A middle-aged man with sudden onset of severe lower back pain radiating to his left leg, inability to urinate, and decreased tendon reflexes in the ankle after lifting a heavy box, what is the most appropriate next step?

Urgent MRI of the Lumbar Spine Without Contrast

This patient requires immediate MRI of the lumbar spine without IV contrast to confirm suspected cauda equina syndrome (CES), followed by emergency neurosurgical consultation if compression is confirmed. 1

Clinical Presentation Confirms CES

This patient presents with the classic triad of CES:

• Urinary retention (inability to urinate) - the most frequent finding in CES with 90% sensitivity 1
• Saddle/regional anesthesia - indicating sacral nerve root dysfunction 1
• Bilateral lower extremity findings - decreased ankle reflexes and radiating leg pain 1

The acute onset after heavy lifting with massive disc herniation as the likely etiology (most commonly at L4-L5 or L5-S1 levels) further supports this diagnosis. 1

Imaging Must Be Performed Immediately

MRI lumbar spine without IV contrast is the imaging study of choice and must be obtained urgently - ideally within 1 hour of clinical suspicion being raised, regardless of time of day. 1, 2

• MRI accurately depicts soft-tissue pathology, assesses vertebral marrow, and evaluates spinal canal patency 1
• A prospective study recommends urgent MRI assessment in all patients presenting with new-onset urinary symptoms in the context of lower back pain or sciatica 1
• Clinical examination alone, including digital rectal examination, does not reliably correlate with cauda equina compression on MRI - imaging is the only reliable method to confirm or exclude CES 2
• A rapid 3-D heavily T2-weighted fat-saturated sequence protocol can expedite evaluation in the emergency department 1

Time-Critical Nature of This Emergency

CES represents a true neurosurgical emergency requiring surgery by day or night. 2, 3

• Neurological damage to cauda equina nerve roots occurs in a continuous and progressive fashion with no safe time thresholds 2
• Neurological deterioration can occur rapidly and is associated with long-term poor outcomes 2
• It is impossible to predict which patients will deteriorate neurologically or how rapidly 2
• Consensus guidelines from the Society of British Neurological Surgeons and British Association of Spinal Surgeons recommend decompressive surgery as soon as practically possible 2
• Delayed recognition results in irreversible disability despite surgical intervention 4

Management Algorithm

1. Obtain urgent MRI lumbar spine without contrast immediately (within 1 hour if possible) 1, 2
2. If MRI confirms cauda equina compression: Emergency neurosurgical consultation for decompressive surgery the same day/night 2, 3
3. If MRI negative: Ensure imaging is complete (not just lumbar spine), provide analgesia, and arrange adequate follow-up 3

Critical Pitfall to Avoid

Do not delay MRI waiting for neurosurgical consultation. 5 A clinical pathway study demonstrated that empowering emergency physicians to order MRI prior to neurosurgical review reduced time to diagnosis by 36% (from 8 hours 16 minutes to 5 hours 17 minutes). 5 In suspected CES, imaging should be ordered immediately upon clinical recognition, with neurosurgery consulted simultaneously or immediately after.