To understand CT myelography we need to first understand what is myelography.
Myelography is a procedure that uses a contrast [A material that enhances image of tissues] and X-rays to visualize spinal canal. A CT myelography uses CT instead of xrays.
A CT myelography can be done to find a tumor, an infection, problems with the spine such as a herniated disc, or narrowing of the spinal canal caused by arthritis.
A dye is put into the subarachnoid space with a thin needle. The dye moves through the subarachnoid space so the nerve roots and spinal cord can be seen more clearly. Pictures may be taken before and after the dye is used. To get more information from the test, a CT scan is often done after the X-rays, while the dye is still present.
Indications of CT myelography
With advent of MRI the indications of CT myelography are so rare that it is almost an obsolete procedure.
Classically a myelogram was done for
- To look for cord compression by tumor or infectiion and determine whether it is extradural or intradural
- The cause of arm or leg numbness, weakness, or pain.
- To check adequacy of spinal canal (spinal stenosis).
- Herniated disc
A detailed history is taken for knowing if there is a history of seizure, drug allergy, any bleeding problems, asthma, diabetes or renal problems.
Four to eight hours fasting is required
This procedure can be dne on out patient basis. A lumbar puncture is done.In lateral position, a sample of cerebrospinal fluid may be taken before the dye is put in the canal.
After the dye is put in, CT pictures are taken.
Patient is to lie bed with head elevated for 4 to 24 hours after the test. Strenuous activity should be avoided for at least one day after myelogram. Patient is instructed to report back immediately if one of the following ocurs
- Increase in pain, weakness, or numbness in legs.
- Severe headache, stiff neck, or your eyes become very sensitive to light.
- A headache that lasts longer than 24 hours.
- Problems urinating or having a bowel movement.
Risks & Complications
- 20% of people develop a headache, nausea, or vomiting after the test.
- Rarely, a seizure may occur after the dye is put. However there is increased risk if the dye moves to the brain. This may happen when head becomes lower than spine
- Infection at the needle site
- Bleeding into the spinal canal.
- Leakage of cerebrospinal fluid
- Allergic reaction to the dye
- Kidney problems if patient takes metformin (Glucophage) to manager diabetes.
- Cord damage.
Results & Inference
- The dye flows evenly through the spinal canal.
- The spinal cord is normal in size, position, and shape. The nerves leaving the spinal cord are normal.
- No narrowing or blockage of the spinal canal is seen.
- The flow of dye is blocked or diverted. This may signify compression due to a ruptured (herniated) disc, spinal stenosis, a nerve injury, an abscess, or a tumor.
- Inflammation of the arachnoid membrane.
- One or more nerves leaving the spinal cord are pinched.
This is a similar procedure in which after the dye is injected, a CT is done instead of xrays
A CT myelography provides a better picture and allows to construct a three dimensional views using a computer.