Myelography is an imaging technique which involves the intrathecal instillation of contrast medium and shows its passage in the lumbar or cervical subarachnoid space around the spinal cord and nerve roots. Myelography uses a real-time form of X-ray called fluoroscopy. The contrast medium is a specially formulated water-soluble iodine containing material.
CT myelography: CT scan is performed after myelography. Combining CT scan with myelography gives a better view of spinal cord and roots which appear as filling defect in the opaque subarachnoid space.
Low-dose CT myelography: The CT scan is performed with a relatively smaller amount of dilute contrast medium and thus ahs advantage of reducing radiation exposure as well as exposure to contrast media. This technique has largely replaced the conventional myelogram. Newer CT scan with multidetector scanners are being used now a days, which quickly reform the images equivalent to traditional myelography projections.
Myelography can be used to detect abnormalities of spinal cord, spinal canal and spinal nerve roots. Myelography can also diagnose the spinal stenosis and herniation of intervertebral disc into spinal canal.
Myelography has largely been replaced by CT myelogram and MRI scans for the diagnosis of spinal cord diseases. There are few condition for which conventional myelography is indicated such as suspected meningeal or arachnoid cyst, CSF fistula.
A myelogram is also helpful in assessing the outcome of surgery in an individual patient and thus helps in planning surgery. Conventional myelography and CT myelography provide highly precise information before the surgeries like spinal fusion and spinal fixation.
Contraindications: Myelography is a quite safe technique but care should be taken in following conditions:
- Raised intracranial pressure
- History of allergic reaction to contrast media
- Suspected spinal block
- Patient with bleeding disorder
- Patient taking anticoagulant medication
- Soft tissue infection or infection at local site
Complications: the most frequent complications are
- Headache ,nausea and vomiting – due to neurotoxic effect of contrast agent
- Postural headache - due to leakage of CSF from the puncture site
- Vasovagal syncope
- Puncture of the spinal cord - rare but serious complication specially in high lumbar puncture and risk in higher in cases of spinal stenosis
- Seizures - reported in 0.1 to 0.3% cases
- Others - hyperthermia, hallucinations, depression, and anxiety
- Most important limitation: only the spinal canal and proximal nerve root can be visualised. The distal areas can be better viewed with MRI.
- Myelography should not be in pregnancy to avoid risk to the foetus
- Findings are not accurate if the patient moves during the procedure