The value of acoustic reflex thresholds and brainstem responses in the investigation of cochlear, retrocochlear, and brainstem lesions

Abstract

Acoustic reflex thresholds (ART) and auditory brainstem responses (ABR) were measured in 69 patients referred to the Neuro-otological clinic on the suspicion of a retro-cochlear lesion. The pure tone selection criterion was an average hearing loss of less than 60 dB at 0.5, 1, 2 and 4 kHz, with no thresholds exceeding 70 dB and only one threshold exceeding 60 dB. Both tests proved independently to be most effective in the diagnosis of cerebello-pontine angle (CPA) tumours and to a lesser extent brainstem lesions. The ABR was positive in 100% of CPA group and 90% in the brainstem group compared to 92.8% and 70% respectively for the ART. The combination of the two tests provides patterns of abnormality which are more disease specific. In the CPA cases the most common and consistent patterns of abnormality were the unilateral delay of wave V or III and V of the ABR associated with a vertical ART pattern indicative of an abnormality of the ipsi and contralateral reflexes on stimulating the affected side. Intrinsic brainstem lesions most commonly resulted in bilateral ABR abnormalities combined with the full house ART pattern indicative of bilateral abnormalities of both ipsi and contralateral reflexes.