Brain-stem Evoked Response Audiometry(B.E.R.A)
Auditory brainstem response (ABR) audiometry is a neurologic test of auditory brainstem function in response to auditory (click) stimuli. ABR audiometry refers to an evoked potential generated by a brief click or tone pip transmitted from an acoustic transducer in the form of an insert earphone or headphone. The elicited waveform response is measured by surface electrodes typically placed at the vertex of the scalp and ear lobes. The amplitude (microvoltage) of the signal is averaged and charted against the time (millisecond), much like an EEG. The waveform peaks are labeled I-VII. These waveforms normally occur within a 10-millisecond time period after a click stimulus presented at high intensities (70-90 dB normal hearing level [nHL]).
While the ABR provides information regarding auditory function and hearing sensitivity, it is not a substitute for a formal hearing evaluation, and results should be used in conjunction with behavioral audiometry whenever possible.
Uses of BERA:
1. It is an effective screening tool for evaluating cases of deafness due to retrocochlear pathology i.e. (Acoustic schwannoma). An abnormal BERA is an indication for MRI scan.
2. Used in screening newborns for deafness .
3. Used for intraoperative monitoring of central and peripheral nervous system .
4. Monitoting patients in intensive care units .
5. Diagnosing suspected demyelinated disorders.
BERA findings suggestive of retrocochlear pathology:
1. Latency differences between interaural wave 5 (prolonged in cases of retrocochlear pathology) .
2. Waves I - V interaural latency differences - prolonged .
3. Absolute latency of wave V - prolonged.
4. Absence of brain stem response in the affected ear.
BERA has 90% sensitivity and 80% specificity in identifying cases of acoustic schwannoma. The sensitivity increases in proportion to the size of the tumor.
Criteria for screening newborn babies using BERA:
1. Parental concern about hearing levels in their child
2. Family history of hearing loss
3. Pre and post natal infections
4. Low birth weight babies
6. Cranio facial deformities
7. Head injury
8. Persistent otitis media
9. Exposure to ototoxic drugs