mercoledì 2 aprile 2008

Temporal bone fracture







Findings

There is air in the infratemporal fossa(Figure 1). There is opacification within the right sphenoid sinus (Figure 2, Figure 3, and Figure 4). There is a longitudinal temporal bone fracture (Figure 2, Figure 3, and Figure 4).


Diagnosis: Temporal bone fracture


Blunt force trauma to the skull base is the most common cause of temporal bone fracture. The location of the injury determines the orientation of the fracture line in relation to the petrous ridge:
- fractures coursing parallel to the petrous ridge are classified as longitudinal
- fractures coursing perpendicular to the petrous ridge are classified as transverse

Longitudinal fractures account for 80% of all temporal bone fractures. Longitudinal fractures are typically sustained as a result of blunt trauma to the temporoparietal region. The fracture line runs along a lateromedial axis. It originates in the squamous temporal bone and runs along the external auditory canal, coursing towards the middle ear space. The otic capsule is typically spared in a longitudinal fracture. However, conductive hearing loss may occur as a result of ossicular discontinuity, hemotympanum, or tympanic membrane perforation. Sound will lateralize to the affected ear on the Weber test.

Transverse fractures account for 20% of all temporal bone fractures. They occur as a result of blunt trauma to the occipital skull. The fracture line runs along a posteroanterior axis. It originates in the region of the foramen magnum and courses anteriorly, through the otic capsule. Disruption of the otic capsule results in sensorineural hearing loss. On the Weber test, sound will localize to the normal ear. Transverse fractures are associated with a greater incidence of complications, including facial nerve paralysis, nystagmus, and cerebrospinal fluid leak.

Temporal bone fractures are often identified on routine computed tomography scans of the head in the setting of trauma. However, high-resolution CT (HRCT) with thin-cut sections in the axial and coronal planes best evaluates the extent of injury to the temporal bone.


Longitudinal

Frequency: 80%
Orientation to petrous ridge: Parallel
Axis of fracture line Posteroanterior: Mediolateral
Hearing loss: Conductive
CN VII complications: 6-13%


Transverse

Frequency: 20%
Orientation to petrous ridge: Perpendicular
Axis of fracture line Posteroanterior: Posteroanterior
Hearing loss: Sensorineural
CN VII complications: 30-50%

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