Spine Imaging - Indications and choice of procedure

By Edward Escott, M.D.

There are a number of reasons to image the spine, but back pain with or without neurologic symptoms is by far the most common reason that these studies are requested. Because of this, the American College of Radiology has developed specific recommendations regarding the use of imaging based on numerous studies. Their conclusions are that uncomplicated low back pain is usually self-limited and requires no imaging. Patients who have a history of trauma, are at risk for infection, are elderly, have osteoporosis or a history of cancer represent a sub-group which may require imaging. This can begin with plain x-rays, particularly if there is a history of trauma. MR scanning is predominantly useful for patients presenting with neurologic symptoms (radiculopathy, cauda equina syndrome, symptoms of cord compression or myelopathy) or signs of infection. In the latter case, it is generally most helpful to do the study with contrast. Contrast is otherwise only needed for evaluation of the post-operative spine, subarachnoid spread of neoplasm or a lesion with the spinal cord or canal, such as a neoplasm or inflammation (myelitis). Contrast is used in the post-operative lumber spine to differentiate residual or recurrent disc herniation from scar (epidural fibrosis).

The timing of studies (i.e. emergent or scheduled) depends on the clinical status of the patient. A study is only truly an emergency if the surgeons deem the patient in need of immediate surgery or if radiation therapy is to be done imminently. Generally the studies can be scheduled during regular working hours unless these conditions exist.

Chronic back pain and symptoms of spinal stenosis or radiculopathy are best evaluated with MR imaging. CT scanning can be performed if there is a question with respect to the bony structures, or as a problem solving technique if questions are raised on the MR scan. CT can also provide evaluation if the patient has contraindications to MR, such as implanted electronic devices, MR-incompatible aneurysm clips or metal in the eye. CT myelography can occasionally provide additional information or evaluation in the patient who can not have MR and the non-contrast CT scan did not provide adequate information. A conventional myelogram, performed with fluoroscopy is generally only used if the patient has hardware in place which would create too much artifact on CT or MR. Some metallic hardware, particularly if it is titanium, can cause surprisingly little artifact, so it may be worthwhile to attempt an MR first, particularly if the area of concern is above or below the hardware.

In trauma, plain films are always indicated as the first study performed in the symptomatic patient, in the patient who can not be examined due to impaired sensorium or in the patient with multiple injuries. The asymptomatic patient who is alert generally does not require a screening study according to the American College of Radiology appropriateness criteria. If the patient is symptomatic with normal plain films, MR can be obtained to evaluate for spinal cord injury. If there is localized pain and there is a high concern for a fracture that may have not been seen on the plain films, occasionally a CT can be helpful. Remember that acute fractures can often not be seen well on MR and they could potentially be missed if this were the only procedure performed. For suspected ligamentous injury without fracture, flexion and extension plain films can be helpful.

In summary, imaging of the spine can provide important information. The choice and timing of studies depend on the particular clinical situation, as discussed briefly above. For more information, the reader is directed to the ACR appropriateness criteria, which can be found at http://www.acr.org/f-products.html.