A Patient's Guide to Myelograms of the Spine

What it is: A myelogram is an older test that is used to examine the spinal canal and spinal cord. Before the CAT scan and then the MRI scan, the myelogram was the best test to determine whether there was pressure on the spinal nerves from various causes. During this test, a special X-ray dye is placed into the spinal sac. Today, the myelogram is still used for very special purposes, but it is not normally the first test that is used if your doctor suspects you may have a herniated disc.

What the test shows: The special myelogram dye shows up on X-rays. Multiple X-rays are taken during the myelogram. The dye outlines the spinal cord and nerve roots. Anything that is pushing into the nerves shows up as an indentation pushing into the spinal sac. This indentation could be from a herniated or bulging disc, lesions, tumors, or injury to the spinal nerve roots. The myelogram is often combined with a CAT scan to get a better view of the spine in cross section.

What the test does not show: The test uses X-rays and dye. It does not show the soft tissues directly (unlike the MRI scan). It shows only the bones and the spinal fluid where the dye has mixed with the fluid. The test is good when there have been metal plates and screws inserted around the spine that may make the CAT scan and the MRI scan hard to obtain.

How the test is done: To conduct the test, the doctor must perform a spinal tap and inject dye into the spinal sac. The dye mixes with the spinal fluid so that the spinal fluid will show up on X-rays. The patient lies on a tilting table, and as the table tilts, the movement of the dye shows the outline of your spinal sac. X-rays are taken as the patient is titled to show the flow of the dye through the spinal region, and the dye helps doctors determine if there is any unusual indentation or an abnormal shape.

What risks the test has: A myelogram requires a spinal tap. This test has more risks associated with it than most other tests. This is one of the reasons that doctors prefer to use the "non-invasive" tests, such as the MRI and CAT scans, first. The risks associated with a spinal tap include: infection of the spinal fluid (meningitis), developing a spinal headache, and having an allergic reaction to the dye. Myelograms are done using X-rays. X-rays use radiation, which in large doses can increase the risks of cancer. The vast majority of patients who get X-rays will never get enough radiation to worry about cancer. Only patients who must have multiple X-rays (hundreds) over many years need worry about this risk.

What the test costs: A myelogram of the spine usually has several costs associated with the test. The first cost is the fee for actually doing the test. This is called the "technical fee". The second cost is the fee of having a specialist, such as a radiologist, read and interpret the test. This is called the "professional fee". There may also be laboratory tests done on the fluid removed during the spinal tap. You may get several bills for this test, including: one from the hospital or clinic where you had the myelogram done, one from the specialist who read the test, and possibly one for the lab tests.

Copyright © 2003 DePuy Acromed.

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