Auditory Brainstem Response(BERA)
Diagnostic Centres are having facility for Brainstem Evoked Response Audiometry (BERA). It evaluates the hearing threshold and diagnose retro-cochlear lesions. The aim of the study is to investigate the hearing level in children with suspected hearing loss or pathological speech development.The auditory brainstem response (ABR) is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp.
Procedure:
The stimulus either in the form of click or tone pip is transmitted to the ear via a transducer placed in the insert ear phone or head phone. The wave forms of impulses generated at the level of brain stem are recorded by the placement of electrodes over the scalp.
Electrode placement: Since the electrodes should be placed over the head, the hair must be oil free. The patient should be instructed to have shampoo bath before coming for investigation. The standard electrode configuration for BERA involves placing a non-inverting electrode over the vertex of the head, and inverting electrodes placed over the ear lobe or mastoid prominence. One more earthing electrode is placed over the forehead. This earthing electrode is important for proper functioning of preamplifier.
The auditory structures that generate the auditory brainstem response are believed to be as follows:
- Wave I through III – generated by the auditory branch of cranial nerve VIII and lower
- Wave IV and V – generated by the upper brainstem
- More in depth location – wave I originates from the dendrites of the auditory nerve fibers, wave II from the cochlear nucleus, III showing activity in the superior olivary complex, and wave IV–V associated with the lateral lemniscus.
Use:
- It is an effective screening tool for evaluating cases of deafness due to retrocochlear pathology. An abnormal BERA is an indication for MRI scan.
- Used in screening newborns for deafness.
- Used for intraoperative monitoring of central and peripheral nervous system
- Monitoting patients in intensive care units
- Diagnosing suspected demyelinated disorders
Criteria for screening newborn babies using BERA:
- Parental concern about hearing levels in their child
- Family history of hearing loss
- Pre and post natal infections
- Low birth weight babies
- Hyperbilirubinemia
- Cranio facial deformities
- Head injury
- Persistent otitis media
- Exposure to ototoxic drugs