Magnetic resonance imaging (MRI) is often the first imaging exam done to evaluate the spinal cord and nerve roots. However, on occasion, a patient has a medical device, such as a cardiac pacemaker, that may prevent them from undergoing MRI. In such cases, a myelogram is performed to better define abnormalities.

Myelography is most commonly used to detect abnormalities affecting the spinal cord, the spinal canal, the spinal nerve roots and the blood vessels that supply the spinal cord, including:

Whether a herniation of the intervertebral disc between the successive vertebral bodies is compressing the nerve roots or the spinal cord. to depict a condition that often accompanies degeneration of the bones and soft tissues surrounding the spinal canal, termed spinal stenosis. In this condition, the spinal canal narrows as the surrounding tissues enlarge due to the development of bony spurs (osteophytes) and thickening of the adjacent ligaments.

Myelography can also be used to assess the following conditions when MR imaging cannot be performed, or in addition to MRI (when additional information is necessary):

• Tumors involving the bony spine, meninges, nerve roots or spinal cord
• Infection involving the bony spine, intervertebral discs, meninges and surrounding soft tissues
• Inflammation of the arachnoid membrane that covers the spinal cord
• Spinal lesions caused by disease or trauma

Myelography can also assist with surgical planning decisions. In patients with spinal instrumentation (screws, plates, rods, etc.), MR imaging may not be optimal because of artifacts generated by these instruments.