What CT study is preferred for a patient with suspected radiculopathy when MRI is unavailable?

CT Imaging for Suspected Radiculopathy When MRI is Unavailable

CT myelography is the preferred CT study for evaluating suspected radiculopathy when MRI is unavailable or contraindicated. 1

Primary Recommendation: CT Myelography

CT myelography should be obtained when MRI cannot be performed in patients with clinically apparent radiculopathy. 1 This technique provides:

• Superior visualization of the thecal sac and small nerve roots at higher spatial resolution than MRI 1
• Excellent depiction of foraminal stenosis, bony lesions, and nerve root compression 1
• Diagnostic accuracy of 81% for cervical radiculopathy lesions (compared to 88% for MRI, 57% for plain myelography, and only 50% for CT alone) 1

The American College of Radiology specifically states that CT myelography offers a complementary benefit to MRI and serves as an excellent alternative in patients with MRI contraindications (such as pacemakers, claustrophobia, or metallic implants). 1

Why Not Plain CT?

Plain CT without myelography is significantly less sensitive for radiculopathy evaluation and should not be substituted for MRI. 1 Key limitations include:

• Only 50% accuracy for detecting cervical radiculopathy lesions 1
• Less sensitive than MRI for nerve root compression, particularly from disc herniations 1
• Cannot adequately assess the cervical cord and nerve roots in plain imaging 2
• Superior only for bony detail (osteophytes, uncovertebral joints, facet joints) but misses soft tissue pathology 1

Plain CT may have limited utility for evaluating osseous structures like OPLL (ossification of posterior longitudinal ligament) but remains inadequate as the primary study for radiculopathy. 1

Important Procedural Considerations

CT myelography requires intrathecal contrast injection via lumbar or cervical puncture, which carries documented risks:

• 30% of patients report unexpected reactions during the procedure 1
• 14% experience maximum pain scores of 10/10 during injection 1
• The invasive nature makes this appropriate only when MRI is truly unavailable, not merely inconvenient 1

Clinical Algorithm

When radiculopathy is suspected:

1. First choice: MRI cervical spine without contrast (88% diagnostic accuracy) 1
2. If MRI contraindicated or unavailable: CT myelography (81% diagnostic accuracy) 1
3. Plain CT is NOT an acceptable substitute (only 50% diagnostic accuracy) 1

Critical Pitfalls to Avoid

• Do not order plain CT as a substitute for MRI when evaluating radiculopathy - it will miss up to 50% of pathology and may necessitate repeat imaging anyway 1, 2
• Remember that degenerative findings are common in asymptomatic patients (65% of patients aged 50-59 show significant degeneration), so clinical correlation is essential 1, 3
• CT myelography and MRI should be viewed as complementary studies, not interchangeable - they have different strengths in characterizing disc versus bony pathology 4