What is the best test to diagnose spinal cord compression if Magnetic Resonance Imaging (MRI) is unavailable?

CT Myelography is the Best Alternative to MRI for Diagnosing Spinal Cord Compression

When MRI is unavailable, CT myelography is the most appropriate alternative test for diagnosing spinal cord compression. 1

Diagnostic Options When MRI is Unavailable

CT Myelography

• First-line alternative to MRI for evaluating spinal cord compression
• Excellent for assessing:
  • Patency of the spinal canal/thecal sac
  • Subarticular recesses and neural foramina 1
  • Spinal canal narrowing due to disc herniation or epidural hematoma 1
• Can effectively diagnose severe canal stenosis in spondylotic myelopathy 1
• Particularly useful for surgical planning before intervention 1
• Sensitivity and specificity comparable to MRI for detecting significant spinal stenosis 1

Standard CT Without Contrast

• Less sensitive than CT myelography for spinal cord compression
• Can detect bony encroachment on the spinal canal from:
  • Disc-osteophyte complexes
  • Subluxation
  • Compression by herniated disc material 1
• A retrospective review showed that 50% thecal sac effacement on CT predicted significant spinal stenosis and reliably excluded cauda equina impingement when less than 50% 1
• Limited in visualizing intraspinal soft tissue pathology compared to CT myelography

Plain Radiography

• Inadequate for evaluating spinal cord compression
• Insensitive to epidural space evaluation and spinal cord compression 1
• May only show indirect signs of compression (e.g., vertebral collapse, alignment issues)
• Not recommended as the initial imaging study for suspected cord compression

Advantages of CT Myelography Over Standard CT

1. Superior visualization of neural structures: The intrathecal contrast highlights the spinal cord and nerve roots, making compression more evident
2. Better detection of lateral recess pathology: More accurate in diagnosing nerve root compression in the lateral recess 1
3. Useful in patients with contraindications to MRI: Safe for patients with non-MRI compatible implants 1
4. Less affected by metallic hardware artifacts: Valuable in postoperative patients with spinal instrumentation 1

Limitations of CT Myelography

• Invasive procedure: Requires lumbar puncture and intrathecal contrast injection 1
• Potential complications: Headache, infection, CSF leak, allergic reactions to contrast
• Inferior to MRI for:
  • Cord contusion assessment
  • Intramedullary pathology
  • Postganglionic nerve root injuries 1
  • Bone marrow abnormalities 1

Clinical Decision Algorithm

1. First choice: MRI without contrast (if available)
2. If MRI unavailable or contraindicated:
   • CT myelography for suspected spinal cord compression
   • Standard CT without contrast if CT myelography cannot be performed
3. Consider plain radiographs only for initial assessment of trauma or alignment issues, but not for definitive diagnosis of cord compression

Special Considerations

• In cases of suspected malignancy causing cord compression, CT myelography can accurately diagnose 96% of cases 2
• For cervical spine evaluation, CT myelography is particularly valuable when shoulder overlap obscures C6-C7 or C7-T1 levels on standard CT 3
• In trauma settings, CT myelography can help assess for traumatic spinal canal narrowing when MRI is unavailable 1

Remember that while CT myelography is the best alternative to MRI, it remains inferior to MRI for comprehensive evaluation of spinal cord pathology, especially for intramedullary lesions and subtle cord signal changes 4, 5.