What is cauda equina syndrome?

Cauda Equina Syndrome: Definition and Clinical Significance

Cauda equina syndrome (CES) is a rare but serious neurological condition caused by compression of the cauda equina nerve roots, characterized by a combination of low back pain, bilateral radiculopathy, bladder/bowel dysfunction, and perineal sensory loss that requires urgent surgical decompression to prevent permanent neurological damage.

Pathophysiology and Causes

• The cauda equina consists of spinal nerve roots L2-L5, S1-S5, and the coccygeal nerve that hang freely within the lumbar spinal canal 1
• Most common cause: Lumbar disc herniation (45% of cases), particularly at L4-L5 and L5-S1 levels 2, 1
• Other etiologies include:
  • Neoplasm (tumors)
  • Infection/inflammation
  • Spinal stenosis
  • Hemorrhage 2
• Prevalence: Rare condition affecting approximately 0.04% of patients with low back pain 2
• Annual incidence ranges from 0.34 to 7 per 100,000 individuals 3

Clinical Presentation and Classification

CES can be classified into three stages with progressive severity:

1. Suspected CES (CESS):

   • Bilateral radiculopathy (bilateral radicular pain, sensory disturbance, or motor weakness)
   • Progressive neurological deficits in the legs
   • At risk for developing CES but no objective evidence yet 2

2. Incomplete CES (CESI):

   • Objective evidence of CES
   • Retains voluntary control of micturition
   • May have other urinary disturbances (urgency, poor stream, hesitancy)
   • Better prognosis if treated at this stage 2

3. Complete CES with Retention (CESR):

   • Urinary retention or incontinence
   • Fecal incontinence
   • Perineal/saddle anesthesia
   • Patulous anus (decreased rectal tone)
   • Poor prognosis even with treatment 2

Key Clinical Features

• Urinary symptoms: Urinary retention is the most sensitive finding (90% sensitivity) 2
• Bowel dysfunction: Fecal incontinence
• Sensory changes: Saddle anesthesia, perineal numbness
• Motor deficits: Lower extremity weakness, often bilateral
• Pain: Low back pain with or without bilateral sciatica 2, 4

Diagnostic Approach

1. Clinical Assessment:

   • Evaluate for urinary retention (most important finding)
   • Check perineal/saddle sensation
   • Assess anal tone
   • Test lower extremity strength, sensation, and reflexes 2

2. Imaging:

   • MRI lumbar spine without contrast: Gold standard and first-line imaging modality 2
   • A single 3-D heavily T2-weighted fat-saturated sequence protocol can provide rapid assessment in emergency settings 2
   • CT lumbar spine without contrast: Alternative if MRI unavailable (≥50% thecal sac effacement on CT predicts significant spinal stenosis) 2
   • CT myelography: Option for surgical planning or when MRI is contraindicated 2

Management

• Surgical decompression: Urgent surgical intervention is the definitive treatment 4, 1
• Timing: Controversy exists regarding optimal timing
  • Better outcomes are generally associated with earlier surgery
  • Treatment at CESI stage prevents progression to CESR 2
  • Some evidence suggests better outcomes with surgery within 12-72 hours of symptom onset 2

Prognosis

• CESI patients: If treated promptly, can achieve normal or socially normal bladder and bowel control
• CESR patients: 48-93% show some improvement, but many have severe long-term impairment:
  • Paralyzed, insensate bladder requiring intermittent self-catheterization
  • Bowel dysfunction requiring manual evacuation or irrigation
  • Sexual dysfunction
  • Only a minority return to work 2
• Better outcomes if some perineal sensation is preserved preoperatively 2

Clinical Pearls and Pitfalls

• High index of suspicion: Early signs may be subtle and easily missed
• Red flag vs. white flag: Traditional "red flags" like urinary retention are actually "white flags" indicating the condition has progressed to an advanced stage 2
• True red flags (warning signs of impending CES):
  • Bilateral radiculopathy
  • Progressive neurological deficits in the legs 2
• Postoperative vigilance: Early signs of postoperative CES may be attributed to common postoperative findings; maintain high suspicion in patients with refractory back/leg pain and urinary retention 4

In patients without urinary retention, the probability of cauda equina syndrome is approximately 1 in 10,000, highlighting the importance of this key clinical finding 2.