Myelography

Definition

Myelography is an x-ray examination of the spinal canal. A contrast agent is injected through a needle into the space around the spinal cord to display the spinal cord, spinal canal, and nerve roots on an x ray.

Purpose

The purpose of a myelogram is to evaluate the spinal cord and nerve roots for suspected compression. Pressure on these delicate structures causes pain or other symptoms. A myelogram is performed when precise detail about the spinal cord is needed to make a definitive diagnosis. In most cases, myelography is used after other studies, such as magnetic resonance imaging (MRI) or a computed tomography scan (CT), have not provided enough information to be certain of the diagnosis. Sometimes myelography followed by CT scan is an alternative for patients who cannot have an MRI scan, because they have a pacemaker or other implanted metallic device.

A herniated or ruptured intervertebral disc, or related condition such as disc bulge or protrusion, popularly known as a slipped disc, is one of the most common causes for pressure on the spinal cord or nerve roots. The condition is popularly known as a pinched nerve. Discs are pads of fiber and cartilage that contain rubbery tissue. They lie between the vertebrae, or individual bones, which make up the spine.

Discs act as cushions, accommodating strains, shocks, and position changes. A disc may rupture suddenly, due to injury or a sudden strain with the spine in an unnatural position. In other cases, the problem may come on gradually as a result of progressive deterioration of the discs with aging. The lower back is the most common area for this problem, but it sometimes occurs in the neck, and rarely in the upper back. A myelogram can help accurately locate the disc or discs involved.

Myelography may be used when a tumor is suspected. Tumors can originate in the spinal cord or in tissues surrounding the cord. Cancers that have started in other parts of the body may spread or metastasize in the spine. It is important to precisely locate the mass causing pressure so effective treatment can be undertaken. Patients with known cancer who develop back pain may require a myelogram for evaluation.

Other conditions that may be diagnosed using myelography include arthritic bony growths (spurs), narrowing of the spinal canal (spinal stenosis), or malformations of the spine.

Description

Myelograms can be performed in a hospital x ray department or in an outpatient radiology facility. The patient lies face down on the x ray table. The radiologist first looks at the spine under fluoroscopy, and the images appear on a monitor screen. This is done to find the best location to position the needle. The skin is cleaned, numbed with local anesthetic, and then the needle is inserted. Occasionally, a small amount of cerebrospinal fluid, the clear fluid that surrounds the spinal cord and brain, may be withdrawn through the needle and sent for laboratory studies. Contrast material (dye that shows up on x rays) is then injected.

The x-ray table is tilted slowly, allowing the contrast material to reach different levels in the spinal canal. The flow is observed under fluoroscopy, and x rays are taken with the table tilted at various angles. A footrest and shoulder straps or supports keep the patient from sliding.

In many instances, a CT scan of the spine is performed immediately after a myelogram, while the contrast material is still in the spinal canal. This helps outline internal structures more clearly.

A myelogram takes approximately 30 to 60 minutes. A CT scan adds about another hour to the examination. If the procedure is done as an outpatient exam, some facilities prefer the patient to stay in a recovery area up to four hours.

Patients who are unable to lie still or cooperate with positioning should not have this examination. Severe congenital spinal abnormalities may make the examination technically difficult to carry out. Patients with a history of severe allergic reaction to contrast material (x-ray dye) should report this to their physician prior to having myelography. Medications to minimize the risk of severe reaction may be recommended before the procedure. Given the invasive nature and risks of myelograms and increased anatomic detail provided by MRI or CT, myelograms are generally not used as the first imaging test.

Preparation

Patients should be well-hydrated at the time they are undergoing a myelogram. Increasing fluids the day before the study is usually recommended. All food and fluid intake should be stopped approximately four hours before the procedure.

Certain medications may need to be stopped for one to two days before myelography is performed. These include some antipsychotics, antidepressants, blood thinners, and diabetic medications. Patients should discuss this with their physician or the staff at the facility where the study is to be done.

Patients who smoke may be asked to stop the day before the test. This helps decrease the chance of nausea or headaches after the myelogram. Immediately before the examination, patients should empty their bowels and bladder.

Aftercare

After the examination is complete, the patient usually rests for several hours, with the head elevated. Extra fluids are encouraged, to help eliminate the contrast material and prevent headaches. A regular diet and routine medications may be resumed. Strenuous physical activities, especially those that involve bending over, may be discouraged for one or two days. The physician should be notified if the patient develops a fever, excessive nausea and vomiting, severe headache, or a stiff neck.

Risks

Headache is a common complication of myelography. It may begin several hours to several days after the examination. The cause is thought to be changes in cerebrospinal fluid pressure, not a reaction to the dye. The headache may be mild and easily alleviated with rest and increased fluids. Sometimes, nonprescription medicines are recommended. In some instances, the headache may be more severe and require stronger medication or other measures for relief. Many factors influence whether the patient develops this problem, including the type of the needle used and his or her age and gender. Patients with a history of chronic or recurrent headaches are more likely to develop a headache after a myelogram.

The chance of a reaction to the contrast material is a very small, but potentially significant risk. It is estimated that only 5–10% of patients experience any effect from contrast exposure. The vast majority of reactions are mild, such as sneezing, nausea, or anxiety. These usually resolve by themselves. A moderate reaction, like wheezing or hives, may be treated with medication, but is not considered life threatening. Severe reactions, such as heart or respiratory failure, occur very infrequently, and require emergency medical treatment.

Rare complications of myelography include injury to the nerve roots from the needle or from bleeding into the spaces around the roots. Inflammation of the delicate covering of the spinal cord, called arachnoiditis, or infections, can also occur. Seizures are another very uncommon complication reported after myelography.

Normal results

A normal myelogram shows nerves that appear normal, and a spinal canal of normal width, with no areas of constriction or obstruction.

Abnormal results

A myelogram may reveal a herniated disk, tumor, bone spurs, or narrowing of the spinal canal (spinal stenosis).

Resources

BOOKS

Daffner, Richard. Clinical Radiology, The Essentials. Baltimore: Williams and Wilkins, 1993.

Pagana, Kathleen Deska. Mosby's Manual of Diagnostic and Laboratory Tests. St. Louis: Mosby, Inc., 1998.

Torres, Lillian. Basic Medical Techniques and Patient Care in Imaging Technology. Philadelphia: Lippincott, 1997.

ORGANIZATIONS

Spine Center. 1911 Arch St., Philadelphia, PA 19103. (215) 665-8300. http://www.thespinecenter.com

Ellen S. Weber, M.S.N.
Lee A. Shratter, M.D.