A myelogram is a specialized diagnostic imaging test used to evaluate the structures within the spinal canal. This procedure involves the injection of a water-soluble contrast material into the fluid-filled space surrounding the spinal cord and nerve roots. Using real-time X-ray technology, known as fluoroscopy, the movement of the dye is tracked, highlighting the contours of the spinal canal. The contrast agent allows medical professionals to visualize the spinal cord and nerve roots as silhouettes against the white-appearing dye, offering a detailed view of soft tissue abnormalities that may be pressing on the nerves.
Specific Conditions Requiring a Myelogram
The primary purpose of a myelogram is to pinpoint the cause of symptoms like pain, weakness, or numbness when initial imaging studies are inconclusive or not possible. The test is highly effective at identifying structural issues that compress the spinal cord or nerve roots, a condition often called radiculopathy. By demonstrating how the contrast dye flows around the neural structures, the radiologist can see precisely where the flow is restricted or blocked.
A frequent indication for this procedure is the assessment of spinal stenosis, which is the narrowing of the spaces within the spine that can put pressure on the nerves. In cases of disc herniation, the myelogram can confirm if the disc is displacing the contrast column and impinging on a nerve. While Magnetic Resonance Imaging (MRI) is often the first choice for these diagnoses, a myelogram can sometimes provide superior detail regarding nerve root compression in the lateral recess of the spine.
The test is also used to evaluate conditions such as spinal tumors or arteriovenous malformations (AVMs) that may be affecting the spinal cord. It can further help in identifying post-surgical complications like arachnoiditis, which is the inflammation and scarring of the delicate membrane covering the spinal cord. For patients with chronic symptoms following spinal surgery, a myelogram can help distinguish between new nerve compression and scar tissue. Specialized myelograms are also utilized to determine the exact location of a cerebrospinal fluid (CSF) leak, which can cause severe positional headaches.
The Myelography Procedure
Preparation for a myelogram generally involves fasting, typically stopping solid food intake six hours before the procedure. Patients are also instructed to review their medications with their physician, as some, like blood thinners or certain diabetes drugs, may need to be temporarily paused. The procedure is usually conducted by a radiologist in a fluoroscopy suite, with the patient lying on their stomach or side on a specialized examination table.
The first step involves a lumbar puncture, performed in the lower back after the area has been thoroughly cleaned and numbed with a local anesthetic. Using fluoroscopic guidance, a thin needle is inserted into the subarachnoid space, the area containing the cerebrospinal fluid that surrounds the spinal cord. A small amount of CSF is sometimes withdrawn for laboratory testing, and then the contrast dye is slowly injected through the needle.
Following the injection, the examination table is gently tilted in various directions to allow gravity to move the contrast material throughout the specific region being examined. The radiologist uses the live X-ray images from the fluoroscope to monitor the flow of the dye and capture images as the contrast outlines the spinal cord and nerve root sleeves. Immediately after fluoroscopy, a Computed Tomography (CT) scan is almost always performed, which provides highly detailed pictures of the bone and soft tissue in combination with the contrast agent.
Safety Considerations and Alternatives
Myelography carries certain risks, though it is generally considered a safe test. The most common side effect is a headache, which occurs in up to 10% of patients and is often related to a small leak of cerebrospinal fluid from the needle insertion site. Nausea and vomiting are also reported side effects that usually resolve within a day or two.
More serious but rare complications include an allergic reaction to the contrast dye, infection in the spinal fluid (meningitis), or a small risk of seizure due to the contrast entering the brain’s fluid spaces. To minimize the risk of a prolonged headache, patients are typically advised to rest with their head elevated and to increase their fluid intake for 24 hours following the test. A severe, persistent post-procedure headache may require a targeted procedure called a blood patch to seal the leak.
The advent of modern imaging, particularly MRI, has made the myelogram a secondary or specialized diagnostic tool in many instances. MRI offers superior soft-tissue contrast without the need for a lumbar puncture or exposure to radiation. However, the myelogram remains the preferred option for patients who have implanted metal devices like pacemakers or certain spinal hardware that are incompatible with the strong magnetic field of an MRI machine. It is also employed when a previous MRI was diagnostically inconclusive or when a surgeon needs specific visualization of the nerve root anatomy for pre-operative planning.