A Reappraisal of the Anatomy of the Frontotemporal Branch of the Facial Nerve

Objective: The anatomy of the temporal branch of the facial nerve (FN) has been widely described in the neurosurgical literature due to its implication in anterolateral approaches to the skull base and avoidance of frontalis palsy. Although much has been understood about the branches of the FN and its relationship to the fascial layers of the temporalis muscle, there remains some unreconciled observations that have kept our understanding of this anatomy incomplete. In this study, we attempt to describe the anatomy of the temporal branches of the FN and identify if there are any FN branches that cross the interfascial space of the superficial and deep temporalis layers of the temporalis muscle.

Material and Methods: Five embalmed postmortem heads were used to study the FN anatomy. Dissections were performed to preserve the relationships of the branches of the FN and its relationship to the temporalis fascial planes, the interfacial fat pad, surrounding nerve branches, and their final terminal endpoints near the frontalis and orbicularis muscles. We correlate our findings intraoperatively and use neuromonitoring to stimulate the FN and any associated twigs that were observed to be interfascial.

Results: In all specimens, we found that the temporal branch of the FN predominantly stays superficial to the superficial layer of the temporalis fascia ([Fig. 1]). As the nerve course over the frontotemporal region, at 0.8 mm behind the frontozygomatic suture, it gives off a twig that pierces the temporalis muscles ([Fig. 2]). This small branch reaches the lateral wall of the orbit and gives off a small branch to the lacrimal gland, and a second branch anastomosed with the zygomaticotemporal branch of the trigeminal nerve ([Fig. 3]). Intraoperative neurostimulation of the interfascial branch does not stimulate muscles of the fascisal expression at 2 mA ([Fig. 4]).

Conclusion: Based on our dissections, there appears to be a previously undescribed anastomoses between the temporal branches of the facial nerve and the zygomaticotemporal branch of the trigeminal nerve (TN), as it exits the orbit and courses through interfascial space of the temporalis muscle. Previous studies that described interfascial twigs may have mistakenly thought this branch to be a motor branch of the FN; however, intraoperative stimulation of this branch does not appear to stimulate muscles of fascial expression. Interfascial surgical techniques aimed at protecting the frontalis branches of the facial nerve are safe in their efforts to prevent frontalis palsy. Injury to the zygomaticotemporal branch, as it courses in the interfascial space, has little to no clinical sequela based on our experience and that of others. More research is needed to understand the nature of this anastomosis between the FN and TN in this region and whether there are any autonomic fibers that are using this anastomosis as a conduit to the lacrimal gland.

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Artikel online veröffentlicht:
15. Februar 2022