[Technique of hearing preservation during acoustic neuroma surgery]

To explore the possibility of hearing protection in acoustic neurinoma (AN) resection and to evaluate the effect of dynamic auditory monitoring and the effect of oto-endoscope for hearing protection.

From July 2003 to July 2007, there were a total of 138 cases of AN received surgical treatment Continuous hearing monitoring was conducted in 18 cases with residual hearing. In these 18 cases, there were 6 males and 12 females, with 12 cases in left side and 6 cases in right. Fifteen cases were solitary AN, 3 cases were diagnosed as neurofibromatosis II. Maximal diameters of the tumor varied between 12 and 33 millimeters with an average of 19.9 millimeters. All cases were operated on by retrosigmoid approach with routine facial nerve monitoring. Ten cases were assisted by oto-endoscope. Eighteen cases were performed accompanying continuous auditory brainstem response (ABR) and electro-cochleogram (EcochG). The patients were given routine hearing function test 7 to 10 days after operation, and reexamined 6 months to 1 year. The duration of follow-up ranged 6 months to 2. 5 years. Hearing data of the last time was thought as the judging result. Preoperative and postoperative hearing standard refer to (AAO-HNS) classifying.

In all 18 cases, tumors were resected completely in 16 cases, but sub-totally removed in 2 cases which were II neurofibromatosis. There was no mortality and no severe complication in this series. All the 18 cases had no facial paralysis before operation, and during operation facial nerves in 18 cases were kept anatomic integrity. According to House-Brackmann grade system, for 18 AN patients 7 days after operation only 50.0% (9/18) were kept at grade I to II , but 88.9% (16/18) were kept at grade I to II 6 months after operation. Out of 18 cases, hearing function were preserved in 11 cases (61.1%, 11/18). After operation, there were 4 cases at hearing grade A, 4 cases at hearing grade B, 2 cases at hearing grade C and 1 cases at hearing grade D. In all 18 cases, there were 5 cases with tumor diameter more than 20 millimeters, in which only 2 cases of them preserved hearing function (2/5). However, 9 cases preserved their hearing function in the other 13 cases whose tumors diameter less than 20 millimeters (69.2%, 9/13). In 10 cases assisted by oto-endoscope, 8 cases obtained hearing protection (80.0%, 8/10) and 2 cases lost hearing. During operative monitoring, when drilling posterior lip of internal auditory canal (IAC), dragging and electric coagulating nearby IAC, especially clamping labyrinthine artery, removing tumor in IAC or electric coagulating arachnoid blood vessel on the top of tumor tissue, the ABR waves were affected greatly.

For the AN patient with preoperative residual hearing, it was necessary to protect hearing by combining continuous auditory monitoring with oto-endoscope technique. Based on these efforts the patient could preserve applicable hearing after operation. Whether or not arachnoidal on the top of AN remain and the conditions about blood supplying were the main factors that affect postoperative hearing. Moreover trauma of labyrinthine artery was the key to postoperative hearing loss.