Can an MRI (Magnetic Resonance Imaging) show nerve root compression?

MRI Can Effectively Demonstrate Nerve Root Compression

Yes, MRI can show nerve root compression and is the imaging modality of choice for evaluating suspected nerve root impingement in both the cervical and lumbar spine. 1

Diagnostic Performance

Cervical Spine

• MRI correctly predicts nerve root compression in 88% of surgically confirmed cases, significantly outperforming CT (50%), conventional myelography (57%), and CT myelography (81%). 1
• MRI has become the preferred method for evaluating cervical nerve root impingement due to its superior soft-tissue contrast and high spatial resolution. 1

Lumbar Spine

• MRI demonstrates nerve root compression in patients with radiculopathy or clinical signs of spinal stenosis, with accurate depiction of disc disease and neural compression. 1
• In symptomatic patients, 57% with low back pain and 65% with radiculopathy show disc herniation on MRI, compared to only 20-28% in asymptomatic individuals. 1
• High-resolution 3D T2-weighted sequences outperform standard 2D imaging, with detection of high-grade stenosis with nerve root deformity increasing from 16.4% (2D) to 41.8-43.6% (3D) for lateral recess stenosis. 2

Important Limitations and Caveats

False Positives and Negatives

• MRI demonstrates frequent false-positive and false-negative findings in cervical radiculopathy, with abnormal MRI levels not always corresponding to clinical examination findings. 1
• MRI significantly underestimates lumbar lateral recess root compression in 28-29% of surgically confirmed cases, particularly in degenerative lateral recess disease. 3
• Degenerative findings are commonly observed in asymptomatic patients, so imaging must be correlated with clinical presentation. 1

Specific Anatomic Challenges

• Conventional myelography remains superior for lateral recess compression, correctly predicting impingement in 93-95% of cases versus MRI's 71-72%. 3
• MRI can detect lateral disc herniations compressing the distal nerve root lateral to the neural foramen that may be missed on standard spine MRI. 1

Clinical Application Algorithm

When to Order MRI

• Patients with radiculopathy who have failed 6 weeks of conservative therapy and are surgical or interventional candidates. 1
• Urgent MRI is indicated for suspected cauda equina syndrome due to its ability to accurately depict soft-tissue pathology and assess spinal canal patency. 1
• New or progressive neurologic deficits with clinical signs of nerve root irritation. 1

Contrast Enhancement

• MRI without IV contrast is the appropriate initial study for evaluating nerve root compression. 1
• Contrast is reserved for postoperative patients to distinguish recurrent/residual disc from fibrosis/scar, or when noncontrast MRI is nondiagnostic. 1

Alternative Imaging When MRI is Inadequate

• CT myelography should be considered when MRI findings are equivocal or nondiagnostic, particularly for lateral recess compression. 1, 3
• CT myelography is occasionally more accurate in diagnosing nerve root compression in the lateral recess. 1
• CT myelography is appropriate for patients with MRI contraindications or significant metallic hardware artifact. 1

Key Clinical Pitfall

The most critical error is relying solely on MRI findings without clinical correlation. The sensitivity of MRI for detecting lumbar nerve root compromise is only 0.25 (25%), while specificity is 0.92 (92%). 4 This means MRI frequently misses true nerve root compression but rarely shows false compression when none exists. Therefore, always correlate MRI findings with patient history, physical examination, and electrodiagnostic studies before making treatment decisions. 4