Auditory middle latency responses in patients with intracranial space-occupying lesions

Auditory middle latency responses (MLRs) and auditory brainstem responses (ABRs) were investigated pre- and postoperatively in three patients operated on of intracranial tumor (craniopharyngioma in cases 1 and 2, left-temporal cystic astrocytoma in case 3). In each case examined, preoperative MLRs were informative in evaluating the damage to supratentorial neural structures owing to the tumor; furthermore, they allowed a precious evaluation of the functional integrity of these structures after surgery. Likewise, in case 2 the ABRs indicated a brainstem injury secondary to overzealous manipulation of the right temporal lobe. Finally, in case 3, the most prominent complex of the MLRs, ie Na-Pa, was abnormal both before and after intervention; indeed, in pre- and postoperative MLRs, Na could be identified in both ears, whereas Pa was greatly reduced in amplitude or absent: this finding would seem to suggest that Na and Pa have different generator sites.