Electrophysiological Mapping of the Temporal Branch of the Facial Nerve

Abstract

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.

Safe Zone for Dissection in Frontotemporal Region to Avoid Injury to the Temporal Branch of Facial Nerve

“…Several studies confirm that a region within 1.5 cm superio-lateral to the orbit represents a safe zone 13,24,5 . Tokimura et al 27 in his study of electrophysiological mapping of the temporal branch of the facial nerve found that akin to previous studies, the TBFN resided in a 15- to 44-mm region measuring from the orbit, the zygomatic suture, and the anterior margin of the zygomatic arch.…”

“…Poblete et al 5 performed 10 hemifacial cadaveric dissections and reported that the nerve to the orbicularis and frontalis muscle commonly originated from the anterior and middle trunk of the temporal nerve and crossed at a mean distance of 4 cm (range 3.5–4.5 cm, SD 3.3 mm) above the lateral canthus of the eye and the most posterior branch to the Frontalis muscle was located at a mean distance of 3.5 cm range (2.9–4.0 cm, SD 4.4 mm) posterior-superior to the lateral canthus. With reference to the lateral brow, Tokimura et al 27 recommended staying 2 cm posterosuperior to the lateral edge of the eyebrow in order to avoid injury to the TBFN. Its distance to the lateral aspect of the orbibularis oculi muscle was found to be 4.0 +/– 0.6 cm 28,29 .…”