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.

Penetrating injury to the brainstem after a nailgun accident: a case study.

Nonfatal penetrating injuries to the brainstem offer a unique opportunity to assess subcortical auditory pathway function. A case study of a patient suffering a severe nailgun accident is presented. Hearing sensitivity and acoustic reflexes were normal bilaterally, but word recognition was reduced for one ear. Auditory brainstem response results indicated waves I-IV were present bilaterally, but wave V was absent bilaterally. Results of vestibular findings indicated central pathology also. Results of audiologic, vestibular, radiologic, neurologic, and physical medicine examinations are discussed.

Head trauma and mid-frequency hearing loss.

Numerous reports in the literature associate head trauma with high-frequency hearing losses, often mimicking "4K notches" attributed to noise exposure. We have observed that some patients with a positive history for head trauma may show midfrequency notches in their audiometric configurations.

Nonsurgical factors predictive of postoperative hearing for patients with vestibular schwannoma.

OBJECTIVE: The purposes of the study were to determine whether preoperative cochlear reserve as measured by evoked otoacoustic emissions (EOAE) as well as other hearing variables often associated with hearing preservation are correlated with hearing preservation after tumor removal and to determine whether any hearing variables are independent of tumor size as a predictor of hearing preservation. STUDY DESIGN: Preoperative audiologic data for 104 patients having vestibular nerve schwannomas removed via a retrosigmoid surgical approach were reviewed and subjected to factor analysis. SETTING: All patients were seen at the Mayo Clinic, Rochester, Minnesota. PATIENTS: The patient sample was divided into two groups based on hearing thresholds after surgery. Group I consisted of 73 ears without hearing preservation. The remaining 31 ears, group II, had preserved hearing (defined as average postoperative pure-tone thresholds < or = 85-dB HL for 0.5, 1, 2, and 3 kHz). MAIN OUTCOME MEASURES: Variables not predictive of hearing preservation were age, gender, tumor laterality, and cochlear reserve (EOAE). Variables predictive of hearing preservation were small tumor size, pure-tone hearing sensitivity, speech reception thresholds, word recognition scores, integrity of cochlear nerve (acoustic reflex thresholds, and auditory brain stem response [ABR] waveforms). RESULTS: A multivariate logistic regression analysis showed that only word recognition scores at 40-dB sensation level were independent of tumor size as a predictor of hearing preservation.

Use of TEOAE, ABR, and Acoustic Reflex Measures to Assess Auditory Function Patients With Acoustic Neuroma.

Cochlear and neural auditory function for a series of 30 patients with acoustic neuroma was assessed pre- and postoperatively by transiently evoked otoacoustic emission (TEOAE), auditory brain stem response (ABR), and acoustic reflex measures. Employing a retrosigmoid surgical approach, physical integrity of the acoustic nerve was preserved for 22 patients. TEOAEs were observed preoperatively for 13 patients and postoperatively for 6 of them. Postoperative neural function remained unchanged or improved following surgery for 7 patients, and cochlear function decreased. TEOAE, ABR, and acoustic reflex measurements were considered valuable in providing information about site of lesion and probable mechanisms of injury associated with tumor removal.

Comparison of ABR amplitudes with TIPtrode and mastoid electrodes.

ABR evaluations were completed for 36 adults (18 males, 18 females) having normal hearing sensitivity and for 91 adult patients having various degrees of sensorineural hearing loss. Amplitudes of waves I and V were compared for ear canal (TIPtrode) electrode and mastoid electrode recordings. Interpeak intervals (I-III, III-V, and I-V) were determined and upper 95% confidence limits defined for normative data. In general, amplitude of wave I was larger when TIPtrodes were used. Wave V amplitude was nearly identical for the two electrodes. Wave I was identified more frequently for TIPtrode than for mastoid recordings of ABR waveforms for the sensorineural hearing loss subjects.

Preoperative and postoperative auditory brain-stem response results for patients with eighth-nerve tumors.

Preoperative and postoperative auditory brain-stem response results and audiologic data were reviewed for seven patients whose hearing was preserved after eighth-nerve tumor surgery. Auditory brain-stem response absolute latencies (I, III, and V) and interpeak intervals (I-III, III-V, and I-V) were identified more often postoperatively than preoperatively. Even though postoperative absolute latencies were usually abnormal, the interpeak intervals were usually normal following surgery. Postoperative hearing sensitivity was unchanged or slightly poorer for five of the seven patients, but postoperative speech discrimination was the same or better for six of the seven patients. All three patients having acoustic reflex testing showed improvement postoperatively.

Wave V interaural latency differences as a function of asymmetry in 2,000-4,000 Hz hearing sensitivity.

Interaural latency differences for wave V (IT5) were measured for 406 patients having cochlear hearing loss and for 36 patients with VIIIth nerve tumors. The incidence of IT5 values exceeding 0.2, 0.3, and 0.4 msec was plotted as a function of the degree of asymmetry in hearing sensitivity for 2,000-4,000 Hz. In general, the patients with cochlear hearing loss and the greatest degree of hearing asymmetry yielded IT5 values that exceeded 0.2, 0.3, or 0.4 msec more frequently than patients with more symmetric hearing losses, and this trend was apparent for all degrees of hearing loss. For the VIIIth nerve tumor patients, IT5 data were scattered widely regardless of symmetry or asymmetry of hearing sensitivity. The false-negative rate was 8% when IT5 was greater than 0.4 msec.

Auditory brainstem responses as a function of average hearing sensitivity for 2,000-4,000 Hz.

Average hearing thresholds for 2,000, 3,000 and 4,000 Hz and ABR results were analyzed for 290 patients having some degree of cochlear hearing loss. As average hearing sensitivity in the 2,000- to 4,000-Hz range became poorer, the incidence of abnormal auditory brainstem responses (ABR) increased. When the 2,000-Hz threshold sensitivity was 0-40 dB and the three-frequency average hearing loss was less than 50 dB, nearly 80% of ABR tracings were normal. Steeply sloping audiograms above 2,000 Hz increased the percent of abnormal ABR results.

The effect of 2000-4000 Hz hearing sensitivity on ABR results.

Pure-tone hearing sensitivity at 2000, 3000, and 4000 Hz and ABR results were reviewed for 458 patients with cochlear hearing loss. Wave V latency and waveform morphology data from the 916 ears yielded percentages of abnormal ABR results as a function of degree and slope of hearing loss. Threshold sensitivity at all three frequencies influenced ABR latency or waveform. A higher incidence of abnormal ABR results was observed when 3000 Hz thresholds were elevated than when 4000 Hz thresholds were elevated to the same levels. ABR results for various audiometric configurations are reported.

Auditory brain-stem response and acoustic reflex test.

Auditory brain-stem response (ABR) and acoustic reflex test (ART) results were reviewed for 30 patients with cerebellopontile angle tumors and for 30 patients without tumor. Patients included in the nontumor group were selected to match the audiometric configurations for individual patients in the tumor group. The ABR waveforms were abnormal for all but one of the patients with tumor and for seven of the patients without tumor. The ART results were abnormal for 25 of the patients with tumor and two of the patients without tumor. Patients without tumor yielding abnormal ABR results usually had more severe hearing losses than the patients without tumor who demonstrated normal ABR waveforms. The ABR and ART merit continued use in the audiologic examination of patients suspected of having retrocochlear lesions, but obviously, degree of hearing loss and other medical information must be considered also when retrocochlear lesions are suspected.

Auditory brain stem response results from 255 patients with suspected retrocochlear involvement.

Auditory brain stem response (ABR) evaluations were conducted on 255 patients with suspected retrocochlear involvement. Twenty-six patients (10%) had surgically confirmed tumors, and ABRs were abnormal in 25 (96%) of these cases. The remaining 229 patients had nontumor medical diagnoses, but 25% of these were found to have abnormalities in ABR recordings. The most common ABR abnormality in the nontumor patients was large wave V interaural latency difference, followed by no response or poor waveform resolution and delayed absolute wave V latency. Peripheral hearing loss, including decreased sensitivity at 2000 and 4000 Hz, appears to have influenced waveform morphology and component latency.

Auditory brainstem responses in ears with hearing loss: case studies.

Auditory brain stem evoked responses (ABRs) were recorded from six selected adult patients with various audiometric configuration, histories, and diagnoses. Although none of the patients were diagnosed medically as having retrocochlear disease, ABR latencies and waveform morphology were considered abnormal in some cases. By contrast, other patients with similar hearing loss configuration yielded normal ABRs. These observations emphasize the potential difficulty encountered in the interpretation of ABRs when hearing loss exists. Further, because ABRs and all other special auditory tests are not diagnostic extreme caution should be exercised prior to any definitive interpretation and subsequent diagnosis.

Head trauma: single-notch and double-notch audiograms.

Single-notch and double-notch sensorineural hearing losses were observed in 27 adult patients. All patients denied having a history of noise exposure, but did report at least one episode of hear trauma. Generally, the laterality and degree of hearing loss did not appear to correlate well with severity and site of head trauma, or post-traumatic symptoms. Although not all individuals suffering head trauma will yield notch audiograms, when an audiometric notch is observed the possibility of head trauma as well as other factors should be explored in the patient's history.

Brainstem responses to tone pip and click stimuli.

Brainstem auditory-evoked responses to tone pips at 1000, 2000, and 4000 Hz and clicks were evaluated for 17 normal-hearing adults. Wave V consistently emerged as the best indicator of auditory sensitivity, whereas waves II, III, and IV generally were not identifiable at lower intensities. An inverse relationship existed between wave V latency and intensity and between wave V latency and stimulus frequency. Large ranges were noted for the levels at which the various components became identifiable. Even though some frequency specificity may have occurred, the range of wave V latencies for 1000- and 4000-Hz tone pips demonstrated considerable overlap.

Alcohol and the acoustic reflex: effects of stimulus spectrum, subject variability, and sex.

Acoustic reflex thresholds were measured for eighteen young adults (9 men and 9 women) at four different blood alcohol levels: 0.00%, ascending 0.10%, 0.15% (peak level), and descending 0.10%. Reflex-eliciting stimuli consisted of three narrow-band noises (300 to 600, 600 to 1200, and 1200 to 2400 Hz) and three broad band noises (white noise, recorded rock music, and recorded factory noise). Prealcohol reflex thresholds were found to be significantly more sensitive than all postalcohol reflex thresholds for all stimuli, and broad-band stimuli demonstrated greater threshold shifts than did narrow-band stimuli. Significant sex differences were not observed for any blood alcohol level. Between subject variability was high, with 10 subjects showing little or no reflex threshold change and the other 8 subjects showing dramatic threshold changes.