HEARING PRESERVATION IN ACOUSTIC NEURINOMA SURGERY

The authors have reviewed hearing results obtained in 99 patients operated on via the suboccipital approach for acoustic neurinoma. who were not deaf prior to surgery (pure tone average < 70 dB). Tumor size was less than 10 mm in four cases, 10 to 19 mm in 26 cases, 20 to 29 mm in 39 cases, and 30 mm or greater in 30 cases. Removal was macroscopically complete in 92 cases and incomplete in seven, including four cases with bilateral acoustic neurofibromatosis. Hearing was preserved in 29 patients (29.3%), of whom 23 had neurinomas smaller than 30 mm and six had tumors exceeding 30 mm in size. Postoperative hearing was good in eight cases (four with neurinomas < 20 mm and four with neurinomas > 20 mm), serviceable in four cases (three with neurinomas < 20 mm and one with a tumor > 30 mm), and poor in 17 cases (eight with neurinomas < 20 mm and nine with tumors > 20 mm). Fifty-seven patients underwent intraoperative brain-stem auditory evoked potential monitoring: the rate of hearing preservation was found to be higher in this group than in the 42 without monitoring (p < 0.05). A statistical study using stepwise regression analysis showed that the two preoperative factors most significantly associated with postoperative hearing preservation are a good auditory level for low frequencies measured by pure tone audiometry and a small-sized tumor. Overall results indicate that. even if hearing is more easily preserved when the neurinoma is small and the preoperative auditory condition is good, the surgeon should try to save hearing in all patients who have preserved hearing before surgery.