Trauma can occur anywhere along the path of the facial nerve, from the brainstem all the way to its connections with facial muscles. Injury to the facial nerve can result in either complete disruption or bruising and inflammation of the nerve. In the event of a complete disruption (also known as “neurotmesis”), the ability for self-repair is absent. In other words, without direct repair or nerve grafting, the facial nerve will fail to regenerate normally.
When only a blunt trauma occurs or if there is swelling and inflammation of adjacent damaged tissues (also known as “neurapraxia”), the nerve is left in continuity and has the ability to fully regenerate and re-establish facial nerve function. There is, at times, an intermediate form of nerve injury where the structural framework of the nerve is maintained but individual nerve fibers may be broken (called, “axonotmesis”). In this event, spontaneous regeneration can occur, but this may sometimes be associated with unwanted twitching or cross-innervation of facial nerve branches, known as “synkinesis.”
Depending upon where along the path the nerve is damaged, the picture of facial paralysis can be quite varied. For example, injury closer to the brainstem or main trunk of the facial nerve as it exits the skull behind the ear can result in complete facial paralysis with no functioning muscles, whereas injury at the level of the branches in the face will result in partial paralysis.
Common causes of trauma-related facial nerve injury include the following:
- Sharp laceration
- Dog bite
- Temporal bone fracture
- Birth trauma
- Severe blunt force trauma
- Gun shot
- Jaw fracture
As with all forms of facial paralysis, early intervention is the gold standard of treatment. A thorough exam and immediate surgical repair, if indicated, are the mainstays of management.