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MyelogramMyelography

Definition
How the test is performed
How to prepare for the test
How the test will feel
What the risks are
Why the test is performed

Definition
Myelography uses X-rays and fluoroscopy to provide pictures of the cavity within the bones of the spine (spinal canal). Myelography may be done to detect blockage of the spinal canal caused by a tumour, infection, a herniated disc, or arthritis.

The spinal canal contains the spinal cord and nerve roots surrounded by a fluid-filled space called the subarachnoid space. For myelography, a dye (contrast material) that contains iodine is injected into the subarachnoid space. X-ray pictures are taken as the contrast material moves into different areas of the subarachnoid space.

Myelography is frequently combined with computed tomography (CT scan). This technique is called CT myelography.

Full-dose myelography uses a full dose of contrast material. CT scans are taken about 3 hours after the contrast material has been injected. Full-dose myelography is rarely used in the United States. Low-dose myelography uses a low dose of contrast material. CT scans are usually done immediately after the contrast material is injected.

For many purposes, magnetic resonance imaging (MRI) has replaced myelography.

How the test is performed

Myelography is done in an outpatient radiology center or in the radiology department of a hospital by a radiologist and assistants.

You will need to remove any jewelry that might interfere with the X-ray pictures. You will need to take off all or most of your clothes, depending on which area is being examined. You may be allowed to keep on your underwear if it does not interfere with the test. You will be given a cloth or paper covering to use during the test.

Most commonly, a lumbar puncture is done to enter the spinal canal. You will lie on your stomach or side on an X-ray table. The doctor examines your lower back (lumbar area) and marks the proper insertion site with a pen. The area is then cleaned with an antiseptic and draped with sterile towels. A local anesthetic may be injected under the skin to numb the area where the needle will be inserted.

After the anesthetic has taken effect, a thin needle is inserted into the spinal canal and a continuous series of X-ray pictures (fluoroscopy) helps the doctor see and place the needle in the desired location. A sample of the liquid from the spinal canal (cerebrospinal fluid) may be removed for analysis before the contrast material is injected. The injection is usually done in your lower back but may occasionally be done at the base of your skull or the upper neck (cervical) spine.

After the contrast material is injected, you continue lying on your stomach or side while the X-ray pictures are taken. If pictures of your upper back or neck are needed, the contrast material may be moved into those areas by tilting the table or you may be asked to move into different positions. You will be held in position as the table is tilted, and your chin will be placed on a small pillow to keep your neck extended. This prevents the contrast material from entering your head, which can cause headaches or seizures. You need to lie very still to avoid blurring the pictures. Your pulse, breathing rate, and blood pressure may be monitored throughout the test.

After the X-ray pictures have been taken, the injection site is bandaged. You will be given instructions on any steps you need to take after having the test.

Frequently, a CT scan of the area (CT myelogram) is done 3 hours after the myelogram to gain additional information.

Low-dose myelograms are most common now. They use the same steps as a standard myelogram, but less contrast material is used and the standard X-rays are not taken. Instead, a CT scan of the area of interest is done immediately after the contrast material is injected.

After the test
A myelogram usually takes between 30 minutes and 1 hour. If a CT scan is also done, that takes an additional 30 minutes to 1 hour. If a full-dose myelogram is done followed by a CT scan, you may need to remain in an observation area for the 3 hours after the X-rays are taken and before the CT scan is done.

You will be monitored for a short time after the myelogram. The amount of time you are monitored depends on the type of myelogram you had. You may be asked to remain in bed with your head elevated for up to 8 hours after the test.

You will be instructed to drink plenty of water after the myelogram. You may also need to avoid taking certain medications for up to 2 days after the test.

How to prepare for the test

Before myelography, tell your health professional if you:

Have a history of epilepsy or other seizure disorder.
Are or might be pregnant.
Are allergic to the iodine dye used in the contrast material or any other substance that contains iodine. Also tell your health professional if you have asthma or have ever had a serious allergic reaction (anaphylaxis) from any substance, such as the venom from a bee sting or from eating shellfish.
Are allergic to any medications.
Have bleeding problems or take blood-thinning medications.
Are taking any medications. Some medications may need to be stopped temporarily before the test is done.
Have a history of kidney problems or diabetes, especially if you take metformin (Glucophage) to control your diabetes. The contrast material used during myelography can cause kidney damage in people with poor kidney function. If you have a history of kidney problems, blood tests (creatinine, blood urea nitrogen) may be done before myelography to check that your kidneys are functioning properly. For more information, see the medical tests Creatinine and Creatinine Clearance and Blood Urea Nitrogen.
You may be instructed not to eat or drink, or to limit your intake to clear liquids, for 8 hours before the test. You may need to take a laxative or have an enema before the test to empty your bowels. Ask your health professional what instructions you need to follow before the myelography test.

If you are not spending the night in the hospital after having this test, you should arrange to have someone take you home. Check with your health professional ahead of time to find out when you will be able to go home.

Talk to your health professional about any concerns you have regarding the need for the test, its risks, or how it will be done. Complete the medical test information form to help you understand the importance of this test.

How the test will feel

The X-rays are painless. You will feel a brief sting from the small needle used for numbing your skin around the myelogram injection site. You will feel slight pressure as the longer spinal needle is inserted into your spinal canal. You may feel an occasional sharp pain while the needle is being positioned in your spine.

You may find it uncomfortable to lie on your stomach or side during the procedure. Some people find it difficult to swallow or to breathe deeply while in this position. However, this position does not usually need to be held for long. You may also find some of the other positions uncomfortable, especially when your head is lower than your body.

You may feel pressure or warmth as the contrast material is injected. The contrast material may also cause a headache, flushing, nausea, or vomiting. Rarely, contrast injections into the fluid-filled space (subarachnoid space) can cause seizures. After the test, you will be instructed to keep your head elevated and to avoid bending over or lying flat. This will help keep the contrast material out of your head and prevent seizures.

After the test, contact your health professional immediately if you:

  • Have a seizure.
  • Notice any increase in pain, weakness, or numbness in your legs.
  • Have a severe headache.
  • Have a headache that lasts longer than 24 hours.
  • Feel extremely irritable.
  • Have problems urinating or having a bowel movement.
  • Develop a fever higher than 100.4°F (38°C).

What the risks are

There is some risk of developing a problem after a myelogram. The risk is greater with a full-dose myelogram than it is with a low-dose myelogram.

There is slight risk of developing an allergic reaction to the iodine contrast material. The reaction can be mild (itching, rash) or severe (difficulty breathing or sudden shock). Death resulting from an allergic reaction is rare. Most reactions can be controlled using medication. Tell your health professional if you have allergies of any kind, such as hay fever, iodine allergy, eczema, hives, or food allergies.
About 20% of people who have a myelogram develop a headache, nausea, or vomiting after the test. Rarely, seizures may occur after an injection of contrast material into the fluid-filled space (subarachnoid space). After the test, you will be instructed to keep your head elevated and to avoid bending over or lying flat. This will help keep the contrast material out of your head and prevent seizures.
There is a slight risk of infection at the injection site or bleeding into the space around the spinal cord.
There is a risk of kidney problems if you take metformin (Glucophage) to control your diabetes. You will need to stop taking your medication for a few days before the test and resume taking it a few days after the test.
The contrast material can cause water loss or damage to the kidneys that may lead to kidney failure. This is a concern if you are dehydrated or have poor kidney function. If you have a history of kidney problems, blood tests (creatinine, blood urea nitrogen) may be done before the myelogram to check that your kidneys are functioning properly. For more information, see the medical tests Creatinine and Creatinine Clearance and Blood Urea Nitrogen.
Very rarely, inflammation of the covering of the spinal cord (arachnoiditis), weakness, numbness, paralysis, or inability to control bowel or bladder function may develop. Any paralysis is usually temporary, but may be permanent.
There is also a very slight risk that the contrast material will cause blockage of the spinal canal. If this occurs, surgery is usually needed.
There is always a slight risk of damage from being exposed to any radiation, including the low levels of X-rays used for this test. However, if this test is really needed, the risk of damage from the X-rays is usually very low compared with the potential benefits of the test.

Why the test is performed

Myelography is done to detect narrowing of the spinal canal or abnormalities of the nerves branching off the canal. This may be caused by:

  • Spinal stenosis.
  • A tumour or infection.
  • A spinal disc that has ruptured (herniated disc).
  • Inflammation of the membrane (arachnoid membrane) that covers the brain and spinal cord.
  • Abnormalities of the blood supply to the spinal cord.

Myelography may help determine or verify the cause of pain that could not be found by other imaging methods, such as magnetic resonance imaging (MRI) or CT scanning.

Text courtesy of WebMD Health web site.

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