Brainstem Auditory Evoked

Responses (BAER or ABR)

• Auditory pathway

• Cranial VIII nerve

• Nucleus brain

click

• Retrocochlear pathology

Identify for sensorineural hearing loss.

Indication

• The main indicate Acoustic neuroma

• Postoperative of cochlear implant

• Who has mental disease

• After illness neuropathy

• The all sensorineural hearing loss

Auditory pathway

Normative Data

7

Latency (ms)

• Wave I=1.50

• Wave III=3.57

• Wave V=5.53

Interpeak intervals

I-III=2.06

III-V=1.96

I-V=4.02

The waveform represents specific

anatomical points along the

auditory neural pathway:

• The cochlear nerve and nuclei (waves I

and II),

• Superior olivary nucleus (wave III)

• Lateral lemniscus (wave IV)

• Inferior colliculi (wave V).

Auditory brainstem response

threshold differences in

patients with vestibular

schwannoma: A new

diagnostic index

From the Division of Otolaryngology–Head and Neck Surgery, Department of Surgery, University of Kentucky College of Medicine, Lexington. Matthew L. Bush, MD, University of Kentucky College of

Medicine,

• Auditory brainstem response (ABR) testing is less sensitive in detecting small vestibular schwannomas than medium-size tumors.

• Magnetic resonance imaging (MRI) is more sensitive than ABR alone for small and large tumors, but it carries with it increased cost and issues of unavailability and patient discomfort.

• We conducted a prospective pilot study of 7 patients with untreated MRI-proven, unilateral vestibular schwannoma to determine if we could increase the sensitivity of ABR testing in detecting small tumors.

• Our method involved the use of a new ABR index that is based on threshold differences.

• All patients underwent pure-tone audiometry followed by a determination of behavioral threshold and neurodiagnostic threshold ABR in the normal ear, which was used as a control, and in the diseased ear. Analysis of results revealed that all 7 patients had an abnormal ABR threshold difference, and 5 patients displayed abnormal traditional ABR indices. The mean difference between the ABR and behavioral click thresholds was 41.4 dB in the diseased ears (with the ABR threshold being higher than the click threshold) and 15.8 dB in the normal ears. None of the control ears had a threshold difference >30 dB.

Introduction• The use of auditory brainstem response (ABR) testing in the screening of

retrocochlear pathology such as vestibular schwannomas is widespread.

• Since ABR testing was first described by Selters and Brackmann in 1977,multiple studies have shown that its sensitivity exceeds 90%, thus establishing it as the most sensitive audiologic test for the detection of vestibular schwannomas.

• However, within the past decade, magnetic resonance imaging (MRI) has emerged as the gold standard for the diagnosis and monitoring of vestibular schwannomas.

• MRI is capable of detecting vestibular schwannomas of any size, while ABR testing tends to be less sensitive for smaller lesions.

• For example, Schmidt et al reported that ABR testing was only 58% sensitive for detecting lesions 1 cm or smaller

• The usefulness of ABR testing is also limited by compromised audiologicfunction, which is typically seen in the setting of retrocochlear pathology. While MRI is more sensitive than ABR alone, it is not always readily available and it adds to treatment costs.6 Moreover, patient discomfort can be an issue.

• Finally, MRI is contraindicated in many patients because of implants or other types of metal in the body.

• Computed tomography (CT) is an option, but it is less sensitive than MRI and it may also miss small lesions.

• ILD of ≥0.3 msec has been reported to

greatly assist in vestibular schwannoma

detection.

• A threshold difference of ≥30 dB in

vestibular schwannomas.

Patients and methods

• This prospective pilot study involved patients with untreated vestibular schwannomas.

• 40 patients with unilateral vestibular schwannomas presented to our clinic. Of these, 33 were excluded on the basis of a PTA >60 dB, previous treatment, or an unwillingness to participate.

• The charts of the remaining 7 patients were reviewed for demographic information and for information on the site and size of the vestibular schwannoma.

• Recent MRIs were also reviewed.

Parameters

• I-V interval ≥4.4 msec for,

• ILD ≥0.4 msec for,

• absolute latency of V ≥6.2 msec

• Threshold difference ≥30 db

Results

• The 7 patients in our study group were aged 49 to 70 years (mean: 59)

• Five of the patients had at least one abnormal index.

• In 3 of the 7 patients (patients 4, 6, and 7), we were unable to detect a wave I, and therefore a wave I-V interval could not be calculated.

• All 3 of these patients had at least one other abnormal index.

• In 1 of those 3 patients (patient 7), therefore the ILD could not be calculated;

• this patient had a significant sensorineural hearing loss on the normal side, which may have accounted for the difficulty in obtaining normal waveforms. Failure to obtain traditional indices was considered abnormal in this study.

Summary of patient demographic

information and ABR results*

pt age Tumor side

Tumor size

I-Vinterval ms

ILD ms

Absolute latency of V ms

Behavioral threshold Db

ABR theshoLdDb

Threshold diffe

1 52 Left 3.0 mm 4.2 0.0 6.0 10/10/ 60/20/ 50/10

2 49 left 4.0 mm 4.6 0.2 6.0 10/25/ 50/30/ 40/5/

3 60 Left 1.1 cm 5.0 0.8 6.7 15/5/ 50/20/ 35/15

4 70 left 1.6 cm cnd 0.4 6.1 35/15/ 90/40/ 55/25/

5 70 rigth 5.0 mm 4.3 0.0 6.1 25/25/ 60/50/ 35/25/

6 58 left 1.2 mm cnd 0.5 6.6 15/15/ 50/30/ 35/15/

7 54 rigth 5.0 mm cnd cnd 6.6 45/35/ 85/cnd 40/cnd

Discussion

• In this study, we evaluated patients with untreated, MRI-proven unilateral vestibular schwannomas with the use of a traditional ABR test and a determination of threshold differences for the purpose of increasing ABR sensitivity.

• Our goal was not to attempt to replace MRI with ABR. Rather, we advocate the development of a cost-effective yet accurate algorithm for the diagnostic evaluation of patients with asymmetrical auditory symptoms.

• The application of the threshold difference is completely dependent on the examiner's ability to determine a reliable neurodiagnostic threshold; this is not possible in all patients, but it does hold promise for the development of new indices in vestibular schwannoma detection.

• The results of ABR testing in patients with significantly diminished auditory function are typically unreliable, and these patients should be evaluated radiographically if asymmetrical symptoms exist.

• As reflected in our exclusion criteria, we attempted to examine patients with PTAs <60 dB in an attempt to gain more reliable ABR results.

• A threshold difference >30 dB may represent an additional index to indicate suspicion of retrocochlear pathology

Criteria for retrocochlear

dysfunction

• Absence of all waves following waves I, II,

or III.

• Abnormal prolongation of I-III, III-V. and I-V

interpeak intervals

• Abnormally increased differences between

the two ears (interaural differences)

in Large Acoustic Neuroma

24

• Large cerebellopontine angle tumor that was compressing the brainstem

• I–V and III–V interpeak intervals are both abnormally prolonged

Thank you