A CT myelogram is an imaging study that pairs a spinal contrast injection with a CT scan to produce highly detailed pictures of the spinal canal, nerve roots, and surrounding structures. The contrast dye, injected into the fluid-filled space around the spinal cord, lights up areas that standard CT or even MRI can miss, making it especially useful for diagnosing nerve compression, spinal stenosis, and cerebrospinal fluid leaks. Though MRI has become the go-to first-line spine imaging tool, the CT myelogram remains a critical backup and, in certain situations, the superior test.
Why Doctors Order a CT Myelogram
The most common reason you’ll hear a CT myelogram recommended is that an MRI either cannot be performed or did not provide a clear enough answer. Some people have implanted devices like certain pacemakers or cochlear implants that make MRI unsafe. Others have spinal hardware from prior surgery, which creates metallic artifact on MRI images and can obscure exactly the area the surgeon needs to see. In these cases a CT myelogram steps in as the primary diagnostic tool. The combination of myelography and high-resolution CT produces detailed views of both the bony spine and the soft tissues inside the spinal canal.1Radiographics. CT Myelography: Clinical Indications and Imaging Findings
Beyond MRI contraindications, CT myelography adds value when there is a mismatch between a patient’s symptoms and what MRI shows. A person with classic signs of spinal stenosis, for instance, might have an MRI that looks only mildly narrowed. Prior work has shown that CT myelography has a higher sensitivity for revealing stenosis compared to MRI, and it identifies additional narrowed levels in patients with multilevel disease more than half the time.2PubMed. When does CT myelography add value beyond MRI for lumbar degenerative disease? That difference can directly change surgical planning: if a second or third compressed level is found, the operation may need to address all of them.
CT myelography also plays a unique role in hunting for cerebrospinal fluid (CSF) leaks and CSF-venous fistulas, conditions that cause spontaneous intracranial hypotension, a headache disorder that worsens when you stand up. These leaks are often tiny and invisible on conventional imaging, and a dynamic CT myelogram, where images are captured in rapid sequence after contrast injection, can pinpoint the exact location of a dural tear when other tests come up empty.3PubMed. Cryptogenic Cerebrospinal Fluid Leaks in Spontaneous Intracranial Hypotension: Role of Dynamic CT Myelography
How It Compares to MRI
MRI is noninvasive, requires no needle, and excels at showing soft-tissue detail like disc herniations and spinal cord abnormalities. So why bother with a test that involves a spinal injection? The answer depends on what information the referring doctor needs and whether MRI can actually deliver it.
CT myelography provides sharper visualization of bony structures and is far less susceptible to distortion from patient movement because the CT images are acquired very quickly.4PubMed Central. Reliability of CT Myelography versus MRI in the Assessment of Spinal Epidural Disease For patients who cannot hold still during a lengthy MRI scan due to pain or claustrophobia, this speed is a practical advantage. CT myelography can also be used when radiation treatment planning needs a direct measurement of tissue density, something MRI cannot provide.
In terms of reliability, the two tests perform comparably on many metrics. When radiologists rate spinal epidural disease on axial (cross-sectional) images, agreement between different readers is somewhat higher with CT myelography than with MRI.4PubMed Central. Reliability of CT Myelography versus MRI in the Assessment of Spinal Epidural Disease An older meta-analysis looking at lumbar spinal stenosis found sensitivity for MRI ranging from about 81% to 97%, CT from 70% to 100%, and standard myelography alone from 67% to 78%.5PubMed. Diagnosis of lumbar spinal stenosis in adults: a metaanalysis of the accuracy of CT, MR, and myelography In practice, the two modalities complement each other more than they compete. MRI is the screening tool; CT myelography is the follow-up when MRI leaves questions unanswered or when it cannot be performed at all.
What Happens During the Procedure
A CT myelogram unfolds in two phases: the contrast injection (the myelography part) and the CT scan. The entire process usually takes between 45 minutes and about an hour and a half, depending on the clinical question and how many spinal levels need to be imaged.
The Contrast Injection
You lie face-down or on your side on a fluoroscopy table. Using real-time X-ray guidance, a radiologist inserts a thin needle into the lumbar spine, typically between the lower vertebrae, to reach the thecal sac, the membrane-lined space filled with cerebrospinal fluid that surrounds the spinal cord and nerve roots.6PubMed Central. Lumbar puncture under fluoroscopy guidance: a technical review for radiologists Before the needle goes in, the skin and deeper tissues are numbed with local anesthetic. You may feel pressure or a brief sting when the needle enters the spinal canal.
Once the needle is in position, a non-ionic iodinated contrast agent is injected into the spinal fluid. The type of contrast matters: only non-ionic agents are used, because ionic contrast media injected into the spinal canal can cause severe and potentially fatal neurotoxic reactions.7PubMed. Inadvertent intrathecal use of ionic contrast agent Modern non-ionic contrast agents carry a much lower risk, a safety improvement that dates back to the mid-1970s when non-ionic formulations first replaced the older, harsher agents.8PubMed. Neurotoxicity of water-soluble contrast media Allergic reactions to the contrast are possible but uncommon, and your medical team will ask about contrast allergies beforehand.
The CT Scan
After the contrast is injected and has had a moment to flow around the spinal structures, you are moved to a CT scanner, often in the same room or one nearby. The scan itself is quick. You lie on the scanner table while the machine captures thin-slice images of the spine. The contrast-enhanced spinal fluid creates a bright outline around the spinal cord and nerve roots, making any compression, herniation, or leak dramatically easier to see.
Timing and contrast density during the scan both affect image quality. Research on CT myelography for detecting CSF-venous fistulas has shown that higher contrast density in the spinal fluid and shorter delays between injection and scanning both improve the odds of finding small abnormalities, with contrast density having roughly four times the impact of timing.9American Journal of Neuroradiology. Maximizing the Conspicuity of CSF-Venous Fistulas on CT Myelography: Assessment of Contrast Density and Timing Effects This is one reason the procedure is done promptly after injection rather than hours later.
What It Actually Feels Like
Compared to an MRI, which is loud and claustrophobic but painless, a CT myelogram involves some physical discomfort. The needle insertion through the numbed skin usually produces a sensation of deep pressure more than sharp pain, though some patients do experience brief shooting sensations if a nerve root is grazed. Studies comparing patient experiences across imaging modalities have found that myelography is the most frequently reported as painful and unpleasant, ahead of both CT and MRI.10PubMed. Patient attitudes to myelography, computed tomography and magnetic resonance imaging when examined for suspected lumbar disc herniation
The injection of contrast itself can produce a warm or tingling sensation that moves along the spine. Some people feel brief nausea or a headache during the injection. Once the CT scan begins, the experience is no different from any other CT: you lie still for a few minutes while the machine hums around you. There is no claustrophobic tube involved, just an open ring-shaped scanner.
After the procedure, you will typically be asked to rest with your head elevated for a period, often a few hours, to reduce the risk of a post-procedure headache. Most facilities observe patients for at least one to two hours before discharge. You can usually go home the same day, but driving yourself is not recommended.
Preparation Before the Test
Your care team will generally ask you to stop eating for several hours before the procedure. You should disclose all medications, particularly blood thinners, which may need to be paused to reduce the risk of bleeding at the needle insertion site. Bring a list of your current medications and any known allergies, especially to iodine-based contrast agents.
One area of preparation that has been debated for decades is whether patients taking medications that lower the seizure threshold, such as certain antidepressants and antipsychotics, need to stop them before myelography. The theoretical concern is that contrast dye in the spinal fluid could provoke a seizure, and that these medications might compound the risk. In practice, the evidence suggests this worry is largely overblown. A large survey of radiologists found that the majority do not routinely discontinue these medications, and the vast majority reported never having seen a patient experience a seizure following myelography. The difference in seizure rates between those who stopped the medications and those who did not was not statistically significant.11American Journal of Neuroradiology. Critical Assessment of Myelography Practices: A Call for Rational Guideline Revision That said, individual practices vary, and your doctor may still ask you to hold certain medications depending on institutional protocol.
Risks and Complications
The most common side effect is a headache after the procedure, known as a post-dural puncture headache. This happens because the needle creates a tiny hole in the membrane surrounding the spinal fluid, and some fluid leaks out, reducing pressure around the brain. These headaches are typically positional: they worsen when you sit or stand and improve when you lie flat. Most resolve on their own within a few days with rest, fluids, and caffeine.
For a small number of patients, the headache is severe enough to require treatment with an epidural blood patch, a procedure where a small amount of your own blood is injected near the puncture site to seal the leak. One study found that when a large volume of contrast dye was seen tracking into the epidural space during the myelogram, the odds of needing a blood patch afterward were substantially higher.12PubMed. Epidural Contrast Volume on Post-Myelogram Lumbar CT Predicts the Rate of Subsequent Blood Patch Treatment This means the radiologist performing the study can sometimes anticipate who is more likely to develop a bad headache based on what happens during the injection.
Other uncommon risks include:
- Infection: any time a needle enters the spinal canal there is a small risk of introducing bacteria, though sterile technique makes this rare.
- Bleeding: a small amount of bleeding at the puncture site is normal, but significant epidural bleeding is uncommon and more of a concern for people on blood thinners.
- Allergic reaction: reactions to the non-ionic contrast used today are infrequent, but hives, itching, and very rarely anaphylaxis can occur.
- Seizure: extremely rare with modern contrast agents, as discussed in the preparation section above.
- Nerve damage: very rare, but transient numbness or tingling in the legs can occur if the needle contacts a nerve root during insertion.
The radiation dose from the CT portion is another consideration. It is comparable to other diagnostic CT scans of the spine and is generally considered acceptable given the clinical information gained, but it is one reason CT myelography is not used as a screening test.
Detecting CSF Leaks and Venous Fistulas
One of the areas where CT myelography has become genuinely indispensable is in the workup of spontaneous intracranial hypotension. This condition, caused by spinal CSF leaks, produces debilitating headaches that worsen with upright posture and can significantly impair daily life. The challenge is that the leak site is often tiny and can be missed on conventional imaging.
A relatively recent discovery in this field is the CSF-venous fistula, an abnormal connection between the spinal fluid space and a nearby vein. Unlike a straightforward dural tear where fluid pools in the epidural space, a fistula drains spinal fluid directly into the venous system, making it even harder to spot. CT myelography, particularly the dynamic version where images are captured in rapid succession after contrast injection, has proven effective at identifying these fistulas. In cases where both standard CT myelography and dynamic myelography were performed, the fistula was found on both in about 88% of cases, and some fistulas were identified even when there was no visible epidural fluid collection.13PubMed. CSF Venous Fistulas in Spontaneous Intracranial Hypotension: Imaging Characteristics on Dynamic and CT Myelography
Finding the fistula or tear matters because treatment is often surgical or procedural. A targeted epidural blood patch at the exact site of the leak, or surgical repair of a dural defect, depends entirely on knowing where the problem is. CT myelography is frequently the test that finally provides that answer after other studies have failed.
Reading the Results
A radiologist interprets the CT myelogram images and generates a report for your referring physician. What they look for depends on the clinical question. For spinal stenosis, they assess how much the spinal canal and nerve root exit passages have narrowed, using the contrast column as a reference: where the bright contrast dye is pinched or cut off, the nerve is being compressed. For disc herniations, the images show where disc material pushes into the contrast-filled space and displaces a nerve root.
In the context of spinal stenosis, CT myelography can pick up narrowing that MRI underestimates. One study found that in patients with multilevel stenosis, CT myelography identified additional stenotic levels beyond what MRI showed in about 58% of cases.2PubMed. When does CT myelography add value beyond MRI for lumbar degenerative disease? For the surgeon, those extra findings can mean the difference between a one-level and a three-level decompression.
For CSF leak evaluations, the radiologist watches for contrast escaping the thecal sac into the epidural space or tracking into a vein. The location along the spine, the side of the body, and the specific nerve root level are all documented because they guide the treatment plan.
Turnaround time for results varies by institution. In urgent clinical settings the images may be read within hours, while outpatient studies might take a day or two. Your referring doctor will discuss the findings with you and outline next steps, which could range from watchful waiting and physical therapy to surgical consultation.
Newer Scanner Technology
CT scanner technology itself is evolving in ways that affect myelography quality. One recent advance is the photon-counting detector (PCD) CT scanner, which processes X-ray photons differently from conventional energy-integrating detector (EID) scanners. In the context of CT myelography, PCD scanners have shown higher image quality scores, better visibility of nerve root sleeves, and improved overall diagnostic confidence compared to conventional scanners, though the newer technology also introduces more image noise.14PubMed Central. Myelography Using Energy-Integrating Detector CT Versus Photon-Counting Detector CT for Detection of CSF-Venous Fistulas in Patients With Spontaneous Intracranial Hypotension
This matters most for the subtle findings that are hardest to catch, like CSF-venous fistulas. Better nerve root sleeve visibility means the radiologist can trace fine anatomic structures more confidently and distinguish a tiny abnormal connection from normal anatomy. PCD scanners are still rolling out to major academic centers, so availability depends on where you are. But the trend is toward CT myelography becoming more sensitive over time as the hardware improves, which is welcome news for patients whose leaks have eluded detection on older equipment.
When a CT Myelogram Might Not Be the Right Test
For all its strengths, CT myelography is not a first-line study for most spinal problems. If you have a straightforward disc herniation or typical sciatica and no contraindication to MRI, an MRI will almost always be ordered first. It provides excellent soft-tissue detail without radiation and without a needle. CT myelography enters the picture when MRI is contraindicated, when MRI results are inconclusive, when surgical planning demands extra anatomic precision, or when a CSF leak is suspected.
Pregnant patients are generally not candidates because of the radiation exposure, and people with certain bleeding disorders or active spinal infections may need to defer the test. A history of severe allergic reaction to iodinated contrast is a relative contraindication, though premedication protocols with steroids and antihistamines can allow the test to proceed in cases where it is truly necessary.
If you have been told you need a CT myelogram, it is worth asking your doctor two questions: what specific information the test is expected to provide beyond what MRI has already shown, and how the result will change your treatment plan. A CT myelogram is a well-established, broadly safe test, but like any invasive procedure it should be done for a clear clinical reason rather than as a routine add-on.