Facial nerve injury following temporal bone fracture: diagnosis and management

Background

Temporal bone trauma accounts for 5% of all facial palsy cases ^, and 3% of all bilateral facial palsy. Only 7% of temporal bone fractures result in facial palsy and 25% of those result in complete facial paralysis. Historically, temporal bone fractures have been classified as either longitudinal or transverse, a classification scheme that refers to the direction of the fracture with respect to the long axis of the petrous temporal bone. Another classification scheme differentiates a fracture based on whether it involves or spares the otic capsule. Approximately 30%–50% of patients with a transverse fracture pattern have facial nerve injury resulting in paralysis. ^, The transverse fracture pattern is associated with more severe facial nerve injury and portends a poorer prognosis when compared with the longitudinal fracture pattern. Facial nerve injury occurs in only 10%–20% of patients with longitudinal fractures in comparison. ^{, ,} Otic capsule violating fractures are quite rare (less than 6%) compared with otic capsule sparing fractures (>94%), and facial nerve injury is twice as common in otic capsule violating fractures than in its counterpart. ^,

Evaluation

It is estimated that close to 1900 lbs of force is necessary to fracture a temporal bone. As such, patients presenting with facial palsy following a temporal bone fracture often present with other injuries. A CT temporal bone protocol with 0.625-mm-thick slices is best suited to evaluate the fracture pattern. Multiplanar formats can be created to enable fracture pattern interpretation that may be difficult to see on routine axial and coronal planes.

In an awake and cooperative patient, a careful history and physical exam should be performed. Patients lucid enough to provide an accurate history should be asked about the mechanism of injury, any lapses in memory or loss of consciousness, vision changes, presence of hearing loss or vertigo, or clear rhinorrhea or otorrhea. A full head and neck examination should be performed. One of many findings may be visible on otoscopic exam including a fracture extending into the EAC with disruption of the canal skin, rupture of the tympanic membrane, ossicular dislocation, clear otorrhea, and hemotympanum. A tuning fork exam may demonstrate sensorineural hearing loss, particularly for fractures violating the otic capsule. Conductive hearing loss may be present for patients with ossicular disruption or middle ear fluid or blood. A full cranial nerve examination should be performed. Documenting the initial facial nerve function is important in predicting nerve recovery, determining need for further electrodiagnostic studies, and deciding on the candidacy for surgical decompression.

In light of the degree of force necessary to cause a temporal bone fracture, many patients present with other concomitant injuries that necessitate intubation and sedation. In an intubated and sedated patient, a physical examination may be very limited. A sternal rub may stimulate the patient enough so that a grimace can be elicited. However, until the sedation can be held and the patient's medical condition is stabilized, it may not be possible to obtain an accurate facial nerve examination in the acute setting.