A CT myelogram is a specialized diagnostic imaging procedure that provides detailed pictures of the spine. The test combines a Computerized Tomography (CT) scan with the injection of a radiopaque contrast dye into the space surrounding the spinal cord. The dye mixes with the cerebrospinal fluid (CSF), which bathes the spinal cord and nerve roots, allowing these structures to be clearly outlined.
Why CT Myelography is Necessary
CT myelography is typically reserved for specific clinical situations, as Magnetic Resonance Imaging (MRI) is often the preferred initial method for spinal issues. The test becomes a necessary alternative when an MRI is contraindicated, such as for patients who have non-MRI-safe implanted medical devices like certain pacemakers or neurostimulators. It is also highly useful when a patient has metallic surgical hardware, like rods or screws, which can cause significant image distortion on an MRI, making the results difficult to interpret.
The procedure offers a distinct advantage in evaluating certain pathologies, particularly those involving the bony structures of the spine. It is highly effective for precisely assessing the degree of nerve root compression, spinal stenosis, and post-surgical changes. The contrast dye directly outlines the nerve roots and the thecal sac, allowing physicians to accurately identify issues like spinal cord tumors, herniated discs, or complications related to a cerebrospinal fluid leak.
Preparing for the Examination
Patients are usually advised to fast, avoiding solid foods for several hours before the exam, though clear liquids may be permitted. It is recommended to increase the intake of clear fluids the day before to ensure good hydration, which can help in the post-procedure recovery.
A review of all medications is conducted, as certain drugs must be temporarily stopped before the procedure. This includes blood-thinning medications, which increase the risk of bleeding at the injection site. Specific seizure or psychiatric medications, such as some antidepressants and antipsychotics, may need to be withheld for 24 to 48 hours because they can lower the seizure threshold. Patients must provide informed consent and arrange for someone to drive them home, as driving is restricted for a full day following the test.
The Step-by-Step Procedure
The CT myelogram procedure begins with the patient lying on an examination table, typically on their stomach or side, to allow access to the spine. The physician uses an antiseptic solution to clean the skin over the injection site, which is usually in the lumbar (lower) spine. A local anesthetic is then administered to numb the area, causing a brief stinging sensation.
Using continuous X-ray guidance, known as fluoroscopy, the physician carefully inserts a fine, hollow needle into the spinal canal. The needle is guided into the subarachnoid space, which is the area that contains the cerebrospinal fluid (CSF). Once the needle is correctly positioned, a small amount of CSF may be withdrawn for testing, followed by the slow injection of the non-ionic, water-soluble contrast dye.
Patients may feel a brief warming sensation or a sense of pressure during the injection, but they must remain very still to ensure accuracy. Following the injection, the needle is immediately removed, and the injection site is bandaged. The patient is then moved to the CT scanner, sometimes while still on the table.
During the CT scanning phase, the table may be tilted or the patient may be asked to change position to help the contrast dye flow to the specific area of the spine being examined, such as the cervical (neck) or thoracic (mid-back) regions. The CT scan captures detailed, cross-sectional images of the spinal structures. The entire injection and imaging process usually takes approximately 30 to 60 minutes.
What to Expect During Recovery
Following the completion of the CT scan, the patient is moved to a recovery area for monitoring, typically for an hour or more. The most important instruction is the requirement to lie flat for four to six hours to minimize the risk of a post-dural puncture headache. This headache is caused by a small leak of cerebrospinal fluid through the needle puncture site, which is exacerbated when sitting or standing upright.
Drinking plenty of fluids, particularly water and caffeinated beverages, is strongly encouraged to help the body replenish the cerebrospinal fluid and flush the contrast dye out of the system. Patients are advised to take it easy for the remainder of the day, avoiding strenuous activity, heavy lifting, and bending for at least 24 hours. While mild soreness at the injection site is common, patients should contact their healthcare provider immediately if they experience a severe headache unrelieved by rest and medication, a fever, neck stiffness, or numbness in the legs.