Auditory Brainstem Response Testing

Auditory brainstem response (ABR) testing uses surface electrodes and a computer to record and average auditory nerve and brainstem potentials in response to click stimuli delivered to the ear. It is useful to screen patients with asymmetric sen-sorineural hearing loss or unilateral tinnitus for retrocochlear lesions. Although ABR is less sensitive than MRI with gado-

TABLE 7-2 Modified House-Brackmann Facial Nerve Grading Scale

Grade Description Characteristics

I Normal Normal facial function in all areas

II Mild dysfunction Gross: slight weakness noticeable on close inspection; may have very slight synkinesis

At rest: normal symmetry and tone Motion:

Forehead: moderate to good function Eye: complete closure with minimum effort Mouth: slight asymmetry

III Moderate dysfunction Gross: obvious but not disfiguring difference between two sides; noticeable but not severe synkinesis, contracture, or hemifacial spasm At rest: normal symmetry and tone Motion:

Forehead: slight to moderate movement Eye: complete closure with effort Mouth: slightly weak with maximal effort

IV Moderately severe dysfunction Gross: obvious weakness or disfiguring asymmetry

At rest: normal symmetry and tone Motion: Forehead: none Eye: incomplete closure Mouth: asymmetric with maximum effort

V Severe dysfunction Gross: only barely perceptible motion

At rest: asymmetry Motion: Forehead: none Eye: incomplete closure Mouth: slight movement

VI Total paralysis No movement linum for the detection of small vestibular schwannomas, it detects most schwannomas larger than 1 cm and is appropriate to screen patients unable or unwilling to undergo MRI or older patients who would be treated only for larger lesions.6

Preoperative ABR testing is useful for patients considered candidates for hearing-preservation approaches for removal of lesions in the IAC. Preoperative ABR testing confirms the presence of recordable responses that can be monitored intra-operatively. Poor or delayed ABR waveforms predict a lower likelihood of hearing preservation.4

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