Tomographic evaluation of trauma to the temporal bone.

Abstract

THE INCIDENCE of trauma to the temporal bone is increasing because of the rising number of automobile accidents. Blows to the head can produce damage within the temporal bone which is difficult to visualize on the conventional radiographic examination of the skull. Using thin-section tomography, however, one can visualize the structures within the temporal bone to identify ossicular dislocation, fractures across the facial nerve canal, and stenosis of the external auditory canal. It is important to identify and localize the damage, since many of these injuries can be corrected surgically. Tomography Technic and Normal Anatomy Thin-section tomography is necessary for the radiological diagnosis of fractures within the temporal bone and dislocation of the auditory ossicles. The pluri-directional tomograph (Philip's Universal Polytome) allows sections 1 mm in thickness. The hypocycloidal movement of the tube results in more efficient blurring of superimposed objects, with resultant finer details of the layer in focus. The frontal and lateral projections are best suited for the middle and inner ear structures, including the malleus and incus. The stapes is seen only in the 20° oblique frontal projection (9). Pathology Two types of fractures occur in the temporal bone: longitudinal and transverse. The longitudinal fracture shown in Fig. 1 is four times more common than the transverse and results from force applied either to the temporoparietal region or to the mandibular condyle. This fracture extends medially along the bony external canal, and at the middle ear turns either anteriorly to end in the region of the carotid canal or posteriorly to end in the mastoid region. The clinical symptoms of a longitudinal fracture are a ruptured drum and bleeding into the middle ear and external canal. If the dura overlying the tegmen is lacerated, cerebrospinal fluid will drain into the external canal. Facial nerve paralysis occurs in 10 to 40 per cent of these patients, but 75 per cent recover spontaneously. They often have a conductive hearing loss; a sensorineural loss may result from labyrinthine concussion. A transverse fracture crosses perpendicularly to the long axis of the petrous pyramid. This fracture is the result of a force applied to either the occipital or the occipitomastoid region. The fracture proceeds through the labyrinthine capsule and may cross the facial nerve canal. Clinically, facial nerve palsy occurs in 30 to 50 per cent of the patients. Total nerve deafness and vertigo are common. Blood or cerebrospinal fluid can leak through the fracture into the middle ear cavity but may go undetected because of an intact ear drum. Rarely, the longitudinal and transverse fractures may be combined.