MRI Protocol for Lumbar and Sacrum Pain with Radiculopathy
Recommended MRI Protocol
MRI lumbar spine without IV contrast is the correct and preferred imaging modality for evaluating lumbar and sacrum pain with radiculopathy. 1, 2
Timing of MRI Acquisition
The timing depends critically on the presence or absence of "red flag" symptoms:
Immediate MRI (Do Not Wait)
Proceed directly to MRI if any of the following are present:
- Cauda equina syndrome (urinary retention/incontinence, bilateral leg weakness, saddle anesthesia) 1, 2
- Progressive or severe neurological deficits (such as progressive foot drop or motor weakness) 1, 2
- Suspected malignancy or metastatic disease 1, 2
- Suspected infection (fever, immunosuppression, IV drug use) 1, 2
- Significant trauma with neurological symptoms 1, 2
Delayed MRI (After Conservative Management)
For patients without red flags, MRI should only be obtained after 6 weeks of failed conservative management and only if the patient is a potential candidate for surgery or epidural steroid injection. 1, 2 This waiting period is justified because:
- Most disc herniations show reabsorption or regression by 8 weeks 2, 3
- The majority of patients improve within the first 4 weeks with conservative treatment 2, 3
- Routine early imaging provides no clinical benefit and increases unnecessary healthcare utilization 1, 2, 4
Technical MRI Specifications
Standard Protocol
- MRI lumbar spine without IV contrast is sufficient for initial evaluation of degenerative disease and radiculopathy 1, 4
- Sagittal T2-weighted sequences are essential 5
- A single FSE T2-weighted Dixon sequence in the sagittal plane can replace the traditional combination of T1-, T2-, and fat-suppressed T2-weighted sequences, reducing acquisition time while maintaining diagnostic accuracy 5
When to Add IV Contrast
Add contrast (MRI with and without IV contrast) only in specific circumstances:
- Prior lumbar surgery with new or progressive symptoms 1
- Suspected infection or malignancy when noncontrast MRI is nondiagnostic 1, 4
- Indeterminate findings on noncontrast imaging 4
Special Consideration for Sacral Involvement
Add coronal T1-weighted sequences when evaluating sacral radiculopathy, particularly in patients with lumbosacral transitional vertebrae, as conventional sagittal and axial sequences may miss S1 nerve root entrapment at the lumbosacral junction. 6 Coronal imaging is critical for identifying hypertrophic degenerative stenosis of the S1 nerve root canal that may not be visible on standard views. 6
Common Pitfalls to Avoid
- Do not order MRI for acute low back pain without radiculopathy or red flags – imaging is usually not appropriate and does not improve outcomes 1, 2
- Do not assume MRI findings correlate with symptoms – disc herniations are present in 20-28% of asymptomatic individuals, and up to 84% of pre-existing abnormalities remain unchanged or improve after symptoms develop 2, 4
- Do not skip the 6-week conservative management period unless red flags are present – this leads to unnecessary interventions without proven benefit 1, 2, 4
- Do not forget coronal sequences for sacral radiculopathy – standard sagittal and axial views may miss S1 nerve root pathology 6
Alternative Imaging if MRI Unavailable
If MRI is contraindicated or delays exceed 2-4 weeks in a patient with persistent radiculopathy who is a surgical candidate:
- CT lumbar spine without contrast is a reasonable alternative with >80% sensitivity and specificity for most lumbar pathologies 2
- CT myelography is the preferred alternative if MRI cannot be performed 4
- Reserve MRI for soft tissue pathology evaluation or if CT results are discordant with clinical presentation 2
Complementary Imaging
Plain radiographs (X-rays) of the lumbar spine may be complementary to MRI for: