This test is similar to a myelogram and uses contrast dye to better visualize the spinal canal and nerve roots in the spine. It may be used to help diagnose back problems such as spinal stenosis, particularly in patients with pacemakers or others who cannot have an MRI. The physician applies a numbing medication to the skin, which may sting for several minutes. Following application of the topical anesthetic, a small sample of spinal fluid is removed by lumbar puncture. Then, using x-ray guidance, the sample is mixed with a very low dose of intrathecal contrast dye and is injected into the spinal sac in the lower back. The patient is then asked to move to a position that will allow the contrast fluid to travel to the area being studied. The dye enables the spinal canal and nerve roots to be visualized more clearly on a CT (See Computed Tomography.) scan. The scan takes 45 to 60 minutes to complete.
Although no special preparations are required, strict bed rest is necessary for at least 24 hours after the test to prevent spinal headaches. These severe headaches can occur because some of the fluid that surrounds the brain and spinal cord may leak out through the injection site.