Neurology · Spinal Cord Compression
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Cauda equina syndrome is a surgical emergency caused by compression of the lumbosacral nerve roots below the level of the conus medullaris.
The most common etiology is a large central lumbar disc herniation at the L4-L5 or L5-S1 level.
Patients classically present with saddle anesthesia, involving sensory loss in the perineum, buttocks, and inner thighs.
Bowel and bladder dysfunction, specifically urinary retention with overflow incontinence, is a hallmark clinical finding.
Physical examination reveals bilateral lower extremity weakness and diminished or absent deep tendon reflexes (commonly the Achilles/ankle reflex with L5-S1 lesions; patellar reflex may be spared).
The diagnostic test of choice is an urgent MRI of the lumbar spine to confirm the level and extent of compression.
Definitive management requires emergent surgical decompression via laminectomy to prevent permanent neurologic deficits.
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A 45-year-old male presents to the emergency department with a 24-hour history of severe low back pain radiating to both legs. He reports progressive difficulty walking and a sensation of numbness in his groin area when wiping after using the toilet. On physical exam, he has bilateral lower extremity weakness and absent ankle jerks. He is unable to void, and a bladder scan reveals 800 mL of residual urine.
What is the most appropriate next step in management?
Urgent MRI of the lumbar spine
The patient presents with classic signs of cauda equina syndrome (saddle anesthesia, urinary retention, and bilateral radiculopathy); urgent MRI is required to confirm the diagnosis before emergent surgical decompression.
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Etiology / Epidemiology
Caused by massive lumbar disc herniation (L4-L5/L5-S1) compressing the nerve roots below the conus medullaris.
Clinical Manifestations
Presents with saddle anesthesia, bladder/bowel incontinence, and bilateral sciatica.
Diagnosis
MRI of the lumbar spine is the gold standard; perform immediately upon suspicion.
Treatment
Urgent surgical decompression (laminectomy) is the definitive treatment to prevent permanent deficit.
Prognosis
Outcome depends on time to surgery; <48 hours is the critical window for recovery.
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Epidemiology & Etiology
Most commonly caused by a large central disc herniation at the L4-L5 level. Other etiologies include spinal epidural hematoma, abscess, or severe spinal stenosis. It is a true surgical emergency requiring rapid identification.
Pertinent Anatomy
The cauda equina consists of the nerve roots from L2 to S5 distal to the conus medullaris. Because these are peripheral nerves, injury results in lower motor neuron signs.
Pathophysiology
Compression of the nerve roots leads to ischemia and mechanical damage. The saddle distribution (S2-S4) is affected early due to the central location of these fibers. Prolonged compression leads to irreversible axonal degeneration.
Clinical Manifestations
Patients present with urinary retention (most sensitive sign), fecal incontinence, and saddle anesthesia. Look for bilateral leg weakness and loss of anal wink reflex. Sudden onset of severe back pain with progressive neurological deficit is a classic red flag.
Diagnosis
MRI of the lumbar spine without contrast is the gold standard. If MRI is contraindicated, CT myelography is the alternative. Do not delay imaging for plain films.
Treatment
Urgent surgical decompression via laminectomy is the standard of care. Do not delay surgery for imaging if clinical suspicion is high. Post-operative care includes physical therapy and monitoring for neuropathic pain.
Prognosis
Surgery within 48 hours significantly improves the likelihood of bladder and bowel function recovery. Delayed intervention leads to permanent paralysis and chronic incontinence.
Differential Diagnosis
Conus Medullaris Syndrome: sudden onset, symmetric, early impotence
Spinal Epidural Abscess: fever, elevated ESR/CRP, history of IV drug use
Guillain-Barre Syndrome: ascending paralysis, areflexia, no saddle anesthesia
Lumbar Disc Herniation: unilateral radiculopathy, no bowel/bladder involvement
Spinal Cord Tumor: insidious onset, constitutional symptoms