Patterns of evoked otoacoustic emissions associated with acoustic neuromas

The effect of hypoxia on hearing function

Background/aim

This study was conducted to determine the critical partial oxygen pressure (pO2) value that would impair hearing function by evaluating the effects of hypoxia on hearing function in subjects diagnosed with chronic obstructive pulmonary disease (CPOD).

Materials and methods

The study included 25 male and 5 female patients referred to our clinic who were diagnosed with COPD, according to spirometry and PaO2 values, and who did not show pathology upon autoscopic examination. The control group consisted of 14 female and 16 male patients who had no lung disease and were in the same age range as the COPD group.

Results

A statistically significant difference was found between the two groups for distortion-product otoacoustic emission (DPOAE) (P < 0.001). The COPD group was divided into two groups according to pO2 levels (pO2 ≤ 70 and pO2 > 70) in order to find a critical pO2 level which might cause significant change at a certain audiological extent.

Conclusion

Hypoxia causes long-term decline in hearing thresholds, deterioration of DPOAE results, and prolongation of I–V interpeak latency in auditory brainstem response. However, the critical oxygen level that disrupts hearing function could not be determined.

Revisiting Oto-Acoustic Emissions

Oto-acoustic emissions (OAEs) are an audiometric diagnostic test that allows quick objective measure of hair cell function in the inner ear. It is a reflection of hearing function at the interface of conductive and sensorineural components in the human ear. Unfortunately, it is not commonly used due to the unique expertise and niche equipment required to successfully carry it out. This article is to further shed light about the use of such tests to junior doctors so that such resources can be better utilised. It also reviews the current and possible future applications of OAEs at the frontiers in otology today.

Distortion-product otoacoustic emission tests evaluate cochlear function and differentiate cochlear and vestibular schwannoma

OBJECTIVES

(1) To investigate cochlear function in patients with acoustic neuroma by distortion-product otoacoustic emission tests and (2) to evaluate the utility of this method for identifying the nerve origin of acoustic neuroma.

STUDY DESIGN

Diagnostic test assessment.

SETTING

Community hospital.

METHODS

The study included 196 patients with unilateral acoustic neuroma who were surgically treated in our hospital between April 2008 and March 2011. In all patients, pure-tone audiometry and distortion-product otoacoustic emission tests were conducted before surgery, and tumor size was measured on magnetic resonance imaging.

RESULTS

Superior vestibular schwannoma (n = 112), inferior vestibular schwannoma (n = 80), and cochlear schwannoma (n = 4) were observed. Positive results of distortion-product otoacoustic emission tests were observed in 11 patients with superior vestibular schwannoma, 14 with inferior vestibular schwannoma, and 3 with cochlear schwannoma. They were predictive of cochlear schwannoma, with 75.0% sensitivity (95% confidence interval [CI], 30.6-95.4) and 87.0% specificity (95% CI, 86.1-87.4). Retrocochlear hearing loss was detected in 5 patients with inferior vestibular schwannoma and 1 with cochlear schwannoma. It was also predictive of cochlear schwannoma. This criterion showed 25.0% sensitivity (95% CI, 4.7-66.1) and 97.4% specificity (95% CI, 97.0-98.3).

CONCLUSION

Percentages of patients with positive results on distortion-product otoacoustic emission tests and those with retrocochlear hearing loss differed by nerve origin. Distortion-product otoacoustic emission tests can be of some assistance in differentiating cochlear and vestibular schwannoma.

Dysfunction of the cochlea contributing to hearing loss in acoustic neuromas: an underappreciated entity

OBJECTIVE

Hearing loss is a common symptom in patients with cochleovestibular schwannoma. Clinical and histologic observations have suggested that the hearing loss may be caused by both retrocochlear and cochlear mechanisms. Our goal was to perform a detailed assessment of cochlear pathology in patients with vestibular schwannoma (VS).

STUDY DESIGN

Retrospective analysis of temporal bone histopathology.

SETTING

Multi-center study.

MATERIAL

Temporal bones from 32 patients with unilateral, sporadic VS within the internal auditory canal.

MAIN OUTCOME MEASURES

Sections through the cochleae on the VS side and opposite (control) ear were evaluated for loss of inner and outer hair cells, atrophy of the stria vascularis, loss of cochlear neurons, and presence of endolymphatic hydrops and precipitate within the endolymph or perilymph. Observed pathologies were correlated to nerve of origin, VS volume, and distance of VS from the cochlea. Hearing thresholds also were assessed.

RESULTS

VS caused significantly more inner and outer hair cell loss, cochlear neuronal loss, precipitate in endolymph and perilymph, and decreased pure tone average, when compared with the opposite ear. Tumor size, distance from the cochlea, and nerve of origin did not correlate with structural changes in the cochlea or the hearing threshold.

CONCLUSION

There is significant degeneration of cochlear structures in ears with VS. Cochlear dysfunction may be an important contributor to the hearing loss caused by VS and can explain certain clinically observed phenomena in patients with VS.

Assessment of the influence of whole body vibration on Cochlear function

Background

Whole body vibration (WBV) is a potentially harmful consequence resulting from the dissipation of energy by industrial machineries. The result of WBV exposure on the auditory system remains unknown. The objective of the present research was to evaluate the influence of WBV on cochlear function, in particular outer hair cell function. It is hypothesized that WBV impairs cochlear function resulting in decreased Distortion Product Otoacoustic Emission (DPOAE) levels (L_dp) in rabbits subjected to WBV.

Methods

Twelve rabbits were equally divided into vibration and control groups. Animals in vibration group were exposed to 1.0 ms^-2 r.m.s vertical WBV at 4–8 Hz for 8 h/day during 5 consecutive days. Outer hair cell function was assessed by comparing repeated-measurements of DPOAE levels (L_dp) across a range of f₂ frequencies in rabbits both exposed and unexposed to WBV. DPOAE level shifts (LS_dp) were compared across ears, frequencies, groups, and times.

Results

No differences were seen over time in DPOAE levels in the non-exposed rabbits (p = 0.082). Post-exposure L_dp in rabbits exposed to WBV were significantly increased at all test frequencies in both ears compared to baseline measures (p = 0.021). The greatest increase in L_dp following exposure was seen at 5888.5 Hz (mean shift = 13.25 dB). Post-exposure L_dp in rabbits exposed to WBV were not significantly different between the right and left ears (p = 0.083).

Conclusion

WBV impairs cochlear function resulting in increased DPOAE responses in rabbits exposed to WBV. DPOAE level shifts occurred over a wide range of frequencies following prolonged WBV in rabbits.

The clinical characteristics of tinnitus in patients with vestibular schwannoma

OBJECTIVES

To review the symptoms, signs, and clinical findings in a large series of patients diagnosed with unilateral sporadic vestibular schwannoma (VS) to describe the clinical characteristics of tinnitus in this population. Further, to ascertain which of the proposed mechanisms of tinnitus generation in VS was supported.

DESIGN

Retrospective case note and database review.

SETTING

Tertiary university teaching hospital departments of audiology and neuro-otology.

PARTICIPANTS

Nine hundred forty-one patients with unilateral sporadic VS, diagnosed during the period 1986 to 2002. Twenty-three additional patients were excluded due to missing clinical data.

MAIN OUTCOME MEASURES

The presence or absence of tinnitus, and its rated subjective severity were analyzed in conjunction with data regarding patient demographics, symptoms, signs, and diagnostic audiovestibular test findings.

RESULTS

No statistical association at the 5% level was found between tinnitus presence/absence and patient age, gender, 2- to 4-kHz audiometric thresholds, ipsilateral auditory brainstem response abnormality, length of history, tumor side, nor caloric test abnormality. Statistically significant associations were found between tinnitus presence/absence and tumor size (p = 0.012) and type of hearing loss (progressive, sudden, fluctuant, nil) with a tendency for patients without hearing loss to be less likely to experience tinnitus. Statistically significant associations were identified between classification of tinnitus severity and age at diagnosis (p < 0.001) (greater age being associated with greater tinnitus severity), abnormal findings on caloric testing (p = 0.01) (abnormal calorics being associated with greater tinnitus severity), and tinnitus as a principal presenting symptom (p < 0.001) (this being associated with greater tinnitus severity).

CONCLUSIONS

The analysis does not identify any single one of the proposed mechanisms for tinnitus as being the obvious culprit. In fact, even in a homogeneous group of patients such as this, there is evidence of multiple mechanisms that are not mutually exclusive. The association between increased tinnitus severity in older patients, patients with canal pareses on caloric testing, and with tinnitus as a principal presenting symptom should be borne in mind by the clinician.

Study of auditory function in children with chronic lung diseases

OBJECTIVE

Chronic hypoxia has an evident effect on cochlear function and hearing sensitivity. Otoacoustic emissions' testing is efficient in detecting subtle cochlear dysfunction. This cross sectional study was designed to assess the cochlear function in children with chronic lung diseases who were exposed to prolonged hypoxia and prolonged use of ototoxic drugs (as aminoglycosides) using basic audiological evaluation and transient evoked otoacoustic emissions testing.

METHODS

The study was carried out on 30 Egyptian children with chronic lung disease recruited from the Pediatric Chest Clinic, Children's hospital, Ain Shams University. Twenty normal children were included as control.

RESULTS

Six patients (20%) showed abnormal otoacoustic emissions. A significant effect of hypoxia on otoacoustic emissions findings was found (P<0.05). However, there was no significant effect of inhaled aminoglycosides on auditory functions whether pure tone audiometry, speech audiometry and transient evoked otoacoustic emissions testing.

CONCLUSIONS

Children with chronic lung diseases are liable to cochlear dysfunction due to prolonged hypoxia. Inhaled aminoglycosides in chronic lung diseases is relatively safe on auditory functions.

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.

Study of auditory function in patients with chronic obstructive pulmonary diseases

This study was designed to measure auditory function in patients with chronic obstructive pulmonary diseases (COPDs) who generally suffer from chronic hypoxemia. Control and COPD subject groups received a battery of tests to assess overall hearing sensitivity and peripheral (end-organ and eighth-nerve) and brain-stem auditory function, as well as blood-gas analysis. Results showed a statistically significant difference for all audiological measures between the control group and a COPD subgroup--the presumptive hypoxic subjects (partial oxygen tensions, PO2, <75 mm Hg). Correlation analyses of results from all subjects (regardless of PO2) also revealed significant covariance with PO2 for overall, RMS, amplitude of click-evoked otoacoustic emissions (RA), hearing threshold level, and auditory brain-stem response (ABR, I-V inter-peak latency). Chi2 or Fisher's exact tests were statistically significant for frequencies of cases classified according to a criterion PO2 of 70 mm Hg (putative critical O2 for completely normal auditory function) and either hearing thresholds falling below or RA values above 1.5 standard deviations of the control-group means, respectively. However, chi2 was not significant for a comparable criterion of ABR I-V IPL. In general, clinically significant hearing loss was uncommon in COPD patients, and the observed effects represented relatively small changes in the auditory measures examined. Still, overall, changes were in the direction of poorer function, and these results suggest physiologically significant impact of chronic hypoxemia and the need for further study to evaluate thoroughly this medical condition as a potential risk factor for audio-vestibular dysfunction.

Intraoperative Neurophysiologic Monitoring: Indications and Techniques for Common Procedures in Otolaryngology–Head and Neck Surgery

Intraoperative cranial nerve monitoring can be an effective adjunct in otolaryngology-head and neck surgery. Monitoring is not considered standard of care, despite indications of cost effectiveness and improved functional outcomes. Lessons learned performing facial nerve monitoring are applicable to upper and lower cranial motor nerves. Auditory nerve monitoring can be modified accord-ing to need for selected otologic and neurotologic surgery. Process standardization and effective communication can lead to improved patient outcomes.

Intraoperative Monitoring of Cochlear Function Using Distortion Product Otoacoustic Emissions (DPOAEs) in Patients with Cerebellopontine Angle Tumors

HYPOTHESIS

Intraoperative monitoring by distortion-product otoacoustic emissions reflects the cochlear function changes in the real-time domain during removal of cerebellopontine angle tumors.

BACKGROUND

Cerebellopontine angle tumor surgery is associated with a significant risk of damaging internal auditory canal contents. Although monitoring facial nerve function intraoperatively has already been effectively developed, such efficacious monitoring of auditory function remains to be established. The aim of this study was to investigate the utility of distortion-product otoacoustic emissions for intraoperative monitoring of the cochlear function in humans during removal of cerebellopontine angle tumors.

METHODS

Continuous intraoperative monitoring of distortion-product otoacoustic emissions was performed in 20 of 62 patients undergoing surgical removal of cerebellopontine angle tumors. All of these 20 patients, who underwent the retrosigmoid approach, had distortion-product otoacoustic emissions present preoperatively. Depending on the amplitude and frequency band at which distortion-product otoacoustic emissions were present, monitoring was carried out at 2.0 to 6.0 kHz with primary stimulus tone amplitudes of 60 to 70 dB sound pressure level.

RESULTS

In patients operated on for cerebellopontine angle tumors, various patterns of distortion-product otoacoustic emission amplitude reductions and recoveries were observed. Distortion-product otoacoustic emissions recorded from the basal part of the cochlea (i.e., high frequencies) changed earlier and more profoundly than those from the middle and apical sections (i.e., lower frequencies). In some cases, cochlear function was affected irreversibly as reflected by loss of distortion-product otoacoustic emissions. Microcoagulation of small vessels, tumor debulking, and compression or stretch of the internal auditory canal contents were found to be procedures affecting distortion-product otoacoustic emissions. The status of distortion-product otoacoustic emissions at the conclusion of tumor dissection correlated with postoperative hearing levels.

CONCLUSION

Distortion-product otoacoustic emissions were used to monitor in the real-time domain auditory function during cerebellopontine angle tumor removal operations. The status of distortion-product otoacoustic emissions at the conclusion of the operations was related to postoperative hearing.

Increased Amplitudes of Distortion Product Otoacoustic Emissions in Patients with Unilateral Acoustic Neuroma

We present a case series of 4 patients with a unilateral acoustic neuroma and increased amplitudes of the distortion products of otoacoustic emissions (DPOAEs) at the low- and middle- frequency bandwidth on the involved side compared to the uninvolved side despite a 28-dB hearing level (HL) worse (compared to the uninvolved side) pure-tone hearing threshold average for standard audiometric frequencies between 1 and 6 kHz at the involved side. In 3 of these patients, 2 with an inferior vestibular nerve origin of the acoustic neuroma and one in whom the nerve of origin could not be unequivocally defined, the tumor was extending extrameatally. One patient had a purely intrameatal acoustic neuroma of superior vestibular nerve origin. Moreover, notable was the presence of the DPOAEs in all of the involved ears despite elevated pure-tone hearing thresholds (pure- tone averages for the standard audiometric frequencies between 1 and 6 kHz ranging between 36 and 62 dB HL).

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.

Effect of acoustic tumor extension into the internal auditory canal on distortion-product otoacoustic emissions

We studied the effects on distortion-product otoacoustic emissions (DPOAEs) of internal auditory canal (IAC) extension of acoustic neuromas (ANs) with the hypothesis that cochlear patterns of DPOAEs would be more commonly observed when the IAC was completely filled with tumor because of direct tumor involvement of either the inner ear or its blood supply. In a retrospective analysis of 86 patients with surgically proven ANs, DPOAEs were classified as having cochlear or noncochlear patterns on the basis of comparisons with the behavioral pure tone thresholds. The results of behavioral audiometry and DPOAEs were compared with the extension of the tumor into the IAC, which was categorized as full or partial. Of the 86 patients, 58 had tumors with full IAC extension, and 28 had tumors with partial IAC involvement. Cochlear patterns of DPOAEs were found in 55.2% of the tumors in the full IAC group and in 71.4% of those in the partial IAC group (not statistically different). It was concluded that the extent of IAC involvement by ANs was not significantly related to the negative effects of the tumor on cochlear function as represented by DPOAEs.

Distortion-product otoacoustic emissions in nonacoustic tumors of the cerebellopontine angle

OBJECTIVES

The goal of the present study was to compare the frequencies of cochlear and non-cochlear patterns of distortion-product otoacoustic emissions (DPOAEs) in patients with nonacoustic (non-AN) tumors of the cerebellopontine angle (CPA)/internal auditory canal with those in patients with acoustic neuroma (AN).

STUDY DESIGN AND SETTING

We conducted a prospective study of patients with non-AN internal auditory canal/CPA tumors treated between 1992 and 1999 in a tertiary care setting. We collected data on behavioral pure tone average, speech discrimination score, acoustic immittance tests, DPOAEs, and tumor size. DPOAEs were divided into those with a cochlear or a noncochlear pattern. Comparisons were made with a control group of patients with AN of the CPA.

RESULTS

Twenty-four patients were included in the study: 12 patients in the non-AN group and 12 patients in the AN group. In the non-AN group, 5 (42%) patients had a cochlear pattern and 7 (58%) had a noncochlear pattern. In the AN group, 7 (58%) patients had a cochlear pattern and 5 (42%) had a noncochlear pattern. The differences between the non-AN and AN groups were statistically significant. In the non-AN group, patients with a cochlear-pattern DPOAE had significantly smaller tumors (P = 0.03) and a trend (P = 0.07) toward higher speech discrimination score. Age and pure tone average were not significantly different in the non-AN tumor patients. In the AN group, none of the study parameters were significantly related to the pattern of DPOAE.

CONCLUSIONS

ANs appear to differ from other tumors of the CPA in their propensity to cause sensory versus neural hearing loss. A larger series of patients would be useful to confirm these preliminary findings.

An objective method of analyzing cochlear versus noncochlear patterns of distortion-product otoacoustic emissions in patients with acoustic neuromas

OBJECTIVES

To objectify the effects of retrocochlear disease on distortion-product otoacoustic emissions (DPOAEs) by developing a computer-based software strategy for classifying DPOAE patterns as cochlear or noncochlear and to evaluate the sensitivities of these techniques in a large series of patients with unilateral acoustic neuromas.

STUDY DESIGN

Development of a novel, software-based method of DPOAE analysis, which was evaluated with data obtained from a retrospective review of the results from audiometric tests performed in a series of patients.

METHODS

A computer-based software strategy was developed, using frequency-specific data from normal-hearing adults, for the purpose of distinguishing cochlear from noncochlear patterns of hearing loss, by determining the discrepancies between DPOAEs and behavioral audiometry. Preoperative pure-tone thresholds and DPOAEs from 97 patients with surgically confirmed acoustic neuroma were compared using an objective method and a standard, subjective technique that was considered to be the gold standard. The effects of bilateral hearing losses, such as noise-induced hearing loss and presbycusis, were accounted for during the analysis to isolate the effects of the tumors on hearing thresholds and DPOAEs.

RESULTS

Overall, 55 (57%) of the tumor ears were assigned to the cochlear group (i.e., DPOAEs consistent with hearing thresholds), 40 (41%) to the noncochlear group (i.e., DPOAEs inconsistent with hearing thresholds), and 2 (2%) to an indeterminate group, using the subjective technique for classifying DPOAEs. There was no significant difference in the categorization of the patients with acoustic neuroma when employing the objective strategy. The objective algorithm, when modified to maximize the number of noncochlear identifications, led to assignments of 36 (37%) to the cochlear, 57 (59%) to the noncochlear, and 4 (4%) to the indeterminate categories.

CONCLUSIONS

Subjective analysis of a large series patients with acoustic neuromas showed that the majority of ears with tumors demonstrated cochlear (57%), rather than non-cochlear (41%), patterns of DPOAEs. The computerized, software-based algorithm developed for differentiating cochlear from noncochlear patterns of DPOAEs in patients with retrocochlear disease had a maximum sensitivity of 59%. This value was significantly higher than that reported in previous studies.

Clinical interpretations of transient otoacoustic emissions

PURPOSE

The purpose of this study was to characterize the relation of different ordinal patterns of transient otoacoustic emissions (TEOAES) with respect to underlying otologic disorders and auditory status.

PATIENTS AND METHODS

The results of TEOAEs in 225 patients with various auditory disorders were investigated and compared with normative data established from 90 subjects of various ages. TEOAEs were categorized according to four patterns: (1) normal (general response level within 90% of normative data, (2) reduced amplitude (general response level was > or =2 dB peak sound pressure level (pSPL), but less than the mean -1.64 SD of the normative data), (3) abnormal morphology of frequency spectrum (general response level was within normal limits, but reduced at > or =2 individual octave frequencies between 1,000 and 5,000 Hz), and (4) total absence (response level <2 dB pSPL).

RESULTS

This study showed that the normal pattern of TEOAEs, in terms of response amplitude, varied with age. Our results further indicated that a reduced amplitude pattern of TEOAEs was noted in patients with a mild sensorineural hearing loss (SNHL), negative tympanometric pressure, a pressure-equalization tube, and Meniere's disease. TEOAEs provided good frequency-specific information for patients with a noise-induced hearing loss. All patients with ossicular chain abnormalities, more than moderate SNHL, and a middle ear mass or effusion had total absence of TEOAEs. Patients with acoustic neuroma and brainstem lesions presented a complex profile of TEOAEs. In the follow-up of auditory function in patients undergoing otologic surgery, different patterns of TEOAEs between the preoperative and postoperative recordings were evident, which correlated with the hearing thresholds and middle ear status. The abnormal findings of TEOAEs due to specific auditory diseases were discussed.

CONCLUSION

The interpretation of TEOAEs can be facilitated through an analysis of specific patterns and in combination with other audiologic tests.

Distortion-product otoacoustic emission monitoring of cochlear blood flow

Distortion-product otoacoustic emissions (DPOAEs) have been shown to be ideally sensitive to interruptions of the cochlear blood flow. However, a 15- to 30-second latency typically occurs between cessation of circulation and measurable DPOAE level changes. DPOAEs can also be characterized by phase measures. The aim of the present study was to determine in 10 rabbits the effects on DPOAE phase of repetitively compressing the internal auditory artery. In contrast to the delays measured by DPOAE level, phase changes were detected 1 to 5 seconds after internal auditory artery compression. These data suggest that the essentially "real time" monitoring of cochlear function with DPOAE phase can be used to ensure hearing preservation during surgery involving the porus acousticus and skull base.

Is the presence of transient evoked otoacoustic emmissions in ears with acoustic neuroma significant?

One hundred sixty-eight patients admitted for acoustic neuroma removal were involved in this study. In all cases, the size of the tumor and the presence or absence of tinnitus and vertigo or dizziness were evaluated. Investigated functional procedures included bilateral measures of pure-tone audiometry (PTA), auditory brainstem response (ABR), electronystagmography (ENG), and transient evoked otoacoustic emissions (TEOAEs). Thirty-five patients (21%) had normal preoperative TEOAEs in the affected ear, whereas 133 patients (79%) failed to show reproducible responses. The aims of this study were 1. to evaluate what distinguishes patients with preoperative TEOAEs in the pathological ear (group A) from those who had no TEOAE (group B); and 2. to determine in cases of attempted hearing preservation whether preoperative TEOAE presence in the neuroma ear (group C) was predictive of postoperative hearing preservation compared with the group of patients without TEOAEs (group D). The presence of vertigo or dizziness was significantly less frequent, the age was lower, and preoperative mean PTA loss in both ears was lower in group A compared with group B. Frequency of the other studied parameters and ABR threshold were similar in both groups. When hearing preservation was attempted, the mean preoperative PTA loss of group C patients was lower in both ears compared with group D. However, postoperative mean PTA loss did not significantly differ in the two groups. In group C, the percentage of hearing preservation (66.6%) was significantly higher than the percentage of deafness (33.4%), whereas in group D the percentage of postoperative preserved audition and deafness did not significantly differ (respectively 44.4% and 55.6%). The findings suggest that 1. TEOAEs in ears with acoustic neuromas are found in younger patients with a lower preoperative mean PTA loss and are accompanied by fewer functional complaints, perhaps because preserved TEOAEs indicate a better preservation of inner ear vasculature; and, 2. along with radiological and electrophysiological investigations, TEOAE presence in the pathological ear could provide an additional criterion or predictive factor for the successful outcome of attempted hearing-conservation surgery in ears with acoustic neuromas.

Individual differences and the reliability of 2F1-F2 distortion-product otoacoustic emissions: effects of time-of-day, stimulus variables, and gender

Distortion product otoacoustic emissions (DPOAEs) measured from the ear canal can be a sensitive tool to detect changes in cochlear function over time. However, if multiple-measurement procedures are to be useful clinically, testing needs to be reliable and sources of variability within individuals should be known. Herein, the influence of time-of-day (TOD), stimulus frequency, stimulus sound pressure level (SPL), and gender were evaluated on 2f1-f2 DPOAE amplitude in 16 adult volunteers with normal hearing. The effects of oral temperature and resting-pulse rate were also assessed. This study demonstrated a TOD main effect, with a period approximating one cycle-per-day. The magnitude of this effect averaged less than one dB and was not dependent on stimulus (frequency or SPL) or participant variables (gender, oral temperature, or resting-pulse rate), nor was it synchronized to a particular point-in-time. Stimulus level and gender effects on DPOAEs across frequency were also observed. Using generalizability theory (GT), DP iso-level/frequency profiles (DPILFPs) were found to be reliable measures within-subjects over a contiguous 24-hour time period. Significant and reliable between-subject differences were also documented. This study demonstrates the influence of stimulus and participant variables, quantifies the within-subject reliability over a 24-hour time period, and confirms that significant and reliable between-subject differences exist on DPOAEs across frequency, SPL, and gender.