Traumatic and Nontraumatic Spine Emergencies

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CHAPTER 7 Traumatic and Nontraumatic Spine Emergencies

Glenn D. Barest

TRAUMATIC SPINE INJURY

Background and Imaging Algorithms

Cervical spine injuries are quite common, causing an estimated 6000 deaths and 5000 new cases of quadriplegia annually in the United States. Imaging is liberally applied with a positive yield of from 1% to 3% of all exams, resulting in an annual cost of approximately $3 billion. Approximately 14,000 cases of spinal cord injury occur each year in the United States, the majority affecting young adults. The cost to individuals and society is enormous due to their long life expectancy. Understandably, this is one area of medicine in which attempts have been made to develop evidence-based diagnostic algorithms. Multivariate analysis of data derived from two major clinical research initiatives, the National Emergency X-Radiography Utilization Study (NEXUS) and the Canadian C-Spine Study, has provided the basis for acute spine trauma imaging pathway development. Decision rules have been created that allow for discrimination of patients in need of imaging and those for whom imaging can be safely avoided, thereby reducing costs when possible. Once the decision to image has been made, the next step is to select the most appropriate modality. Plain film radiography has traditionally been the initial examination to evaluate for possible fracture or malalignment. It is readily available, relatively inexpensive to perform, and highly sensitive. It continues to be a cost-effective option for patients with a low probability of injury. However, it has been supplanted by computed tomography (CT) in the setting of moderate-to-high probability of injury, based on cost-effectiveness analysis that takes into account the high medical and legal costs of the rare missed fracture that leads to severe neurologic deficit. Studies of CT as the initial modality have demonstrated higher sensitivity for the detection of fractures; however, the clinical significance of many of the radiographically occult injuries is uncertain owing to the lack of studies addressing outcomes. Another clinical prediction rule that has been developed, based on data from the Harborview study, may be used to stratify risk based on injury mechanism and other clinical parameters. This type of approach is supported by trauma surgery societies and is commonly applied at trauma centers.

With the increasing availability of multidetector-row CT (MDCT), it seems that this is quickly becoming the new standard of care, even for patients with a low probability of injury. A zero-tolerance (for missed injury) approach to diagnosis using the fastest, most accurate exam is easily adopted by the emergency department or trauma team rather than an evidence-based approach. It used to be that for patients with negative radiographs but persistent pain, tenderness, or limited range of motion, symptomatic treatment with analgesics, soft collar application, and clinical follow-up were the rule. At the follow-up visit, if symptoms had not resolved, flexion-extension radiographs were obtained to evaluate for the possibility of ligamentous injury or instability. Flexion-extension views have been shown to have little utility in the acute setting, primarily due to limited range of motion secondary to muscle spasm. In low-probability settings, this approach may still be followed, but more commonly, CT is requested to exclude occult fracture. The higher direct cost of CT may be offset by the increase in emergency department throughput, albeit at a higher radiation exposure. On some occasions, after a negative CT exam, magnetic resonance (MR) imaging may be pursued to screen for signs of potential ligamentous injury before allowing the patient to be discharged.

The cost-effectiveness of MR for the detection of clinically significant ligamentous injuries has not yet been determined. This is another instance where technology is being applied because of its availability and perhaps for theoretical limitation of liability. Clearly, when a neurologic deficit is present and CT fails to identify a cause, MR may offer additional sensitivity for the detection of soft tissue injuries, including disc extrusion, hematoma within the spinal canal, cord compression or contusion, and unstable ligamentous injury. Other injuries such as unsuspected bone marrow edema (microfractures) and vascular injuries may also be detected. One study that correlated MR imaging and intraoperative findings found that MR had moderate to high sensitivity for injury to specific ligamentous structures but suggested that it may overestimate the extent of disruptive injury. MR, with its increased sensitivity, also brings with it a small false-positive rate that may lead to added costs related to treatment/workup of clinically insignificant or unrelated abnormalities, such as thyroid lesions and lymphadenopathy. Special consideration has been given to the obtunded patient, since some studies have shown a 2% incidence of unstable cervical spine injuries that were not detected by radiography and CT due to the lack of associated fracture or malalignment. Although other authors have suggested that it is not necessary, MR “clearance” of the cervical spine has become a reality. At our institution, we generally adhere to the algorithm shown below.

Regarding the thoracolumbar spine, clinical prediction rules have been evaluated but provide only a very small decrease in the number of exams performed. In those patients with blunt trauma undergoing CT of the chest, abdomen, and pelvis with thin-section CT (2.5 mm or less), sagittal and coronal reformats have been shown to be more sensitive and specific for detection of fractures, and therefore radiography can be avoided. When the viscera are not in need of examination, the role of CT for screening the spine is not as clear. Mechanism of injury is an important determinant for further workup in this category of patients. Similar to the logic applied to the cervical spine, screening is warranted if a high-energy mechanism of injury is known or suspected, including falls from significant height (greater than 10 feet), motor vehicle or bicycle crash, pedestrians struck, assault, sport or crush accident, and a concomitant cervical spine fracture. Other

valid indications are altered mental status, evidence of intoxication with ethanol or drugs, painful distracting injuries, neurologic deficits, and spine pain or palpation tenderness.

For patients with neurologic deficits referable to a thoracolumbar spine injury, current Eastern Association for the Surgery of Trauma guidelines recommend obtaining an MR exam as soon as possible after admission to the emergency department. Early decompression of mass lesions, such as traumatic herniated discs or epidural hematomas, is likely to improve neurologic outcome.

A somewhat unintuitive finding is that the absence of symptoms does not exclude injury to the thoracolumbar spine. In one study, only 60% of trauma patients with a confirmed fracture were symptomatic. In a review from Maryland’s Shock Trauma Center of 183 fractures in 110 patients who were neurologically intact with a Glasgow Coma Scale score between 13 and 15 and considered amenable to clinical examination, 31% of these patients were recorded as having no pain or tenderness, yet all had fractures. The evidence would suggest that many of these fractures were not truly asymptomatic but rather occult as a result of intoxication or an unreliable physical exam. It is clear from the literature that no imaging modality is accurate 100% of the time. Most studies have found that radiographs of the thoracolumbar spine are commonly inadequate, especially in obese patients, and provide a sensitivity and specificity of only 60% to 70%.

Separate studies to develop guidelines for the pediatric population have not been performed. The increasing use of MDCT and the long-term effects of radiation exposure are topics of concern and current research.

Patterns of Spine Injury and Imaging Findings

Following is a brief review of the many different types of spine injuries that one must be familiar with when evaluating victims of trauma. There are many texts devoted solely to the imaging of spine trauma, with a few that truly reward the reader with insight into the anatomy, physiology, biomechanics, and pathology of this extensive topic. This section should serve as a valuable aid to the radiologist on call and be used as a starting point for further study. Rather than taking a how-to approach to evaluating spinal imaging, this section relies on a working knowledge of the normal anatomy and basic principles of plain film, CT, and MR analysis. The general classifications of injuries are covered through a review of classic examples, using primarily CT with important plain film and MR correlations where appropriate.

Imaging of the spine can be thought of as a continuum, with radiography providing an overview of alignment and soft tissues, CT adding greater detail regarding fractures, and MR yielding finer detail with respect to soft tissues including the spinal cord. Attention must be paid to the technical factors necessary to achieve a satisfactory (and safe) exam, including patient immobilization and positioning, image acquisition parameters, and multiplanar analysis.

Lateral, anteroposterior, and open-mouth odontoid views are the minimum requirement for plain films. A “swimmer’s” view may be necessary to adequately demonstrate the cervicothoracic junction. Thin-section CT (section thickness of 2 mm or less) with similar-thickness sagittal and coronal reformats generally suffices. However, anecdotal cases have arisen in which hairline fractures were detected on scans performed with submillimeter thickness that were not detected prospectively with the standard technique. Clearly there is a trade-off between level of anatomic detail and number of images that must be reviewed. With isotropic voxel size now possible with modern scanners, some have proposed primary review of sagittal and coronal reformats in order to increase patient throughput. Thankfully, many of the missed fractures will be clinically insignificant due to their small size and inherent stability. In addition to the standard T1- and T2-weighted sequences used to evaluate the cervical spine, fat-suppressed T2-weighted sequences, with either chemical selective or short tau inversion recovery (STIR) technique and gradient-echo sagittal imaging, are useful in the trauma setting. MR angiographic sequences may be indicated in certain circumstances.

Careful analysis of the structures (vertebrae, intervertebral discs, spinal cord, and other soft tissues) and their normal and abnormal attributes (size, shape, alignment, density, and signal intensity) requires an understanding of mechanisms of injury, including magnitude and acuity, and underlying diseases. The mechanisms can generally be grouped into hyperflexion, hyperextension, rotation, axial loading, lateral flexion, and others. Box 7-1 attempts to categorize the injuries of the cervical spine based on these mechanisms. Combined mechanisms, such as flexion and rotation, are common and may lead to multiple injuries at different sites and vertebral levels within the same patient. Rather than relaxing after detecting an injury, the examiner should intensify the search for other lesions.

Box 7-1 Categories of Injuries of the Cervical Spine Based on Mechanism

HYPERFLEXION

Anterior subluxation (including atlantoaxial dissociation)

Clay shoveler’s fracture

Facet fracture-dislocation

Flexion teardrop

Interfacetal dislocation (unilateral or bilateral)

Wedge compression fracture

AXIAL LOADING

Burst fracture

Jefferson fracture (C1 burst)

LATERAL FLEXION

C1 lateral mass fracture

Occipital condyle fracture

Transverse process fracture

Uncinate process fracture

OTHER OR UNKNOWN MECHANISMS

Atlantoaxial rotatory subluxation

Atlanto-occipital (craniocervical) dissociation

Odontoid fracture

The determination of instability, which may be associated with or have the potential to progress to neurologic injury, major deformity, or incapacitating pain, is an important part of this process. There are general principles that may apply based on specific imaging findings, but the final determination is probably best made by an expert in the treatment of these injuries. One should note that the classifications of these injuries are constantly being revised based on new treatment techniques and clinical outcomes. Some of the more commonly used classifications will be mentioned. The three-column approach to stability proposed by Denis divides the spine into anterior column (anterior longitudinal ligament, annulus, and anterior two thirds of the vertebral body and disc), middle column (posterior third of vertebral body and disc, annulus, posterior longitudinal ligament), and posterior column (posterior elements, ligamentum flavum, joint capsules, intertransverse, interspinal, and supraspinal ligaments). Instability is generally based on disruption of two of the three columns.

Injuries of the Cervicocranium

The cervical spine can be subdivided into the cervicocranium (including the basiocciput, craniocervical junction, atlas [C1], and axis [C2]) and the subaxial spine (C3 through C7). Following is a top-down review of the major types of injuries and the mechanisms that cause them. It is not possible to describe all of the features of each injury in this abbreviated format; however, the general principles and commonly used classifications are described.

Atlantoaxial dissociation includes partial (subluxation) and complete (dislocation) disruptions of the articulations of C1 and C2. Disruption of the transverse atlantal ligament (TAL), the horizontal component of the cruciform ligament complex, allows for widening of the anterior atlantodental interval (AADI) (Fig. 7-4). Greater than 3 mm in adults or greater than 5 mm in children is considered abnormal. Conditions that may predispose to atlantoaxial dissociation include rheumatoid arthritis, Down syndrome, neurofibromatosis, and other syndromes and congenital anomalies. Rotatory dissociation (fixation) is rare and has been subdivided into four types based on extent and direction of displacement of the atlas. Type I may appear similar to physiologic rotation. Therefore, to confirm the diagnosis, CT may be repeated after voluntary contralateral rotation of the head to assess for a locked position. Torticollis refers to simultaneous lateral tilt and rotation of the head and may be caused by disorders affecting either the atlantoaxial joint or the sternocleidomastoid muscle. Since it may produce the same imaging findings as type I rotatory fixation, diagnosis may rely on clinical judgment and a trial of conservative treatment. Types II, III, and IV are determined based on direction and extent of displacement of the cranium.

Figure 7-4 Atlantoaxial dissociation. A, Extension view shows a normal anterior atlanto-dental interval (AADI). B, The AADI is abnormally widened on flexion view, confirming disruption of the TAL. The abnormal atlanto-axial relationship was incidentally noted on a routine head CT done after a minor fall at the nursing home. The patient had a history of mild chronic neck pain, without exacerbation reported.

C2 Fractures

Approximately 20% of cervical fractures involve the axis (C2). Of these, more than half are traumatic spondylolysis/spondylolisthesis—fracture between the superior and inferior facets (pars interarticularis) of C2—often described as the “hangman” fracture (Fig. 7-5). Due to the unique shape of C2, this fracture involves the pedicles, whereas a pars fracture of the subaxial spine is termed the “pillar” fracture. Aside from the mechanism implied by the name, other forms of hyperextension, such as motor vehicle dashboard impact, are usually to blame. At least three types have been described, based on degree of fragment distraction, angulation at the fracture site, and disruption of the C2-C3 disc.

Figure 7-5 C2 hangman fracture. Contrast-enhanced axial CT (left) shows fracture through the body of C2 involving the left transverse foramen. Sagittal reformat (right) shows the oblique course of the fracture that separates the superior and inferior articulating facets of C2.

The dens (odontoid process) may be involved in approximately 25% of C2 fractures. The classification system of Anderson and D’Alonso is commonly applied. Type I is uncommon—an avulsion of the tip by the alar ligament—and may be associated with AOD. Type II is the most common (about 60%) and involves the base of the dens (Fig. 7-6). Operative repair via transoral screw fixation or posterior arthrodesis of C1 and C2 is often necessary. Type III involves the dens and body of C2. Due to the larger surface area, this type of fracture is more likely to heal without the need for instrumentation (Fig. 7-7). As the plane may be nearly horizontal, dens fractures may be quite subtle on axial CT. Sagittal reformats therefore demand careful review. Beware of misregistration artifact of axial CT, due to patient movement between adjacent images, although this has become less of a problem since the advent of helical and MDCT techniques. Since the scanning process is so fast with these techniques, a different type of artifact can result—motion blur. Distorted images should signal the need to repeat the scan. For uncooperative patients, a lateral plain film may provide complementary demonstration of proper alignment.

Figure 7-6 Ankylosing spondylitis—C2 fracture. CT sagittal reformat (left) shows dens fracture and ankylosis of C2 through C6 vertebral bodies. Coronal reformat (right upper) and axial source image (right lower) show extensive hypertrophic bone formation resulting in ankylosis of the occiput to C1 and C1 to the tip of the dens. The altered biomechanics are a setup for dens fracture.

Figure 7-7 Dens fracture—type III. CT coronal reformat (A) and volume-rendered image from CT angiogram (B) show fracture of the dens involving the body of C2 and distraction of fragments.

Injuries of the Subaxial Cervical Spine

Hyperflexion

Injury of the subaxial spine generally follows a set of patterns based on the mechanism and degree to which the subaxial spine has been stressed beyond physiologic limits. Of the injuries caused by hyperflexion, the simple wedge compression fracture (involving the anterior column) and the isolated spinous process (clay shoveler) fracture are relatively straightforward in terms of diagnosis. Although generally considered stable injuries, they can occur in association with other, more insidious injuries, and therefore flexion/extension radiographs or MR may be indicated. Anterior subluxation (or hyperflexion sprain) is indicative of injury to the posterior ligamentous structures. It can be quite subtle, presenting with focal kyphotic angulation, very mild malalignment of facets, and widening of the posterior margin of the disc space and interspinous distance. Failure to diagnose and treat this injury may result in delayed instability in up to 50% of cases. As the degree of anterior vertebral body translation, facet joint distraction, and “fanning” of spinous processes increases, the signs of instability become more obvious. Facets may become perched or jumped (complete dislocation). Anterior translation of a vertebral body by more than 50% relative to the subjacent body is a sign of bilateral interfacetal dislocation (BID) (Figs. 7-8 and 7-9). With perched facets, the “naked facet” sign will be seen on axial CT. With BID, the convex surfaces of the articular masses will be apposed rather than the usual concave articular surfaces. Anterior, middle, and the posterior ligamentous structures will be disrupted, and the extent of soft tissue injuries (including cord compression and contusion) will be best assessed by MR. If there is any rotational component to the mechanism of injury, unilateral interfacetal dislocation (UID) or combination of perched and jumped facets may occur. Fractures of the subjacent vertebral body or articular masses will result in a fracture-dislocation. The flexion teardrop fracture is thought to result from a combination of hyperflexion and axial loading. It is feared because of the high incidence of permanent neurologic damage resulting from the more complex variety, which usually includes fractures of the posterior elements. Although it can be difficult to distinguish this from the hyperextension teardrop fracture based on the configuration of the vertebral body fracture alone, the kyphosis and posterior element distraction are important clues.

Figure 7-8 Hyperflexion—bilateral interfacetal dislocation. A, CT sagittal reformats show greater than 50% offset of C5 on C6, jumped left facet, and fracture of right C5 inferior facet (black arrow) with dislocation. B, Sagittal STIR and gradient-echo images show associated small epidural hematoma versus C5-C6 disc extrusion (white arrow). Also note hemorrhage in the disc space extending inferiorly in the prevertebral region. Hyperintense signal in the spinal cord is consistent with edema. The central isointense region is noted to be hypointense on gradient-echo image (black arrow), indicating hemorrhage (cord contusion).

Figure 7-9 Hyperflexion—anterior subluxation. Lateral radiograph shows complete subluxation of C5 on C6 (spondyloptosis). This patient with previous C3 through C5 laminectomies for canal stenosis was the unfortunate victim of an accidental gas main explosion.

Hyperextension

The types of injuries to the subaxial spine resulting from hyperextension mechanisms are analogous to those sustained by hyperflexion, but with a few differences. Hyperextension sprain, dislocation, and fracture-dislocation encompass a spectrum that may result from a blow to the face, as from impact against the dashboard during a motor vehicle collision, an assault, or a fall. Soft tissue structures are involved in a progressive fashion from anterior to posterior, including prevertebral muscles, anterior longitudinal ligament, anterior portion of annulus, intervertebral disc, posterior longitudinal ligament, and so on. A sprain usually leaves the middle and posterior columns intact. A dislocation also disrupts the middle and possibly posterior ligaments. A fracture-dislocation may result in fractures of the posterior aspect of the vertebral body and any of the posterior elements due to impaction forces. When underlying ankylosis is present, such as in diffuse idiopathic skeletal hyperostosis or ankylosing spondylitis, a relatively mild hyperextension force may result in fracture-dislocation (see Fig. 7-6). This is due to the loss of normal ligamentous laxity, a lever arm up to several spinal segments long, and coexistent osteoporosis. An extension teardrop fracture fragment is the result of avulsion by the anterior longitudinal ligament. The vertical dimension of the fragment is generally greater than the horizontal dimension (Fig. 7-10).

Figure 7-10 Extension teardrop fracture. Lateral radiograph shows that the height of the fracture fragment is greater than the width.

Extension combined with rotation and lateral or tilting forces may result in articular mass (also known as pillar) fractures (Fig. 7-11). A fracture of the pedicle and ipsilateral lamina may result in a freely mobile articular mass (pedicolaminar separation). Occasionally, isolated fracture(s) of the lamina(e) will be occult on anteroposterior and lateral films. This is one advantage of oblique radiographs. Anotheradvantage is confirmation of unilateral facet dislocation, but, alas, MDCT has made these films nearly obsolete. It is the rare technologist who can still obtain perfect trauma oblique views taken without removing the cervical collar or turning the patient’s head. It seems that most centers have abandoned oblique views from the routine cervical spine series. The extra clues provided by oblique views may still have value in centers where trainees interpret plain film exams on call.

Figure 7-11 Articular facet fracture—vascular injury. A, CT axial and sagittal reformats show C4 right pillar fracture. B, Volume-rendered image from CT angiogram shows segmental occlusion of the right vertebral artery. Reconstitution via muscular collaterals is a common finding in vertebral artery injuries.

Axial Loading

Axial loading due to diving injuries, falls, or ejections from vehicles may result in a burst fracture, with comminuted fractures of the vertebral body and often displaced fractures of the posterior elements. As pressure is transmitted through the intervertebral disc, the body may be split in a sagittal plane, or the disc may lose vertical height, causing retropulsion of the posterior portion of the body into the spinal canal. The latter form clearly has a higher potential to result in spinal cord injury. Involvement of the anterior and middle columns is generally considered an unstable injury and requires operative fixation.

Many of the injuries described above may present with relatively preserved alignment owing to rebound of structures after traumatic displacement. The snapshot provided by imaging after stabilization and transport to the trauma center may provide clues to the cause of a neurologic deficit. In many cases, the cause will still be evident—cord compression due to severe canal stenosis, malalignment, displaced bone fragment, hematoma within the spinal canal, cord contusion, or edema.

Lateral Bending

Injuries due to lateral bending do not seem to be very common, but an occasional uncinate process or transverse process fracture may be detected by CT. Fracture involving the foramen transversarium brings a risk of dissection or occlusion of the vertebral artery and, with it, the possibility of stroke. A discussion of the workup of vascular injuries of the neck and head is included in Chapter 1 in the section on cerebrovascular disorders.

Pitfalls in Spine Imaging

One must become familiar with the normal pattern of development and congenital anomalies in children, such as os odontoideum, incomplete ossification of the neural arches, and pseudosubluxation in order to avoid false-positive diagnoses (Fig. 7-12).

Figure 7-12 Normal developmental anatomy—C2. A, Lateral radiograph in a small child was interpreted as prevertebral soft tissue swelling (arrowheads) and dens fracture (arrow). B, CT sagittal and coronal reformats show normal developmental anatomy—subdental synchondrosis (white arrow), neurocentral and neurodental synchondroses (black arrowheads). Tip of dens ossification center (ossiculum terminale) is not yet visible (white arrowhead). The apparent soft tissue swelling was due to normally lax tissues and phase of respiration. Note also the normal spheno-occipital synchondrosis (curved arrow).

It is often helpful to realize that abnormalities need to be evaluated in context. For example, not every malalignment is an acute one. Mild subluxations of the cervical spine are quite common due to chronic osteoarthritis. Therefore, analysis of the pattern of facet hypertrophy may provide confidence that the deformity is chronic. Dynamic testing with flexion-extension radiographs may support such a conclusion. On the other hand, sometimes it is necessary to call attention to a clearly chronic finding detected serendipitously. An os odontoideum that is well corticated but chronically unstable provides just one such example (Fig. 7-13).

Figure 7-13 Os odontoideum—unstable. A, Sagittal T1-weighted image of a teenager with headaches and visual scotomata revealed an anomaly of the cervicocranium (arrow). B, Sagittal reformat of cervical spine CT confirmed an os odontoideum and incomplete posterior arch of C1 variants. Flexion-extension radiographs demonstrated instability (not shown). Transient compression of the basilar artery related to instability was thought to be responsible for the visual changes. The patient is asymptomatic following C1-C2 fusion.

Injuries of the Thoracolumbar Spine

Although similar mechanisms of injury apply, differences in biomechanics between the cervical and thoracolumbar spine result in different patterns of findings. Compression fractures due to flexion are very common (Fig. 7-14). Osteoporotic compression fractures are common, with more than 700,000 occurring annually in the United States, with costs from treatment approaching $1.5 billion. While the majority may be considered stable, medical therapies required to treat the associated pain may lead to other serious complications. The increase in age-adjusted 5-year mortality approaches 25% for female patients. Use of alcohol and certain medications, including steroids, anticonvulsants, cytotoxic drugs, thyroid hormones, and heparin, may all be associated with osteoporotic compression fractures. Metastatic disease may predispose to the development of pathologic compression fractures. One fracture also increases the risk for development of other fractures due to altered biomechanics of the kyphotic spine. Vertebroplasty and kyphoplasty are minimally invasive spine procedures that are possible treatments for those patients who do not respond to an appropriate trial of conservative therapies. With more than 50% loss of anterior vertebral body height, disruption of the posterior longitudinal ligament may occur, leading to the possibility of instability.

Figure 7-14 Lumbar compression fracture. A, Lateral radiograph in a patient with calcaneal fractures after jumping from a roof. Slight anterior wedging of L1 vertebral body with a triangular fragment. B, CT sagittal reformat shows increased density of impaction zone. C, MR STIR sagittal image shows fracture fragment, marrow edema in impaction zone, and small prevertebral hematoma. Contrast these findings with the endplate irregularity and sclerotic changes at the inferior aspect of L4 vertebral body due to chronic degenerative disease.

Axial loading mechanism may result in a burst fracture. These fractures occur most commonly near the thoracolumbar junction but may also affect the mid- and lower lumbar levels. The extent of retropulsion of the posterior portion of the vertebral body, the relative size of the spinal canal, and the position of the conus medullaris are factors affecting the risk of neurologic injury. Screening exam of the thoracolumbar spine should be performed when calcaneal fractures result from a jump or fall from a height due to the high association of these injuries (Fig. 7-15).

Thoracic burst fracture. Sagittal T1-weighted image (left) and T2-weighted image (right) show retropulsion of the posterior portion of the T11 vertebral body resulting in cord compression. Cord T2 hyperintensity is consistent with edema. A contusion should be suspected based on the degree of compression; however, there is no T2 or gradient-echo hypointensity to confirm the presence of hemorrhage.

The combination of flexion and distraction, common in lap belt deceleration injuries, results in a rather unique pattern of findings. A horizontally oriented fracture plane through the intervertebral disc and posterior elements has come to be called the “Chance” fracture. Since there are many variations in terms of bony and ligamentous components, the term “Chance-type fracture” may be applied to these horizontal fractures most commonly affecting the upper lumbar spine (Fig. 7-16). The abdominal viscera should be carefully evaluated in patients with Chance-type fractures, since there is strong association with intestinal and solid organ injuries.

Figure 7-16 Chance-type fracture. Axial (left) and sagittal reformatted (right) images from a contrast-enhanced CT of the abdomen following a motor vehicle collision. Images show anterior wedge deformity of a lower thoracic vertebra. Note longitudinal (arrows) and horizontal (arrowheads) fracture planes and distraction of the posterior elements.

Hyperextension injuries may result in disc and anterior ligamentous injury or impaction fractures of the posterior elements. Patients with ankylosing spondylitis are particularly prone to extension injuries and may also develop horizontally oriented fractures through the vertebral bodies.

A type of injury unique to the thoracic region is rib dislocation. It is usually not found as an isolated injury. Spinal cord transection due to the guillotine effect of a displaced rib has been reported but is exceedingly rare.

Lumbar transverse process fractures due to avulsions by the paraspinal muscles are commonly detected in association with visceral injuries, sacral fractures, and pelvic fractures. When detected on plain films, CT of the abdomen and pelvis may be in order due to this association. Sacral fractures and sacroiliac joint disruptions are easily diagnosed by pelvic CT when displacement is gross. As with any other portion of the spine, subtle displacements may be easily overlooked. Insufficiency fractures of the sacrum are common in the setting of osteoporosis. Attention to the arcuate lines of the sacrum is important when reviewing plain films of the pelvis. Coccygeal fractures may be a source of persistent pain, with patients therefore presenting to the urgent care clinic. Plain film radiography is generally sufficient to assess this site of injury. Anatomic variations are common, many presumably the result of prior trauma.

Evaluation of Spinal Soft Tissue Injuries

Spinal Cord Injury

In some of the cases illustrated so far, findings of spinal cord injury (SCI) have been present. In each of these cases, there were injuries to the spinal column as well. Spinal cord injuries may also occur in the absence of injury to the spinal column. The acronym SCIWORA (spinal cord injury without radiographic abnormality) was coined in 1982. SCIWORA may be due to longitudinal distraction of the cord; in some cases, MR imaging may demonstrate evidence of the cause of spinal cord dysfunction due to hemorrhage or edema within the cord or from extrinsic compression or transection. SCI may be complete (complete loss of motor and sensory function) or incomplete (partial loss of sensory and/or motor function). Different constellations of neurologic dysfunction may result owing to the topographic organization of pathways, including anterior cord, central cord, and Brown-Séquard and conus medullaris syndromes. Cauda equina syndrome results from injury to spinal nerve roots. Spinal cord concussion is analogous to the cerebral transient ischemic attack.

Spinal cord edema appears as a zone of T2 hyperintensity almost immediately upon injury. Gross swelling of the cord may be very subtle. In many cases it may be possible to detect hemorrhage located centrally within the region of edema (a true contusion). This may appear relatively isointense or hypointense to normal cord with greater sensitivity on gradient-echo usually due to the presence of deoxyhemoglobin. Within a few days, T1 hyperintensity, and still later T2 hyperintensity, may develop due to the conversion to methemoglobin. Many authors have attempted to develop classification systems to predict functional outcomes based on MR imaging findings, and these have worked to varying degrees. Detection of a hemorrhage larger than 1 cm in longitudinal dimension and lack of resolution of signal abnormalities on follow-up imaging generally indicate the poorest prognosis for recovery. Normal cord signal or edema alone is more likely to be associated with better clinical outcomes. It should be noted that cord compression by bone fragments, disc, or hematoma is predictive of development of hemorrhage and is, therefore, the basis for early decompression by many spine surgeons.

Diagnosis of injury to any of the other soft tissue structures listed below can be based on T2 hyperintensity. In addition, anterior and posterior longitudinal ligaments may be displaced (elevated) or disrupted. Discs may be widened or extruded. Facet capsules may be widened and fluid-filled, or facets may be dislocated. Ligamentum flavum and interspinous ligaments may be disrupted. Cervical root avulsion as a cause of brachial plexopathy may present with abnormal enlargement of nerve root sleeve(s)—pseudomeningocele (Fig. 7-17).

Figure 7-17 Cervical root avulsion. Axial T2-weighted image in a patient with right brachial plexopathy following a motorcycle collision. Note the right-sided pseudomeningocele and nonvisualization of ventral and dorsal roots. Normal roots are indicated on the left side (white arrowheads).

Although MR is indicated primarily for evaluation of soft tissues, STIR sequence is especially well suited for the detection of bone marrow edema. Fractures may be detected as changes in shape of the vertebrae or linear hypointensities but are generally more easily detected using CT.

Spinal Hematomas

Hemorrhage within the spinal cord is most often the result of trauma. Spontaneous hemorrhage within the spinal cord (intramedullary hemorrhage) can result from intrinsic cord lesions, such as ependymoma or cavernous malformation, and may present with sudden onset of weakness of the extremities.

Hemorrhage can occur within the other compartments of the spinal canal, usually as a result of trauma but, on occasion, without provocation. The spinal epidural, subdural, and subarachnoid spaces are contiguous with their intracranial counterparts. Hematoma/hemorrhage can collect in these areas by extension or occur primarily within the spine. As seen in many of the figures demonstrating spine fractures and subluxations, epidural hematomas arise commonly in the setting of trauma, and, if they are causing cord or conus compression, emergent evacuation may prove beneficial. Emergency surgical evacuation is generally considered the standard treatment for patients with disabling and/or persistent neurologic deficit. A conservative approach under close neurologic observation may be suitable for patients with no, or mild, deficits, for patients who show early and continuous clinical improvement, and for patients with noncompressive epidural hematomas. Reported cases of spontaneous remission are very rare.

MR imaging features of spinal epidural hematoma include variable, often heterogeneous T1 and T2 signal intensity; capping of epidural fat; direct continuity with the adjacent osseous structures; compression of epidural fat, subarachnoid sac, and spinal cord; and usual posterolateral location in the spinal canal. Tapered appearance of the cerebrospinal fluid space due to extrinsic hematoma is usually apparent.

On the other hand, hemorrhage confined by the thecal sac must be within either the subdural or subarachnoid space. Differentiation of the three types of extramedullary spinal hemorrhage can sometimes be quite difficult. Extension into the neural foramen, beyond the expected confines of the thecal sac, is a sure indication that the hemorrhage is in the epidural space. Subarachnoid hemorrhage often collects in a uniform circumferential configuration around the spinal cord, mixes uniformly with cerebrospinal fluid and intermingles with the roots of cauda equina, and seeks a dependent position in the spinal canal. Spinal subdural hematoma is easiest to differentiate when the arachnoid mater and roots are displaced by a hematoma confined to the thecal sac (Figs. 7-18 to 7-20).

Figure 7-18 Spinal epidural hematoma—cord compression. This patient sustained an isolated C4 lamina fracture after a fall from a loading dock and developed right hand weakness following CT. A, Sagittal T2-weighted image shows an intermediate-intensity posterior epidural hematoma causing cord compression. B, Axial gradient-echo T2-weighted image shows the extent of cord compression.

Figure 7-19 Spinal subdural hematoma. Sagittal T1-weighted image and T2-weighted image and axial T1-weighted image demonstrate a long, lobulated intradural hematoma that displaces the roots of cauda equina. The hematoma is limited by the displaced arachnoid membrane.

Figure 7-20 Spinal subarachnoid hemorrhage. Sagittal and axial T2-weighted images show a hypointense fluid level within the subarachnoid space.

Advanced MR techniques are now being applied to spine imaging, with much research in the field of spinal cord injury. Diffusion-weighted and diffusion tensor imaging, MR spectroscopy, and functional imaging have great potential for future clinical applications. These techniques are not yet widely available. There are still many technical limitations to be overcome before they can be routinely applied.

Vascular Injuries of the Neck Associated with Spine Trauma

The spectrum of traumatic vascular injuries of the neck related to spine trauma and the imaging features are reviewed in Chapter 1.

NONTRAUMATIC SPINE EMERGENCIES

The spontaneous development of limb weakness, pain or paresthesia, and progressive inability to ambulate may be causes for presentation to the emergency department. In many cases, the history and physical exam localize the abnormality to the spine and prompt imaging is required to evaluate for the possibility of cord or root compression or an intrinsic process of the spinal cord. MR imaging is generally the modality of choice; the addition of gadolinium-enhanced sequences, especially with fat-suppression, to the routine protocols is often useful. The following brief review illustrates the spectrum of nontraumatic disorders and the common differential diagnoses to be considered.

Congenital Disorders

Although congenital/developmental anomalies and abnormalities are not likely to present emergently, they may be unknown until an unrelated acute event occurs. Occasionally, a Chiari I malformation may be found during a trauma workup. A preexisting syrinx should not be mistaken for an acute spinal cord injury. A tethered cord or lipoma of the filum terminale might be found in the process of workup for an acute episode of sciatica.

Degenerative Disease/Arthropathy

As mentioned in the section on spine trauma, underlying conditions resulting in narrowing of the spinal canal are often found in patients presenting with spinal cord injuries, sometimes resulting from rather minor trauma. There are many causes of canal stenosis, including routine spondylosis, ossification of the posterior longitudinal ligament (OPLL) ossification of ligamentum flavum, synovial cyst, and epidural lipomatosis. Underlying disorders such as these are often discovered in the setting of an acute disc extrusion that results in a new neurologic deficit. Degenerative disc disease is ubiquitous, and the imaging findings are generally straightforward. One should not be fooled by the T2 hyperintensity of a disc extrusion that simulates fluid or by a sequestered fragment displaced a considerable distance from the remainder of the disc. Gadolinium-enhanced images may help to identify root inflammation or arachnoiditis and differentiate granulation tissue (scar) from a recurrent disc extrusion in the setting of a postoperative patient presenting with recurrent symptoms. Familiarity with expected routine postoperative findings is important, but one must also be able to analyze features in a systematic fashion, for example, to determine if a cerebrospinal fluid leak/pseudomeningocele might be causing root compression (Fig. 7-21).

Figure 7-21 Postoperative pseudomeningocele—root compression. This patient developed progressive weakness 1 week after decompressive laminectomies for spinal stenosis. Sagittal (A) and axial (B) T2-weighted images show large fluid collection with signal isointense to cerebrospinal fluid, which causes root displacement and compression. Neurologic improvement followed repair of the leak.

Patients with rheumatoid arthritis may show a variety of findings, including laxity of the transverse atlantal ligament and atlantoaxial subluxation, vertical subluxation or erosion of the odontoid, or development of granulation tissue around the odontoid (pannus). Spinal cord compression can result from acute trauma or the combination of pannus and chronic instability.

Other arthritides such as amyloidosis or crystal pyrophosphate deposition may present with mass lesions or destructive changes of the spine, mimicking malignancy or infection (Fig. 7-22).

Figure 7-22 Calcium pyrophosphate disease—cord compression. Sagittal (A) T2-weighted image and axial (B) T1-weighted image show a soft tissue pannus related to the dens (asterisk) in a patient with “pseudogout” who developed symptoms of myelopathy as a result of chronic cord compression.

Neoplasms and Tumorlike Conditions

Tumors of the spine may be divided into intramedullary, and extramedullary intradural and extradural, categories. Development of symptoms is usually slowly progressive, but acute presentations due to inability to ambulate or incontinence, or related to hemorrhage, are not uncommon.

Extradural lesions are encountered most commonly, and these include the disc herniations and degenerative changes from arthritis and traumatic conditions already discussed. Metastatic disease makes up the majority of the neoplastic extradural masses, usually from carcinomas of the lung, breast, and prostate. Although metastasis to the bone with extradural extension is typical, metastasis to or primary involvement of the extradural soft tissues may also result in neural compromise. Lymphoma may present this way or by extension from the retroperitoneum through the neural foramen (Fig. 7-23). Vertebral involvement by multiple myeloma may present with an extradural mass or pathologic compression fracture (Fig. 7-24). Common osseous lesions such as aneurysmal bone cyst, osteoblastoma, osteochondroma, and Paget disease may occasionally present with symptoms related to cord compression. Chordoma, a destructive bone tumor arising from notochord rests, accounts for approximately 5% of primary bone tumors. Most commonly occurring in the sacrum, it may also arise in the clivus, cervical, or lumbar region. A large soft tissue mass, calcifications, and residual bone fragments are typical features.

Figure 7-23 Epidural lymphoma—conus compression. Sagittal pre- and postgadolinium T1-weighted images (left) show an enhancing extradural mass (arrowheads) that surrounds the conus medullaris in a patient with AIDS. Axial post-gadolinium T1-weighted image (right upper) and T2-weighted image (right lower) show tumor filling the neural foramina (arrowheads) and causing mild compression of the conus.

Figure 7-24 Multiple myeloma—cord compression. Sagittal pre- and axial postgadolinium T1-weighted images show a large mass arising within an upper thoracic vertebra with extraosseous extension that results in cord compression. Note the diamond shape of the cord (arrow).

Many tumorlike lesions may affect the spine. Hemangiomas are commonly found in the vertebral bodies on routine exams and are generally not cause for concern. Composed of thin-walled blood vessels and a variable amount of adipose tissue within the bony trabeculae, these lesions have signal characteristics determined by the relative amounts of vascular, bone, and fat components. They are usually slow-growing, benign lesions, but, occasionally, expansion of the vertebral body and extension of the lesion into the epidural space may compromise the spinal canal. Thoracic cord compression due to extramedullary hematopoiesis occurs rarely in patients with hematologic disorders, such as thalassemia. Notice of diffuse signal abnormality of the vertebral marrow may be important to making this diagnosis.

Extramedullary intradural masses include meningiomas, tumors of nerve sheath origin, metastases, and others. Meningiomas and nerve sheath tumors (schwannomas and neurofibromas) account for approximately half of all intraspinal neoplasms. These three lesions may be associated with neurofibromatosis (types I and II), but a description of the patterns of occurrence are beyond the scope of this review. Like their intracranial counterparts, spinal meningiomas are more commonly found in women, especially in the thoracic region. Schwannomas are found equally in males and females and occur throughout the spine. Secondary signs of bone remodeling may be seen due to these slow-growing lesions. Combined intradural-extradural or isolated extradural involvement of nerve sheath tumors and meningiomas occurs much less commonly than the usual intradural extramedullary form. Lipomas, dermoids, and epidermoids may occur in this compartment and occasionally have combined intramedullary involvement as well.

Extramedullary intradural metastatic disease more commonly arises from tumors of the central nervous system via cerebrospinal fluid dissemination. These include ependymoma, pineal tumors, and choroid plexus tumors. Seeding generally results in nodular lesions in the lumbosacral subarachnoid space. The majority of metastases via hematogenous spread are the result of lung and breast carcinoma and melanoma.

Intramedullary tumors account for approximately 10% of primary intraspinal tumors; the majority of these are gliomas (approximately 70% ependymomas and the rest astrocytomas). These may be indistinguishable by imaging; both may show enlargement of the cord and irregular T2 hyperintensity and enhancement, and have associated cystic changes or syrinx formation (Fig. 7-25). Ependymomas have a predilection for the conus medullaris and a tendency to bleed. Slow-growing primary lesions may cause expansion of the spinal canal, scalloping of the posterior margins of the vertebral bodies, and pressure atrophy of pedicles. Other intramedullary tumors include hemangioblastoma, medulloblastoma, and metastatic disease from pineal or other intracranial site.

Figure 7-25 Ependymoma. Sagittal T2-weighted image and post-gadolinium T1-weighted image show a multiseptate fluid collection that expands the thoracic cord with a solid enhancing nodule (arrow). This 45-year-old female presented with progressive difficulty ambulating.

Inflammation/Demyelination

Multiple sclerosis (MS) may be the first disorder that comes to mind in this category. The cause of this disorder, characterized by breakdown of the myelin sheath and inflammation, is unknown. Spinal cord plaques tend to occur most frequently in the cervical region and show imaging features similar to those found in the brain—T1 iso- to hypointense, T2 hyperintense—and may enhance following contrast administration (Fig. 7-26). The cord may be swollen due to active inflammation. Lesions in different states of activity and the presence of lesions in the brain add to confidence in the diagnosis of MS. Cord atrophy and lack of enhancement may be expected in the chronic phase.

Figure 7-26 Multiple sclerosis. Sagittal and axial T2-weighted images show patchy hyperintensities throughout the entire spinal cord. None of the spine lesions showed abnormal enhancement. The post-gadolinium axial T1-weighted image of the brain in the same patient shows an enhancing plaque in the periventricular white matter (arrow).

Imaging features of myelitis are nonspecific and include T2 hyperintensity, swelling, and variable enhancement. Idiopathic inflammation of the cord (transverse myelitis) or inflammation due to connective tissue disorders (lupus, rheumatoid arthritis, etc.) may have the same appearance. Postinfectious demyelination is sometimes the cause. Follow-up may be necessary to differentiate these disorders from a spinal cord neoplasm.

Sarcoidosis is a noncaseating, granulomatous disease that may affect the brain and spinal cord. Simultaneous involvement of the cord and meninges may help to distinguish it from other causes of myelitis. Of course, other granulomatous processes such as tuberculosis would have to be considered.

Guillain-Barré syndrome, an acute inflammatory demyelinating neuropathy, and a chronic form (CIDP) may present with ascending progressive muscle weakness, areflexia, and other symptoms including cranial neuropathy. Enhancement of lumbosacral roots, especially isolated involvement of ventral roots, may be detected by MR imaging.

Infection

Abscess formation within the spinal cord (intramedullary) is extremely uncommon, usually occurring secondary to spread from another location. Intravenous drug use and HIV infection are risk factors.

On the other hand, meningitis is extremely common. Of the infectious cases, viral infection is most common, with bacterial, fungal, and parasitic making up the rest. Noninfectious causes include nonsteroidal anti-inflammatory medications and antibiotics. Neoplastic causes are mentioned below. Imaging is generally reserved for complex cases, such as those with localizing neurologic deficits or those that do not respond to therapy, in order to locate a parameningeal focus of infection. Thickened enhancement of meninges and nerve roots may be seen.

Epidural (bacterial) abscess may arise via hematogenous route or from direct extension of discitis/osteomyelitis or other paraspinal source (Fig. 7-27). Staphylococcus aureus is the most common organism, and risk factors include spinal instrumentation, intravenous drug use, immunodeficiency, diabetes, renal failure, alcoholism, and malignancy. Because of the loose connection of the dura to the spine, infection may spread along multiple contiguous levels. Lumbar and cervical regions are most commonly affected. On MR, this appears as a rim-enhancing, tapered fluid collection that displaces the dura. The collection may be located anteriorly, posteriorly, or circumferentially around the thecal sac and may cause compression of the spinal cord or cauda equina. The term “phlegmon” may be applied to an enhancing inflammatory mass without a central fluid collection. Definitive treatment is surgical, although mild cases without a focal neurologic deficit may be treated with antibiotics and careful monitoring. Determination of the cranial and caudal extent of the infection is imperative prior to any planned intervention.