Latency of the acoustic reflex in eighth-nerve tumor

We evaluated acoustic reflex morphologic features in four subjects with confirmed, unilateral acoustic neuroma. All four subjects showed marked reduction in absolute reflex amplitude and alteration in the reflex amplitude-intensity function in the ear with the eighth-nerve disorder. The early, fast-rising component of the normal reflex was also typically absent in the ears with tumor. Interaural latency comparisons were made in three ways. At equal reflex sensation levels and equal reflex sound pressure levels, latency ws substantially delayed in the ear with the eighth-nerve disorder. At equivalent reflex amplitudes, however, latency was equivalent in normal ears and ears with eighth-nerve disorder. Results suggest that delayed onset of the acoustic reflex in subjects with eighth-nerve disorder may reflect amplitude and wave-form morphologic effects rather than a latency prolongation per se.