By Timothy Thomason, M.D.

A significant amount of force is required to fracture the petrous temporal bone.  Motor vehicle accidents, assaults, falls, bicycle accidents, and gunshot wounds are the most common causes of temporal bone injuries.  Seventy percent of fractures occur in the second thru fourth decades of life.  There is a 3:1 ratio of males to females, likely attributable to the higher proportion of males involved in traumatic events.  Eight to 29% of fractures are bilateral.  The fractures may be asymptomatic or may be associated with a number of possible complications.  The otolaryngologist must be familiar with evaluation and management of these injuries.

            Temporal bone injuries can be categorized by mechanism of injury (blunt vs. penetrating) or by anatomic characteristics of the fracture.  Traditionally, the fractures are described as longitudinal or transverse in relation to the long axis of the petrous temporal bone.  In reality, most fractures are mixed or oblique.  Another, perhaps more useful, way to categorize temporal bone fractures is whether or not the fracture involves the otic capsule.  Fractures that involve the otic capsule (very dense bone surrounding the labyrinth) are associated with a higher chance of facial nerve injury, cerebrospinal fluid leaks, meningitis, and sensory-neural hearing loss.

The initial assessment of a patient with a temporal bone fracture should involve a survey of their overall condition as would be done for any trauma patient.  Airway, breathing, circulation, neurologic disability, and exposure (ABCDE) are the first priorities in trauma patients.  Identifying and treating any life-threatening injuries must be done first.  The symptoms of a temporal bone injury in an awake patient may be hearing loss, vertigo, aural fullness, facial weakness, or they may be asymptomatic.  Physical exam signs include Battle’s sign (post-auricular ecchymosis), hemotympanum, bloody otorrhea, laceration of external auditory canal skin or tympanic membrane, or facial weakness.  Accompanying injuries might include intracranial hematomas, auricular hematomas, or facial fractures.  It is critically important that the patient’s facial nerve function be evaluated as soon after the injury as possible.  Sometimes this is not possible because the patient requires intubation with sedation because of other injuries.  If the patient has profuse bleeding from the ear canal then it should be packed and an angiogram should be obtained.  Irrigation or insufflation of the canal should be avoided in the acute setting.  If there is clear otorrhea then it should be checked for beta-2-transferrin to determine if it is cerebrospinal fluid.  Tuning fork tests should be done if and when the patient is awake.  High resolution CT should be performed only if otologic surgery is planned.  Audiogram can usually be obtained 4-6 weeks after the injury but must be performed before any otologic surgery.

Facial Nerve Injury
Facial nerve injuries occur in about seven percent of temporal bone fractures and are a source of significant morbidity.  The prognosis of recovery is dependent on whether there is complete or partial paralysis and on whether complete paralysis is immediate-onset or delayed-onset.  Patients with either delayed-onset or incomplete paralysis have a good prognosis for complete or near-complete recovery of facial nerve function.  In these situations, there is likely edema of the nerve causing dysfunction and therefore systemic corticosteroids are often given. 

Patients with immediate-onset, complete paralysis need an electrophysiological test to help determine prognosis.  Electroneurography is a type of evoked electromyography that can quantify the amount of nerve degeneration relative to the healthy side.  Generally, degeneration greater than 90% within the first 14 days after injury is considered severe enough to warrant surgical decompression.  Other evoked electrophysiological tests include the nerve excitability test (NET) and the maximum stimulation test (MST).  The NET is performed using a Hilger facial nerve stimulator.  The bipolar leads are placed over the main trunk and a distal branch of the facial nerve.  Current is applied and gradually increased until visible facial twitching is seen.  The healthy side is done first and then the affected side.  A difference of 3.5 mA or more is considered significant.  The MST is performed in a similar fashion, but the current is increased on the healthy side until there is maximal facial twitching.  The same amount of current is applied to the affected side and the amount of twitching is categorized as the same, decreased, or absent.  Absent twitching indicates a poor prognosis.  Traditional electromyography may also be useful as a confirmatory test.  Polyphasic reinnervation potentials indicate a good prognosis whereas fibrillation potentials indicate denervation.

If facial nerve decompression is warranted then the surgical approach depends on whether or not there is concomitant sensory-neural hearing loss.  If there is no useful hearing then translabyrinthine decompression provides excellent exposure from the meatal segment to the stylomastoid foramen.  If the hearing is intact then a combined middle cranial fossa and transmastoid approach is utilized.  Most injuries are in the peri-geniculate region but the entire facial nerve should be explored because co-existent injuries at other sites occur with some frequency.

Cerebrospinal Fluid Leak
Cerebrospinal fluid (CSF) leaks occur in temporal bone fractures if the subdural space communicates with the middle ear, mastoid, or eustacian tube as a result of the fracture.  This may present with clear otorrhea or rhinorrhea, depending on whether or not the tympanic membrane is intact.  Most traumatic CSF leaks will resolve spontaneously with conservative measures, such as bed rest, elevation of the head, and stool softeners.  If the leak persists despite these measures, then placement of a lumbar drain may help resolve the leak.  CSF leaks that continue after lumbar drain placement may require surgical repair of the leak.  In this case a high-resolution CT of the skull base may be helpful in identifying the location of the leak.  If the patient has a profound sensory-neural hearing loss then obliteration of the middle ear cleft and closure of the external auditory canal is indicated.  The patient with intact hearing would require a middle cranial fossa approach for repair of the leak.  Prolonged CSF leaks are associated with an increased risk of meningitis.  Therefore, prophylactic antibiotics are recommended in temporal bone fractures that are associated with CSF leaks.

Hearing Loss
Fractures that disrupt the otic capsule are generally associated with a profound sensory-neural hearing loss with a poor prognosis for recovery.  The patient with mild to moderate sensory-neural hearing loss may benefit from systemic corticosteroids.  Fluctuating hearing loss is suggestive of a perilymphatic fistula, in which case middle ear exploration and repair of the fistula may help prevent progression of the hearing loss. 

            Conductive hearing loss is quite common immediately after temporal bone fractures because of the high incidence of hemotympanum or tympanic membrane perforation.  Hemotympanum will usually reabsorb in several weeks, after which an audiogram should be obtained to document any residual hearing loss.  Likewise, traumatic perforations will often heal spontaneously, but an audiogram should be obtained to evaluate for ossicular discontinuity.  A large conductive hearing loss with an intact, hypermobile tympanic membrane is highly suggestive of ossicular discontinuity.  In this case the middle ear should be explored in a attempt to restore the hearing.  The most common site of ossicular discontinuity is the incudostapedial joint, but all of the ossicles should be carefully examined and palpated to ensure that the chain is intact and mobile.  Partial or total ossicular reconstruction prostheses may be utilized in restoring the chain.  Generally, the results of ossicular reconstruction after trauma are favorable compared to those patients with chronic ear disease.

Other Complications
A variety of other complications are possible after temporal bone trauma.  For example, a badly fractured external auditory canal may subsequently lead to canal stenosis.  In the acute setting, oto-wicks may be helpful in preventing this stenosis.  Likewise, a fracture involving the external auditory canal may be associated with entrapment of skin and later development of canal cholesteatoma. 

            Vascular injuries are a potential source of significant morbidity in patients with temporal bone injuries.  About one-quarter of skull base fractures involve the carotid canal.  If a patient with such a fracture also has a neurologic disability, then angiography should be performed.  The carotid artery may be lacerated or may have a pseudoaneurysm.  Arterovenous fistulas are also possible between the carotid artery and jugular vein or cavernous sinus.  Such injuries may require endovascular repair or open repair in some cases. 

Conclusion
High-energy impact is usually necessary to cause a fracture of the petrous temporal bone.  These patients require a full evaluation for associated life-threatening injuries.  A variety of complications are possible as a result of these fractures.  The treating physician must be aware of potential complications and the treatment algorithms associated with each complication.