eMedicine Specialties > Radiology > Musculoskeletal

Thoracic Spine, Trauma: Imaging

Author: Lennard A Nadalo, MD, Clinical Professor, Department of Radiology, University of Texas Southwestern Medical School; Consulting Staff, Envision Imaging of Allen and Radiological Consultants Association
Coauthor(s): James A Moody, MD, Chief, Neurosurgery Section, Department of Surgery, Methodist Medical Center
Contributor Information and Disclosures

Updated: Mar 23, 2007

Radiography

Findings

Radiographic features of an anterior compression (wedge) fracture include soft tissue swelling, anterior superior cortical impaction, loss of vertical height of the anterior vertebral body, buckling of the anterior cortex of the vertebral body, trabecular compaction, endplate fractures, and disk-space narrowing.

Among the more serious injuries of the thoracic spine, the burst fracture usually is detected easily by using standard radiographs of the thoracic spine. In the lateral view, the criteria for instability include a greater than 50% loss of vertebral body height, a greater than 20° angulation of the thoracolumbar junction, neurologic injury, and a canal narrowing of greater than 30%. Early surgical repair is indicated for such an injury because additional compression of the fracture and more severe neurologic injury can be expected if weight bearing is attempted without surgical fixation. The normal thoracolumbar spine junction presents with a 0° of angular measurement between the T12 and L1 levels.

Degree of Confidence

The degree of confidence in the initial identification of thoracic spine fractures is related directly to the severity of the spinal deformity and inversely related to technical factors such as the size of the patient, patient movement, and the type of radiologic equipment available.

The degree of compression and changes in the disk interspaces are important factors that help in determining if a compression fracture is clinically significant. A compression with intervertebral disk narrowing of more than 50% has a less favorable prognosis for successful treatment. Beyond acute trauma, anterior wedge fractures are subject to differential diagnostic considerations that include congenital hemivertebra, infections, primary tumors, metastatic tumors, metabolic bone disease, Scheuermann disease, Kummell disease, and Schmorl nodes.

False Positives/Negatives

Many spinal anomalies may be mistaken for a fracture. Horizontal residual venous sinus grooves may appear as suspected fractures. In young children, the anterior corners of the vertebral body may have a small depression, which represents the epiphyseal margin. The ossification centers at the ends of transverse processes may appear as fractures. Ossification centers may be irregular in appearance without pathologic fractures. Spina bifida occulta may occur in the posterior spine at any level. The body of T12 is often slightly wedged anteriorly, described as physiologic wedging.

Asymmetry of the pedicles of the lower thoracic spine has been reported in 7% of persons without spinal fracture. The best interobserver agreement can be obtained by measuring from the superior endplate of the vertebral body 1 level above the injured vertebral body to the inferior endplate of the vertebral body 1 level below.

A congenital butterfly vertebral body appears as a compression fracture viewed in the lateral projection. Superimposed shadows of the glenoid process of the scapula may give a false impression of a compression fracture when viewed in the lateral project, whereas the outline of the mandible may suggest a fracture in an anterior view. False-positive findings can result from previous (chronic) kyphosis due to osteoporosis or prior injury. Kyphosis after trauma is best compared by using prior lateral radiographs if such images are available.

Computed Tomography

Findings

Thin-section axial CT performed by using a bone algorithm is the single most sensitive means by which to diagnose fractures of the thoracic spine. Routine helical CT scans of the thoracic spine are valuable because multisection CT scanners can generate high-resolution spinal images, even during a primary multisystemic trauma evaluation.

Good-quality CT imaging depicts more thoracic spinal injuries than do conventional radiographic studies; however, the percentage of clinically important spinal fractures seen in the thoracic region on CT scans and not seen on radiographs is lower than similar studies in the evaluation of cervical spinal fractures. Most of the fractures missed on radiographs were spinous process fractures, transverse processes fractures, and fractures in large patients.

In general, the appearance of fractures on CT scans is similar to that seen by using radiographs of the thoracic spine. As a result of its superior contrast definition and the absence of superimposed structures, CT imaging of the spine is highly effective and accurate in the diagnosis of fractures. The confidence level for the diagnosis of a thoracic spinal fracture by using 2-mm axial sections (possible with a multisection CT unit) is greater than 98% and reportedly 99%. Because axial CT is performed with patients in a neutral position, bony distraction of the fracture fragments and subluxations of the spinal articulations may not be as significant on CT images as on they are on acute trauma-series radiographs.

The level of a burst fracture and the percentage of spinal canal stenosis have been correlated with associated neurologic deficits. A significant correlation exists between neurologic deficit and the percentage of spinal canal stenosis. The higher the level of injury, the greater the probability of neurologic deficit. This association may be related to the smaller canal diameter in the upper thoracic spine. The severity of neurologic deficit cannot be predicted.

Degree of Confidence

The confidence level for the diagnosis of a thoracic spinal fracture with 2-mm axial sections (possible with a multisection CT unit) is greater than 98% and reportedly 99%.

False Positives/Negatives

Because axial CT is performed with the patient in a neutral position, bony distraction of the fracture fragments and subluxations of the spinal articulations may not be as significant on CT images as on acute trauma-series radiographs.

False-positive results may occur in patients with a Schmorl node, which is a chronic internal herniation of the vertebral disk into the thoracic vertebral body endplate and failure of the fusion of the anterior vertebral endplate epiphysis, resulting in a limbus vertebra. False-negative CT studies may occur in chronic stress injuries and in severe generalized osteoporotic endplate fractures.

Magnetic Resonance Imaging

Findings

Thoracic spinal MRI can demonstrate many vertebral fractures and most abnormalities of alignment. The patterns of injury are similar to those demonstrated on radiographs. MRI is superior to both radiography and CT in the detection of soft tissue injury to the ligaments, facet capsules, and prevertebral spaces. MRI is unique in the ability to depict epidural bleeding and spinal cord injury. Injury to the thoracic cord is particularly critical because such injury may result in paralysis. However, MRI has fewer line pairs of resolution than does CT, which makes MRI a secondary method for fracture evaluation.

With a T2-weighted gradient-echo technique, the cortical break can be demonstrated in some fractures. MRI is superior to CT in the identification of the indirect signs of a fracture, such as paraspinal edema or hemorrhage, epidural bleeding, and sprains of the paraspinal and intraspinal ligaments.

A gradient-echo sagittal T2-weighted MRI of the spine demonstrates the compression fracture by showing the cortical bone as dark (black), while the T2-weighted quality shows cerebrospinal fluid and spinal cord edema as bright (white). Subacute hemorrhage within the spinal cord or in the epidural space may be seen as a susceptibility area of lost signal brightness.

Degree of Confidence

Thoracic spine MRIs demonstrate many vertebral fractures and most abnormalities of alignment. MRI is superior to CT in the identification of indirect signs of a fracture, such as perivertebral edema or hemorrhage, epidural bleeding, and sprains of the paraspinal and intraspinal ligaments. Associated injuries to intracranial structures are evaluated better by using MRI than CT imaging.

False Positives/Negatives

False-positive MRI results are often associated with movement artifacts of metal near the site of injury. Blood-vessel canals may mimic bone injury. The use of upper cervical and intracranial magnetic resonance angiography may help in differentiating certain vascular variations.

False-negative findings may result from motion on the part of the patient. Artifacts related to implanted metal may mask spinal fractures. In older patients or in patients with known neoplastic disease, a pathologic fracture should be considered. In these patients, MRI with Gd-DTPA enhancement demonstrates a spinal mass or osteomyelitis. MRI has less line-pair resolution than does CT scanning. With T2-weighted gradient-echo sequences, the cortical break can be demonstrated in some fractures; however, even with adequate MRI technique, minimally displaced fracture lines may not be seen by using MRI.

Ultrasonography

Findings

The use of thoracic ultrasonography is usually limited to the localization of pleural effusions, which may occur after significant thoracic spinal and chest wall injury. Diagnostic thoracentesis is more easily performed by using sonographic guidance. Paraspinal abscess may be localized prior to aspiration in select patients.

Degree of Confidence

As a result of the limitations of sonographic studies of bone and the lungs, sonography should be used only in specific patients.

False Positives/Negatives

Ultrasound does not penetrate the air in the lungs or the bones of the spine and ribs. Ultrasonography may be applied in select patients for localization studies.

Nuclear Imaging

Findings

Nuclear medicine studies have a limited role in the acute phase of thoracic spine injury; however, in a possible congenital anomaly, an acute fracture can be differentiated from a limbus vertebra.

After 12-24 hours, a bone scan with technetium-99m hydroxydimethylpyrimidine demonstrates increased uptake in the area of a fracture. Later in the clinical course, persistent back pain may be explained by a nondisplaced facet injury or pedicle fracture, which is also associated with an area of increased uptake. After surgery or in open spinal fractures, diskitis and osteomyelitis can be identified by focal areas of increased activity; however, indium 111–tagged white blood cells (WBCs) act as a more specific agent in the detection of abscess and osteomyelitis. Unfortunately,¹¹¹ In-tagged WBC scans have a poor sensitivity for the detection of diskitis.

Fat-saturated T1-weighted MRI with intravenous gadolinium enhancement may demonstrate the enhancement of osteomyelitis or diskitis, even in cases in which the¹¹¹ In WBC scan was negative. MRI is also superior in the detection of an associated epidural abscess.

In cases in which MRI is contraindicated (pacemaker, aneurysm clip, etc) or in the presence severe MRI artifacts resulting from fixation plates, wires, or screws, a combined^99m Tc hydroxydimethylpyrimidine-gallium scan is recommended. In all patients, the tomographic qualities of single-photon emission computed tomography (SPECT) improve both accuracy and specificity.

Degree of Confidence

In the absence of prior surgery, radionuclear bone imaging is fairly sensitive. If bone scans are needed, SPECT should be applied in all patients with suspected upper thoracic spine trauma.

False Positives/Negatives

Many false-positive findings can be expected in older adults. Osteomyelitis, diskitis, metastatic disease, degenerative spondylosis, rheumatoid arthritis, and ankylosing spondylitis may result in abnormal spinal images that are not related directly to acute trauma. In the young child, variations of thoracic spine development may mimic acute injury. SPECT helps improve visualization of these conditions, reducing the occurrence of false-positive findings

False-negative results may occur in the first hours after an acute trauma. If possible, 24 hours should be allowed to pass prior to attempting nuclear bone scans of the thoracic spine.

Angiography

Findings

Angiography has a limited but critical indirect role in the assessment of thoracic spinal injury. After a gunshot wound to the chest, injuries to the aorta and the proximal great vessels are best evaluated by using angiography. New higher-resolution CT angiography makes catheter angiography less essential. Evaluation of injury to the aorta, subclavian arteries, and innominate artery are routinely performed during the assessment of patients with multisystemic trauma. Trauma, including arterial laceration with hemorrhage, may be seen associated with displaced rib and transverse-process fractures.

Degree of Confidence

The higher resolution of digital subtraction angiography results in excellent image quality. Rarely are other vascular images necessary. Use of angiography is typically reserved for possible interventional repair of arterial injuries and in patients in whom the diagnosis is confused.

False Positives/Negatives

Standing waves within the proximal carotid artery or innominate artery may mimic vascular injury with spasm. In the older adult, arteriosclerotic vascular disease may mimic spasm. Intercostal arteries may be in spasm at the time of an examination, preventing localization of a bleeding site.

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