From the Guidelines
The first test to rule out cauda equina syndrome in the emergency department should be an MRI lumbar spine without IV contrast, as it is the most useful study in evaluating suspected CES due to its ability to accurately depict soft-tissue pathology, assess vertebral marrow, and assess the spinal canal patency 1.
Key Points to Consider
- Cauda equina syndrome (CES) is a rare condition resulting from dysfunction of the sacral and lumbar nerve roots within the vertebral canal, producing impairment of the bladder, bowel, or sexual function and perianal or saddle numbness 1.
- The most common cause of CES is lumbar disc herniation at the L4-L5 and L5-S1 levels, but other etiologies include neoplasm, infection/inflammation, spinal stenosis, and hemorrhage 1.
- MRI is superior in soft-tissue contrast and characterizing the etiology of CES, making it the preferred initial study for evaluating suspected CES 1.
- A recent study has shown that a single 3-D heavily T2-weighted fat-saturated sequence protocol can be a rapid, highly sensitive tool for evaluating CES in the emergency department, improving efficiency and throughput 1.
- While CT lumbar spine without IV contrast can answer the question of whether or not cauda equina compression is present, it is not the preferred initial study due to its limited ability to visualize soft-tissue pathology and assess vertebral marrow 1.
Clinical Considerations
- Clinical suspicion of CES should be high in patients presenting with new onset saddle anesthesia, bladder or bowel dysfunction, bilateral leg weakness or sensory changes, and severe low back pain.
- A thorough neurological examination, including assessment of perianal sensation, anal tone, and post-void residual bladder volume, should be performed while waiting for the MRI results.
- Urgent MRI assessment is recommended in all patients who present with new-onset urinary symptoms in the context of low back pain or sciatica 1.
From the Research
Diagnostic Approach for Cauda Equina Syndrome
The first test to rule out cauda equina syndrome in the emergency department is a topic of discussion in several studies.
- According to 2, CT scans can be used to detect significant spinal stenosis and cauda equina impingement, with a high sensitivity and negative predictive value.
- The study found that a CT percentage thecal sac effacement of <50% can reliably rule out cauda equina impingement.
- However, other studies such as 3, 4, and 5 recommend the use of MRI as the primary diagnostic tool for suspected cauda equina syndrome.
- 4 proposes the use of limited sequence MRI to improve standards of care for suspected cauda equina syndrome, which can be performed quickly and safely.
- 5 provides a systematic review of existing international guidelines and summarizes the current evidence, recommending urgent MRI with the presence of red flag findings.
Red Flag Findings
Red flag findings that warrant urgent MRI include:
- Perianal/perineal/saddle sensory disturbance
- Bladder or bowel dysfunction
- Radicular/sciatic pain
- New motor weakness
- Digital rectal examination (DRE) findings
- Post void residual (PVR) measurement
Imaging Modalities
- CT scans: can be used to detect significant spinal stenosis and cauda equina impingement, but may not be as sensitive as MRI.
- MRI: recommended as the primary diagnostic tool for suspected cauda equina syndrome, with limited sequence MRI being a potential option for quick and safe diagnosis.
- Limited sequence MRI: proposed as a potential option for improving standards of care for suspected cauda equina syndrome, but further research is needed to assess its safety and efficacy.