Electrophysiological mapping of the temporal branch of the facial nerve.

Background  Minimized frontal and frontolateral approaches have been proposed for the clipping of aneurysms and for removal of deep-seated supra- and parasellar lesions. To avoid postoperative facial nerve palsy, anatomical studies have been conducted; however, only one electrophysiological investigation has been reported. We studied the course of the facial nerve in the temporal region and identify the optimal pterional keyhole craniotomy from the perspective of facial nerve protection. Materials and Methods  We stimulated the temporal branch of the facial nerve in nine healthy volunteers and identified its course electrophysiologically. Electromyographic (EMG) responses were recorded from the superior orbicularis oculi, corrugator, and frontal muscles. The course of the temporal branch of the facial nerve was identified by tracking the stimulation points that elicited the best EMG responses. Results and Conclusion  The distances from the tragus to the canthus, the tragus to the point where the facial nerve crosses over the zygomatic arch, the tragus to the first nerve bifurcation, the tragus to the second nerve bifurcation, and from the orbit to the middle rami were 80.8 ± 1.8 mm, 40.2 ± 1.6 mm, 58.1 ± 2.8 mm, 79.1 ± 3.4 mm, and 16.4 ± 0.9 mm, respectively. We found that the temporal branch of the facial nerve innervates each muscle in posterior-anterior direction. Based on these results, we prefer the pterional keyhole approach and incise the skin at a site posterior to the temporal branch of the facial nerve.