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Auditory Brainstem Response Audiometry
Updated: Mar 10, 2017
Author: Neil Bhattacharyya, MD; Chief Editor: Arlen D Meyers, MD, MBA more...
OVERVIEW
Overview
Auditory brainstem response (ABR) audiometry is a neurologic test of auditory brainstem function
in response to auditory (click) stimuli. First described by Jewett and Williston in 1971, ABR
audiometry is the most common application of auditory evoked responses. Test administration and
interpretation is typically performed by an audiologist. This article provides an overview of the test
and its most common applications. For purposes of clarity and brevity, specialized ABR techniques
and more technical issues have been omitted.
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 I­VII. These waveforms
normally occur within a 10­millisecond time period after a click stimulus presented at high
intensities (70­90 dB normal hearing level [nHL]). (See image below.)
Normal adult auditory brainstem response (ABR) audiometry waveform response.
Although 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.
Physiology

2. Auditory brainstem response (ABR) audiometry typically uses a click stimulus that generates a
response from the basilar region of the cochlea. The signal travels along the auditory pathway from
the cochlear nuclear complex proximally to the inferior colliculus. ABR waves I and II correspond to
true action potentials. Later waves may reflect postsynaptic activity in major brainstem auditory
centers that concomitantly contribute to waveform peaks and troughs. The positive peaks of the
waveforms reflect combined afferent (and likely efferent) activity from axonal pathways in the
auditory brain stem.
In the United States, the waveforms are typically plotted with the vertex site electrode in the
positive voltage input of the amplifier, resulting in I, III, and V wave peaks. In other countries, the
waves are plotted with a negative voltage.
Waveform components
Wave I
The ABR wave I response is the far­field representation of the compound auditory nerve action
potential in the distal portion of cranial nerve (CN) VIII. The response is believed to originate from
afferent activity of the CN VIII fibers (first­order neurons) as they leave the cochlea and enter the
internal auditory canal.
A study by Lin et al indicated that in the assessment of ABR in patients with idiopathic sudden
sensorineural hearing loss (ISSNHL), wave I latency is significantly associated with hearing
outcomes, with a trend toward prolongation found between patients with complete hearing
recovery and those experiencing only slight recovery. [1]
A study by Bramhall et al indicated that in persons with normal pure­tone auditory thresholds,
those with a history of greater noise exposure tend to have smaller ABR wave I amplitudes at
suprathreshold levels. The study included military veterans exposed to high levels of military noise
and non­veterans with a history of firearm use, as well as veterans and non­veterans with less
noise exposure. Suprathreshold ABR measurements were made at 1, 3, 4, and 6 kHz, using
alternating polarity tone bursts, with the ABR wave I amplitudes at suprathreshold levels being
smaller at all four frequencies in the high­noise­level groups. The amplitude differences between
the groups could not be attributed to either sex or outer hair cell function variability. The
investigators could not confirm whether the differences were due to synaptopathy without
postmortem temporal bone examination. [2]
Wave II
The ABR wave II is generated by the proximal VIII nerve as it enters the brain stem.
Wave III
The ABR wave III arises from second­order neuron activity (beyond CN VIII) in or near the
cochlear nucleus. Literature suggests wave III is generated in the caudal portion of the auditory
pons. The cochlear nucleus contains approximately 100,000 neurons, most of which are
innervated by eighth nerve fibers.
Wave IV
The ABR wave IV, which often shares the same peak with wave V, is thought to arise from pontine
third­order neurons mostly located in the superior olivary complex, but additional contributions may
come from the cochlear nucleus and nucleus of lateral lemniscus.
Wave V
Generation of wave V likely reflects activity of multiple anatomic auditory structures. The ABR
wave V is the component analyzed most often in clinical applications of the ABR. Although some

3. debate exists regarding the precise generation of wave V, it is believed to originate from the vicinity
of the inferior colliculus. The second­order neuron activity may additionally contribute in some way
to wave V. The inferior colliculus is a complex structure, with more than 99% of the axons from
lower auditory brainstem regions going through the lateral lemniscus to the inferior colliculus.
A study by Spitzer et al of 71 preschoolers aged 3.12­4.99 years found a systematic decrease in
wave V latency in these subjects, indicating that the ABR is not fully mature by age 2 years, as has
been thought, but instead continues to develop through a child’s preschool years. [3]
Waves VI and VII
Thalamic (medial geniculate body) origin is suggested for generation of waves VI and VII, but the
actual site of generation is uncertain.
Applications
Identification of retrocochlear pathology
Auditory brainstem response (ABR) audiometry is considered an effective screening tool in the
evaluation of suspected retrocochlear pathology such as an acoustic neuroma or vestibular
schwannoma. However, an abnormal ABR finding suggestive of retrocochlear pathology indicates
the need for MRI of the cerebellopontine angle.
Symptoms of eighth nerve pathology
Clinical symptoms may include but are not limited to the following:
Asymmetrical or unilateral sensorineural hearing loss
Asymmetrical high­frequency hearing loss
Unilateral tinnitus
Unilaterally or bilaterally poor word recognition scores as compared with degree of
sensorineural hearing loss
Perceived distortion of sounds when peripheral hearing is essentially normal
Auditory brainstem response evaluation
In addition to retrocochlear pathologies, many factors may influence ABR results, including the
degree of sensorineural hearing loss, asymmetry of hearing loss, test parameters, and other
patient factors. These influences must be factored in when performing and analyzing an ABR
result.
Findings suggestive of retrocochlear pathology may include any 1 or more of the following:
Absolute latency interaural difference wave V (IT5) ­ Prolonged
I­V interpeak interval interaural difference ­ Prolonged
Absolute latency of wave V ­ Prolonged as compared with normative data
Absolute latencies and interpeak intervals latencies I­III, I­V, III­V ­ Prolonged as compared
with normative data
Absent auditory brainstem response in the involved ear
In general, ABR exhibits a sensitivity of over 90% and a specificity of approximately 70­90%.
Sensitivity for small tumors is not as high. For this reason, a symptomatic patient with a normal
ABR result should receive a follow­up audiogram in 6 months to monitor for any changes in
hearing sensitivity or tinnitus. The ABR may be repeated if indicated. Alternatively, MRI with
gadolinium enhancement, which has become the new criterion standard, can be used to identify
very small (3­mm) vestibular schwannomas.

4. The ABR sensitivity in the diagnosis of CN VIII tumors by size according to several studies is as
follows:
In a 1994 study by Dornhoffer, Helms, and Hoehmann, the sensitivity was 93% for tumors
smaller than 1 cm. [4]
In 1997, Zappia, O'Connor, Wiet, and Dinces reported a sensitivity of 89% for small tumors
smaller than 1 cm, 98% for medium tumors 1.1­2 cm, and 100% for tumors larger than 2 cm.
The overall sensitivity was 95%. [5]
In a 1995 study, Chandrasekhar, Brackmann, and Devgan reported a sensitivity of 83.1% for
tumors smaller than 1 cm and a sensitivity of 100% for tumors larger than 3 cm. Overall
sensitivity was 92%. [6]
In 1995, Gordon and Cohen reported the following sensitivities: 69% for tumors smaller than
9 mm, 89% for tumors 1­1.5 cm, 86% for tumors 1.6­2 cm, and 100% for tumors larger than 2
cm. [7]
In a 2001 report by Schmidt, Sataloff, Newman, Spiegel, and Myers, the sensitivity was 58%
for tumors smaller than 1 cm, 94% for tumors 1.1­1.5 cm, and 100% for tumors larger than
1.5 cm. The overall sensitivity was 90%. [8]
In a large prospective study that compared ABR with contrast­enhanced MRI (the criterion
standard) in 312 patients with asymmetric sensorineural hearing loss, Cueva found that APR
yielded a sensitivity and specificity of 71% and 74%, respectively, in revealing the cause of
lesions for asymmetric sense and oral hearing loss (including, but not limited to, vestibular
schwannoma). The ABR­positive predictive value was only 23%, whereas its negative
predictive value was 96%. Seven of 31 positive cases had other lesions that ABR could not
identify as a cause of the hearing loss. [9]
Although traditional ABR measures decrease in sensitivity as a factor of tumor size, recent studies
have shown that by using a new stacked derived­band ABR that measures amplitude, very small
tumors may be detected more accurately. This new technique, combined with traditional ABR
audiometry, may soon make possible the detection of very small tumors with accuracy approaching
100% using ABR audiometry.
Other applications of auditory brainstem response
Other applications of ABR continue to evolve. Recent research suggests that although the overall
ABR wave latencies are within normal limits in patients with tinnitus, those patients have longer
latencies than control patients without tinnitus. [10] This suggests that ABR may be useful in
monitoring and understanding tinnitus. ABR has also been used for prognostication in patients with
coma. Researchers have found that patients with a Glasgow coma scale of 3 and who also have a
significantly abnormal ABR had a greater probability of dying than those with a normal ABR [11]
(see the Glasgow Coma Scale calculator).
A study by Sköld et al indicated that ABR wave patterns are significantly different between patients
with bipolar disorder type I (BPI) and those with schizophrenia, suggesting that ABR may be useful
as a BPI biomarker. The study, which involved 23 patients with BPI and 20 patients with
schizophrenia, as well as 20 controls, found that wave III and VII amplitudes were significantly
higher in the patients with BPI than in those with schizophrenia. The report also found that in BPI
patients, as well as (somewhat less strongly) those with schizophrenia, the portion of the ABR
curve containing waves VI and VII did not correlate well will that belonging to the controls.
According to the investigators, the study’s results indicate that BPI may be associated with
thalamocortical circuitry abnormalities. [12]
Newborn Hearing Screening
Auditory brainstem response (ABR) technology is used in testing newborns. Approximately 1 of
every 1000 children is born deaf; many more are born with less severe degrees of hearing

5. impairment, while others may acquire hearing loss during early childhood.
Historically, only infants who met one or more criteria on the high­risk register were tested.
Universal hearing screening has been recommended because about 50% of the infants later
identified with hearing loss are not tested when neonatal hearing screening is restricted to high­risk
groups. Recently, hospitals across the United States have been implementing universal newborn
hearing screening programs. These programs are possible because of the combination of
technological advances in ABR and otoacoustic emissions (OAE) testing methods and equipment
availability, which enables accurate and cost­effective evaluation of hearing in newborns.
Several clinical trials have shown automated auditory brainstem response (AABR) testing (eg,
Algo­1 Plus) as an effective screening tool in the evaluation of hearing in newborns, with a
sensitivity of 100% and specificity of 96­98%.
When used as a threshold measure to screen for normal hearing, each ear may be evaluated
independently, with a stimulus presented at an intensity level of 35­40 dB nHL. Click­evoked ABR
is highly correlated with hearing sensitivity in the frequency range from 1000­4000 Hz. AABRs test
for the presence or absence of wave V at soft stimulus levels. No operator interpretation is
required. AABR can be used on the ward and during oxygen therapy without disturbance from
ambient noise.
The 2000 Joint Committee on Infant Hearing has recommended that infants with at least 1 of the
following risk indicators for progressive or delayed­onset hearing loss who may have passed the
hearing screening should, nonetheless, receive audiologic monitoring every 6 months until age 3
years: [13]
Parental or caregiver concern regarding hearing, speech, language, and/or developmental
delay
Family history of permanent childhood hearing loss
Stigmata or other findings associated with a syndrome known to include a sensorineural or
conductive hearing loss or eustachian tube dysfunction
Postnatal infections associated with sensorineural hearing loss, including bacterial meningitis
In utero infections such as cytomegalovirus, herpes, rubella, syphilis, and toxoplasmosis
Neonatal indicators, specifically hyperbilirubinemia at a serum level requiring exchange
transfusion, persistent pulmonary hypertension of the newborn associated with mechanical
ventilation, conditions that require the use of extracorporeal membrane oxygenation (ECMO),
bronchopulmonary dysplasia, cytomegalovirus infection, and craniofacial anatomy (Lieu and
Champion recently confirmed these results.)
Syndromes associated with progressive hearing loss, such as neurofibromatosis,
osteopetrosis, and Usher syndrome
Neurodegenerative disorders, such as Hunter syndrome, or sensory motor neuropathies,
such as Friedreich ataxia and Charcot­Marie­Tooth syndrome
Head trauma
Recurrent or persistent otitis media with effusion for at least 3 months
Ototoxic medications (aminoglycosides)
ABRs may be used to detect auditory neuropathy or neural conduction disorders in newborns.
Because ABRs are reflective of auditory nerve and brainstem function, these infants can have an
abnormal ABR screening result even when peripheral hearing is normal.
Infants that do not pass the newborn hearing screenings do not necessarily have hearing
problems. When hearing loss is suspected because of an abnormal ABR screening result, a follow­
up diagnostic threshold ABR test is scheduled to determine frequency­specific hearing status.
Estimation of hearing at specific frequencies may be obtained through use of brief tone stimulation,
such as a tone burst.
Auditory Brainstem Response in Surgery

6. Intraoperative monitoring
Auditory brainstem response (ABR), often used intraoperatively with electrocochleography,
provides early identification of changes in the neurophysiologic status of the peripheral and central
nervous systems. This information is useful in the prevention of neurotologic dysfunction and the
preservation of postoperative hearing loss. For many patients with tumors of CN VIII or the
cerebellopontine angle, hearing may be diminished or completely lost postoperatively, even when
the auditory nerve has been preserved anatomically.
Auditory brainstem response evaluation
Wave I, which is generated by the cochlear end of CN VIII, provides valuable real­time information
regarding blood flow to the cochlea. Because ischemia is a primary cause of surgery­related
hearing loss, wave I is monitored closely for any shift in latency or decrease of amplitude.
Wave I­II and I­III interpeak intervals can provide distal and proximal information during CN VIII
surgeries.
Wave V and the I­V interpeak interval latencies are monitored for shifts or alterations in latency and
amplitude. The I­V latency provides information regarding the integrity of CN VIII to the auditory
brain stem.
Limitations
Wave V alterations occurring intraoperatively do not necessarily reflect changes in hearing status.
Changes in latency may instead be caused by desynchronization of neurons or other outside
factors. Also, a potential time delay exists between the actual occurrence of insult and when the
shift in wave V appears. Patients with preexisting sensorineural hearing loss may have poor
waveform morphology and no wave I response.
Typical uses of intraoperative auditory brainstem response
Monitoring cochlear function directed at hearing preservation
Cerebellopontine angle tumor resection (acoustic neuroma surgery)
Vascular decompression of trigeminal neuralgia
Vestibular nerve section for the relief of vertigo
Exploration of the facial nerve for facial nerve decompression
Endolymphatic sac decompression for Mèniére disease
Monitoring brainstem integrity
Brainstem tumor resection
Brainstem aneurysm clipping or arteriovenous malformation resection
Conclusion
Auditory brainstem response (ABR) audiometry has a wide range of clinical applications, including
screening for retrocochlear pathology, universal newborn hearing screening, and intraoperative
monitoring. Additional applications include ICU monitoring, frequency­specific estimation of
auditory sensitivity, and diagnostic information regarding suspected demyelinating disorders (eg,
multiple sclerosis). As technology continues to evolve, ABR will likely provide more qualitative and
quantitative information regarding the function of the auditory nerve and brainstem pathways
involved in hearing.
References

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Normal adult auditory brainstem response (ABR) audiometry waveform response.
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Contributor Information and Disclosures
Author
Neil Bhattacharyya, MD Associate Professor of Otology and Laryngology, Harvard Medical
School; Consulting Surgeon, Department of Surgery, Division of Otolaryngology, Brigham and
Women's Hospital
Neil Bhattacharyya, MD is a member of the following medical societies: American Academy of
Otolaryngology­Head and Neck Surgery, The Triological Society, American Rhinologic Society,
American Bronchoesophagological Association, American College of Surgeons, American Medical
Association, Society of University Otolaryngologists­Head and Neck Surgeons
Disclosure: Received consulting fee from Entellus, Inc for consulting; Received consulting fee from
IntersectENT, Inc for consulting.
Specialty Editor Board
Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical
Center College of Pharmacy; Editor­in­Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Gerard J Gianoli, MD Clinical Associate Professor, Departments of Otolaryngology­Head and
Neck Surgery and Pediatrics, Tulane University School of Medicine; President, The Ear and
Balance Institute; Board of Directors, Ponchartrain Surgery Center
Gerard J Gianoli, MD is a member of the following medical societies: American Academy of
Otolaryngology­Head and Neck Surgery, American College of Surgeons, American Neurotology

9. Society, American Otological Society, Society of University Otolaryngologists­Head and Neck
Surgeons, Triological Society
Disclosure: Nothing to disclose.
Chief Editor
Arlen D Meyers, MD, MBA Professor of Otolaryngology, Dentistry, and Engineering, University of
Colorado School of Medicine
Arlen D Meyers, MD, MBA is a member of the following medical societies: American Academy of
Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology­Head and Neck
Surgery, American Head and Neck Society
Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for:
Cerescan;RxRevu;SymbiaAllergySolutions<br/>Received income in an amount equal to or greater
than $250 from: Symbia<br/>Received from Allergy Solutions, Inc for board membership; Received
honoraria from RxRevu for chief medical editor; Received salary from Medvoy for founder and
president; Received consulting fee from Corvectra for senior medical advisor; Received ownership
interest from Cerescan for consulting; Received consulting fee from Essiahealth for advisor;
Received consulting fee from Carespan for advisor; Received consulting fee from Covidien for
consulting.
Additional Contributors
Cliff A Megerian, MD, FACS Medical Director of Adult and Pediatric Cochlear Implant Program,
Director of Otology and Neurotology, University Hospitals of Cleveland; Chairman of
Otolaryngology­Head and Neck Surgery, Professor of Otolaryngology­Head and Neck Surgery and
Neurological Surgery, Case Western Reserve University School of Medicine
Cliff A Megerian, MD, FACS is a member of the following medical societies: American Otological
Society, Association for Research in Otolaryngology, American Academy of Otolaryngology­Head
and Neck Surgery, Society of University Otolaryngologists­Head and Neck Surgeons, Triological
Society, American Neurotology Society, American College of Surgeons, Massachusetts Medical
Society, Society for Neuroscience
Disclosure: Received consulting fee from Cochlear Americas for board membership; Received
consulting fee from Grace Corporation for board membership.
Acknowledgements
The authors and editors of Medscape Reference gratefully acknowledge the contributions of
previous author Melanie E Scott, MAud, to the development and writing of this article.