|Year : 2020 | Volume
| Issue : 4 | Page : 164-168
Acoustic reflex decay and acoustic reflex latency threshold test findings in patients with cerebellopontine angle tumors: Correlation with tumor type, size, and extent
Prem G Nair1, N Shivashankar2, B Indira Devi3, SG Srikanth4, V Shanmugham5, KS Gayathri1
1 Department of Speech Pathology and Audiology, Amrita Institute of Medical Sciences and Research Centre, Amrita Vishwa Vidyapeetham, Kochi, Kerala, India
2 Department of Speech Pathology and Audiology, National Institute of Mental Health and Neuro Sciences, Bengaluru, Karnataka, India
3 Department of Neurosurgery, National Institute of Mental Health and Neuro Sciences, Bengaluru, Karnataka, India
4 Department of Radiology, National Institute of Mental Health and Neuro Sciences, Bengaluru, Karnataka, India
5 Department of Bio-Statistics, National Institute of Mental Health and Neuro Sciences, Bengaluru, Karnataka, India
|Date of Submission||05-Nov-2019|
|Date of Acceptance||19-Feb-2020|
|Date of Web Publication||23-Dec-2020|
Ms. K S Gayathri
Department of Speech Pathology and Audiology, Amrita Institute of Medical Sciences and Research Centre, Amrita Vishwa Vidyapeetham, Kochi, Kerala
Source of Support: None, Conflict of Interest: None
Context: This was a comparative prospective study. Aims: (1) To characterize acoustic reflex decay (ARD) and acoustic reflex latency threshold (ARLT) profiles in cerebellopontine angle (CPA) tumors. (2) To correlate ARD and ARLT test results with the type, size, and extent of tumors. Study Design: Comparative prospective study. Setting: Primary versus Tertiary referral center. Subjects: The clinical group comprised 98 patients with CPA tumor and the control group comprised 100 normal hearing subjects. Subjects and Methods: ARD and ARLT were estimated at 500 Hz and 1000 Hz both ipsilaterally and contralaterally for both the groups. Statistical Analysis Used: Statistical analysis for clinical group versus control group was carried out using analysis of covariance for age and gender covariates. For discrete clinical groups, analysis of variance followed by post hoc (Turkey) test was used. An independent sample t-test was used for the statistical analysis of tumor ear versus nontumor ear. Results: Test results indicated that the proportion of ears with abnormal reflex decay (0%–25%) was less compared to those with normal findings (75%–100%) in the patient group reflecting the poor efficacy of ARD to identify the presence of CPA tumors. Statistical analysis for ARLT was possible mainly for nontumor ear stimulation and it did not give any clear indications regarding the presence of brain stem compression. Conclusions: In the present study, an estimation of ARD and ARLT did not appear to be useful indices for CPA tumor identification.
Keywords: Acoustic reflex decay, acoustic reflex latency threshold, cerebellopontine angle
|How to cite this article:|
Nair PG, Shivashankar N, Devi B I, Srikanth S G, Shanmugham V, Gayathri K S. Acoustic reflex decay and acoustic reflex latency threshold test findings in patients with cerebellopontine angle tumors: Correlation with tumor type, size, and extent. Amrita J Med 2020;16:164-8
|How to cite this URL:|
Nair PG, Shivashankar N, Devi B I, Srikanth S G, Shanmugham V, Gayathri K S. Acoustic reflex decay and acoustic reflex latency threshold test findings in patients with cerebellopontine angle tumors: Correlation with tumor type, size, and extent. Amrita J Med [serial online] 2020 [cited 2021 May 11];16:164-8. Available from: https://www.ajmonline.org.in/text.asp?2020/16/4/164/304584
| Introduction|| |
The cerebellopontine angle (CPA) is one of the most common sites of intracranial tumors and approximately 10% of them originate in this region. Vestibular schwannomas constitute 60%–90% of tumors in the CPA and are the most common type. The overall incidence of nonacoustic schwannomas is approximately 2%–3% of CPA tumors.
The CPA tumors are persuasive to cause direct and/or indirect pathological effects on the auditory system. These effects generally are in the form of eighth nerve compression, destruction, infiltration, vascular compression or occlusion of the blood supply to the eighth nerve or to the cochlea, deafferentation, biochemical changes within the inner ear, and toxicity of the inner ear. Pressure on adjacent structures including compression or displacement of the brain stem may also contribute to auditory dysfunction.
Immittance audiometry is one of the most common procedures widely employed by audiologists. In the present study, the focus is given on understanding the efficacy of acoustic reflex decay (ARD) and acoustic reflex latency threshold (ARLT) in evaluating CPA tumors. Such results will be of very much clinical utility.
In the presence of normal tympanometric findings, ARD and ARLT test results may vary depending on the functional integrity of the cochlea, auditory nerve, brain stem level auditory nuclei such as ventral cochlear nucleus and medial superior olivary complex, facial motor neuron, and facial nerve. In a busy hospital setup, ARD and ARLT could be the initial special tests of choice for establishing the presence of retrocochlear pathology as these tests are cost-effective and noninvasive. Keeping the above views in mind, the present study was formulated.
The study aimed to understand the pathophysiological basis of the CPA tumors from ARD and ARLT test perspective. The objectives of the study are:
- To characterize ARD and ARLT profiles in CPA tumors
- To correlate ARD and ARLT test results with the type, size, and extent of tumors.
| Subjects and Methods|| |
This group comprised 98 patients with CPA tumor.
- Confirmed CPA tumor patients as evidenced by neuroradiological findings on magnetic resonance imaging (MRI) or computed tomography (CT)
- Patients aged between 15 and 55 years.
History of occupational noise exposure, ear infections, or any other neurological/psychiatric conditions.
This group comprised 100 normal hearing subjects.
- Subjects aged between 15 and 55 years
- Having normal hearing.
- Impaired hearing
- History of occupational noise exposure, ear infections or any other neurological/psychiatric conditions.
Informed consent was obtained from all subjects (clinical and control groups). The institute ethics committee had approved the protocol for the study.
Acoustic reflex decay and acoustic reflex latency threshold
Immittance audiometry was performed using Amplaid 728 immittance audiometer (Amplifon Group, Assago, Milan, Italy) with TDH49 P earphones. Baseline tympanometric measurements were obtained to rule out the presence of any middle ear pathology. Patients with 'A' type tympanogram were only considered for acoustic reflex threshold (ART) estimation.
ARD was estimated at 500 Hz and 1000 Hz both ipsilaterally and contralaterally. ARD is defined as the reduction in the magnitude of the acoustic reflex response during the presentation of a sustained stimulus. Reflex decay was considered positive whenever the reflex magnitude decreased by 50% or more within 5 s. The stimulus for ARD was presented for 10 s at a level of 10 dB above the ART.
ARLT was estimated both ipsilaterally and contralaterally. The ARLT is the time taken for the acoustic reflex to occur after the stimulus is presented. Testing was limited to 500 Hz and 1000 Hz. The presentation level of the stimulus was 10 dB above ART.
Note: Statistical analysis was performed only for ARLT measures.
Grouping and statistical analysis of the data
Statistical Package for the Social Sciences (SPSS) software version 18.0 was employed (IBM Corp., Armonk, NY, USA). Statistical analysis for the clinical group versus control group was carried out using the analysis of covariance for age and gender covariates. For discrete clinical groups classified based on tumor type, size, and extent versus control group, acoustic versus nonacoustic tumor types, Group I versus Group II versus Group III tumor volumes, and Group A versus Group B tumor extents, analysis of variance (ANOVA) followed by post hoc (Turkey) test was used. Independent sample t-test was used for the statistical analysis of tumor ear versus nontumor ear. The mean difference between variables was considered statistically significant at P < 0.05.
The results obtained on ARLT for CPA tumor patients (tumor and nontumor ear) were compared with the control (normal hearing) group separately. Comparison between the tumor and nontumor ears was also done. A similar analysis was done for tumor subtypes classified based on tumor type, size, and extent.
Histopathological findings categorized the tumors into acoustic and nonacoustic types. A comparison between acoustic and nonacoustic types was done separately for tumor and nontumor ears.
Tumor volume was estimated from MRI or CT scans. Based on volumetric measurements of the tumor, they were classified into Group I having tumor volume ≤30 cc, Group II having tumor volume 31–60 cc, Group III having volume >60 cc, and Group IV where tumor volume could not be ascertained (Group IV was not considered for statistical analysis due to limited number of cases). A comparison between the Groups was done.
Tumor extent was estimated from MRI or CT scans. The patients were classified into Group A having internal auditory meatus (IAM) and brain stem involvement, Group B having only brain stem involvement, and Group C which is an un-assorted group having patients with the lesion extension to IAM only; patients with no involvement of IAM and brain stem and patients in whom the tumor extent could not be estimated (Group C was not considered for statistical analysis due to limited number of cases). Comparison between Groups A and B was done for tumor ears to determine dissimilarity, if any, between tumor extents in terms of ARLT findings.
| Results|| |
The clinical group consisted of 98 patients (mean age: 37.4 years) of unilateral CPA tumors. Matched to the age range of the clinical group, the control group (normal hearing) was comprised 100 subjects (mean age: 33.6 years) [Table 1].
Description of the clinical group
Acoustic reflex decay in the clinical group
The test results indicated positive reflex decay in less number of ears [Table 2] and [Table 3].
Acoustic reflex latency threshold
Normative data for ARLT were computed. The mean difference in ARLT between the right and left ears was found to be statistically not significant in independent samples t-test. Hence, a combined mean value of ARLT of 98.8 ms (standard deviation [SD] =26.71) and 99.53 ms (SD = 37.22) was considered normative for 500 Hz and 1000 Hz for ipsilateral stimulation. The corresponding values for contralateral stimulation were 95.85 ms (SD = 34.1) and 92.89 ms (SD = 33.39).
Comparison of acoustic reflex latency threshold between the control group and clinical group
Statistical analysis was not done for tumor ear ipsilateral ARLT in all clinical groups as well as nontumor ear contralateral ARLT in the clinical groups classified based on type, size, and extent due to a limited number of cases. [Table 4] depicts the mean ARLT values in both the control and the patient groups.
A statistically significant difference (P < 0.05) was observed for nontumor ears on ipsilateral and contralateral stimulation at 500 Hz. ANOVA was utilized to analyze the difference in the mean ARLT of the control group with discrete clinical groups and found significant at P < 0.05. The post hoc (Tukey) test was used for pair-wise comparisons of the control group with discrete clinical groups, and a statistically significant difference at P < 0.05 was observed for nonacoustic nontumor ears and Group II nontumor ears on ipsilateral stimulation at 500 Hz. However, at 1000 Hz, none of the clinical groups showed a statistically significant difference with the control group (P > 0.05) on ipsilateral stimulation. Similar findings were observed on contralateral stimulation [Table 5].
|Table 5: Statistical significance on comparison of mean ARLT between control group and clinical group|
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Comparison of acoustic reflex latency threshold between tumor and nontumor ears
The contralateral ARLT obtained for tumor ears and nontumor ears was significantly different at 500 Hz (P = 0.027) on independent samples t-test, with poor scores in nontumor ears.
Comparison of acoustic reflex latency threshold between clinical groups classified based on tumor type, size, and extent
To analyze the difference in mean ARLT of the control group with discrete clinical groups, ANOVA was used and found significant at P < 0.05. There was no significant difference for ipsilateral ARLT (P > 0.05) between acoustic and nonacoustic nontumor ears and between Groups I, II, and III nontumor ears. Similar findings for contralateral ARLT were noted for tumor ears. Comparison between Group A and B tumor ear contralateral ARLT showed a statistically significant difference (P = 0.046) at 1000 Hz, with Group B demonstrating poor scores [Table 6].
|Table 6: Statistical significance on comparison of mean ARLT between clinical groups classified based on tumor type, size and extent|
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| Discussion|| |
Acoustic reflex decay
In the present study, a reduction of acoustic reflex response amplitude of 50% or more occurring within 5 s was the criteria adopted for defining the presence of retrocochlear pathology. The test results indicated that the proportion of ears with abnormal reflex decay (0%–25%) was less compared to those with normal findings (75%–100%) in the patient group reflecting the poor efficacy of ARD to identify the presence of CPA tumors.
For tumor ear ipsilateral stimulation, the percentage of ears with abnormal ARD was 0% and 17% at 500 and 1000 Hz, respectively. For nontumor ear contralateral stimulation, the proportion of abnormal ARD findings at 500 Hz and 1000 Hz was 22% and 25%, respectively. The inefficacy of ARD for CPA tumor identification has also been reported.,,,,, Tumor identification percentage using ARD in these studies was 33%, 50%, 44%, 17%, 20%, and 0%, respectively. The criterion for ARD abnormality adopted in the present study concurred with those used by Cashman et al., Neary et al. and Ferguson et al.,,
In the present study, the proportion of ears with abnormal ARD on the nontumor ear ipsilateral stimulation was 3% and 7% at 500 Hz and 1000 Hz, respectively. The corresponding fraction for the tumor ear contralateral stimulation was 5% and 7% at 500 Hz and 1000 Hz, respectively. These results suggest the inefficacy of ARD in identifying the nontumor ear deficits associated with brain stem compression in CPA tumors.
Acoustic reflex latency threshold
ARLT was administered at a presentation level of 10 dB sensation level above ART. The test could not be administered in all the ears due to elevated or absent SR. For ipsilateral stimulation, the test was possible in approximately 5% of the tumor ears, whereas it could be administered in 40%–50% of the nontumor ears (all test frequencies considered). For contralateral stimulation, the test was possible in approximately 15% of the nontumor ears and 45% of the tumor ears. Clearly, the number of ears tested for the tumor ear stimulation was very less.
Statistical analysis could not be carried out for the tumor ear ipsilateral ARLT due to a limited number of cases. On contralateral stimulation, the nontumor ear ARLT was significantly different from the control group and the tumor ear ARLT at 500 Hz, indicating the presence of retrocochlear pathology. However at 1000 Hz, no differences were noted.
With respect to ipsilateral stimulation in the nontumor ears, no difference with the control group was observed at 1000 Hz. Similarly, for the tumor ear contralateral stimulation, ARLT obtained at 500 Hz and 1000 Hz did not differ with the control group. Thus, the inefficacy of ARLT in identifying pathological effects of brain stem compression was obvious. A comparison of a control group with subcategories of tumor type and size strengthened this finding. Further, Groups A and B tumor ear contralateral ARLT scores also did not differ with the normative indicating the insignificance of ARLT in identifying deficits associated with brain stem compression and IAM involvement by the tumor.
Analysis of the data revealed that the nontumor ear ARLT (both ipsilateral and contralateral stimulation) did not differ with respect to tumor type or size. Analysis based on tumor extent also did not give any clear indication regarding the role of intracanalicular component of tumors in affecting the tumor ear contralateral ARLT.
| Conclusion|| |
In the present study, the estimation of ARD and ARLT did not appear to be useful indices for CPA tumor identification.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]