LOCALIZING RETROCOCHLEAR HEARING-LOSS

Purpose: The origin of acute/sudden hearing loss is multifactorial. Th e association of vestibular symptoms does not necessarily isolate the pathologic condition to the inner ear. The audiogram provides a screen for differentiating conductive from sensorineural loss but often fail s to provide more localizing information. Methods: Three unusual patie nts with a variety of retrocochlear presentations of hearing loss are presented. Along with conventional auditory brainstem response (ABR) t esting, newer auditory tests, including otoacoustic emissions and thre e-dimensional ABR analysis, can facilitate site-of-lesion testing. Mag netic resonance imaging (MRI) also provides graphic documentation for sources of retrocochlear hearing loss. Results: One patient had gamma- knife treatment of an arteriovenous malformation, incurring a localize d lesion to the inferior colliculus contralateral to the side of heari ng loss. This effectively eliminated wave V, as confirmed by three-dim ensional ABR analysis. A second patient with human immunodeficiency vi rus developed sudden complete hearing loss with retained otoacoustic e missions, confirming a retrocochlear lesion. A third patient with acut e otitis media with sudden hearing loss and vertigo had an abnormal AB R and ''mass lesion'' on MRI. Hearing subsequently returned to normal, as did a repeated scan. Conclusions: The unique aspects of each case of retrocochlear hearing loss and the applied auditory electrophysiolo gic tests are reviewed.