What is it?
A discogram is an enhanced X-ray examination of the intervertebral discs. Dye is injected into the center of the injured disc(s). The dye makes the disc clearly visible on X-ray film and on a fluoroscope (special X-ray TV screen).
Why is it done?
This test is used to determine which disc has structural damage and whether it is causing pain. A discogram can show if a disc has begun to rupture and if it has tears in the tough outer ring (the annulus). By injecting fluid into the disc to increase pressure, the doctor can tell if it is painful. This type of structural damage is a primary cause of pain within a damaged disc. Normal discs, and even those that are severely degenerated, do not usually cause pain. This test is usually done prior to surgery to help the doctor know the location of the problem and the type of operation needed.
How is it done?
You will be given medication to help you relax. A local anesthetic is applied to numb the area of the back to be tested. A long needle is inserted from the back. It goes into the nucleus pulposus (the very center of the intervertebral disc). The fluoroscope makes it possible for a doctor to see on the screen your spine and the needle as it moves. The doctor watches the screen as the needle is inserted to make sure it goes into the correct disc space. Once the needle is inside the right disc, a small amount of fluid is injected to cause an increase in pressure. More than one level is tested to determine which levels are normal. If this test causes pain that is similar to your back or leg pain, it is a good indication that the disc is causing problems. Dye is inserted into the disc, and then X-rays are taken. Commonly, a CT scan is also done to see a cross section of the disc. The procedure lasts about 40 minutes.
What are the limitations?
The discogram does not show the bones or nerves very well-only the inside of the intervertebral disc. This test is not frequently used. It is usually done after an MRI fails to show a herniated disc. Doctors also rely on the discogram when disc surgery is being seriously considered.
What are the risks?
The risks associated with a discogram include infection inside the disc and an allergic reaction to the dye. Discograms require X-rays, which use radiation. In large doses, 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 must have large numbers of X-rays-hundreds-over many years need to be concerned. This test has more risks associated with it than most. This is one reason that doctors prefer to use "noninvasive" tests first, such as the MRI and CT scan.