Normal cervical spine

After assessing that the lateral radiograph is a true lateral, the following lines should always be checked.

Normal Cervix Appearance
Fig. 4.4 Rotated lateral radiograph. Lack of superimposition of the articular masses, giving the appearance of double articular facets (arrows).
Fig. 4.5 Normal AP radiograph. The AP view usually only demonstrates C3-C7. The uncovertebral joints (arrows) and spinous processes (dotted arrows) can be evaluated. Note the equidistance between the spinous processes.

Fig. 4.6 Normal odontoid process view or 'Open mouth' peg view. This view best evaluates the alignment of the lateral masses of C1 (arrows) on the articular pillars of C2 (dotted arrows), the space on either side of the dens with respect to the C1 lateral masses (lateral atlantodens interval), and the odontoid process (dens).

Fig. 4.6 Normal odontoid process view or 'Open mouth' peg view. This view best evaluates the alignment of the lateral masses of C1 (arrows) on the articular pillars of C2 (dotted arrows), the space on either side of the dens with respect to the C1 lateral masses (lateral atlantodens interval), and the odontoid process (dens).

Fig. 4.7 Oblique view of cervical spine. This is helpful in demonstrating not only the intervertebral foramen (arrow) and facet joint alignment (dotted arrow), but also provides additional views of the cervicothoracic junction for alignment.

Soft tissue contour

Position of the normal contour of the prevertebral soft tissue shadow along both the cervical cranium and cervical thoracic junction is extremely important (Fig. 4.8). The cervical cranial prevertebral soft tissue contour should follow the contour of the anterior cortex of the atlas, axis and caudal portion of the clivus. At the cervical thoracic junction, the normal 169

Fig. 4.8 Normal cervical cranial prevertebral soft tissue contour. Cranio cervical prevertebral soft tissue contour (black line between arrow levels) should have a concave, convex (over C1 anterior arch) and concave contour. A measurement of more than 5-7 mm at the C2 level is abnormal, and anterior to vertebra C4-C7 less than 20-22 mm.

Fig. 4.8 Normal cervical cranial prevertebral soft tissue contour. Cranio cervical prevertebral soft tissue contour (black line between arrow levels) should have a concave, convex (over C1 anterior arch) and concave contour. A measurement of more than 5-7 mm at the C2 level is abnormal, and anterior to vertebra C4-C7 less than 20-22 mm.

Fig. 4.9 Prominence of the soft tissue contour. Cervical spine osteomyelitis, with prevertebral abscess. Lateral cervical spine.This lateral cervical-spine radiograph shows marked widening of the lower prevertebral soft tissues (arrows) anterior to the C5 level with bony destruction of the C4 vertebral body. This was due to prevertebral abscess in association with cervical osteomyelitis. Gas can sometimes migrate into this potential space from aerodigestive tract injuries. Haemorrhage identified here may be the most prominent radiographic sign of a subtle 170 cervical-spine fracture.

Fig. 4.9 Prominence of the soft tissue contour. Cervical spine osteomyelitis, with prevertebral abscess. Lateral cervical spine.This lateral cervical-spine radiograph shows marked widening of the lower prevertebral soft tissues (arrows) anterior to the C5 level with bony destruction of the C4 vertebral body. This was due to prevertebral abscess in association with cervical osteomyelitis. Gas can sometimes migrate into this potential space from aerodigestive tract injuries. Haemorrhage identified here may be the most prominent radiographic sign of a subtle 170 cervical-spine fracture.

contour of the prevertebral soft tissue should also follow the contour of the anterior cortex of the lower cervical vertebral bodies and demonstrate no convexity as it dips and tucks into the thoracic inlet [2, 4]. Prominence of the soft tissue contour may indicate haemorrhage, which can be the most prominent radiographic sign of subtle cervical-spine fracture (Figs 4.9 and 4.10). Various measurements have been described in the literature regarding prevertebral soft tissue thickness. However, the most reliable is the cervical soft tissue thickness present anterior to the cortex of the body of C2 [2] while the remainder are usually unreliable and variable. Anterior to vertebra C2, the distance should be less than 6 mm, and anterior to vertebra C4-C7 less than 20-22 mm.

Clearing the craniocervical junction

The atlantodental interval (Fig. 4.11) normally is less than 3 mm in adults whether or not the head is flexed or extended. In children under 8 years of age, the distance has been reported to be as much as 4-5 mm (particularly in flexion) secondary to the greater ligamentous laxity [5].

Anterior pseudosubluxation (physiological subluxation) of C2 on C3 or C3 on C4 is a normal finding on the lateral cervical spine in children (usually under 8 years of age or young adults) and is due to greater ligamentous laxity. This is caused by the relative laxity of the ligaments combined with the shallow facet joints seen in these young adults. To distinguish it from true subluxation, one must draw a line from 171

Fig. 4.10 Transverse CT image with IV contrast. The CT image shows a large prevertebral abscess (white arrows) from C5 osteomyelitis. An epidural abscess component is also present encroaching on the thecal sac (black arrow).

Fig. 4.11 The atlantodental interval ADI normally is less than 3 mm in adults whether or not the head is flexed or extended. In children under 8-years of age, the distance has been reported to be as much as 4-5 mm. Normal measurements ADI (anterior dens interval) «3 mm. DBI (dens basion interval) «12 mm. PAL (posterior axial line) «12 mm.

the spinal lamina of C1 to the spinal lamina of C3 [Fig. 4.12]. This is known as the posterocervical line and it establishes that the apparent subluxation is physiological. Usually, the spinal lamina line of C2 should not be offset by more than 1 mm from the posterocervical line. The radiographic absence of this posterospinal lamina line usually at C1 reflects incomplete fusion of the posterior arches, which is relatively common and precludes use of the C1/C3 spinal lamina relationships discussed. In older people, there may be osteophytic extension beyond this line, and this may be ignored.

The best means of detecting subtle displacements at the craniocervical junction (dislocation/subluxations) is usually the measurement of the shortest distance between the dens and the basion, and the shortest distance between the posterior axial line (PAL) and the basion, not exceeding 12 mm [2] (Fig. 4.13).

Important caveat

Large precervical haematoma is a common finding amongst serious maxillofacial fractures (Le Fort spectrum) [4]. This should be considered when an abnormal cervical cranium prevertebral soft tissue thickening is identified, and precludes using the prevertebral soft tissue interface prominence as a means of identifying cervical-spine fractures.

Open mouth AP radiograph

Usually, on the neutral AP open mouth radiograph, the margin of the atlas and the axis are aligned. The distance between the peg and the lateral masses of C1 should also be equal. Lateral translation of C1 on C2 is normally less than 2 mm. Side-to-side difference in the lateral atlantodens 172 interval exceeding 2 mm is considered abnormal [4] (Fig. 4.14).

Fig. 4.12 Diagram of C1-C3 spinolaminar line, and Wackenheim's line. Spinolaminar line intact. Wackenheim clivus line should intersect the posterior aspect of the odontoid process, however this is not as reliable as the DBI or PAL line in assessing for occipito-atlantal dissociation, given that this line can vary with the steepness of the clivus, or the angulation of the odontoid process.

Fig. 4.13 Craniocervical dissociation. The DBI is normal if less than 12 mm. When the interval is greater than 12 mm, this indicates craniocervical dissociation.

Fig. 4.14 Diagram of AP peg view. This diagram demonstrates the LDI (lateral dens interval) which should be symmetric. This can be asymmetric, due to rotation. No 'overhang' of the C1 lateral masses should be present.

Fig. 4.14 Diagram of AP peg view. This diagram demonstrates the LDI (lateral dens interval) which should be symmetric. This can be asymmetric, due to rotation. No 'overhang' of the C1 lateral masses should be present.

EIt is important to remember the sclerotic ring (Harris ring) that is usually seen to project over the C2 vertebral body represents superimposition of the pedicles of C2. When this is disrupted, it signifies a type 3 odontoid fracture (fracture of the body of C2), and can be the only clue in revealing a type 3 fracture. This can be deficient posteriorly and inferiorly due to the superimposition of the foramina transversarium of C2 [2].

Additional lines to be checked on the lateral radiograph (Fig. 4.15) include the anterior and posterior margins of the vertebral bodies known as the anterior and posterior vertebral body lines. These should be gently curved and continuous. Thirdly, the spinal lamina line is drawn along longitudinally through the sclerotic line at the junction of the spinous process with the lamina and should also form a smooth continuous arc. The exception to this rule is that there may be a slight step of less than 2 mm in the spinous process arc, especially in children. A step greater than 2 mm is abnormal and may indicate a fracture or dislocation. Fourthly, a continuous concave line should follow along the tips of the spinous processes. Usually disruption of the anterovertebral line can be seen in anterior subluxations that is normally seen with cervical degenerative joint disease change. Anterior listhesis of 2-3 mm is usually seen in severe degenerative disc disease and if more than 3 mm, it needs to be further evaluated depending on the clinical scenario with either flexion/extension views or a CT scan.

AP view

The spinous process should lie in a straight line (remembering that there are bifid spinous processes within the cervical spine), and must be approximately equidistant from the levels above and below. If this is not 174 the case, it is suggestive of a unilateral or bilateral facet joint dislocation.

Special caveats

The lateral view of the upper cervical spine and lower part of the skull is important in evaluating (vertical subluxation) vertical superior migration of the odontoid process into the foramen magnum. There are certain measurements that are helpful in determining atlanto-axial migration/cranial settling or vertical migration of the odontoid process (terms that are often used interchangeably) (Fig. 4.16). This condition can be seen in rheumatoid arthritis, trauma, Paget's disease and congenital conditions such as Down's syndrome [6].

Second caveat

Stenosis on a lateral radiograph can be inferred if the AP dimension of the canal measures less than 16 mm at C1/C2 or usually less than 13 mm from C3 through to C7 (see Fig. 4.15). However, canal stenosis is most accurately assessed on CT and MRI, and MRI can also display intrinsic cord abnormalities [6].

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