Myelography is the x-ray examination of the spinal canal after administration of a contrast dye to provide definition on the images. To perform this test, the contrast dye is injected into the subarachnoid space—the compartment surrounding the spinal cord and brain that contains the cerebrospinal fluid (CSF). Because the contrast agent is heavier than CSF, it flows through the spinal canal to selected areas as an examining table is tilted up or down. Continuous x-ray imaging, or fluoroscopy, is used to track the movement of the dye and visualize the contents of the spinal canal. Any abnormalities, such as narrowed areas, may then be recorded on x-ray film or by a CT scanning machine.
Purpose of the Myelogram
- To diagnose abnormalities affecting the spinal cord—such as tumors, herniated disks, arthritic bone spurs, or an abscess—in people with severe back pain or neurologic symptoms that suggest problems in the spinal canal
- To assess abnormalities in the spinal cord prior to surgery
- To identify injuries to the nerve roots that branch off from the spinal cord
- To detect tumors in the lower part of the brain
Who Performs It
- A radiologist
- Pregnant women should not undergo this test because exposure to ionizing radiation may harm the fetus.
- Myelogram is not appropriate for individuals who have increased intracranial pressure, infection at the site of the needle insertion, or multiple sclerosis.
- Different types of contrast dyes—either oil-based or water-soluble—may be used for this procedure. Oil-based dyes must be withdrawn after myelogram before the needle is removed; this is not necessary with water-soluble dyes, which are absorbed by the body and excreted through the kidneys.
- People with allergies to iodine or shellfish may experience an allergic reaction to iodinated, oil-based contrast dyes.
- Certain drugs can increase the risk for seizures in patients receiving a water-soluble contrast agent, such as metrizamide.
- People who experience claustrophobia may find it difficult to undergo a CT scan, which takes place in a narrow, tunnel-like structure. In addition, the CT scan may not be possible for severely overweight individuals (over 300 lbs).
Before the Myelogram
- If iodinated dye is to be used, inform your doctor if you have an allergy to iodine or shellfish. You may be given a combined antihistamine-steroid preparation to reduce the risk of an allergic reaction.
- Tell your doctor if you are taking any medications, herbs, or supplements. You may be advised to discontinue certain of these agents before the test.
- Tell your doctor if you are or think that you could be pregnant.
- Disclose any past seizures or if you are taking medication for seizures.
- Do not smoke the day before or of the test.
- Do not eat or drink anything for 8 hours before the test.
- You will be advised to empty your bladder and bowels before the test.
- You may be given an anticholinergic drug, such as atropine, in addition to a sedative to reduce swallowing during the procedure.
- You will be asked to remove your clothes and any metal objects (including watches, hair clips, and jewelry) and put on a hospital gown.
What You Experience
- You will lie on your side on a table or bed, with your knees drawn up toward your chest and your forehead bent toward your knees. (Less often, the procedure is done while you are sitting.)
- The needle insertion site on your lower back is cleansed with an antiseptic solution, and a local anesthetic is injected to numb the area. You may feel a brief stinging during this injection.
- Next, a long needle is carefully inserted into the spinal canal. Fluoroscopic imaging is used to guide it into the subarachnoid space, which is located between membranes that surround the spinal cord. You may feel some pressure as the needle is inserted.
- Once the needle is in place, a small amount of CSF may be removed for laboratory analysis (a procedure called lumbar puncture).
- A contrast dye is then injected through the needle into the spinal canal. You may feel a transient flushing sensation, warmth, a headache, a salty taste, or nausea after the material is injected.
- With the needle in place, you will be positioned on your stomach and strapped in place with a foot support and shoulder brace or harness. Your chin will be hyperextended outward with a towel or sponge placed underneath for comfort.
- The flow of the contrast agent is followed using fluoroscopy, and representative x-ray films are obtained of any abnormalities. (Alternatively, you will be advanced into a CT scanning machine.)
- To move the dye to selected areas, the table may be adjusted so that your head is tilted down during parts of the test, which may be uncomfortable.
- Once the procedure has been completed, the needle is removed. (If an oil-based contrast dye was used for the test, as much dye as possible must be aspirated through the needle before it is withdrawn. This may cause some discomfort.)
- The puncture site is cleansed with an antiseptic solution and a dressing is applied.
- The procedure usually takes about 1 hour.
Risks and Complications
- Radiation exposure is minimal, but if the test includes a CT scan, you will receive a higher dose of radiation than during standard x-ray procedures.
- Headache or soreness in the back may occur for a short time after the procedure. Rarely, serious complications such as meningitis or (when water-based dye is used) seizures may develop.
- Some people may experience an allergic reaction to the iodine-based contrast dye, which can cause symptoms such as nausea, sneezing, vomiting, hives, and occasionally a life-threatening response called anaphylactic shock. Emergency medications and equipment are kept readily available.
- If a lumbar puncture is performed, it carries the associated risks.
- You may experience temporary leg numbness or lower back pain.
After the Myelogram
- If an oil-based contrast agent was used, you must lie flat in bed for up to 12 hours and positioned with your head raised at least 30 degrees after the procedure. If a water-based dye was used, you must rest with your head elevated for about 6 to 8 hours.
- Your blood pressure and other vital signs will be checked periodically and you will be monitored for signs of complications.
- You may return home. If there are no complications or adverse reactions, you may resume your normal diet and activities the day after the test.
- You are encouraged to drink clear fluids to avoid dehydration and to help flush the contrast dye out of your system. (If a lumbar puncture was done, extra fluids also help to speed the replacement of CSF.)
- Delayed allergic reactions to the contrast dye, such as hives, rash, or itching, may appear 2 to 6 hours after the procedure. If this occurs, your doctor will prescribe antihistamines or steroids to ease your discomfort.
- The doctor will examine the x-ray or CT images and other test data for evidence of abnormalities, such as blocked or narrowed areas, affecting the spinal canal or the base of the brain.
- If a sample of CSF is taken, it will be sent to a laboratory for analysis to provide further diagnostic information.
- If a definitive diagnosis can be made, your doctor will recommend an appropriate course of medical or surgical treatment, depending on the specific problem.
- In some situations, additional diagnostic tests, such as a skeletal MRI, may be needed to further evaluate abnormal results.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media