One possible cause of back and leg pain is compression of the spinal cord or nerve roots. Neck or back myelography is a diagnostic test that produces an image to help your doctor determine if anything is compressing nerves.
Nerve compression may be caused by bone, disc, scar tissue, tumor, infection, cysts or other structures. The spinal nerves are enclosed in a thin covering, or sac, called the dura. During a myelogram, a doctor injects a dye inside the dura. The dye is a material that can be seen on x-rays. If there is tissue altering the flow of the dye into the regions where it normally spreads, this may indicate that nerve tissue is compressed.
Myelography is used to evaluate several types of spinal conditions including stenosis or other conditions where nerve root compression is suspected.