A discogram is an X-ray examination of the intervertebral discs. The test is performed by injecting dye into the center of the injured disc(s). The dye makes the disc clearly visible on X-ray film and a fluoroscope screen.
What the test shows:
This test is used to determine which disc(s) are damaged and if those discs are causing pain. This test will show if a disc has begun to rupture and will show if the disc has tears in the tough outer ring called the “annulus”. By injecting fluid to increase the pressure in the disc, the doctor can tell if the disc is painful. This is sometimes helpful in determining exactly which disc is causing the pain.
What the test does not show:
The discogram is not a test that is done frequently. Usually the test is done after an MRI if the MRI fails to show a herniated disc. The discogram is normally done when surgery is being seriously considered, because the pain has not responded to treatment, and there is no evidence that the disc is actually herniated. The discogram does not really show the bones or the nerves that well - only the inside of the intervertebral disc.
How the test is done:
A discogram is done by inserting a long needle into the center of the intervertebral disc itself - into the nucleus pulposus. The needle is inserted from the back. During a discogram, you will first be given medication to help you relax, and then a local anesthetic in the skin around the area of the back where the needle will be inserted. The doctor watches on a fluoroscope as he inserts the needle to make sure it goes into the correct disc space. The fluoroscope is a special X-ray TV that allows the doctor to see your spine and the needle as it moves. Once the doctor is sure the needle is in the disc space, he will inject a small amount of fluid to cause pressure in the disc space. If this causes pain, it is a good indication that the disc is abnormal. Dye is then inserted into the disc that will show up on X-rays. The X-rays are taken, and generally, a CAT scan is done as well, to see the disc in cross section. The procedure usually lasts about 40 minutes.
What risks the test has:
A discogram requires a needle to be inserted into the disc. 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 scan, first. The risks associated with a discogram include infection of the disc space, as well as an allergic reaction to the dye. Discograms 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 risks the test has:
A discogram requires a needle to be inserted into the disc. This test has more risks associated with it than most other tests. This is one reason that doctors prefer to use the “non-invasive” tests, such as the MRI and CAT scan, first. The risks associated with a discogram include infection of the disc space and an allergic reaction to the dye.