Anatomical dissection and modified Sihler stain of the lower branches of the facial nerve.

Background: The cervical branch of the facial nerve and the muscles it supplies play a role in perioral function and neck aesthetics. Paralysis of the cervical branch in some patients may result in lip depressor deficiency and an asymmetric smile. It is unclear whether this is the result of platysmal weakness alone, or attributable to coinnervation of the lip depressor muscles by the cervical and marginal mandibular branches of the facial nerve. The purpose of this study was to provide a detailed description of the anatomy and function of the cervical branch to assist surgeons operating in the face and neck.

Methods: Anatomical dissection of the marginal mandibular and cervical branches was performed in 20 hemifacial human cadaver specimens. The modified Sihler stain was used to stain the extramuscular and intramuscular nerve branches in eight specimens. The course, branching patterns, and neuromuscular relationships of the cervical and marginal mandibular branches were examined.

Results: Multiple cervical branches were identified in 85 percent of specimens, and an anastomosis with the transverse cervical cutaneous nerve was documented consistently. A communication between the marginal mandibular and cervical branches was identified in seven specimens, and coinnervation of the depressor anguli oris by intramuscular cervical branch ramifications was seen in one.

Conclusions: A detailed description of the anatomy of the cervical branch is provided. Coinnervation of the lower lip depressors by the cervical branch remains a plausible explanation for the lower lip deformity attributed to cervical branch paralysis in some patients.