| Myelography
What is Myelography? Back to Top
Myelography is an x-ray
examination of the spinal cord and the space surrounding it, 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 demonstrate distortions of the spinal cord,
the spinal canal within which it lies, and the spinal nerve roots
connected to it. It is an effective means of identifying spinal lesions
caused by disease or trauma. This exam, done about 350,000 times a year
in the United States, is relatively safe and painless.
A myelogram is done to provide a very detailed picture of the spinal
cord and spinal column, and of any abnormalities that may be present.
Often myelography is performed when other tests—such as computed
tomography (CT) scans or magnetic resonance imaging (MRI) have not
provided adequate information. For patients who cannot have an MRI exam
for any reason, myelography may be performed, followed by a CT scan.
What are some common uses of the procedure? Back to Top
Myelography
can identify a herniated or ruptured intervertebral disk. Slipped disk
is a common term for this problem. 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,
whether from heavy lifting, sudden strain, change in position, or
injury. There may be sudden severe back pain if the disk ruptures, or
pain may develop gradually with advancing age as the disks degenerate.
The lower part of the back is most often 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. This
information is especially important when surgical treatment is a
possibility.
People with spinal arthritis sometimes develop sharp outgrowths of
vertebral bone called bone spurs; these may press on spinal nerves and
cause pain. Here again, a myelogram can indicate whether surgery might
help. The exam also can identify a condition called spinal stenosis
where the entire spinal canal is narrowed.
Tumors may develop within the spinal cord or surrounding tissues. In
addition, cancer from elsewhere in the body may spread to the spine. A
myelogram will accurately locate a tumor mass in this region and may
suggest the most effective treatment.
Other conditions that may be
shown by a myelogram include infection, inflammation of the arachnoid
membrane that covers the spinal cord, abnormalities of blood vessels
that supply the spinal cord, and traumatic injuries.
How should I prepare for the procedure? Back to Top
Usually
patients are advised to increase their fluid intake the day before a
scheduled myelogram, as it is important to be well hydrated. Solid
foods are avoided for several hours before the exam, but fluids may be
continued. You should provide the radiologist or technologist with a
list of drugs you are taking. Some drugs should be stopped one or two
days before myelography. They include certain antipsychotic
medications, antidepressants, blood thinners, and drugs—especially
metformin—that are used to treat diabetes. It is important that medical
staff know if you have had seizures, or that you are—or might be—
pregnant. If you smoke, stopping the day before the test will lessen
the chance of your becoming nauseous or having headache after
myelography. You will be asked to empty your bladder and bowel, using a
laxative if needed, just before the exam begins so as not to have to
interrupt it.
If you have had a severe allergic reaction to medication or anything
else, or have a history of asthma, you will be watched especially
carefully to check for a reaction when injecting the contrast material.
Allergy to iodine-containing substances can be especially risky. If you
have had kidney problems, tests will be done to make sure that your
kidneys are functioning properly at the time of myelography.
You will need to remove any jewelry near the area of your body being
examined. After disrobing, you will be given a hospital gown to wear.
Unless you are to spend the night in hospital, you should arrange to
have a relative or friend take you home.
What does the equipment look like? Back to Top
There is no
equipment exclusively devoted to myelography. In addition to the needle
and syringe used to inject contrast material, a fluoroscope will be at
hand so that the radiologist may guide the needle into a proper
position and the radiologist can watch as the contrast material enters
and fills the space around the spinal cord and nerve roots.
How does the procedure work? Back to Top
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 serves to cushion and protect
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? Back to Top
Myelography may
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.
If needed, a small amount of cerebrospinal fluid will be withdrawn
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 then are taken while you
are lying face-down. You will be asked to lay as still as possible
while the table is tilted at different angles. The exam focuses on the
area where you are feeling symptoms: the lower back area, the middle
part of the back, or the neck. A foot rest and straps or supports will
keep you from sliding out of position. A computed tomography (CT) scan
sometimes is 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? Back to Top
You
will feel a brief sting when 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 30 to 60 minutes, and a CT scan
adds another 30-60 minutes to the total examination time. Some
facilities have patients 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 headache. You probably will be
asked not to engage in strenuous physical activity or bend over for one
or two days. This will ensure that what contrast material remains 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? Back to Top
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? Back to Top
Benefits
- 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.
Risks
- Special care is 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 radiologic 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 readily relieve mild
headache, but more severe headache 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. In
addition, 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, probably making surgery necessary.
What are the limitations of Myelography? Back to Top
Myelography usually is avoided during pregnancy because of the risk that x-ray will harm the developing fetus.
The findings may not be accurate if the patient moves during the exam.
It may be difficult to inject contrast material in patients having
structural defects of the spine or some forms of spinal injury.
Myelography cannot be done if the injection site is infected. Back to Top |
