56 Facial Asymmetry (Including Paralysis) Facial asymmetry in the patient with normal facial nerve function is consequently due to mass effect. The causative factors in this subset of patients are infectious, inflammatory, and neoplastic. A specific focus can usually be identified fairly easily by history and physical examination of the facial skin and sub-cutaneous tissue, parotid glands, and maxillofacial skeleton. Occasionally, laboratory and radiographic imaging are necessary to make an accurate diagnosis. More commonly, facial asymmetry results from paresis or paralysis of the facial nerve. Again, history and presentation are invaluable in making the correct diagnosis. The timing and course of progression, presence of associated symptoms, identification of inciting events, duration of noted abnormalities, and patient age and medical history are all necessary inquiries. An exhaustive list of potential causes of facial palsy can become tedious and impractical. The three most common causes—trauma, Bell palsy, and iatrogenesis—deserve further discussion, as do the additional causes listed below.
Trauma is a common cause of facial nerve palsy, especially in the adult and neonatal (birth trauma) populations.
Blunt injury causing temporal bone fracture or fracture of the basilar skull adjacent to the stylomastoid foramen can account for facial palsy. As is the case with all potential etiologies, history, physical examination, and radiographic evaluation should attempt to identify complete facial paralysis of immediate onset versus delayed or progressive paralysis, to better direct the option of surgical repair.
Penetrating injury to the extratemporal portion of the facial nerve can also lead to abrupt complete paralysis from nerve transection versus delayed paralysis or paresis from associated inflammation.
Birth trauma is more commonly associated with unilateral facial palsy in the neonatal population. The underdeveloped mastoid process exposes the facial nerve for injury, especially during forceps delivery of the large neonate or neonate with arrested descent.
Penetrating injury to the middle ear can transect or injure the facial nerve along its horizontal course through the middle ear space.
Bell palsy, also referred to as idiopathic facial paralysis, is a common cause of facial paralysis in all patient populations. It is thought to be caused by herpes simplex virus type 1 infection (either directly or reactivated from dormancy within the geniculate ganglion). Microcirculatory or autoimmune phenomena may also play a role. Bell palsy is a unilateral paralysis or paresis that manifests acutely (usually within 48 hours). By contrast, facial palsy that progresses over weeks to months suggests neoplasm. Most patients will report a variable prodrome or malaise in the days or weeks preceding onset if asked. Other causes must be excluded to make the diagnosis. Most patients fully recover within 6 months, with the first signs of recovery usually within 3 weeks. Some patients never attain complete recovery, and late recovery beginning after 3 months is more commonly associated with sequelae (synkinesis, dyskinesis).
Iatrogenic injuries
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