What is it?
A myelogram is an older test that is still used to examine the spinal canal and spinal cord. A special dye is placed into the spinal sac that shows up on X-rays to indicate any abnormalities. Before there were CT scans and MRI scans, the myelogram was the best test to determine the cause of pressure on the spinal cord or spinal nerves. Today the myelogram is used only for very special purposes, such as for complicated revision spine surgeries. It is sometimes used if your doctor suspects you have a herniated disc.
Why is it done?
The dye used during a myelogram outlines the spinal cord and nerve roots. This helps your doctor determine whether there are any unusual indentations or abnormal shapes in the spinal cord. Anything that is pushing into the nerves shows up as an indentation into the spinal sac. This indentation could be from a herniated or bulging disc, a tumor, or an injury to the spinal nerve roots. The myelogram is useful for patients who have metal plates and screws in their spine, which prevents them from having either a CT or MRI scan.
How is it done?
The doctor must perform a spinal tap to inject dye into the spinal sac. The dye mixes with the spinal fluid so the fluid shows up on X-rays. You will be asked to lie on a tilting table while multiple X-rays are taken to show the flow of the dye through the spine. The myelogram is usually combined with a CT scan to get a better view of your spine in cross section and to check the health of your bones and nerves.
What are the limitations?
A myelogram does not show the soft tissues. It shows only the bones and the spinal fluid where the dye has mixed with the fluid.
What are the risks?
Because the myelogram requires a spinal tap, there are more risks associated with it than most other tests. This is one reason that doctors prefer to use “noninvasive” tests first, such as the MRI and CT scan. The risks associated with a spinal tap include meningitis (infection of the spinal fluid), spinal headache, and allergic reaction to the dye. There is also a very small chance that the needle will cause bleeding around the spinal sac. The myelogram requires X-rays, which use radiation. Large doses of radiation can increase the risk of cancer. The vast majority of patients who have X-rays taken will never get enough radiation to worry about cancer. Only patients who have large numbers of X-rays – hundreds over many years – need to be concerned.
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.