[Peroperative auditory evoked potentials in surgery of the posterior fossa]

Intraoperative brainstem audiometry electric responses were measured in 22 operations of the posterior fossa, including 11 acoustic neurinomas. The first observation shows the recordings obtained during the exeresis of a voluminous tumor of the cerebellopontine angle and wave V disappearance for 90 minutes. At the end of the operation we noted a better plotting synchronization and the wave V form reappeared. The wave preservation was confirmed by an electrocochleography carried out few days after intervention. The second observation enables the visualization of modifications on ipsi- and contralateral plottings of the cerebellum retraction and brainstem mobilization during a cerebellum medulloblastoma operation. The third observation shows the immediate and considerable extension of wave V latency during mobilization of the antero-inferior cerebellar artery during an acoustic neurinoma operation. The authors discuss the various operative times leading to significant variations in the latency of waves I, V and I-V delays and the advantages of such a monitoring for the brainstem vital functions and hearing preservation.