Best Imaging for Sciatica
MRI without contrast is the preferred imaging modality for diagnosing sciatica when imaging is indicated, as it directly visualizes soft tissues including the spinal cord, nerve roots, intervertebral discs, and ligaments without ionizing radiation exposure. 1, 2
When to Image
Imaging is not routinely indicated for acute sciatica without red flags. 1 Most sciatica improves within 2-4 weeks with conservative treatment regardless of intervention. 2
Order imaging only if:
- Severe symptoms persist beyond 6-8 weeks of conservative treatment 2
- Red flags are present suggesting infection, malignancy, cauda equina syndrome, or progressive neurological deficits 1
- Surgical intervention is being considered 2, 3
MRI as First-Line Imaging
MRI without contrast should be the initial imaging study when evaluation is warranted. 1, 2
Advantages of MRI:
- Superior soft tissue visualization compared to CT, directly showing disc herniations, nerve root compression, and spinal cord pathology 1, 2
- No ionizing radiation exposure 2
- Can identify alternative diagnoses including piriformis syndrome, distal nerve entrapments, tumors, and infections 4
- Sensitivity of 75% and specificity of 77% for lumbar disc herniation when compared to surgical findings 5
Technical Requirements:
- T2-weighted sequences and fat suppression techniques are necessary for evaluating marrow edema and paraspinal pathology 1
- Contrast is not routinely needed unless infection or tumor is suspected 1
Alternative Imaging Modalities
CT Scan
CT is a second-line option only when MRI is contraindicated or unavailable. 1, 6
- Provides excellent bone detail but suboptimal visualization of intraspinal contents and soft tissues 1
- Higher sensitivity than myelography for disc herniation but inferior to MRI 6
- Exposes patient to ionizing radiation 2
Plain Radiographs
Radiographs have limited utility in sciatica evaluation. 1
- Cannot visualize disc herniations or nerve root compression
- May identify spondylolysis, destructive lesions, or anatomical variants 6
- Little evidence supports routine use in acute back pain without trauma 1
Other Modalities Not Recommended:
- SPECT bone scan: Not indicated for sciatica evaluation without red flags 1
- Myelography: Invasive and only considered if MRI is contraindicated and advanced imaging is essential 1
Clinical Interpretation Caveats
Important limitations to recognize:
- Observer variation exists: Even among experienced radiologists, moderate agreement (kappa 0.57-0.77) occurs for probability of disc herniation, though excellent agreement exists for affected disc level (kappa 0.81-0.86) 3
- Imaging-clinical correlation is essential: Up to 25% of asymptomatic individuals have disc abnormalities on MRI; findings must match clinical presentation 5
- Standard lumbar MRI may miss non-disc causes: In patients with persistent symptoms despite negative standard MRI, consider MR neurography to evaluate for piriformis syndrome (most common alternative diagnosis at 67.8%), distal nerve entrapments, or other extra-spinal causes 4
Post-Surgical Patients
For patients with persistent pain after lumbar surgery, start with upright flexion-extension radiographs before MRI to assess hardware integrity, alignment, and dynamic instability. 7 MRI without contrast follows if radiographs show concerning findings or to evaluate for recurrent stenosis, disc herniation, or epidural fibrosis. 7