On the Site of Transcranial Magnetic Stimulation of the Facial Nerve

The site of stimulation of the facial nerve after transcranial temporo-occipital magnetic stimulation is being controversially discussed, particularly whether the nerve is stimulated in the root exit zone in the cerebellopontine angle or whether stimulation originates within the bony canal of the facial nerve. In two case reports, the neurophysiological findings after the surgical transection of the facial nerve during the extirpation of a large acoustic and a facial nerve neuroma are presented. In both cases, transcranial magnetic stimulation of the facial nerve produced compound muscle action potential 4 and 2 days after the dissection of the facial nerve at the internal auditory canal and in the supralabyrinthine portion. These findings indicate that the site of stimulation in transcranial magnetic stimulation can be located to the course of the facial nerve within its bony petrosal canal distal to the external genu.