Selective unilateral absence or attenuation of wave V of brain-stem auditory evoked potentials with intrinsic brain-stem lesions.

The contribution of ipsilateral and contralateral auditory brain-stem structures to the generation of wave V of brain-stem auditory evoked potentials is a controversial subject. We describe two cases with an intrinsic brain-stem lesion that involved the lateral lemniscus unilaterally in the middle and upper pons. The focal nature of the auditory structures was confirmed by detailed neuropathologic data in one case and by magnetic resonance scans in the other one. In both cases, brain-stem auditory evoked potentials revealed the unilateral absence (case 1) or marked attenuation (case 2) of wave V on stimulation of the ear contralateral to the intrinsic pontine lesion. Findings in both cases strongly suggest that wave V is predominantly generated by pontine structures contralateral to the stimulated ear and that the integrity of the contralateral lateral lemniscus is essential.