The efficacy of brainstem auditory evoked potentials in acoustic tumor surgery

As the identification of patients with small acoustic neuromas and salvageable hearing increases, intraoperative auditory nerve monitoring has been used increasingly in an attempt to improve the hearing preservation rate. Far-field recordings obtained by brainstem auditory evoked potentials (BAEP), at times enhanced by electrocochleography, have become a standard method of intraoperative auditory nerve assessment. To evaluate the usefulness of this monitoring technique, the hearing preservation results of a series of unmonitored acoustic tumor removals were compared to a series of patients monitored via the standard brainstem auditory evoked potentials. With comparable average tumor sizes, 4 of 7 unmonitored patients had hearing preserved at preoperative levels compared to 4 of 9 monitored patients. Neither preoperative BAEP assessments nor absolute tumor size were predictive of hearing preservation. This report brings into question the effectiveness of far-field intraoperative BAEP monitoring during acoustic tumor resection and suggests that direct auditory nerve monitoring may be more appropriate.