FACIAL-NERVE INVOLVEMENT IN PATIENTS WITH ACOUSTIC NEURINOMAS - EXAMINATION WITH MAGNETIC SINGLE-STIMULATION AND BI-STIMULATION

The diagnosis of acoustic neurinomas is usually made by auditory and v estibular testing and magnetic resonance imaging. As clinical involvem ent of the facial nerve is infrequent. occurring only in large rumours , only little is known about the subclinical involvement of the facial nerve. Transcranial magnetic stimulation of the VIIth cranial nerve i n the temporal bone, adjacent to acoustic neurinoma growth, seems to b e an adequate instrument for electrophysiological measurements of mini mal nerve lesions without clinically obvious Facial palsy. In 70% out of 97 patients with surgically and histologically confirmed acoustic n eurinomas, obvious elongation of the intratemporal conduction time of the Facial nerve was found. This affection was dependent on tumour siz e. No correlation was found to preoperative or postoperative facial ne rve function and hearing function. The latencies of the conduction tim e showed a tendential increase inpatients with a more difficult grade of surgery and of facial nerve preparation due to fibrous adhesions an d nerve spreading on the tumour capsule. A completely new stimulation modality, the application of two magnetic stimuli in quick succession, was applied for the first time in acoustic neurinoma patients, and re vealed facial nerve involvement by acoustic neurinoma growth. Facial n erve involvement in acoustic neurinoma can be detected by transcranial magnetic stimulation even in patients with small and medium sized tum ours but with clinically normal facial function.