Intraoperative auditory brain stem response monitoring during ultrasonic aspiration of posterior fossa tumors.

The use of an ultrasonic aspirator may decrease the morbidity associated with the surgical removal of intracranial tumors by reducing the duration of surgery. In this study we monitored the auditory brain stem response (ABR) during ultrasonic surgical aspiration of 20 posterior fossa tumors. Twelve subjects had a transient decrement in the ABR during use of the ultrasonic aspirator; one had a temporary sensorineural hearing loss contralateral to the side of the surgery. Monitoring of the ABR during use of the ultrasonic aspirator in the posterior fossa helped minimize the risk of injury to normal structures. Changes in latency, amplitude, and interpeak interval of the ABR waves alert the surgeon to the need to adjust the aspirator settings or the conditions in the operative field before continuing to use the tool.