Diagnostic Imaging

Certainly one of the real dilemmas facing the clinician in the ED is which patient requires evaluation for a potential spinal cord injury ( Flg.,.,2..4,8,-,8). A multiplicity of examinations exists. Blind application of expensive diagnostic testing risks inappropriately increasing the cost of medical care and potentially rendering resources unavailable to other patients. Diagnostic testing must evaluate the possibility of injury to both bone and spinal cord. While these often occur in concert, this is not always the case. While one would always like to limit diagnostic testing to those who require it, the consequences of a missed spinal cord injury can be devastating. Removing a collar or allowing a patient to walk with an unstable spine risks converting a patient with no spinal cord injury to one with a complete level. Thus, it is prudent to completely image and evaluate all patients with the possibility of spinal cord pathology.

FIG. 248-8. Algorithm for blunt spinal trauma.

In general, an x-ray of the cervical spine is part of the standard triage for blunt trauma. The utility of plain films of the cervical spine over the clinical examination to identify injury in patients who are alert, oriented, and have no neck or back pain is questionable. 1819 Many centers have abandoned use of cervical spine x-rays in such patients. There is a substantial difference, however, in patients who are not alert and awake. The frequency of cervical spine injury in association with blunt head trauma is about 2 to 5 percent. However, it increases to almost 9 percent in patients with significant head injury, defined as a Glasgow Coma Scale score <10. 20

Plain x-rays are clearly indicated in all patients with neck pain or cervical tenderness. The presence of pain or tenderness has over an 80 percent sensitivity for cervical spine injury. Cervical spine injury is very unusual in patients without pain or tenderness but may occur in approximately 1 percent. 19 Thus, the mechanism of injury should also be taken into account when the decision is made whether to image a patient's cervical spine. In a study of 233 patients, nine variables correlated significantly with cervical spine injury. They were: falls, symptoms of numbness, sensory loss, weakness, neck spasm, neck tenderness, objective sensory and motor loss, and weakness or loss of anal sphincter tone. Correlation of cervical injury with involvement in a motor vehicle crash approached statistical significance. 21 Unfortunately, there are significant limitations to the study that do not allow accurate assessments. Apart from a paucity of patient-related information, the study appears to show that falls greater than 10 ft are not significantly associated with spine injury. The question of how much force is required before cervical spine injury is likely remains largely unanswered at this time, but studies are underway to develop decision guidelines.

The "gold standard" for the identification of bony cervical injury includes three views of the cervical spine: AP, lateral, and odontoid. They allow for imaging of the entire cervical spine. It is important that all seven cervical vertebrae be imaged, including the junction between the seventh cervical and the first thoracic vertebrae. A single lateral cervical spine film is important as an initial screening radiograph. It will identify 90 percent of injuries to bone and ligaments. Cervical immobilization must be maintained until the patient also has an AP and open-mouth odontoid view. If the initial lateral view is normal and the patient is neurologically intact, the AP and open-mouth views can be delayed until other injuries are adequately stabilized. The combination of lateral, AP, and odontoid views is generally adequate to identify or at least raise the suspicion of cervical spine injury.

Visualization of the entire cervical spine often can be problematic. Patients' body habitus or the presence of upper extremity injuries may limit the clinician's ability to pull on the arms, a maneuver necessary to visualize all seven vertebral bodies. An alternative is a swimmer's view, which is aimed through the axilla in an attempt to image the lower cervical spine. Oblique views (45°) can also be obtained. These views have the added advantage of showing the neural foramina well. They demonstrate the pedicles as well as the laminae, which should stack like shingles on a roof. A newer technique is CT scanning of the cervical spine which can visualize the entire cervical spine well but not the atlantooccipital junction.

Patients can have cervical spine injury even with normal plain films. In fact, a normal lateral cervical spine film may only identify 90 percent of significant bony and ligamentous injuries. The film must be examined for the presence or absence of prevertebral swelling. The prevertebral space anterior to C3 should be less than 5 mm. The predental space should be less than 3 mm. The open-mouth odontoid view will identify many of the remaining abnormalities. 22 Still, plain films of the neck may not identify patients with pure ligamentous injuries. In these patients, ligaments are disrupted but the spine spontaneously reduces to a normal position. Motion, however, risks neurologic injury.

Flexion and extension views demonstrate the degree of spinal column stability. In general, these views are obtained when patients have pain or tenderness but normal plain films.23 They can only be obtained in a fully awake, unsedated cooperative patient. The patient carefully and slowly flexes and extends the neck. Motion should be limited by increasing pain or the appearance of any neurologic symptomatology. A stepoff of 3.7 mm or an angulation of greater than 11° denotes cervical spine instability.24 It is possible to have ligamentous injury even with normal flexion/extension films, since muscle tone can splint the bones in a stable configuration. Most patients in this latter category note pain improvement with analgesics after a few days. Reliable patients without a substantial mechanism of injury with persistent pain but normal radiographs, including flexion/extension views, can be discharged in a hard collar with outpatient follow-up. Most patients' symptoms will resolve over a few days. A patient with persistent symptoms will require additional outpatient workup. Unreliable patients or those with a significant mechanism of injury or risk factors, such as advanced age, should undergo MRI.

Plain films of the thoracic and lumbar spine are the initial examinations generally utilized to image these spinal levels. Many of the same principles used for cervical spine imaging are important for thoracic and lumbar imaging. All patients with a mechanism of injury, those with complaints of back pain, and those who have tenderness on physical examination must be assumed to have a fracture of the thoracic or lumbar spine. They must be kept immobilized. AP and lateral films are generally obtained and examined for abnormality. In general, the lateral x-rays are much more easily obtained with patients still on a backboard. Skin breakdown and pressure sores can develop very quickly, particularly in obese patients. Our goal is to remove patients from the backboard in less than 2 h. Patients can then be nursed supine in a bed as long as they are logrolled. A standard hospital mattress provides adequate spinal support. However, patients must be carefully moved and care must be taken to keep spinal immobilization complete in transfers from bed to stretcher. It may be helpful to place patients back on a backboard for the transportation phases of their care. Alternatively, a scoop stretcher may be used for transport.

It can be difficult to image the upper thoracic spine adequately, even if maximal power of the x-ray beam is used. One alternative is to clear the reliable patient by physical examination. Unreliable or unexaminable patients with a concerning mechanism should be log-rolled until they become examinable. Patients with point tenderness and normal films are a special subset. CT scanning can be useful in this subset, though the yield is low. The thoracic spine has inherent stability from the rib cage. Few fractures in these patients will be unstable. Alternatively, patients can be treated with analgesics and investigated selectively if symptoms persist.

More recently, CT has assumed a much more important role in the imaging of spine injuries. Plain films can be imperfect and may miss a number of such patients. Newer-generation helical scanning is rapid, and CT allows for a complete three-dimensional imaging of bony structures. CT scanning is indicated in almost all patients with proven bony spinal injury, as it allows for more precise anatomic description of the fractures. CT can reveal the exact anatomy of an osseous injury and the extent of spinal canal impingement by bone fragments. CT is vital in helping to determine the stability of an injury. CT scans are indicated for all patients with subluxations or fractures that can be seen on plain films. CT scans are also useful in patients with neurologic deficits but no apparent abnormalities on plain films, those with severe neck or back pain and normal plain films, and those in whom the thoracic and lumbar spine should be examined to define the anatomy of a fracture and the extent of impingement on the spinal canal. CT is especially useful when the lower cervical spine cannot be adequately visualized on plain films because of overlying soft tissues.

MRI is not as sensitive as CT for picturing bone injuries precisely. On the other hand, MRI is superb at defining neurologic, muscular, and soft tissue injury. It is the diagnostic test of choice for describing the anatomy of nerve injury. Entities such as herniated disks or spinal cord contusions are easily seen on MRI. Many of these require only supportive therapy. However, some require acute surgical intervention. Early identification helps plan therapy. MRI may also be used to identify ligamentous injury and it is indicated in all patients with neurologic symptoms or physical findings but no clear explanation on plain films and/or CT scanning.

MRI is indicated and should be part of the ED workup in patients with neurologic findings with no clear explanation following plain films and CT scanning. CT myelography is an alternative when MRI is unavailable and immediate diagnosis of a neurologic lesion is required. If the patient is neurologically stable and MRI is unavailable, delayed MRI and/or transfer to a tertiary care facility may be appropriate.

The determination of a spinal column injury at one level should prompt imaging of the remainder of the spine. Approximately 10 percent of patients with one spine fracture will have a second fracture. Often plain films will suffice, but multilevel CT scanning and/or MRI may be necessary to investigate such patients completely.

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