What imaging study is appropriate for evaluating left leg numbness and tingling?

MRI Lumbar Spine Without IV Contrast

For left leg numbness and tingling, obtain an MRI of the lumbar spine without IV contrast if symptoms have persisted despite 6 weeks of conservative management and the patient is a candidate for surgery or intervention. 1

Clinical Decision Algorithm

Acute Symptoms (<6 weeks) WITHOUT Red Flags

• No imaging initially indicated 1
• Proceed with conservative management
• Red flags to screen for include:
  • Bowel/bladder dysfunction (cauda equina syndrome)
  • Saddle anesthesia
  • Progressive neurologic deficits
  • History of cancer, infection, or immunosuppression
  • Recent trauma with osteoporosis or chronic steroid use
  • Fever or unexplained weight loss

Subacute/Chronic Symptoms (≥6 weeks) WITHOUT Red Flags

• MRI lumbar spine without IV contrast is the appropriate study if:
  • Symptoms persist or progress after 6 weeks of conservative therapy
  • Physical examination shows nerve root irritation
  • Patient is a surgical or interventional candidate 1

ANY Duration WITH Red Flags

Suspected Cauda Equina Syndrome (bowel/bladder dysfunction, saddle numbness, bilateral leg symptoms):

• Urgent MRI lumbar spine without IV contrast (or with and without contrast as equivalent alternatives) 1
• This is a surgical emergency requiring immediate imaging

Suspected Cancer, Infection, or Immunosuppression:

• MRI lumbar spine without and with IV contrast OR without contrast alone 1
• Contrast helps distinguish abscess from phlegmon and characterizes malignancy 1

History of Prior Lumbar Surgery:

• MRI lumbar spine without IV contrast (or with and without contrast) 1
• Contrast useful to distinguish recurrent disc from scar tissue

Why MRI Without Contrast is Preferred

MRI without IV contrast accurately depicts:

• Disc herniation and nerve root compression (57% prevalence in symptomatic patients with radiculopathy vs. 20-28% in asymptomatic individuals) 1
• Soft-tissue pathology
• Vertebral marrow abnormalities
• Spinal canal patency 1

The addition of IV contrast is typically unnecessary unless the noncontrast study is nondiagnostic or when specific pathologies (infection, malignancy, post-surgical changes) are suspected 1.

Common Pitfalls to Avoid

• Do not image acute symptoms without red flags - disc abnormalities are common in asymptomatic patients, leading to false-positive findings and unnecessary interventions 1
• Do not delay imaging for suspected cauda equina syndrome - this requires urgent MRI assessment 1
• Do not order contrast initially unless there is clinical suspicion for infection, malignancy, or post-surgical evaluation 1

Alternative Imaging Considerations

If MRI is contraindicated or unavailable, CT lumbar spine without IV contrast can assess for cauda equina compression, though it is inferior for soft-tissue characterization 1. Plain radiography has limited utility for radiculopathy evaluation but may be complementary in trauma, osteoporosis, or elderly patients 1.

For extraspinal peripheral nerve pathology (lumbosacral plexus or sciatic nerve entrapment), MR neurography using specialized high-resolution sequences may be indicated if routine lumbar spine MRI is unrevealing 2, 3, 4.