Special Procedures - Myelography
What is a Myelography?
Myelography is an x-ray examination of the spinal cord and its surrounding area called the subarachnoid space. The x-ray film or myelogram is taken after injecting a radiopaque contrast material through a needle placed in this space. Myelography can show distortions of the spinal cord, the spinal canal and the spinal nerve roots. It is effective in identifying spinal lesions caused by disease or trauma. The exam is relatively safe and painless.
A myelogram is performed to provide a very detailed picture of the spinal cord and spinal column and any abnormalities that might be present. Often it is performed when other tests have not provided enough information. For patients who cannot have an MRI, a myelography may be performed, followed by a CT scan.
What are some common uses of the procedure?
Myelography can identify a herniated or ruptured intervetebral disk, commonly called a slipped disk. The disks are pads of rubbery tissue that lie between the vertebrae, the bones that make up the spine. Disks act to cushion the vertebrae when the backbone comes under pressure from heavy lifting, sudden strains, a change in position or an injury. There may be a sudden severe back pain if the disk ruptures, or pain may develop gradually with advancing age as the disks degrade. The lower part of the back is usually affected. A myelogram can accurately locate the disk or disks involved and show whether disk tissue is pressing on nerves connected to the spinal cord.
People with spinal arthritis can sometimes develop sharp growths of vertebral bone called bone spurs that may press on the spinal nerves and cause pain. The procedure can indicate whether surgery would help. It can also identify a condition called spinal stenosis where the entire spinal canal is narrowed.
Tumors may develop within the spinal cord or surrounding tissues. Also, cancer from elsewhere in the body may spread to the spine. A myelogram will accurately find a tumor mass in this region and may suggest the best treatment.
Infection, inflammation of the arachnoid membrane that covers the spinal cord, abnormalities of blood vessels that supply the spinal cord and traumatic injuries can also be showed with a myelogram.
How should I prepare for the procedure?
Increase your fluid intake the day before a scheduled myelogram, as being well hydrated is important. Avoid solid foods for several hours before the exam, but fluids can be continued. Provide the radiologist or technologist with a list of drugs you are taking. Some drugs should be stopped one or two days before a myelography. They include certain antipsychotic medications, antidepressants, blood thinners, and diabetic drugs. It is important that medical staff know if you have had seizures, or that you are—or might be— pregnant. If you smoke, stop smoking the day before the test to lessen the chance of your becoming nauseous or having headache after the procedure. You will be asked to empty your bladder and bowel, using a laxative if needed, just before the exam begins.
If you have had a severe allergic reaction to medication, or have a history of asthma, you will be watched carefully to check for a reaction when injecting the contrast material. Allergy to iodine-containing substances may cause problems. If you have had kidney problems, additional tests will be done to make sure that your kidneys are functioning properly at the time of myelography.
You will need to remove all jewelry near the examination area and will be given a hospital gown to wear. Unless you are going to spend the night in hospital, you should arrange for someone else to drive you home.
What does the equipment look like?
There is no special equipment used for a myelography. In addition to the needle and syringe used to inject contrast material, a fluoroscope will be used so that the radiologist can guide the needle into a proper position and watch as the contrast material enters and fills the space around the spinal cord and nerve roots.
How does the procedure work?
Within the spinal canal, the spinal cord and nerve roots are surrounded by a fluid-filled area, the subarachnoid space. This fluid, called cerebrospinal fluid, is confined by the arachnoid membrane and cushions and protects the spinal cord. For myelography, contrast material is injected into the subarachnoid space and x-rays are taken as the contrast flows into different areas. The contrast material outlines areas of the spine that usually are not visible on plain x-rays. The table that is used for myelography can be tilted so that contrast material will run up and down the spine and surround the nerve roots that enter and exit the spinal cord.
How is the procedure performed?
Myelography can be done in either a hospital x-ray department or an outpatient radiology unit. After lying face down on the x-ray table, fluoroscopy is performed and images of the spine are projected onto the screen of a monitor. After locating the best placement for the needle, your skin will be cleaned and numbed with a local anesthetic. Usually you will be positioned lying on one side with your knees drawn up and chin tucked into your chest while the spinal needle is inserted. In some cases, patients will be in a sitting position.
In some cases, a small amount of cerebrospinal fluid may be drawn for lab studies. Iodine-containing contrast material then is injected and the x-ray table is slowly tilted. During this time, the flow of contrast is monitored by fluoroscopy. X-rays are then taken while you are lying face down. You will be asked to lie as still as possible while the table is tilted at different angles. A footrest and straps or supports will keep you from sliding out of position. A computed tomography (CT) scan will occasionally be done immediately after myelography while contrast material is still present in the spinal canal. This combination of imaging studies is known as CT myelography.
What will I experience during the procedure?
You will feel a brief sting when the local anesthetic is injected, and slight pressure as the spinal needle is inserted. Positioning the needle may cause occasional sharp pain. Although you may find the face down position uncomfortable or have trouble breathing deeply or swallowing, the position is not usually maintained for very long. When contrast material is injected you may feel some pressure or warmth. Headache, flushing, or nausea may follow contrast injection. Seizures are possible, but are rare.
Myelography itself usually takes about 30-60 minutes, and a CT scan adds another 30-60 minutes to the total examination time. You may stay in a recovery area for as long as four hours, resting with the head elevated at a 30° to 45° angle. You will be encouraged to take fluids at this time to help eliminate contrast material from your body and prevent headaches. You will be asked not to refrain from strenuous physical activity or bend over for one or two days. This will ensure that remaining contrast material will not get to the level of the brain. You should notify your health professional if you experience fever higher than 100.4°F, excessive nausea or vomiting, severe headache for more than 24 hours, neck stiffness, or numbness in your legs. You should also report if you have trouble urinating or passing stool.
Who interprets the results and how do I get them?
The radiologist will examine your x-rays and forward the results to your referring physician. You likely will visit your physician shortly after the exam to discuss the findings and decide on the next step.
What are the benefits vs. risks?
- Myelography using contrast material is an accurate way of examining the status of the spinal cord, nerve roots, and intervertebral disks. Spinal arthritis, tumors, and injuries can be shown precisely.
- A myelogram can show whether surgical treatment is promising in a given case and, if it is, can help in planning surgery.
- Myelography may be combined with computed tomography (CT) scanning or magnetic resonance imaging (MRI) to obtain a very detailed and precise idea of what changes have taken place in the spinal region.
- In some cases, myelography will show the cause of pain and other spinal symptoms even when a CT scan or MRI is negative.
- Care should be taken during x-ray examinations to ensure maximum safety for the patient by shielding the abdomen and pelvis with a lead apron, with the exception of those examinations in which the abdomen and pelvis are being imaged.
- Women should always inform their doctor or technologist if there is any possibility that they are pregnant.
- Headache commonly follows myelography but may not begin for several days after the exam. Rest and increased fluid intake can relieve a mild headache, but more severe headaches may call for medication. In rare circumstances some patients continue to experience spinal headaches, which may necessitate a special procedure to stop leakage of cerebrospinal fluid from the puncture site.
- There is a small chance that you will have a reaction to contrast material. Probably only five percent to 10 percent of patients are affected and most reactions are mild, consisting of itching, rash, sneezing, nausea or anxiety. Wheezing or hives may be treated with medication. Severe allergic reactions affecting the heart or lungs are very infrequent but require emergency care.
- Rare complications of myelography include nerve injury from the spinal needle and bleeding around the nerve roots as they enter or exit the spinal cord. Also, the membrane covering the spinal cord may become inflamed or infected. Seizures are a very uncommon complication of myelography. Kidney failure is a risk for patients who are dehydrated or who have poor kidney function.
- There is a very small risk that contrast material will block the spinal canal, which would make surgery necessary.
What are the limitations of Myelography?
- Myelography usually is avoided during pregnancy because of the risk that x-ray will harm the fetus.
- If a patient moves during the procedure the findings may not be compromised
- Defects of the spine, or some form of spinal injury may make it difficult to inject contrast material
- Myelography cannot be done if the injection site is infected.
Call your physician if you develop a fever over 101 degrees in the next 12 to 24 hours.