decreased. These histological findings suggest that clear compound action potentials were recorded from the distal portion of the cochlear nerve in spite of the presence of the vestibular schwannoma, but ABR could not be detected because of the blockade of the proximal portion of the cochlear nerve by the vestibular schwannoma.

Normative auditory brainstem response data for hearing threshold and neuro-otological diagnosis in the dog

There is growing interest in the application of auditory brainstem response (ABR) audiometry for hearing assessment in dogs. The technique is far from standardised, however, resulting in large discrepancies between studies. This study aimed to obtain normative data, under clearly defined conditions, for two breeds of significantly different size; head size being a potential factor determining ABR latency values. The subjects, 20 dalmatians and 20 Jack Russell terriers, were sedated prior to ABR testing, and subcutaneous scalp electrodes used to detect the evoked potential elicited by a click stimulus presented via insert earphones. The mean ABR thresholds for the two breeds, 0 and -5 decibels re normal hearing level (dB nHL), respectively, were very similar to those for humans. The latency values of the main ABR waves and the interval between them were statistically significantly smaller for the smaller breed, but there was no correlation with head size within either breed. The results provide a baseline to assist with confirmation of hearing impairment and neuro-otological diagnosis in the dog.

The effects of cochlear hearing loss, age and sex on the auditory brainstem response

This study analyzed the effects of auditory impairment, age and sex on the auditory brainstem response (ABR) wave latencies. ABR wave I, wave V and I-V interval measures were extracted from the clinical records of 201 patients with cochlear hearing loss. Females had consistently earlier wave V latencies and shorter I-V intervals than males. No age effects were observed. Degree of impairment had a systematic effect on ABR wave latencies and I-V intervals. Wave I displayed latency extension with increasing levels of high-frequency hearing loss, whilst for wave V increases in latency were dependent upon both degree and slope of the hearing loss. Present results suggest that many of the previously reported sex differences and variable interactions seen for the ABR can be accounted for by differences in the underlying distribution of audiogram shapes within and between study populations. Different audiometric configurations were found to produce consistent differential effects on both wave I and wave V latency and thus influence the I-V interval. This study underlines the need to develop a more detailed model of impairment effects if correction factors are to be employed more effectively in ABR testing for retrocochlear pathology.

Acoustic reflexes, auditory brainstem response, and MRI in the evaluation of acoustic neuromas

Patient records were reviewed to determine whether persons with absent acoustic reflexes have a higher incidence of abnormal auditory brainstem response (ABR) results in the absence of a cerebellopontine angle (CPA) tumor than those with normal acoustic reflexes. Results showed patients with absent reflexes to have borderline or abnormal ABR results in 45.2% of the cases. Patients with normal reflexes had borderline or abnormal ABR results in 14.2% of the cases. Results indicate that magnetic resonance imaging is a more appropriate test for patients with absent reflexes, since ABR was often nondiagnostic for a CPA tumor in this group.

ABR Indices

ABR absolute latencies and interpeak intervals were reviewed for 684 non-tumor ears and 75 eighth-nerve tumor ears having various degrees of high frequency hearing loss. For non-tumor ears, the percentage of abnormal absolute latencies for waves I, III, and V increased rather systematically as hearing loss increased, whereas absolute latencies for eighth-nerve tumor ears were largely abnormal regardless of hearing loss. Interpeak intervals were normal for most of the non-tumor ears, but the I–III and I–V intervals were abnormal for most of the tumor ears. The most sensitive index for otoneurologic assessment was a combination of abnormal wave V interaural latency differences or I–V interpeak interval, and the most specific criterion was the I–V interpeak interval. Tumor size influenced sensitivity of most ABR indices.

Hit and False-Alarm Rates of Selected ABR Indices in Differentiating Cochlear Disorders From Acoustic Tumors

We performed a retrospective study of 26 patients with acoustic tumors and 26 patients with otologically diagnosed cochlear pathology to determine the sensitivity (hit rate), specificity (false-alarm rate), and efficiency of six auditory brainstem response indices. In addition, a utility value was determined for each of these six indices. The I–V interwave interval, the interaural latency difference, and the absolute latency of wave V provided the highest hit rates, the best A’ values and good utility. The V/I amplitude ratio index provided high specificity but low sensitivity scores. In regard to sensitivity and specificity, using the combination of two indices provided little overall improvement over the best one-index measures.

Brainstem auditory evoked responses in patients with tinnitus

Brainstem auditory evoked responses of 355 patients with uni- or bilateral tinnitus were recorded in order to evaluate the effect of tinnitus on the central auditory system. The amplitudes of waves I, III and V and the latencies of each wave and interpeak latencies were compared to those of a group of 129 controls with normal hearing. The study of the control group initially identified a certain number of concurrent parameters. The brainstem evoked responses of men and women evolved differently from the age of 30 years, latencies of I-III and I-V in men lengthening with age and those of women tending to shorten. The patient groups were therefore compared to a control group of the same sex ratio or of the same sex, half being between 30 and 56 years of age. The tinnitus patients were divided into three groups according to the side affected by tinnitus. Latencies and amplitudes in these groups differed significantly from those of the control group. In order to eliminate hearing loss, the most difficult concurrent factor and almost always associated with tinnitus, the results of individuals with symmetrical hearing loss were compared to those of the control group. Tinnitus was always associated with significant lengthening of 0-I and I-V latencies on the tinnitus-affected side, with a significant reduction in amplitudes of waves I and III, and sometimes of wave V, particularly in the group with left-sided tinnitus. Comparison of tinnitus patients with symmetrical and asymmetrical hearing by sex showed that tinnitus patients of all groups had lengthening of right and left 0-I latencies, apart from the women in the group with right-sided tinnitus, and significant reduction in amplitudes of waves I and III in women and of left III only in men. When hearing loss was asymmetrical and on the tinnitus-affected side, there was also lengthening of 0-I latencies on the tinnitus-affected side in both sexes and of ipsi- and contralateral I-V latencies in women. Right- and left-sided tinnitus was associated with additional differences between the three groups. Correlation coefficient study confirmed that 0-I, I- III and I-V latencies were independent of the mean degree of deafness, deafness at high frequencies and at frequencies around the tinnitus, up to a threshold of hearing loss of 40 dB, above which 0-I and 0-V lengthened in addition to tinnitus. On the other hand, whatever the frequency, tinnitus involved significant lengthening of wave I latencies and modification of the previously recorded amplitudes. Two groups of tinnitus patients could be distinguished: the first, with symmetrical hearing loss, with symmetrical normal latencies, apart from 0-I latencies and the amplitude of the wave on the tinnitus side, and the second with hearing loss predominant on the tinnitus-affected side, with different latencies on each side, 0-I being shorter on the unaffected side, I-III and I-V being lengthened on the unaffected side and 0-I being lengthened on the tinnitus-affected side. Moreover, as disturbances of brainstem evoked responses caused by tinnitus particularly affected waves I and III, the hypothesis of possible involvement of the efferent systems could be proposed.

Maturation of the auditory brainstem in low risk-preterm infants: a comparison with age-matched full term infants up to 6 years

Whether preterm birth has a significant effect on the maturation of the human brain remains an equivocal issue. Since experience plays a crucial role in the development of the brain, it is conceivable that extra-uterine preterm exposure could exert some effects on the maturation of the developing human brain. The present study compared the post-term maturation of the central components of brainstem auditory evoked response (BAER) in low risk preterm infants with that of age-matched full term infants up to 6 years. The preterm infants demonstrated similar maturational profiles to those of the term infants in both interpeak intervals and amplitude measures. No systematic, statistically significant differences were found between the preterm and term infants in any of the BAER variables although the I-V interval tended to be slightly shortened in the prematurely born infants. These results suggest that preterm birth or earlier exposure to sound environment extra utero is unlikely to lead to significant neurophysiological consequence in the developing auditory brainstem of low risk infants.

ABR amplitude and dispersion variables. Relation to audiogram shape and click polarity

ABR amplitude behaviour to condensation (C) and rarefaction (R) clicks was investigated in normal ears, ears affected by Ménière's disease and ears with high-frequency hearing loss (HF ears). The wave IV-V amplitude-intensity function was steeper in ABRs evoked by R than by C clicks. This may suggest that two different cochlear generator components, one intensity-dependent as well as one polarity-dependent, contribute to click-evoked ABRs. Wave IV-V amplitude was significantly higher in Ménière ears compared to HF ears in spite of comparable 2-4 kHz hearing loss in the two groups. Hence, audiometric steepness (which is lower in Ménière ears than in HF ears) seems to predict the wave IV-V amplitude decline more precisely than the 2-4 kHz perception threshold. The wave IV-V dispersion variable (SR IV-V) was close to normal in Ménière ears, while wave IV-V was more dispersed in HF ears. In general, C click ABRs were less affected than R click ABRs by 'peripheral' factors (i.e. intensity and audiometric steepness).

Transient evoked otoacoustic emissions: clinical applications and technical considerations

Otoacoustic emissions are defined as sound energy emitted by the cochlea. They are believed to be generated by the outer hair cells of the Organ of Corti. Several types of evoked otoacoustic emissions have been described. At present, transient-evoked otoacoustic emissions (TEOAEs) equipment is readily available commercially for clinical purposes. This paper describes our early experience with this equipment from a clinician's perspective. It reviews some of the technical problems we have encountered and their solutions. It also presents selected clinical examples where TEOAEs were particularly helpful in the clinical setting, thus illustrating the potential usefulness of this new clinical tool.

ABR screening for acoustic neuromata: the role of rate-induced latency shift measurements

The audiological assessment of patients considered 'at risk' for an acoustic neuroma is problematic when the patient has a severe hearing loss. The utility of ABR rate-induced latency shift (RLS) measurements was investigated in 189 patients who had passed a conventional assessment and 31 patients with an acoustic neuroma. A test based on the RLS of wave V using rates of 11.1 s-1 and 88.8 s-1 had a sensitivity of 89.5% and a specificity of 90.8% when applied with a dual interpretive criterion which included the loss of wave V at the higher rate. This test was included in an ABR screening protocol which had a sensitivity of 100% and a specificity of 97.9%. The RLS test requires no correction for age, sex, hearing loss or stimulus intensity and may be used in patients with severe hearing loss for whom other ABR tests are inappropriate.

Pressure-induced modifications of the acoustic nerve. Part II: Auditory brain stem responses

The auditory brain stem response is a diagnostic tool commonly used in the evaluation of patients suspected of having an acoustic neuroma. The mechanism by which the auditory brain stem response is altered in the presence of an acoustic neuroma is unclear. In this report, an experimental model is presented as an investigative tool for future studies of this mechanism: acute compression of the nerves of the internal auditory canal in cats stimulates the changes observed in patients with acoustic neuromas.

Canal electrode electrocochleography in patients with absent wave I ABRs

Fifteen patients (23 ears) who demonstrated no recordable wave I at the time of clinical auditory brainstem response testing were subsequently retested under three auditory brainstem response-electrocochleography conditions. One condition was the traditional auditory brainstem response, another was the auditory brainstem response with electrocochleography filtering, and the third was an electrocochleographic condition using a canal electrode (Tiptrode). The electrocochleographic recording condition provided more readable wave I responses than the other conditions. In addition, the electrocochleographic condition provided wave I amplitudes that were greater than those of the traditional auditory brainstem response. The later waves of the auditory brainstem response (III and V) were similar in wave presence amplitudes and latencies for all three test conditions.

Statistical properties of ABR amplitudes and latencies. Implications for computation of reference limits and relation to click phase

A method for statistical analysis and computation of reference limits for ABR latency and amplitude variables is presented. Condensation and rarefaction ABRs from 47 healthy controls aged 4-58 years were investigated. With respect to gaussianity of distributions, the square root transformation was superior to the logarithmic transformation for amplitudes, while the logarithmic transformation performed better for amplitude ratios. Wave V latency and the I-V interpeak latency were nearly normally distributed, while other latencies and inter-peak latencies displayed varying displacement from a normal distribution. Rarefaction ABR distributions were slightly closer to normality than were condensation ABRs. Amplitude vs. following amplitude and latency vs. amplitude correlation coefficients were larger for R than for C click ABRs; thus R clicks seem to evoke a better synchronized neural volley. Most of the correlation between amplitude and latency could be explained by the influence of age and sex. Hence, age and sex matched reference limits for ABR amplitudes, without correction for latency, seem to be adequate in practical clinical work.

Factors influencing the preservation of the facial nerve during acoustic surgery

We reviewed the last 30 acoustic neuromas excised in our department and attempted to find out the factors associated with preservation of the facial and cochlear nerves. While the size of the tumour was the most important factor, vascularity and consistency were both important. Facial and cochlear nerves were preserved in 63% and 10% of the patients respectively. The importance of early diagnosis cannot be overemphasized.

Strategy and benefits of acoustic neuroma searching

Advances in audiological, radiological and microsurgical techniques have enabled otologists to diagnose and excise very small acoustic tumours with a low morbidity and mortality. Is this cost effective? In an attempt to answer this question, an analysis of 66 cases of surgically treated acoustic neuromas is presented. This represents part of a series of skull base procedures carried out at Addenbrooke's Hospital over the last five years. As a result of this work an investigative protocol is suggested. By studying the relative morbidity of early and late surgical intervention in these cases, and by costing the exercise, the justification for early diagnosis and treatment is presented both in financial and human terms.

False-negative brainstem auditory evoked potential recordings in a case of multiple acoustic neuroma

A case history is reported to demonstrate that electrophysiological testing (brainstem auditory evoked potentials, BAEP and stapedius reflex) may fail in the search for cerebello-pontine angle tumours. The clinical history began with repeated episodes indicating a disorder of the vestibular system. Repeated testing of BAEP exhibited normal curves before and after surgery on the right side. This case serves as a reminder that normal BAEP do not necessarily exclude the presence of an acoustic neuroma developing in the immediate vicinity of the vestibular nerve.

Intra-operative electrocochleography to monitor cochlear potentials during acoustic neuroma excision

Intra-operative electrocochleography (ECochG) was used in an attempt to monitor the action potential of the cochlear nerve during acoustic neuroma surgery in 14 patients with useful pre-operative hearing. Five patients had ECochG potentials preserved and yet only three could hear when tested audiometrically later. Of those losing the potentials intra-operatively all were subsequently deaf and the pattern of waveform loss allowed determination of the probable cause of hearing loss. Complete excision of the tumour was achieved in each case regardless of the ultimate effect on the AP as it was not felt justified to risk subsequent recurrence. In common with other studies one of the best prognostic factors for these preservation of hearing was found to be the size of the tumour.

The Audiologic Evaluation of Cerebellopontine Angle Tumor Suspects: A Review of Tumor and Non-Tumor Suspects

In an initial study from January 1981 through December 1983, audiologic data were gathered on 41 patients with proven cerebellopontine angle (CPA) tumors and 82 tumor suspects who revealed no tumor on computed tomography with air cisternography of the internal auditory canal. The acoustic reflex threshold and decay, performance intensity function for phonetically balanced (PB) words, and several auditory brainstem response (ABR) variables were examined. Sensitivity, specificity, and diagnostic efficiency were calculated for each test. The ABR was better than the other tests. The interaural wave V latency difference (IT5) had a sensitivity of 100%, specificity of 80%, and diagnostic efficiency of 87%. In a subsequent study, from January 1984 to June 1985,52 patients with abnormal IT5 values were examined to determine the predictive value of a positive IT5 in detection of a CPA tumor. Nineteen of these patients had CPA tumors, for a detection rate of 36%. The high diagnostic efficiency of the ABR, coupled with the prevalence of a CPA tumor in a tumor suspect population, will translate into a yield of approximately one tumor for every three abnormal IT5 tests.

Hearing loss in a uraemic patient: indications of involvement of the VIIIth nerve

A case of acute renal failure associated with severe uraemic hearing loss is presented. Audiometric site-of-lesion testing revealed cochlear as well as neural involvement. After therapy hearing recovered up to an almost normal level, with normal auditory nerve conduction velocities. This case report supports the suggestion that the improvement of hearing after renal transplantation or dialysis might be correlated with the influences of these forms of therapy upon the peripheral neuropathy.

Stapedius reflex and cerebellopontine angle tumours

The stapedius reflex was investigated in 61 patients with cerebellopontine angle tumours, in order to evaluate the reliability of the reflex-decay test in VIIIth nerve disorders. The reflex was completely normal in 11% of the patients. The 2 most frequently observed abnormalities were (1) an absence of the reflex when stimulating the ear on the side of the tumour, and (2) the conjunction of pathological reflex-decay at 0.5 kHz with a unilateral threshold elevation and/or absence of the reflex at other frequencies. The decay test was normal in one-third of the patients with a preserved reflex.

Electrically elicited blink reflex and early acoustic evoked potentials in circumscribed and diffuse brain stem lesions

In the present paper, the function of the brain stem in patients with brain stem lesions of various aetiology is investigated with electrophysiological methods. The clinical observations are supplemented by experimental investigations on cats, in which the blink reflex and the early acoustic evoked potentials were registered during the acute elevation of intracranial pressure. The findings in patients with circumscribed space-occupying lesions in the posterior fossa document that the registration of the BR and the BAEP have a functional diagnostic significance above and beyond the neurological and radiological investigation. In the case of the cerebellar space occupations, specific alterations could not be observed. On the contrary, the alterations of BR and BAEP indicate a general disturbance of brain stem function, possibly as a result of a general increase of intracranial pressure. In cerebellopontine angle tumours, both BR and BAEP showed specific alterations which were usually asymmetrical. The BR changes ipsilateral to the tumour are of major topodiagnostic significance, whereas the alterations of the contralateral potential are especially informative in the registration of BAEP. The alterations of BR and BAEP also allow an appraisal of the localization and extent of the lesion in primary space occupations in the brain stem: A pathological R1 indicates a pontine lesion, whereas pathological R2 responses are found in medullary and in oral pontine and mesencephalic lesions. In contrast to cerebellopontine angle tumours, the BAEP tends to show symmetrical alterations in primary brain stem lesions. The prolongations of interpeak latencies correspond to the brain stem segment concerned, and the same also applies to pathological amplitude reduction and deformations of individual potentials. In patients with localized brain stem damage, the reflex pathway of R2 is discussed on the basis of the BR findings. In contrast to the view held up to now that only structures situated caudal of the facial nucleus area are responsible for the genesis of the R2 response, it is assumed on the basis of our own observations that pontomesencephalic structures rostral to the facial nuclei are also important for the genesis of R2. Registration of BR and BAEP in patients with acute diffuse brain stem damage shows that both methods have a high diagnostic and prognostic value. Isolated damage and combined brain stem lesion can be demonstrated and the course can be followed up. Normalization of pathological findings reflects clinical recovery, and conversely a secondary deterioration indicates the presence of complications.(ABSTRACT TRUNCATED AT 400 WORDS)

Alterations of auditory evoked potentials during the course of chloroquine treatment

Chloroquine phosphate is now used extensively in the treatment of active rheumatoid arthritis and in some collagen diseases. The ototoxic potential of this drug during long term use was assessed in 74 patients. At a time when pure tone and speech audiometry failed to demonstrate any hearing change, brainstem audiometry became abnormal in 13 patients. Abnormalities disappeared if chloroquine was withdrawn. Pathogenesis will be discussed on the basis of data obtained from animal experiments.

The application of evoked potentials in the diagnosis and follow-up of children with intracranial tumors

Somatosensory and brainstem auditory evoked potentials (SSEPs and BAEPs) provide sensitive measures of the central conduction functions of the auditory and somatosensory input systems at different levels of the central nervous system. The contribution of SSEPs and BAEPs in the primary diagnosis and follow-up of 26 children with infra- and supratentorial tumors were reviewed. The SSEPs, especially the specific complex, showed a latency increase in patients with supratentorial and brainstem mass lesions involving directly or distantly the somatosensory tracts. The BAEPs were sensitive for supratentorial pressure effects and for local and distant posterior fossa tumor effects. In the follow-up of children, evoked potentials offer a good method of detecting tumor recurrence, whereas neuroradiological procedures may be obscured by surgical or radiation artifacts.