In this invasive study, watery-appearing contrast material containing iodine that shows on X-rays is placed into the spinal canal via a spinal tap, where it can flow freely up and down the spinal canal over the backs of the discs. X-rays can then detect a disc protrusion as a defect or deformity in the dye column. The advantage over non-invasive CT and MRI is in the detection of spinal stenosis. MRI, CT and Myelograpy may not show stenosis while the subject is lying down, without weight on their spine. But a myelogram is done on a tilt table, so the patient can be stood up and X-rays taken.
This weight-bearing may then show a gap or an “hour glass” defect in the dye column, diagnostic of spinal stenosis not seen on CT or MRI. They key is to stand the patient up. Some radiologists now just put in the contrast, then do a CT scan without any weight-bearing films. If you have SINC and your MRI isn’t conclusive for an area of stenosis and if you then also have a myelogram, be sure they stand you up.