Facial paralysis can be a devastating consequence of blunt or penetrating trauma. The facial nerve is injured in 7% to 10% of temporal bone fractures. After facial nerve injury, the ensuing paralysis is immediate in 27% of cases and has a delayed presentation in 73% of patients. Penetrating trauma can occur anywhere along the nerve tract but is especially vulnerable after it exits the skull, just posterior to the styloid process of the temporal bone, traveling anterior to the external ear to the parotid gland. Within the gland, the nerve terminates splitting into five branches. Injury to the nerve extracranially causes purely motor deficits to the muscle of facial expression. Intracranial injury, proximal to the stylomastoid foramen, produces mixed motor and sensory deficits. The signs and symptoms differ depending on the distance from the origin of the nerve and any branches from the nerve before and after the area of injury. Possible deficits include ipsilateral hyperacusis (sound hypersensitivity); ipsilateral loss of taste to the anterior two-thirds of the tongue; reduced parasympathetic innervation to the mucus glands of the oral cavity, nose, and pharynx (decreasing salivation); ipsilateral reduced lacrimal fluid production; and motor paresis as seen with extracranial injury.
Management and Disposition
Immediate complete traumatic paralysis warrants surgical exploration; delayed paralysis or incomplete paresis should be treated medically with high-dose steroids. Operating on these patients in a delayed fashion is reasonable as most patients require other acute management. This delay does not necessarily worsen their prognosis, and surgery can still be of benefit even 3 months following injury.
Manifestations of traumatic CN7 injury are delayed in 73% of patients.
Temporal bone fractures are often associated with facial nerve injury.
Injury to CN7 motor nerve fibers affects muscles of facial expression and the stapedius muscle.
Injury to CN7 parasympathetic nerve fibers affects glands of the oral cavity and the lacrimal gland.
Inury to CN7 sensory nerve fibers affects external auditory meatus, tympanic membrane, the pinna, and taste sensation from the anterior two-thirds of the tongue.
Traumatic Crania Nerve 7 (CN7) Palsy—Laceration. Patient was involved in a bar fight and was cut with a broken beer bottle lacerating CN7 along with the tissues adjacent to the external ear. (Photo contributor: Christopher L. Stark, DO.)
Traumatic CN7 Palsy—Motor Findings. Laceration of the nerve occurred close to the exit from the skull posterior to the styloid process. Injury to the nerve extracranially causes purely motor deficits to the muscle of facial expression. (Photo contributor: Christopher L. Stark, DO.)
CN7 Pathway. Main trunk of CN7 exits the skull, through the stylomastoid foramen, just posterior to the styloid process of the temporal ...