Brainstem evoked response audiometry (synonym: brainstem evoked response audiometry, ABR) is a diagnostic procedure in neurology and otolaryngology that can be used for electrophysiological assessment of objective hearing ability. By means of the ABR it is possible to measure the acoustically evoked (lat. evocare, “to summon”, “to evoke”) brainstem potentials (AEHP). With the help of this method, it is thus possible to make a statement about the hearing ability independently of the subjective perception of the patients and their description of these perceptions. AEHP have the advantage that they are fully developed after 18 months of life and are almost completely independent of cooperation and level of alertness, so that they can also be used with infants and young children. AEHP represent potentials whose origin is found in the auditory pathway between the cochlea, the auditory nerve to a variety of nuclear areas in the brainstem.
Indications (areas of application)
- Newborn screening – Various methods can be used to detect hearing disorders in newborns. Both the measurement of otoacoustic emissions (acoustic emissions) and the use of ABR are suitable for this purpose because of a sensitivity (percentage of diseased newborns in whom the disease is detected by the use of the test, i.e., a positive test result occurs) of almost 100%. However, there is a significantly higher specificity (probability that actually healthy individuals who do not have the disease in question will be detected as healthy by the procedure) with ABR, making it superior to otoacoustic emissions as a screening method. Newborn screening by ABR is indicated in newborns with:
- Familial hearing impairment,
- Proven congenital infection such as rubella infection,
- Birth weight below 1,500 g
- An ototoxic medication (drugs that damage hearing), for example, with aminoglycosides (antibiotics),
- A bacterial meningitis (meningitis) or sepsis (blood poisoning),
- A low APGAR score (scoring scheme used to assess the clinical condition of newborns in a standardized manner),
- Several days of mechanical ventilation or the presence of syndromes with hearing impairment.
- Hearing threshold determination – In pediatric audiology examinations (science of hearing disorders (of hearing) and auditory perception in childhood), but also in uncooperative patients, the procedure is indicated. In addition, the hearing threshold can also be derived under sedation (twilight sleep) or general anesthesia. A frequency-specific hearing threshold determination can be achieved by using stimulus filtering methods.
- Acoustic neuroma (tumor of the auditory nerve) – Various studies cite brainstem audiometry as an adequate procedure for screening because of a sensitivity to detect acoustic neuromas between 95% and 100%, regardless of size. On the basis of this, ABR is routinely used in:
- Suspicion of an acoustic neuroma.
- Hearing loss
- Tinnitus (ringing in the ears) or vertigo (dizziness)
However, imaging techniques, particularly magnetic resonance imaging (MRI, magnetic resonance imaging), are increasingly being used to detect and evaluate acoustic neuromas.
Contraindications
Because brainstem measurement is a noninvasive diagnostic procedure, there are no contraindications when indicated.
Before the examination
Before the examination can be performed, a detailed educational discussion with behavioral instructions must be conducted. To perform the procedure, the patient should lie relaxed so that there is little muscle activity. Precise instruction can significantly improve the measurement results.
The procedure
The basic principle of the procedure is based on the imaging of electrical potentials in waveform during successful processing of an acoustic stimulus. The depicted potentials show the activity of the auditory pathway between the auditory nerve and the midbrain. The potentials are measured by electroencephalography (EEG)-based recordings. Thus, brainstem audiometry evaluates the EEG during acoustic stimulation.When performing the procedure, one electrode conducts at the vertex and one electrode conducts at the mastoid (part of the temporal bone, colloquially known as the “mastoid process”). A third electrode, placed centrally on the forehead, is used as a reference electrode. In brainstem measurement, the potentials detected via EEG can be divided into early, middle, late and very late potentials. This division is based on the response time of the EEG to auditory stimulation.
After the examination
No special measures need to be taken following the examination. Depending on the results of the examination, further diagnostic or therapeutic procedures may be used.
Possible complications
No complications are expected.