Can cauda equina syndrome be diagnosed with a Computed Tomography (CT) scan?

Can Cauda Equina Syndrome Be Diagnosed with CT Scan?

CT scan can detect cauda equina compression but is significantly inferior to MRI and should only be used when MRI is unavailable or contraindicated. 1, 2

CT Diagnostic Performance

CT lumbar spine without IV contrast can answer whether cauda equina compression is present, but with important limitations 1, 2:

• Sensitivity: 100% for detecting compression when present 1
• Specificity: 60-83% compared to MRI 1
• CT has extremely low sensitivity (only 6%) for identifying epidural abscess and neural compression, and cannot adequately visualize the intraspinal contents, epidural space, or nerve root compression that defines cauda equina syndrome 3

When CT Can Be Useful

CT provides reliable negative predictive value using thecal sac effacement as a marker 1, 4:

• <50% thecal sac effacement on CT reliably excludes cauda equina impingement with a negative predictive value of 0.99 1, 4
• ≥50% thecal sac effacement predicts significant spinal stenosis with 98% sensitivity 1, 4
• Among patients with ≥50% effacement on CT, 19 of 40 (47.5%) had confirmed cauda equina impingement on subsequent MRI 1

Recent photon-counting CT technology shows promise with 100% sensitivity and 60-83% specificity versus MRI, though this remains investigational 5.

Critical Limitations of CT

CT scan alone is insufficient for surgical planning, even if it shows gross spinal canal compromise 3:

• CT cannot adequately visualize soft-tissue pathology, nerve root compression details, or epidural space abnormalities necessary for surgical decision-making 3
• Do not rely on CT findings alone to rule out cauda equina syndrome when clinical suspicion is high, as significant neural compression can be missed 3
• CT with contrast provides no additional benefit and is not recommended 1

MRI Remains the Gold Standard

MRI lumbar spine without IV contrast is the imaging study of choice with 96% sensitivity and 94% specificity 2:

• MRI accurately depicts soft-tissue pathology, assesses vertebral marrow, and evaluates spinal canal patency 2
• MRI provides optimal visualization of the cauda equina nerve roots, epidural space, and degree of compression necessary for surgical decision-making 3
• MRI is essential for surgical planning and cannot be substituted by CT 3

Clinical Algorithm

When cauda equina syndrome is suspected with red flag symptoms (urinary retention, saddle anesthesia, bilateral radiculopathy) 2:

1. First-line: Emergency MRI lumbar spine without contrast 1, 2
2. If MRI unavailable or contraindicated: CT lumbar spine without contrast 1, 2
   • If CT shows <50% thecal sac effacement: cauda equina impingement reliably excluded 1, 4
   • If CT shows ≥50% thecal sac effacement: urgent MRI still required as nearly half may have cauda equina impingement requiring surgical decompression 1
3. CT myelography can be considered for surgical planning in confirmed cases when MRI remains contraindicated 1

Common Pitfalls

• Never discharge patients with ≥50% thecal sac effacement on CT without arranging urgent MRI, as nearly half may have cauda equina impingement 1
• Radiography is insensitive to evaluation of the epidural space and spinal cord compression and should not be used 6, 1
• Delaying MRI when cauda equina syndrome is suspected based on CT findings alone risks worse outcomes, as surgical intervention before complete bladder dysfunction yields significantly better results 1, 3