Before the availability of MRI, myelography was the “gold standard” of imaging structures for imaging structures including the spinal cord and roots. The procedure requires a spinal puncture. A spinal puncture is done by advancing a needle between the spinous processes past the dura, the outer covering of the spinal canal. Once the needle is positioned, contrast dye is injected into the space. The dye outlines the bones and disc placement. The procedure can cause a headache, and rarely, a seizure if the contrast reaches the brain. One advantage of a myelogram is that it can be taken in a standing or sitting position. The ability to test in a “functional” position that reproduces pain is particularly helpful for diagnosing spinal stenosis.
What is a myelogram?
A myelogram is a technique where contrast dye is injected into the spinal canal through a spinal needle. The flow of the dye and its eventual location in the spinal canal identify anatomical abnormalities. In the past, oil-based contrast dye was used but was associated with inflammation of the interior of the spinal canal. Currently, water-based dyes are used with a smaller risk of inflammation but a shorter time to generate the images and an increased risk of seizures.
How is a myelogram taken?
Myelograms are used for evaluation of neck and low back disorders. The injection of the dye into the spinal canal is instilled near the base of the skull or in the lumbar area. The neck injection is more painful than the lumbar injections since a greater amount of tissue needs to be entered in order to gain access to the cervical canal. However, the amount of dye needed for a cervical image is less. The images need to be completed within 20 to 30 minutes after the injection to avoid dilution.
Certain precautions are necessary before and after myelography. Any drugs that lower seizure thresholds should be discontinued for 2 days before the procedure. Food should be avoided for 4 hours before the procedure. After the procedure, patients sit in a semi erect position in bed for several hours. After, lyng down with the head slightly raised is allowed. The most common complaints after a myelogram is headache followed by nausea and vomiting.