Background: Despite a wealth of literature describing the anatomy of the temporal region, controversy still exists over the depth of the frontal branch of the facial nerve as it travels over the zygomatic arch. It is commonly stated that the frontal branch travels within the superficial musculoaponeurotic system (SMAS) as it crosses the zygomatic arch. Clinically, however, it is apparent that the nerve runs at a deeper level as it crosses the arch, allowing for safe elevation and division of the SMAS to a point at or above the superior border of the zygomatic arch. The purpose of this study was to define the path of the frontal branches along fascial planes and to clarify the relationship of the fascial layers of the cheek and temporal region.
Methods: Eighteen fresh-frozen cadaver hemifaces were dissected in a layer-by-layer fashion to evaluate the relationship between the nerve and the fascial planes above and below the zygomatic arch. Histologic evaluation was performed on six hemifaces.
Results: In all dissections, the frontal branch traveled within the innominate fascia as it crossed the zygomatic arch into the temporal region. A fascial transition zone was identified in a region 1.5 to 3.0 cm above the zygomatic arch and 0.9 to 1.4 cm posterior to the lateral orbital rim, where the frontal branches crossed from the innominate fascia to run within the superficial temporal fascia.
Conclusion: As the frontal branch crosses the zygomatic arch, it is within the innominate fascia, a plane deep to the SMAS and superficial temporal fascia.