Myelography Health Article

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.