To the Editor.听
鈥擨n patients with apparently unilateral brain-stem lesions, brain-stem auditory-evoked potentials have usually shown the most marked abnormality when the ear ipsilateral to the lesion has been monaurally stimulated. This observation is curious in view of the generally acaccepted predominance of contralateral pathways when studied behaviorally. In keeping with most previous observations, Markand et al1 report five cases of ipsilateral wave IV/V suppression associated with unilateral midbrain lesions, indicated by increased signal in T-2-weighted images in magnetic resonance scans. They make the point that unilateral lesions at the mesencephalic level are more likely to produce effects on brain-stem auditory-evoked potentials evoked from either ear than more caudal lesions, whose effects are more predictably ipsilateral. They go on to state, however, that when effects are asymmetric, the response from the ipsilateral ear is more abnormal.In conflict with these observations and conclusions are at least two cases in which unilateral