What is it?
A discogram is an enhanced X-ray examination designed to look specifically at theintervertebral discs in the spine. Dye is injected into the center of the injured disc(s) to make them clearly visible on X-ray film and on a fluoroscope, which is a special X-ray TV screen.
Why is it done?
The discogram is used to identify a disc or discs in the spine that have structural damage that may be causing pain. It can show whether a disc has begun to rupture and whether it has tears in the tough outer ring, called the annulus. 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.
A discogram 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. The discogram is usually done prior to surgery to help the doctor determine the location of the problem and the type of operation that may be needed.
How is it done?
You will be given medication to help you relax. A local anesthetic is then applied to numb the area of the back to be tested. A long needle is inserted from the back into the nucleus pulposus , which is the very center of the intervertebral disc. A fluoroscope makes it possible for the doctor to see your spine and the needle as it moves. The doctor will watch the fluoroscope screen as the needle is inserted to make sure it goes into the correct disc space. Once the needle is inside the disc, a small amount of fluid is injected to cause an increase in pressure within the disc. More than one disc is tested to determine which levels are normal.
If the discogram causes pain that is similar to the back or leg pain you are experiencing, it is a good indication that the doctor has located the disc that is causing problems. Dye is then inserted into the disc, and X-rays are taken. Commonly, a CT scan is also done to see a cross section of the disc. The discogram procedure lasts about 40 minutes.
What are the limitations?
The discogram does not show the bones or nerves very well. It only shows the inside of the intervertebral disc.
What are the risks?
The discogram has more risks associated with it than most other tests used to diagnose spinal problems. For this reason, doctors prefer to use “noninvasive” tests first, such as the MRI and CT scan.
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.