Radiographic Diagnosis of Radiculopathy

MRI effectively demonstrates the bony architecture of the spine, the contours of the intervertebral disk, the paraspinal soft tissues, and the contents of the spinal canal. Various MRI sequences can be used to confirm disk herniation and visualize degenerative or traumatic changes, such as annular tears and end-plate edema. Changes that would suggest the presence of a radiculopathy include foraminal narrowing as well as a decreased amount of adipose tissue surrounding neuroforaminal nerve roots and dorsal root ganglia.

Computed tomography (CT) myelography, a fluoroscopic procedure in which a water-soluble contrast medium is injected into the spinal canal, followed by CT imaging of the spine, may also help with localization in that it can further delineate the extradural, bony and paraspinal tissues, especially in patients who have undergone previous spine surgery, resulting in technical artifacts that can obscure the MRI.

The cervical region has little, if any, epidural fat, and frequently only a small fragment of disk is enough to cause severe nerve root compression. Because of the lack of epidural fat and the small size of disk herniations, CT is less effective than myelography for diagnosing cervical radiculopathy. In disk herniation, myelography commonly demonstrates displacement of the dural sac, impaired filling or displacement of an axillary sleeve, or nerve root swelling.

When either MRI or CT myelography fails to suggest a clear-cut diagnosis, the other procedure should be considered. CT myelography may be more effective in patients with a prior history of spine surgery and metal hardware placement or when MRI is contraindicated, as when the patient has an internal cardiac pacemaker.

In the cervical region, CT and myelography are complementary. The combination of both studies clearly shows the nature and degree of spinal cord distortion, which is valuable in determining the proper treatment. The diagnosis of cervical spinal nerve root avulsion from traction injury of the arm is best visualized with a combination of CT and myelography; imaging identifies the diagnostic leakage of cerebrospinal fluid (CSF) into the neuroforaminal and extraspinal space.

Clinical localization of cauda equina compression may be difficult. In this case, MRI of the lumbosacral spine (LS) is helpful in localizing the compressive lesion. In the majority of patients with cauda equina compression related to disk disease, the MRI will demonstrate extensive disk material occupying over one third of the intraspinal canal space. CT myelogram may also demonstrate a myelographic block, the degree of which can help quantitate the severity of neural compression and be monitored in several different patient positions.

However, MRI is the test of choice because it is more rapidly performed with minimal risk of complications; characterization of the LS spine with MRI in conjunction with the clinical picture may be sufficient for planning surgery.

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