A myelography, often called a myelogram, is a specialized medical imaging procedure that provides detailed pictures of the spinal canal, spinal cord, and nerve roots. It uses X-rays or computed tomography (CT) scanning combined with a contrast agent (dye) injected into the space surrounding the spinal cord. This dye makes spinal structures visible, which are typically obscured during standard X-rays. Myelography is generally performed when non-invasive methods, such as MRI or CT without contrast, fail to provide a clear diagnosis or are not possible for the patient. For instance, individuals with metallic implants or pacemakers cannot safely undergo an MRI, making the myelogram an important diagnostic alternative.
Clinical Indications for Myelography
A doctor recommends myelography to investigate conditions affecting the spinal column and nervous tissue. The procedure is particularly useful for diagnosing structural issues that compress the spinal cord or the nerve roots branching off it. Common indications include identifying spinal stenosis, which is a narrowing of the spaces within the spine that puts pressure on nerves.
It is frequently ordered to assess the impact of a herniated disc, where the material between vertebrae bulges and presses on nearby nerves. The detailed visualization helps pinpoint the exact location and severity of nerve root compression. Myelography also serves to diagnose spinal tumors, cysts, or arachnoiditis (inflammation of the membrane covering the nerve roots). When standard MRI or CT results are inconclusive, myelography provides the necessary clarity for treatment planning.
The Myelography Procedure
The myelography procedure is typically performed by a neuroradiologist in a hospital or specialized imaging center and usually takes about an hour. The patient is positioned on an imaging table, and the skin on the lower back is cleaned with an antiseptic solution. A local anesthetic is then injected to numb the area, minimizing discomfort during needle insertion.
Using fluoroscopy (real-time X-ray), the radiologist guides a thin needle between two vertebrae into the subarachnoid space. Fluoroscopic guidance ensures precise placement before the contrast agent is slowly injected into this space. Patients may feel pressure or warmth as the dye enters the spinal canal.
After injection, the imaging table is often tilted, or the patient is asked to change positions. This allows gravity to move the contrast agent, ensuring the dye fully coats the spinal cord and nerve roots. The final step involves taking a series of X-rays or, more commonly, a CT scan while the contrast is active, providing high-resolution images of the spine.
Preparation and Recovery
Before the myelogram, patients are instructed to discontinue certain medications, especially blood thinners like aspirin, several days in advance to reduce bleeding risk. Doctors must also be informed about any medications that may lower the seizure threshold, as these can interact with the contrast agent. Patients are typically asked not to eat for a few hours before the appointment but should drink clear fluids for hydration.
The recovery phase focuses on preventing a post-puncture spinal headache, the most common side effect. Patients are instructed to lie flat or keep their head slightly elevated for several hours. This allows the puncture site to seal and minimizes the risk of a cerebrospinal fluid leak. Increased fluid intake is also encouraged to help replenish spinal fluid and flush the contrast dye from the body.
Potential Risks and Complications
The most frequent complication of myelography is a headache, which occurs when cerebrospinal fluid leaks through the puncture site after the needle is removed. This headache is often posture-related, worsening when sitting or standing and improving when lying down.
Rare, but serious, complications include an allergic reaction to the contrast dye, ranging from mild itching to a severe anaphylactic response. Since the procedure involves a spinal puncture, there is a small potential for infection, such as meningitis, or bleeding around the spinal cord. In rare instances, the contrast agent can irritate the central nervous system, leading to temporary muscle spasms or seizures.
Interpreting the Diagnostic Results
The radiologist interprets myelography images by observing how the contrast agent flows within the subarachnoid space, outlining the spinal cord and nerve roots. A normal result shows a smooth, continuous column of contrast outlining the spinal structures.
An abnormal finding is indicated by a filling defect, an area where the contrast flow is interrupted or narrowed. This obstruction can be caused by a bulging disc, a tumor, or the bony encroachment of spinal stenosis. The images reveal if nerve roots are displaced or compressed, which guides subsequent treatment decisions, such as targeted injection, physical therapy, or surgical intervention.