A myelogram is an x-ray test in which dye is injected directly into your spinal canal to help show places where the vertebrae in your back may be pinching the spinal cord.It is utilized to diagnose disorders of the spinal canal and cord, such as nerve compression causing pain and weakness.It is sometimes used to help diagnose back or leg pain problems, especially if surgery is being planned.
The test is usually performed on an outpatient basis at a hospital or other medical facility by a neuroradiologist. Neuroradiology is a sub-specialty of radiology that conducts studies of the central nervous system.
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A myelogram requires introduction of radiographic contrast media (dye) into the sac (dura) surrounding the spinal cord and nerves. The patient lies on their stomach during the test. After the skin area has been numbed, the dye is injected into the spinal sac followed by x-rays, CT, or MRI scans. After the images are processed, a neuroradiologist interprets the results and sends a report to the referring physician.
Following the myelogram, the patient is taken to a recovery area where they rest lying down with their head elevated for several hours. Once at home, quiet non-strenuous activities are recommended for 24 hours to allow the puncture site to heal. Plenty of fluids (e.g. water, juice) should be consumed to clear the dye from the body.
Important Considerations :-
Certain medical conditions, drugs, or allergies should be discussed with the referring physician prior to the myelogram. Some of these topics are listed below.
1. Metallic components such as a pacemaker, aneurysm clip, or other metal implants prohibit the patient from an MRI scan.
2. Allergies to an IVP (intravenous pyelography) or other contrast dye should be reported. Adverse reactions include hives, swelling, and difficulty breathing. Fore knowledge of an allergy can often be controlled by pre-medicating.
3. Epilepsy or seizure disorder, and if medication is taken to control episodes.
4. Angina or kidney disorders.
5. Diabetic patients who control their disease with medication need to discuss this with their physician. Certain drugs may need to be discontinued for 48 hours prior to the test.
6. Blood thinners may need to be discontinued prior to the test.
7. Difficulty lying flat on the stomach or inability to remain still.
How do you prepare for the test?
Tell your doctor ahead of time if you have ever had an allergic reaction to lidocaine or the numbing medicine used at the dentist’s office, or to x-ray dyes. You should also tell your doctor if you might be pregnant.
1. The patient will need someone to drive them home following the test. This should be prearranged in advance of the scheduled test day.
2. Leave valuables at home.
3. Bring prior relevant x-rays, CT or MRI scan for the neuroradiologist’s review.
4. Do not eat anything after midnight the night before the myelogram. Some patients experience side effects such as nausea and vomiting. Clear liquids are acceptable.
5. Take scheduled medication with clear liquid, unless the referring physician has instructed otherwise (e.g. diabetics).
What happens when the test is performed?
Patients usually wear a hospital gown. Typically, you lie on your side with your knees curled up against your chest. In some cases, the doctor asks you to sit on the bed or a table instead, leaning forward against some pillows.
The doctor feels your back to locate your lower vertebrae and feels the bones in the back of your pelvis. An area on your lower back is cleaned with soap. Medicine is injected through a small needle to numb the skin and the tissue underneath the skin in the area. This causes some very brief stinging.
A different needle is then placed in the same area and moved forward until fluid can be injected through it into the spinal canal. This fluid is a type of dye that shows up on x-rays; this allows your doctors to get a clear picture of the fluid space around your spinal cord and to see places where the space is narrowed by bones around it. Because the needle must be placed through a small opening between two bones, the doctor must sometimes move the needle in and out several times to locate the opening. Because of the numbing medicine used in this area, most patients experience only a feeling of pressure from this movement. Occasionally some patients do get a sharp feeling in the back or (rarely) in the leg. Let your doctor know if you feel any pain.
Once the dye has been injected, the needle is removed and several x-ray pictures are taken of your back. Sometimes a CT (computed tomography) scan picture is taken instead.
The process usually involves lying face down on a table, and your feet are secured tightly with straps to the table itself. The Radiologist will perform the spinal tap, introducing the contrast medium. The table is then slowly rotated in a circular motion, first down at the head end for approximately 4-6 minutes, then rotated up at the head end for the same duration. Several more minutes lying flat and the process is complete. This movement insures the contrast has sufficiently worked its way through the spinal cord.
It is very important to not lift anything for at least 24 hours following this procedure, and to lie flat for at least the same amount of time. There is a high chance that excessive movement or any lifting will release the ‘plug’ at the site of the spinal tap, and CSF will then drain from your brain and cause very severe headaches. This can be corrected by returning to the medical facility and having them perform a ‘blood patch’, a small amount of blood from your arm, injected into the exact spinal tap location, to stop the leaking of CSF.
What are the benefits vs. risks?
* Myelography is relatively safe and painless.
* When a contrast material is injected into the space surrounding the spinal cord, it allows the radiologist to view outlines of the different areas of the spine that usually are not visible or distinguishable on x-rays.
* No radiation remains in a patient’s body after an x-ray examination.
* X-rays usually have no side effects in the diagnostic range*Special care is taken during x-ray examinations to use the lowest radiation dose possible while producing the best images for evaluation. National and international radiology protection councils continually review and update the technique standards used by radiology professionals.
# Minimizing Radiation Exposure:State-of-the-art x-ray systems have tightly controlled x-ray beams with significant filtration and dose control methods to minimize stray or scatter radiation. This ensures that those parts of a patient’s body not being imaged receive minimal radiation exposure.
* There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk.
* The effective radiation dose from this procedure is about 4 mSv, which is about the same as the average person receives from background radiation in 16 months. See the Safety page for more information about radiation dose.
* Although it is uncommon, headache due to the needle puncture following myelography is one risk. The headache, when it occurs, usually begins when the patient begins to sit upright or stand. One of the common features of this type of headache is that it is improved when the patient lays flat. When present, the headache usually begins within 2-3 days after the procedure. Rest while laying on one’s back and increased fluid intake readily relieve mild headaches, 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.
* Adverse reactions to injection of contrast material during a myelogram are infrequent and usually mild in nature, including itching, rash, sneezing, nausea, or anxiety. The development of hives or wheezing may require treatment with medication. More severe reactions involving the heart or lungs are rare.
* Other 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.
* There is a very small risk that contrast material will block the spinal canal, which can make surgery necessary.
* Women should always inform their physician or x-ray technologist if there is any possibility that they are pregnant. See the Safety page for more information about pregnancy and x-rays.
If symptoms persist 48 hours, contact the referring physician and/or medical facility.
Must you do anything special after the test is over?
Nothing. Usually a Band-Aid is the only dressing necessary for your back.
How long is it before the result of the test is known?
It takes about an hour to have your x-rays or CT scan developed and some time for the films to be reviewed by a radiologist. Usually your doctor can get the results within a day.
* The most significant limitation of myelography is that it only sees inside the spinal canal and the very proximal nerve roots. Abnormalities outside these areas may be better imaged with MRI.
* Myelography usually is avoided during pregnancy because of the potential risk to the baby.
* The findings may not be accurate if the patient moves during the exam.
* It may be difficult to inject contrast material in patients with structural defects of the spine or some forms of spinal injury.
* Myelography cannot be done if the injection site is infected.