Variability in facial-muscle innervation: A comparative study based on electrostimulation and anatomical dissection.

Facial-nerve palsy is the most common complication during facial surgery. However, there are few detailed reports on the distribution of the terminal branches of the facial nerve to the mimetic muscles. This also applies to the communicating branches. The aim of our study was to assess the variability of communicant and terminal branches of the facial nerve in humans. This prospective study involved anatomical dissections and intraoperative electric stimulation of facial nerves. We first performed 30 dissections to define the branching patterns of the extracranial facial nerve, with particular focus on the penetrating points into the mimetic muscles. We then studied and compared these preliminary data with 14 operative facial stimulations conducted during parotidectomies. Each trunk and branch received systematic electrostimulation. The electrostimulation and facial-and-neck movements were analyzed by two independent reviewers. The peripheral branching and intercommunication of the facial branches were highly variable. Combining electrostimulation and dissections, the frontalis muscle, the depressor labii inferioris and the platysma showed little nerve recuperation whereas the sphincter muscles (orbicularis ori and oculi) were anatomically protected. Facial-muscle innervation differed among individuals. We found complex variations in the facial branching mode. Our study highlights the branches and corresponding areas that could be considered anatomically risky. Clin. Anat. 32:169-175, 2019.