Facial Nerve Involvement and Testing in Acoustic Neuromas

Developing acoustic neuromas subject the facial nerve to pressure within the internal auditory canal and to displacement around the surface of the enlarging tumor in the cerebellopontine angle. While the acoustic tumor is confined to the internal auditory canal, very few patients have obvious evidence of facial nerve involvement. However, when the tumor extends into the cerebellopontine angle and gradually becomes larger, the stretching of the facial nerve causes obvious facial weakness. In this series of 53 acoustic neuromas, five patients had facial weakness (cases No. 4,16, 24, 30, and 49) and three patients had facial twitching (cases No. 3, 21, and 28). It is our feeling that most patients with acoustic neuroma will ultimately develop gross obvious evidence of facial weakness if the tumor is allowed to progress far enough. Since the facial nerve can become involved in almost all cases, we felt that a quantitation of facial nerve