Indications for hearing preservation in acoustic tumor surgery.

This study addresses the problem of how to counsel patients with acoustic tumors concerning the issue of hearing preservation. Rather than the traditional yes or no answer, we wish to give the patient the probability that hearing can be preserved given the size of the tumor and the patient's preoperative hearing level. The subjects were 77 patients of the Seattle Ear Clinic who underwent total removal of unilateral acoustic tumors with attempted hearing preservation using a suboccipital approach. Other criteria for inclusion in the study were: tumor size, measured from a preoperative diagnostic image, and availability of pre- and postoperative hearing test results. We reviewed published data from other centers using similar inclusion criteria to determine if our findings were representative of the experience of surgeons at other institutions. We found a significant relationship between hearing preservation success and tumor size, but not between success and preoperative hearing level. The probability of success varied from 78 percent for 0.5-cm tumors to about 15 percent for tumors 2.0 cm and larger. If surgery was successful, 82 percent of patients had hearing that was the same or better than their preoperative hearing level.

Analysis of the glycerin test for Menière's disease.

The glycerin test has low sensitivity for Menière's disease using present published criteria. The purpose of this study is to compare the efficacy of standard empirical criteria with our theoretically based criteria. Subjects were 47 patients with Menière's disease and 45 patients with other causes of hearing loss and dizziness. Pure-tone thresholds and word-identification scores were determined before and 3 hours after administration of glycerin. The results were submitted to decision and multivariate discriminate analyses. The theoretically based criterion applied to pure-tone threshold testing alone was the most effective protocol for glycerin testing. Combining pure-tone thresholds and word-identification increased the false-positive rate without adequately increasing the true-positive rate, and provided no advantage over testing thresholds alone.

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.