How to choose an imaging method
The examination algorithm depends on the severity of the patient's condition and the mechanism of injury:
- Isolated low-energy trauma. Start with standard radiography. The lateral projection (lateral radiograph) is the most informative.
- Polytrauma. Computed tomography (CT) is performed immediately; radiography is unjustified in this case.
The modern ATLS protocol has removed the mandatory lateral neck view from the primary survey. If CT is available, the value of radiography drops sharply; however, the principles of reading conventional radiographs fully apply to the analysis of tomographic reconstructions.
Evaluation of lateral radiograph
Analysis of the spinal alignment is based on four smooth and continuous lines:
- Anterior vertebral line: follows the anterior contours of the vertebral bodies.
- Posterior vertebral line: follows the posterior surfaces of the vertebral bodies.
- Spinolaminar line: connects the bases of the spinous processes.
- Facet joint line: on a strict lateral view, the right and left joints merge into a single shadow.
Important normal criteria:
- The atlantodental interval (from the C1 arch to the dens) must not exceed 3 mm in adults and 5 mm in children.
- Prevertebral soft tissue thickness: above the larynx — no more than 1/3 of the anteroposterior dimension of the vertebral body, below the larynx — no more than one full dimension.
Pathological radiographic patterns
Spinal alignment analysis can reveal specific signs indicating the nature of the injury:
- «Bow-tie» sign (bow tie sign). The appearance of a double joint line at the same level indicates a unilateral dislocation or rotational anomaly.
- Hangman's fracture (Hangman fracture). The anterior line is disrupted due to the loss of connection between the vertebral body and the posterior elements, but the spinolaminar line remains intact. This differentiates it from pediatric pseudosubluxation, where both lines are displaced.
- Posterior ligamentous complex rupture. Manifests as local kyphosis and fan-like widening of the spinous processes on the radiograph.
CT and MRI in the diagnosis of neck trauma
Computed tomography in trauma covers the area from the craniocervical junction to the body of the third thoracic vertebra (Th3). The method is ideal for detecting fractures, but has limitations: a normal CT does not rule out an isolated ligamentous tear.
If clinical suspicion persists, magnetic resonance imaging (MRI) is used:
- This is the gold standard for visualizing ligaments and the spinal cord.
- Fat-suppression sequences (T2 fat-sat or STIR) best demonstrate edema and soft tissue injuries.
- Gradient echo sequence (Gradient echo) is used to detect hemorrhage within the spinal cord, which is a marker of poor neurological prognosis.
Specific injuries
Certain injuries of the craniocervical junction deserve special attention:
- Atlanto-occipital dissociation. An extremely severe, often fatal injury. Manifests as displacement of the clivus line (clivus) relative to the tip of the C2 dens. MRI reveals disruption of the apical ligament.
- Occipital condyle fractures. Most commonly occur with axial loading and remain stable. However, if an avulsion of the alar ligament (alar ligament) occurs, the injury becomes unstable (clearly visible on coronal CT).
- C1 rotatory subluxation. Occurs in children, often provoked not by trauma, but by a prior respiratory infection.
Briefly: answers to topical questions
What are the types of C2 dens fractures according to the Anderson-D'Alonzo classification?
The sources do not mention the Anderson-D'Alonzo classification, but three types of C2 dens fractures are described.
- Type I — avulsion of the tip of the dens (practically never seen in acute trauma).
- Type II — the fracture runs through the base of the dens.
- Type III — the fracture extends into the C2 body (has the best prognosis for bone union).
Which specific anatomical structures form the radiographic shadow of the «Harris ring»?
The «Harris ring» (Harris ring) shadow is not a distinct anatomical structure, but rather a composite shadow. The C2 vertebral body participates in the formation of this shadow. Specific additional anatomical structures forming this ring are not detailed in the sources. In Type III dens fractures, disruption of this ring is visualized, most commonly in its posterior part.
What are the indications for CT angiography of the neck vessels in cervical spine trauma?
The sources indicate the need for additional imaging when vascular injury or arterial dissection is suspected following trauma. Horner's syndrome, pulsatile tinnitus, and transient blindness require attention. In penetrating trauma, the decision regarding additional imaging is made jointly with trauma surgeons, taking into account the location of the injury, entry and exit wounds, and the type of projectile. The most frequent location of dissection is the cervical segment of the internal carotid artery.
What are the exact normal values for prevertebral soft tissue thickness in millimeters at the C2 and C6 levels?
Exact normal values for prevertebral soft tissue thickness in millimeters are not specified in the sources. Assessment is performed using relative criteria:
- Above the level of the larynx — the thickness should be no more than 1/3 of the anteroposterior diameter of the vertebral body.
- Below the level of the larynx (at the C3–C4 level and below) — the thickness should be no more than one full anteroposterior diameter of the vertebral body.
In intubated patients, the assessment is unreliable due to tissue distortion caused by the tube.
Class and exam questions
Why are flexion and extension radiographs contraindicated in acute trauma?
An unrecognized ligamentous tear may be present in the acute phase. Movement of the neck in this condition can lead to vertebral displacement and severe neurological damage.
How to differentiate a pathological fracture from pediatric pseudosubluxation?
In physiological pseudosubluxation in children (usually C2 on C3), the alignment of both anterior lines—both the vertebral and spinolaminar lines—is disrupted simultaneously. In injuries such as a hangman's fracture, the spinolaminar line often remains intact.
What is Harris ring?
This is a composite radiographic shadow at the base of the C2 dens on a lateral view. Its integrity must be evaluated to rule out fractures of the base of the dens.
What else to study on this topic
- Evaluation of anteroposterior open-mouth radiograph
- Differential diagnosis of avulsion fractures and secondary ossification centers
- MRI signs of ligamentum flavum and interspinous ligament rupture
- Features of diagnostic imaging in thoracolumbar junction injuries
- Marginal vertebral body defect (limbus vertebra) and its differentiation from trauma
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