Imaging of the Spine: Radiology Technique Selection

TECHNIQUE SELECTION

A great many clinical circumstances may necessitate spine imaging. The purpose of this section is to convey a sense of which techniques would be most appropriate for the given clinical setting. In some instances, the choice is clear. In others, the test to be performed is determined by the tech-nology available, and often the decision is influenced by thepreferences of the person ordering the test. In some clinical settings, more than one imaging modality is acceptable as a first test. If the clinician consults with the radiologist be-fore deciding on the initial test, unnecessary examinations may be avoided. Perhaps most importantly, however, if the clinician consults with the radiologist and conveys to him or her the clinical information, imaging often can be tailored to hone in on the most likely site or type of abnormality.

Still, general guidelines can be established to help decide which imaging test is appropriate. What follows is a brief outline providing general imaging recommendations for common clinical problems related to the spine. Only rarely is a particular test the only useful one for a suspected ab-normality. In many cases, any of the modalities would be useful as a baseline examination, with the understanding that additional imaging might be required to answer all clinical questions.

Trauma

Plain films still are used as an initial examination for the eval-uation of spine trauma in stable and alert patients. This is fol-lowed by CT scan, especially if other parts of the body are being assessed, the patient has altered consciousness, or the clinical examination is positive or equivocal. In the character-ization of complex fractures, for conditions in which plain films were inadequate (eg, the cervical thoracic junction), or when additional information is required (eg, to rule out canal compromise by a bone fragment), CT is the best imaging study. In certain circumstances, such as suspected spinal cord injury (contusion or transaction), hemorrhage within the spinal canal, or ligamentous injury, MR imaging is indicated. It is also useful in evaluating the patient with delayed onset of neurological dysfunction after trauma to rule out myeloma-lacia (softening) of the spinal cord or posttraumatic syrinx.

Back Pain

Back pain is one of the most common medical complaints. Though most cases are caused by muscle strains, new or per-sistent severe pain, sciatica (a shooting pain down the leg), or neurologic deficits such as weakness, decreased sensation, or abnormal reflexes should prompt a search for an underlying structural abnormality. The most common pathologic condi-tions are related to bony degenerative disease (osteoarthritis) or intervertebral disk abnormalities. Though disk herniations (protrusion or extrusion of the nucleus pulposus beyond the annulus fibrosus) are not visible on plain films, degenerative changes are generally quite apparent, and any unsuspected le-sions such as compression fractures or metastatic disease (both of which are common in older patients) may be de-tected. For patients with a suspected herniated disk, MR im-aging is the most sensitive examination. CT when combined with intrathecal contrast (CT myelography) is still a good ex-amination for the detection of disk herniation, and it can be useful in patients who are unable to obtain an MRI. MRI is most sensitive for detecting disk abnormalities and is espe-cially useful for the identification of other pathologic condi-tions that might mimic disk herniation, such as lesions of the conus medullaris or metastatic disease. A possible exception to the use of MR imaging as a first-line cross-sectional imag-ing procedure in degenerative spine disease is for patients suspected of having foraminal nerve impingement by an os-teophyte. Osteophytes are small, sharp projections of bone that occur in patients with osteoarthritis, and they may im-pinge on the spinal cord or nerve roots. Such osteophytes in the cervical spine may be difficult to characterize with MR imaging unless special sequences are employed. However, it is not always possible to differentiate clinically between patients who have disk herniations and those whose nerves are com-pressed by osteophytes, and MR imaging is the best test to order for these patients.

Myelopathy

In patients who are suspected of having a myelopathy (a true cord syndrome as opposed to radicular symptoms), MR imaging is unequivocally the first study to be per-formed. MR imaging is the only imaging procedure that al-lows direct visualization of the spinal cord, and it is effective for diagnosing or excluding primary spinal cord lesions such as infarct, tumor, hemorrhage, or inflammatory condi-tions (eg, multiple sclerosis, idiopathic transverse myelitis, or sarcoidosis).

Congenital Spine Lesions

A variety of congenital lesions may affect the spine. Plain films may be useful to initially survey the spine, but ulti-mately MR imaging is the modality of choice. Multidetector CT with multiplanar reconstruction abilities is gaining use-fulness in evaluation of bone lesions and defects.

Metastatic Disease

If metastatic disease in the spine is suspected, plain films are an economical way to carry out a preliminary evaluation for bony lesions. However, plain films do not demonstrate such abnormalities until a significant amount of destruction has taken place. MR imaging, on the other hand, is quite sensitive to replacement of normal bone marrow by tumor and can es-tablish the diagnosis much earlier. Addition of gadolinium-enhanced MR imaging improves detection of bone lesions and of intraspinal spread of tumor to the subarachnoid space (carcinomatous meningitis or leptomeningeal carcinomato-sis), if this is suspected clinically.