FACIAL-NERVE INJURY IN ACOUSTIC NEUROMA (VESTIBULAR SCHWANNOMA) SURGERY - ETIOLOGY AND PREVENTION

Facial nerve injury associated with acoustic neuroma surgery has decli ned in incidence but remains a clinical concern. A retrospective analy sis of 611 patient:, surgically treated for acoustic neuroma between 1 973 and 1994 was undertaken to understand patterns of facial nerve inj ury more clearly and to identify factors that influence facial nerve o utcome. Anatomical preservation of the facial nerve was achieved in 59 6 patients (97.5%). In the immediate postoperative period. 62.1% of pa tients displayed normal or near-normal facial nerve function (House-Br ackmann Grade 1 or 2). This number rose to 85.3% of patients at 6 mont hs after surgery and by 1 year, 89.7% of patients who had undergone ac oustic neuroma surgery demonstrated normal or near-normal facial nerve function.The surgical approach appeared to have no effect on the inci dence of facial nerve injury, Poor facial nerve outcome (House-Brackma nn Grade 5 or 6) was seen in 1.58% of patients treated via the subocci pital approach and in 2.6% of patients treated via the translabyrinthi ne approach. When facial nerve outcome was examined with respect to tu mor size, there clearly was an increased incidence of facial nerve pal sy seen in the immediate postoperative period in cases of larger rumor s: 60.8% of patients with tumors smaller than 2.5 cm had normal facial nerve function, whereas as only 37.5% of patients with tumors larger than 4 cm had normal function. This difference was less pronounced, ho wever. 6 months after surgery. when 92.1% of patients with tumors smal ler than 2.5 cm had normal or near normal facial function, versus 75% of patients with tumors larger than 4 cm. The etiology of facial nerve injury is discussed with emphasis on the pathophysiology of facial ne rve palsy. In addition, on the basis of the authors' experience with t hese complex tumors techniques of preventing facial nerve injury are d iscussed.