A

Endotracheal Tube Mri

Fig. 6. (A) Lateral radiograph was obtained following trauma in a patient with acute quadriparesis. The endotracheal tube precluded obtaining a satisfactory odontoid view. The lateral view was initially interpreted as showing no fracture. Axial CT (B) and sagittal CT reformation (C) demonstrate minimally displaced fractures of the anterior arch of C1, which extended into the C1 lateral mass bilaterally. (D) Sagittal STIR reveals spinal cord edema at the C3-4 level, which is not directly related to the fractures. The likely mechanism is a hyperextension injury in the setting of degenerative spinal stenosis. Note the dorsal osteophyte complex at C3-4 on the sagittal CT image. This example underscores the complementary nature of CT and MRI in the trauma setting.

Fig. 6. (A) Lateral radiograph was obtained following trauma in a patient with acute quadriparesis. The endotracheal tube precluded obtaining a satisfactory odontoid view. The lateral view was initially interpreted as showing no fracture. Axial CT (B) and sagittal CT reformation (C) demonstrate minimally displaced fractures of the anterior arch of C1, which extended into the C1 lateral mass bilaterally. (D) Sagittal STIR reveals spinal cord edema at the C3-4 level, which is not directly related to the fractures. The likely mechanism is a hyperextension injury in the setting of degenerative spinal stenosis. Note the dorsal osteophyte complex at C3-4 on the sagittal CT image. This example underscores the complementary nature of CT and MRI in the trauma setting.

tion in 100 patients at high risk for cervical spine injury. They found eight fractures (8%) that were not directly identified on plain radiographs although prevertebral soft tissue swelling was seen in three of those patients (17). Berne et al. studied 58 patients with severe, blunt trauma who had multiple injuries and were clinically unevaluable for cervical spine injury (due to head injury, shock, intoxication, pharmacologic sedation, or paralysis). All patients were evaluated with standard cervical spine radiographs and all underwent complete cervical spine helical CT studies. Twenty patients (34.4%) had cervical spine fractures. Plain radiography failed to detect eight fractures, three of which were deemed unstable. Two fractures were missed on CT although both were considered stable. The authors concluded that a protocol of initial complete cervical spine CT combined with cervical radiography would lead to more rapid and accurate diagnosis of cervical fractures in high-risk patients (1). Undoubtedly, management algorithms will continue to be modified and imaging protocols will vary between institutions. Other factors such as expense and scanner availability will inevitably factor into the equation. As CT technology continues to improve and scan times decrease, the use of CT in the evaluation of cervical spine injury will likely increase.

Careful attention to technique is critical to maximize both sensitivity and specificity of spine CT in the setting of trauma. Thin-section helical axial CT images are acquired through the region of interest with both sagittal and coronal reformations performed in all cases. The latter are critical to the evaluation of fractures in the axial plane, such as a nondisplaced odontoid fracture. Compression fractures may also be quite subtle on axial images but are readily seen on sagittal reformations. The sagittal plane is also best for characterizing abnormalities of alignment, particularly of the facet joints. Such reformatted images easily distinguish a high riding facet from one that is either perched or completely jumped. Facet fractures are best confirmed in the axial plane since those images have the highest spatial resolution. At our institution, helical (MDCT) 2.5-mm axial unenhanced CT images are obtained from the skull base through the upper thoracic spine. The base data are then reconstructed to 1.25 mm slice thickness at 1.25-mm intervals and then reformatted as 2.5-mm slices in the sagittal and coronal planes. The images are reconstructed in both soft tissue and bone algorithm.

Image interpretation should utilize both bone and soft tissue windows. Close inspection of the latter may reveal a disc extrusion or epidural hematoma, which may be unsuspected in a severely injured patient. Such a finding should prompt evaluation with MRI to confirm the abnormality and to assess for accompanying spinal cord injury, which is not possible on CT. MRI has the added advantage of detecting ligamentous injury in the acute phase without the need for flexion and extension of a potentially unstable spine. The sensitivity of MRI for soft tissue injury diminishes with time, and thus flexion-extension views are still of use in looking for delayed instability. They are also indicated in the acute setting for cooperative patients who have been cleared of fracture by previous imaging.

The principles for imaging the thoracic and lumbar spine are the same as in the cervical spine. Generally speaking, the force required to produce a fracture in the thoracic region is higher than in the cervical or lumbar spine because of the stabilizing effect of the thoracic cage. For that reason, thoracic spine injuries are less common but tend to be more severe. There is a high incidence of associated neurologic deficit, occurring in approx 50% of cases. Comorbid visceral injury is another important factor in these patients. Thoracic spine fractures may be associated with cardiac contusion, pulmonary contusion or laceration, tracheobronchial rupture, pneumothorax, and aortic rupture. With lumbar fractures, potential concurrent injury to the solid organs or hollow viscera in the abdomen necessitates efficient evaluation of the spine. The obvious goal of imaging is accurate and rapid diagnosis while allowing for continued monitoring and resuscitation efforts. Although it is beyond the scope of this chapter to examine these visceral injuries, suffice to say that CT plays a vital and ever increasing role in their evaluation.

The mechanism of injury to the thoracolumbar spine is usually related to axial loading and flexion and results in a predictable array of fracture patterns, including compression fracture, burst fracture, flexion-distraction (Chance fracture), and fracture-dislocation. Over the years, many schemes have been proposed for the classification of injuries to the thoracic and lumbar spine. One of the most commonly utilized is the three-column system devised by Denis, who divided the spine into anterior, middle, and posterior components in an attempt to categorize fractures on the basis of mechanism and to make predictions regarding vertebral stability. The anterior column consists of the anterior longitudinal ligament, the ventral half of the vertebral body, and the corresponding intervertebral disc. The middle column is composed of the posterior half of the vertebral body, the corresponding disc segment, and the posterior longitudinal ligament. The posterior column is made up of the bony posterior elements and the supporting ligaments, including the liga-mentum flavum and interspinous ligaments. Denis asserted that spinal instability would ensue if any two of these columns were disrupted (18). Simple compression fractures, because they involve only the anterior column, are considered stable. Burst-type fractures, which by definition involve the middle column, are by this system always classified as unstable (Fig. 7). Fracture-dislocation (dislocation is usually anterior or lateral) and flexion-distraction injuries involve all three columns and are obviously unstable (18). Regardless of the classification system used, imaging remains the fundamental basis for the diagnosis and thus the management of patients with spinal injury.

With few exceptions, the modality initially employed in the investigation of spinal trauma is plain film radiography. It has the advantages of rapid acquisition and low cost, and it also provides an easy basis for comparison in

Double Facet Sign Plain Film

Fig. 7. (A, B) AP and lateral radiographs demonstrate the classic findings of a burst fracture at the L2 level. There is vertebral collapse, retropulsion, and widening of the interpedicular distance. Axial CT (C) and sagittal CT reformation (D) show to better advantage the distribution of fracture fragments and the degree of retropulsion. (E) Sagittal STIR reveals ligamentous disruption posteriorly. Notice also edema

Fig. 7. (A, B) AP and lateral radiographs demonstrate the classic findings of a burst fracture at the L2 level. There is vertebral collapse, retropulsion, and widening of the interpedicular distance. Axial CT (C) and sagittal CT reformation (D) show to better advantage the distribution of fracture fragments and the degree of retropulsion. (E) Sagittal STIR reveals ligamentous disruption posteriorly. Notice also edema

Axial Shoulder Ray CaudalPersistent Disease Body

in the adjacent L1 and L3 vertebral bodies despite a normal appearance on CT. This points to the sensitivity of STIR images in detecting marrow and soft tissue edema. (F) Sagittal T1 reveals a moderate ventral epidural hematoma.

the anticipation of serial exams (6). There are, however, limitations. Because of the overlapping soft tissues of the shoulder girdle, the upper thoracic spine is often poorly evaluated on plain X-ray images. Respiratory motion, external radiopaque material overlying the spine, and localized differences in beam penetration (most commonly related to the diaphragm) often result in suboptimal radiographs in the severely injured patient. Even high-quality images fail to detect subtle fractures and tend to underestimate the degree of retropulsion. Taking the case of a fracture-dislocation, CT more accurately depicts the extent of the fractures (especially with regard to the posterior elements), the relationship of the bone fragments, and the degree of retropulsion. The sagittal and coronal reformations clearly demonstrate loss of vertebral body height, vertebral subluxation, and abnormal alignment of the facet joints. This has obvious implications in terms of fracture classification and the assessment of stability. MRI adds important information for patients with complex spine fractures and those with neurologic deficits. Spinal cord contusion, epidural hematoma, disc extrusion, and ligamentous disruption are all best evalu ated with MRI. This modality also is ideal for detecting delayed complications of spinal trauma such as myelomalacia, cord atrophy, and syrinx formation.

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