Retrocochlear Flashcards
What test battery will be implemented to assess for retrocochlear lesion?
- Word rec at multiple levels
- ARTs
- Acoustic reflex adaptation
- ABR
What results are expected for word rec for cochlear lesions?
- Speech audiometry performance will vary between patients, usually between 50 and 90%.
- The performance versus intensity function (PI-PB) will reach maximum performance and then plateau or decline very slightly
What results are expected for word rec for retrocochlear lesions?
- There will be a significant reduction in speech recognition scores that occurs at intensities about the presentation level where PB max is obtained.
- On the PI-PB function, individuals with retrocochlear lesions will reach maximum performance at a low intensity level and then show a severe decline in performance as intensity increases.
- It is not uncommon for individuals with retrocochlear lesions to have poor performance (<50%) on speech audiometry tests.
- Word recognition scores between ears may be asymmetrical or poorer than expected based on the pure tone thresholds.
What results are expected for ARTs for cochlear lesions?
- Dynamic range: 20-70 dB sensation level (SL)
- Usually present acoustic reflex thresholds
- Will see loudness recruitment, or an abnormal growth of response with increasing sound level
What results are expected for ARTs for retrocochlear lesions?
- ARTs elevated or absent (>90th percentile)
- ARTs may be absent in the presence of hearing thresholds that should elicit the ART
- May see absent/elevated contralateral reflexes for intra-axial brainstem disorders
What is acoustic reflex adaptation?
- The acoustic reflex decay measures the fatigue of the auditory system during the presentation of a constant stimulus.
- A 226-Hz probe tone is used with a 500-Hz or 1,000 Hz activator, which is presented at 10 seconds at 10 dB above the contralateral acoustic reflex for the selected frequency.
- Useful in confirming a suspected retrocochlear site of lesion.
What are the three disadvantages for the acoustic reflex adaptation?
- Cannot be tested if the contralateral acoustic reflexes are absent or highly elevated so that the stimulus cannot be presented at 10 dB SL
- Poorer sensitivity/specificity than the ABR for retrocochlear disorders
- High intensity stimuli can result in NIHL
What results are expected for acoustic reflex adaptation for cochlear losses?
- A positive decay can be observed in some patients with cochlear lesions.
- However, it is expected that a negative decay will be present in individuals with a cochlear loss.
What results are expected for acoustic reflex adaptation for retrocochlear losses?
- If amplitude declines 50% within 5 seconds, the result is indicative of a retrocochlear lesion
- Abnormal or positive decay will be observed when the amplitude of the reflex decreases 50% or more in its initial magnitude in less than 10 seconds
What test parameters are recommended for ABR recording?
Click-evoked ABR with a 2-channel ipsilateral/contralateral recording
- Use a low stimulation rate (21.1/sec) as well as a high stimulation rate (83.3/sec)
- It is necessary to use a combination of ipsilateral and contralateral recordings.
- The ipsilateral recording will emphasize Wave I and the contralateral recording will separate waves IV and V
- Need to determine the I-V delay as well as the IT5 to compare interaural latencies.
What results are expected for the ABR for cochlear losses?
- A sharply sloping high-frequency SNHL will show wave V delays
- When thresholds from 2000-4000 Hz are in the 50-70 dB HL range, abnormal ABRs are often seen.
- When thresholds at 4000 Hz are greater than 50 dB HL, wave I is often absent.
What results are expected for the ABR for lower brainstem retrocochlear losses?
- Earlier waves or entire waveform may be absent
- More common interwave latency prolongation is between I-III.
- Ipsilateral abnormalities are commonly observed, unless the lesion is large
What results are expected for the ABR for higher brainstem retrocochlear lesions?
- Earlier waves are present and later waves may be absent
- Most common interwave prolongation is between III-V
- Bilateral, ipsilateral, and contralateral abnormalities may be present
Why are the behavioral measures selected preferable for this type of diagnosis and why?
- All diagnostic measures described above are preferable for the diagnosis of cochlear versus retrocochlear lesions.
- The battery of tests described are progressive and are designed to indicate the site-of-lesion
- The identification accuracy of retrocochlear hearing loss is improved by combining behavioral, physiological, and electrophysiological measures.
- There is not a single test that will indicate whether the hearing loss is cochlear or retrocochlear in origin.
- Thus, it is important to include all measures to delineate site of lesion.
What is the gold standard for diagnosing retrocochlear disorders?
- However, the gold standard for the diagnosis of retrocochlear pathology is magnetic resonance imaging (MRI) of the brain, brainstem, and internal auditory canals (IACs)
- The audiologic test battery alone cannot confirm the presence of retrocochlear pathology.
- Any abnormalities detected in the audiologic test battery require an MRI to corroborate findings.
