What is a myelogram and when is it recommended?

Myelogram: Definition and Recommendations

A myelogram is a diagnostic imaging procedure that involves injecting contrast material into the spinal canal to evaluate the spinal cord, nerve roots, and surrounding structures, and it is primarily recommended when MRI is contraindicated, unavailable, or has yielded inconclusive results. 1

What is a Myelogram?

• A myelogram involves the instillation of intrathecal contrast media for imaging evaluation of spinal canal pathology 2
• The procedure has evolved over its 90-year history with progressively less toxic contrast agents and advanced imaging acquisition technology 2
• Modern myelography is typically performed in conjunction with CT (CT myelography) or fluoroscopy 3

Types of Myelography

• CT Myelography: Combines CT imaging with intrathecal contrast to provide detailed cross-sectional images of the spine 3
• Fluoroscopic Myelography: Uses real-time X-ray imaging during contrast injection to visualize the flow of contrast material 3, 4
• Dynamic Digital Subtraction Myelography: Involves continuous real-time fluoroscopic imaging of the spine, particularly useful for detecting subtle CSF leaks 3

When is a Myelogram Recommended?

Primary Indications:

• When MRI is contraindicated or unavailable: 1, 2

  • Patients with pacemakers or other non-MRI compatible implants
  • Patients with severe claustrophobia
  • Settings where MRI technology is not accessible

• When MRI results are inconclusive or non-diagnostic: 3

  • Cases where hardware artifacts on MRI limit diagnostic accuracy
  • When more detailed evaluation of bony structures is needed

• Specific clinical scenarios:

  • Evaluation of suspected cerebrospinal fluid (CSF) leaks 3
  • Assessment of brachial plexus injury 2
  • Radiation therapy treatment planning 2
  • Detailed assessment of spinal canal stenosis when MRI is inadequate 3

Clinical Applications by Spinal Region:

• Cervical spine:

  • CT myelography can help identify regions of position-dependent cord compression related to cervical spinal stenosis 3
  • Useful for evaluating nerve root compression in patients with cervical radiculopathy when MRI is not an option 3

• Thoracic and lumbar spine:

  • Assessment of spinal canal/thecal sac patency and evaluation of subarticular recesses and neural foramina 3
  • Occasionally more accurate than MRI in diagnosing nerve root compression in the lateral recess 3

Limitations and Considerations

• Invasive procedure: Requires lumbar puncture for intrathecal injection of contrast 3
• Radiation exposure: Involves ionizing radiation, especially when combined with CT 3
• Potential complications: Headache, nausea, seizures (rare), and allergic reactions to contrast 5
• Diagnostic limitations: Shows significant interobserver variability in interpretation 6
• Reduced role in modern practice: The use of myelography for routine evaluation of spinal disease has diminished greatly due to the superior soft-tissue contrast of MRI 2, 7

Appropriate Imaging Pathway

1. Initial evaluation: Plain radiographs if clinically indicated 1
2. Primary advanced imaging: MRI without contrast as the first-line advanced imaging modality 1
3. Secondary option: CT myelography when MRI is contraindicated, unavailable, or results are inconclusive 1, 2

Important Caveats

• According to ACR Appropriateness Criteria, myelography is rated as "usually not appropriate" for back pain evaluation when MRI has already been performed and provided sufficient diagnostic information 1
• CT myelography may be superior to MRI in certain scenarios, such as detailed evaluation of bony structures and assessment of patients with extensive metallic hardware 3
• The ultimate judgment regarding the appropriateness of myelography, including the route of contrast administration and imaging coverage, must be made by the radiologist with appropriate documentation 3