CT Scan for Cervical Nerve Root Entrapment
CT scan of the cervical spine can show nerve root entrapment, but it is significantly less sensitive than MRI and should not be relied upon as the primary diagnostic modality for this indication. 1
CT Capabilities and Limitations
CT offers superior visualization of osseous structures that may contribute to nerve impingement, including:
- Osteophytes 1
- Uncovertebral joint hypertrophy 1, 2
- Facet joint abnormalities 1, 2
- Foraminal stenosis from bony narrowing 2, 3
However, CT is less sensitive for evaluating nerve root compression compared to MRI, particularly when compression is caused by herniated discs rather than bony structures. 1, 2
Comparative Diagnostic Accuracy
The evidence demonstrates clear performance differences:
- MRI correctly predicts 88% of nerve root compression lesions in surgically confirmed cases 2, 4
- CT myelography achieves 81% accuracy 2, 4
- Plain CT achieves only 50% accuracy 2, 4
CT is significantly inferior to MRI for identifying soft-tissue pathologies including spinal cord contusion, epidural hematoma, and nerve root avulsions that cause neurologic deficits. 5, 6
When CT May Be Appropriate
CT without contrast has specific utility in:
- Patients with MRI contraindications (pacemakers, certain implants) 6
- Evaluation of ossification of the posterior longitudinal ligament (OPLL), where CT offers superior assessment of subtype, extent, and ossification complications including nerve root compression 1
- Complementary imaging to MRI in a subset of patients with chronic radiculopathy, particularly for surgical planning when bony anatomy detail is needed 1
- Post-surgical evaluation where metallic hardware creates significant MRI artifact 2, 6
CT Myelography as an Alternative
CT myelography can be considered when MRI is contraindicated or nondiagnostic, as it:
- Achieves 81% accuracy for nerve root compression 2, 4
- Provides excellent depiction of the thecal sac and small nerve roots at higher spatial resolution than MRI 1
- Proves useful in diagnosing foraminal stenosis, bony lesions, and nerve root compression 2
- Shows better agreement for foraminal stenosis and bony lesions compared to MRI 3
However, CT myelography is invasive with documented risks, including 30% of patients reporting unexpected reactions and 14% experiencing maximum pain scores during the procedure. 1
Critical Pitfall to Avoid
Do not rely on CT alone when clinical examination suggests nerve root or spinal cord involvement. 6 CT cannot adequately exclude significant soft-tissue pathology in patients presenting with signs or symptoms of cervical nerve root injury. 5
The addition of IV contrast to CT does not add significant value for evaluating nerve root entrapment in the absence of "red flag" symptoms. 1, 6
Recommended Imaging Algorithm
For suspected nerve root entrapment:
- First-line: MRI cervical spine without contrast 7, 6, 4
- Alternative: CT myelography if MRI is contraindicated or equivocal 2, 6, 4
- CT without contrast only when evaluating primarily osseous pathology or when MRI is absolutely unavailable 1, 6
MRI remains the preferred method to evaluate the cervical spine in suspected nerve root impingement due to its superior soft-tissue contrast and spatial resolution. 2