From the Guidelines
For diagnosing cauda equina syndrome, an MRI lumbar spine without IV contrast is the recommended initial imaging study. This is because MRI can accurately depict soft-tissue pathology, assess vertebral marrow, and assess the spinal canal patency, making it the imaging study of choice in the evaluation of suspected cauda equina syndrome, multifocal deficit, or progressive neurologic deficit 1. The MRI should include sagittal and axial views of the lower spine, focusing on the region where the cauda equina nerve roots are located.
Some key points to consider when ordering an MRI for cauda equina syndrome include:
- The use of a single 3-D heavily T2-weighted fat-saturated sequence protocol, which has been shown to be a rapid, highly sensitive tool for evaluating cauda equina syndrome in the emergency department 1
- The potential for MRI lumbar spine without and with IV contrast to be helpful in delineating the etiology of cauda equina syndrome when underlying malignancy, infection, or inflammation is clinically suspected 1
- The importance of urgent MRI assessment in all patients who present with new-onset urinary symptoms in the context of low back pain or sciatica 1
It's worth noting that while CT lumbar spine without IV contrast can answer the question of whether or not cauda equina compression is present, MRI is superior in soft-tissue contrast and characterizing the etiology of cauda equina syndrome 1. CT myelography of the lumbar spine can be useful for surgical planning in patients with cauda equina syndrome and in patients with significant spinal stenosis on CT lumbar spine without IV contrast 1.
Overall, the goal of imaging in cauda equina syndrome is to quickly and accurately identify compression of the cauda equina nerve roots, which may be caused by a variety of factors, including large central disc herniation, tumor, abscess, hematoma, or other space-occupying lesion. Rapid MRI acquisition is essential when cauda equina syndrome is suspected, as delays in diagnosis and treatment can significantly worsen outcomes, including bowel and bladder dysfunction, sexual dysfunction, and lower limb weakness or paralysis.
From the Research
MRI Needed for Cauda Equina Syndrome
- The diagnosis of cauda equina syndrome typically requires emergent MR imaging to detect compressive lesions on the cauda equina, which may require surgical decompression 2.
- A limited sequence (LS) lumbosacral MRI could be used to diagnose cauda equina syndrome safely in patients under the age of 55 years, with a mean scan time of 9.9 minutes 3.
- The use of CT scans as a complementary imaging technique to evaluate osseous integrity in patients with cauda equina syndrome has been studied, with results showing that CT percentage thecal sac effacement of ≥50% predicts significant spinal stenosis on MR imaging in patients with clinically suspected cauda equina syndrome 2.
- Urgent MRI assessment is recommended in all patients who present with new onset urinary symptoms in the context of lumbar back pain or sciatica, as it is impossible to exclude the diagnosis of prolapsed intervertebral disc in a significant proportion of patients 4.
Types of MRI
- Limited sequence (LS) lumbosacral MRI: a shorter MRI scan that can be used to diagnose cauda equina syndrome in patients under the age of 55 years 3.
- Full MRI scan: a more comprehensive scan that can provide detailed images of the spine and surrounding tissues, but may take longer to perform.
Clinical Correlation
- Clinical symptoms such as urinary retention, urinary frequency, urinary incontinence, altered urinary sensation, and altered perineal sensation have been studied in relation to MRI findings, with results showing that these symptoms do not reliably correlate with MRI abnormalities 4, 5.
- Functional comorbidities, such as mental health diagnoses and somatic symptoms, are more common in patients with scan-negative cauda equina syndrome, suggesting a possible functional neurological disorder 6.