Brainstem Evoked Response Audiometry

1. Brainstem Evoked
Audiometry Response
-Dr. Richa
PMCH, Patna
1

2. Introduction
 It is an objective electrophysiological test of auditory
system.
 Checks the structural and functional integrity of an
important part of auditory system.
 Patient has no active role to play.
 But unlike PTA it cannot assess the conscious perception
of hearing.
 This investigation was first described by Jewett and
Williston in 1971.
 Never a substitute for other audiological tests
2

3. Features
 Objective test
 BAER, BSER, BAEP,ABR
 Noninvasive
 Ear specific
 Performed in quiet or sleep state
 Performed with frequency non-specific stimuli
3

4. Underlying Principles
 Normal auditory system
 Transmit acoustic stimuli into an electrical impulse
 The passage of these impulses through the auditory pathway generates an
electrical activity
 In BERA we record this electrical activity by placing electrodes over the scalp.
4

5. 5

6. • Stimulus – triggers “Action Potentials”
• Response to the stimulus is extremely small
• Repeated stimuli –response patterns “averaged” over
time result in a robust tracing over graph
• The waveforms normally occur within a 10-millisecond
time period after a click stimulus presented at high
intensities
• Time that it takes for sounds to travel can be measured
on the acquired waveforms
• The amplitude (microvoltage) of the signal is averaged
and charted against the time (millisecond), much like an
EEG.
6

7. 7

8. Uses:
 Detection and quantification of deafness in hard-to-test
patients
 Infants and children
 Mentally retarded patients
 Deeply sedated or anaesthetized
 Malingering
 Locating site of lesion (cochlear and retrocochlear)
 Study of central auditory disorders(MLR and LLR)
 Study of CNS maturity in infants
 Objective identification of brain-death
 Prognostic indicator with head trauma/comatosed pt.
8

9. Prerequisites
 Done in AC room with
patient lying down, eyes
closed and preferably
asleep.
 Room should have good
earthing.
 Must be away from heavy
electrical equipment.
 Physical relaxation is
must.
9

10. Method of recording BERA
 Stimulus- Click stimulus of intensity 50 to 60 dB above the avg. pure tune
hearing level.
 Delivered via supra aural headphones or insert earphones
 Electrode placement
 Cz: Recording electrode: at Vertex
 A1: Reference Electrode: Ipsilateral Ear Lobule or Mastoid Process
 A2: Ground Electrode: Contralateral ear Lobule or forehead
10

11.  In adults BERA response for the first 10msec are recorded
 In children it is recorded for first 15 msec
 The median time taken for ABR 25 min including 10 min of patient preparation.
11

12. Interpretation of BERA
 A normal BERA recording has 5 prominent peaks and 2
small peaks.
 The waveform peaks are labeled I-VII.
 The parameters of BERA that are studied are as follows:
 Latency-Absolute, Interwave and interaural
 Amplitude
 Waveform morphology
12

13. 13
Cochlear Nucleus
Superior Olivary Complex
Lateral Leminscus and Inferior
Colliculus

14. Parameters
 Absolute Latency
 It is the time interval between the onset
of stimulus to the peak of the wave
 Wave I- 1.5-1.75 msec
 Wave II- 2.8 msec
 Wave III- 3.8 msec
 Wave V- 5.5-5.8 msec
14

15. Parameters
 Interwave Latency
 Time interval between
two peaks in the same
BERA tracing.
 I-III : 2 msec
 III-V : 2 msec
 I-V : 4 msec
15

16. Parameters
 Interaural latency
 It is the time interval of the same wave between the two ears.
 If this difference is >0.4 msec, the existence of some lesion in
the neural pathway should be suspected on the side having
higher latency.
 Amplitude
 Amplitude is not very useful clinically as it is very variable
even in the same normal individual at different point of time.
 But if studied, then amplitude of wave peak I and V are only
studied.
16

17. Identifying waves:
 Wave V
 It is the most robust and easily identifiable wave in BERA tracing.
 Occurs at 5.5-5.8 msec after stimulus
 There is the sharp downward deflection immediately following the
peak.
 Wave III
 The peak just beyond 3 msec mark on graph.
 Wave I
 The peak just beyond 1 msec mark on graph.
 Wave II is often absent and Wave IV is frequently buried and, therefore,
indistinguishable from wave V.
17

18. 18

19. Clinical uses
19

20. Estimation of Hearing Loss
 Gives fairly good idea of degree of hearing impairment
 Assessed by decreasing the intensity of the sound stimulus until wave
V is no longer identifiable.
 PTA threshold will be 5 or 10 dB below that point.
20

21. Normal Hearing:
21
Wave V threshold
@ 20 dB:
Suggests normal
hearing

22. Threshold ABR - Moderate HL
 Wave V responses
observed down to 55
dB HL
 Results suggest a
possible moderate
hearing loss
22

23. Threshold ABR: Severe HL
23

24. Examples of Differential Diagnosis
24

25. Location of lesion 25
• Most accurate audiological test for diagnosing lesions in the
vestibulocochlear and auditory pathway in brainstem
• Wave I : small amplitude, delayed or absent may indicate cochlear
lesion or CHL
• Wave V : small amplitude, delayed or absent may indicate upper
brainstem lesion
• I – III inter-peak latency: prolongation may indicate 8th nerve or
lower brainstem lesion.
• III – V inter-peak latency: prolongation may indicate upper
brainstem lesion(MC- demyelinating disorders).
• I – V inter-peak latency: prolongation may indicate whole brainstem
lesion.

26. Acoustic Neuroma
 Most commonly encountered and most dreaded lesion for neurotologist
 Small Unilateral AN-Increase in IPL of I-III
 If large can increase IPL of I-V
 In case only wave V is seen in small AN- Interaural Latency should be
considered(>0.4 msec)
 Presence or absence of wave I shouln’t be use to diagnose AN
 Absent-if pressure on cochlear vessls
 Present-different sites of origin
 Wave I present but III and V absent-AN or low brainstem lesion
 A normal BERA rules out AN greater than size 1cm.
26

27. 27
IPL I-III on right is 2.65 at 110 dB: suggestive of AN of right side

28. Screening ABR
 Prevalence of HL
 NICU: .5-5%
 Well baby <1%
 Conducted on newborns prior to discharge
 Test at 2 levels: 60 dB HL and 30 dB HL
 Factors influencing outcome:
 Neurologic abnormalities
 Poor health
 Transient conductive problems
 Muscle artifact
 Collapsing canals
 Earphone placement
28

29. Prognosis of comatose patient
 Normal BERA:
 No structural of functional damage to brainstem
 Probably metabolic cause
 Good prognosis
 Abnormal BERA:
 Poor prognosis
29

30. Factors that influence ABR
 Age of subject (<2yrs., >65 yrs)
 Longer latency values for older and younger clients
 Gender-
 Females have marginally shorter latency period than
males(0.2 msec)
 Not affected by most drugs (including sedatives)
 Movement
 Heavy Electrical Instruments
30

31. Clinical limitations
 ABR mostly reflects higher freq hearing
 Frequency range 2000-4000 Hz, most
important to ABR
 Does not estimate hearing levels in lower
frequency ranges
 ABR is NOT a test of hearing
 Response provides no information on the
auditory system above the brainstem level
 Threshold estimation-wrong identification
of BERA wave peaks by the built-in system,
So it depends on the expertise of clinician
in correctly identifying the peaks.
31

32. Other Auditory Evoked Responses
 Middle Latency Response (MLR)
 Late Latency Response (LLR)
32

33. MLR
 Between 10-50 msec
 Documentation of CNS
dysfunction above brainstem
through thalamus
 Most important wave-P30
 estimation of auditory
sensitivity in older children /
adults (malingerers)
 State of arousal
33

34. LLR
 Between 50-500 msec
 Assesses higher cortical
processing
 P300 –most imp wave
 Latencies slow with
age
 Used to test cognitive
function like Auditory
processing
34

35. 35