Auditory Brainstem Response audiometry. Applications in central disorders.

ABR is the most sensitive and specific test in the audiology battery for detecting disorders that affect the brainstem. When combined with central speech audiometry, ABR can detect most intra- and extra-axial tumors, demyelinating lesions, and polyneuropathies that affect brainstem auditory structures. Alone, it is a promising tool for monitoring neural maturation, tumor growth, coma, and neurologic or vascular therapies. The test can be severely compromised by peripheral hearing loss and knowledge of the audiogram is a prerequisite for any central testing application of ABR. Six cases of intra- or extra-axial brainstem pathology are described here. ABR results were abnormal in all but one case, based on response latency measurements. In two cases, ABR was the only audiologic test that detected the abnormality. In general, ABR was sensitive to and conventional tests were insensitive to central lesions involving the eighth nerve. ABR abnormalities were not in themselves sufficient to define the precise site of the lesion, nor could they determine the kind of lesion present. However, they were indicative of the level and extent of direct involvement by the disease process or of the pressure and distortion effects of the lesion on the brainstem. In one case where ABR failed to detect the lesion, central speech testing was abnormal. The potential usefulness of ABR to monitor brainstem status is emphasized. A case is described where ABR provided valuable information on the effects of an experimental embolic therapy for AVM. Special precautions are described for monitoring ABR in neonates. ABR is an important screening test for the detection of brainstem disorders, especially those that cannot be detected radiographically. Its greatest use, however, may prove to be as inexpensive and noninvasive monitor of brainstem status in patients with confirmed or suspected brainstem disorders.