The main difference between a CT scan and a myelogram is that a CT scan is non-invasive, while a myelogram involves the insertion of a needle into the spinal canal, as explained by Johns Hopkins Medicine. In some cases, a myelogram is performed in conjunction with a CT scan.
A lumbar CT creates images of the lower back, according to MedlinePlus. During this test, the patient lies on a narrow table inside a scanner. The X-ray beams inside the scanner rotate around the patient, creating slices, which are images taken from different angles. The slices are put together to create three-dimensional images of the spine. In some cases, contrast dye is used to produce better images.
During a myelogram, contrast dye is injected into the spinal column, as explained by Johns Hopkins Medicine. The contrast dye makes it possible for the radiologist to view the spinal cord and other structures in the spinal column. Myelograms are performed to identify spinal cord tumors, bone spurs, herniated discs, spinal cysts and other problems with the spinal cord and associated structures. Because the radiologist inserts a needle into the spinal column during this test, the myelogram is riskier than the CT scan. In some cases, spinal fluid leaks out of the insertion site, causing headaches, and there is also a risk of infection because the needle pierces the skin.