Temporal Bone Fractures Workup

Updated: Sep 09, 2019
  • Author: Antonio Riera March, MD, FACS; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Workup

Imaging Studies

Temporal bone injury can be associated with severe trauma to the head, spine, and maxillofacial region; most patients with temporal bone fracture have a CT scan of these. [1]

Contemporary CT imaging will be able to identify temporal bone fractures, including the type and direction, as well as the presence or absence of otic capsular involvement and the involved segment of temporal bone. Axial CT imaging is best to identify fractures with otic capsule involvement. (Pneumolabyrinth is an indication that the otic capsule is involved.) Furthermore, CT scanning will be able to identify complications such as hemotympanum, tympanic membrane perforation, ossicular injury, perilymphatic fistula, CSF leak, cochlea-vestibular injury, facial nerve injury, and vascular injury.

High-resolution CT (HRCT) scanning of the temporal bone is useful in assessing injuries complicated by CSF leak, facial paralysis, or suspected vascular injury. Axial and coronal images are usually obtained with 1-mm sections, as are magnified views of the temporal bone. Bone windows are necessary. Axial high-resolution CT of a fractured right temporal bone is seen below.

Axial high-resolution CT of the right temporal bon Axial high-resolution CT of the right temporal bone that represents a longitudinal fracture line that extends from the roof of the external auditory canal to the middle ear cavity.

HRCT of the temporal bone is indicated if surgical intervention for management of otologic complications is required.

If transient or persistent neurologic deficits are present in a patient with basilar skull fracture, HRCT of temporal bone with CT angiography is indicated to evaluate for petrous carotid injury.

A study by Ulano et al indicated that in trauma cases in which a temporal bone fracture is not visible on CT scanning, the presence of air around the temporal bone and a finding of mastoid air cell or middle ear cavity opacity should raise suspicions for the presence of fracture. The study, which included 152 temporal bone fractures, found air adjacent to the styloid process (94 fractures, 61.8%), in the temporomandibular joint (80 fractures, 52.6%), adjacent to the mastoid process (57 fractures, 37.5%), and along the adjacent dural venous sinus (33 fractures, 21.7%). Moreover, 139 fractures (91.4%) were accompanied by mastoid opacification, and 121 fractures (79.6%) showed opacity of the middle ear cavity. The investigators also found a positive association between complex fracture and pneumocephalus. [27]

Magnetic resonance imaging (MRI) cannot identify temporal bone fracture. MRI has both poor sensitivity and specificity in this respect. It is useful in assessment of the intracranial contents and/or a nerve palsy not explained by the HRCT. [6, 28, 29]  MRI is best to identify bleeding inside the otic capsule. The MRI can demonstrate hemorrhage into the vestibular apparatus, vestibular nucleus, and brainstem. It also can identify nerve compression and herniation of intracranial contents into the mastoid cavity. [6] MRI is also useful prior to neurosurgical intervention for temporal bone fractures, particularly with a middle cranial fossa approach. [28]

See also the Medscape Drugs & Diseases topics Temporal Bone Fracture Imaging and MR Imaging of the Temporal Bone.

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Other Tests

Electrodiagnostic tests

Electrodiagnostic testing is used to assess and quantify injury to the facial nerve and to determine status of the facial musculature. The most common tests used today in the evaluation of trauma to the facial nerve are maximum stimulation, nerve excitability, electroneurography (ENOG), and electromyography.

Maximum stimulation test

This test is based on the observation of twitch of the facial musculature using the Hilger facial nerve stimulator after the third day of the injury, usually between 3-14 days postinjury. It is used only in the case of complete facial nerve paralysis (as determined by the House-Brackmann grading) because of the pain caused by the facial stimulation. Supramaximal stimulation is applied with a maximal tolerated current on the normal side. The affected side is compared with the normal side, using the same stimulating current. An absent or markedly decreased response (barely perceptible movement) indicates a poor and incomplete return of facial nerve function.

Nerve excitability test (minimal nerve excitability test)

This test is similar to the previous test that used the Hilger nerve stimulator after the third day of injury; this test compares the amperage site-to-site necessary to initiate a barely visible response on the affected side. A difference of 3.5 mA or more is significant, carries a poor prognosis, and indicates the need to consider surgical exploration.

Electroneurography

ENOG is the technique designed by Fisch. It is used every 2 days between the third and the 21st day after the initial trauma. The results are expressed as a percentage of the amplitude of the action potentials on the paralyzed side as compared with the nonparalyzed side. The results correlate well with the percentage of nerve degeneration. According to Fisch, 90% degeneration of the involved nerve is considered significant and represents the threshold for surgical management. [30, 31] .

Fisch has developed accepted indications for surgical management based on the “percentage of nerve degeneration,” advocating exploration and decompression or repair when the ENOG indicates 90% degeneration. In other words, degeneration with 10% or less of nerve function compared with the normal side is considered the critical turning point for surgical management recommendation. Fisch found, histologically, that traumatic .injury at the geniculate ganglion induces retrograde degeneration through the labyrinthine and distal meatal segments of the facial nerve. Fisch believes that fibrosis occurs and blocks regenerating fibers and, therefore, advises early surgery in order to avoid this fibrotic complication within the fallopian canal.

Nosan et al believe that ENOG is of paramount importance in determining the need for and the timing of surgery for facial paralysis after trauma. They believe that ENOG has made the determination of the clinical onset of paralysis less necessary and that patients with delayed paralysis can have more severe injuries than those patients with more rapid ENOG degeneration. They believe that the time of paralysis from onset of injury should not confuse the issue.

Electromyography

Normal resting muscle does not produce spontaneous electrical activity. Spontaneous electromyographic activity (fibrillation potentials) found in the muscle indicates complete denervation. Take into consideration that fibrillation potentials take at least 3 weeks to be detected with electromyography. The presence of voluntary motor units (polyphasic action potentials), on the contrary, is a good prognostic factor and the best indicator that regeneration is taking place.

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