CT Myelogram

A CT myelogram is a CT scan performed after a special dye has been injected into the fluid-filled space surrounding the spinal cord and nerves. The dye outlines these structures, so the scan can show where the cord or nerve roots are being pressed on. It is used mainly as an alternative when an MRI cannot be performed — for example in some people with pacemakers or certain implants — or when previous surgery and metalwork make an MRI hard to interpret.

Using X-ray guidance and local anaesthetic, a thin needle is placed into the lower back to reach the sac of spinal fluid (a procedure similar to a lumbar puncture), and a small amount of contrast dye is introduced into that fluid. The dye mixes with the fluid and outlines the cord and nerve roots. A CT scan is then taken; wherever a disc, bone spur or narrowing is pressing on the nerves, the dye column shows an indentation or blockage, pinpointing the problem in fine bony detail.

This is a more involved test than a plain CT because of the injection. It is carried out by a radiologist, usually as a day-case procedure. You may be positioned lying down and tilted to help the dye spread. Afterwards you will rest for a period and are advised to take it easy and drink plenty of fluids, as a headache can sometimes follow the needle into the spinal fluid. You will normally need someone to take you home. The team will give you specific after-care advice.

For most people, MRI has replaced the myelogram because it shows the same structures without a needle into the spinal fluid or any radiation. But the CT myelogram remains a valuable back-up: when MRI is impossible or its images are degraded by metal, it can still reveal exactly where nerves or the cord are compressed, often with superb bony detail — information that can be essential for planning surgery.

• —Royal College of Radiologists — iRefer: Making the Best Use of Clinical Radiology
• —Royal College of Radiologists — Standards for Intravascular Contrast Agent Administration
• —British Association of Spine Surgeons (BASS)

This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.