Anatomy of Lower Lumbar and Sacral Spine (Lavy 2009)

Definition: Syndrome characterized by dysfunction of multiple lumbar and sacral nerve roots in the lumbar vertebral canal due to compression


  • The spinal cord terminates in the conus medullaris at the T12/L1 vertebral body in adults
  • Cauda equina
    • Collection of nerve roots from L1-S5
    • Compression from various causes results in lower motor neuron pathology

Compressive Causes

  • Disc herniation (most common cause)
  • Epidural abscess
  • Spinal epidural hematoma
  • Diskitis
  • Tumor (metastatic or primary CNS)
  • Trauma (retropulsion of fracture fragment)
  • Spinal stenosis

Presentation (Lavy 2009)

  • Symptoms may develop acutely or progressively over time
  • Symptoms
    • Back pain
    • Sciatica
      • Seen in up to 97% of patients (Korse 2017)
      • Bilateral leg pain and/or weakness common
    • Change in sensation in the lower extremities
    • Bladder dysfunction (retention and/or incontinence) – up to 92% (Korse 2017)
      • Disruption of autonomic innervation leads to retention and overflow incontinence
    • Bowel dysfunction (constipation and/or incontinence) – up to 74% (Korse 2017)
    • Decreased sensation in the perianal area – up to 93% (Korse 2017)
    • Sexual dysfunction (i.e. impotence)

      Saddle Anesthesia

  • Physical Exam
    • Lower extremity weakness, numbness or paresthesias (usually bilateral)
    • Decreased or absent lower extremity reflexes
    • Hypotonia/atrophy of the lower extremities (in chronic presentations)
    • Urinary retention (increased post void residual)
    • Saddle anesthesia: Reduced or absent sensation in the perineal area (S2-S4 innervation)
    • Decreased or absent rectal tone

Differential Diagnosis (non-compressive causes of spinal cord dysfunction)

  • Multiple Sclerosis
  • Transverse Myelitis
  • Myelopathies (e.g. HIV related)
  • Spinal cord infarction
  • Spinal AVM
  • Syringomyelia

Lumbar Disc Herniation (Case courtesy of A.Prof Frank Gaillard, From the case rID: 6754)

ED Evaluation and Management

  • Imaging
    • Bladder US
      • Normal post-void residual (PVR) < 50 ml (may be up to 100 ml in patients > 65 years)
      • PVR = 0.5 X AP diameter X lateral diameter X sagittal diameter of the bladder
    • Plain X-rays and CT scans can show bone and soft tissue abnormalities but not spinal cord abnormalities
    • CT Myelogram
      • Allows for visualization of the spinal cord and associated abnormalities
      • Requires spinal tap followed by injection of contrast. This limits it’s utility
      • Can be used for patients who have contraindications for MRI or when MRI unavailable
    • MRI
      • Imaging modality of choice for cauda equine syndrome
      • Image types: Obtain sagittal and axial T1 and T2 sequences
  • Neurosurgical or orthopedic consultation for emergency surgery
    • Surgery should be performed within 24 hours to increase the chance of better outcomes (Todd 2005)
    • The presence of urinary retention/incontinence at presentation is a predictor of poor outcomes

Traumatic Burst Fracture (Case courtesy of Dr Ian Bickle, From the case rID: 25701)

Take Home Points

  • Cauda equina syndrome is a rare emergency with devastating consequences
  • Early recognition is paramount as the presence of bladder dysfunction portends bad functional outcomes
  • The presence of bilateral lower extremity weakness or sensory changes should alert clinicians to the diagnosis. Saddle anesthesia (or change in sensation) and any bladder/bowel changes in function should also raise suspicion for the disorder
  • MRI is the diagnostic modality of choice though CT myelogram can be performed if necessary
  • Prompt surgical consultation is mandatory for all patients with cauda equina syndrome regardless of symptoms at presentation

Read More

EM Cases: Best Case Ever 11: Cauda Equina Syndrome

OrthoBullets: Cauda Equina Syndrome

Radiopaedia: Cauda Equina Syndrome

Perron AD, Huff JS: Spinal Cord Disorders, in Marx JA, Hockberger RS, Walls RM, et al (eds): Rosen’s Emergency Medicine: Concepts and Clinical Practice, ed 8. St. Louis, Mosby, Inc., 2010, (Ch) 106: p 1419-30.


Lavy C et al. Cauda Equina Syndrome. BMJ 2009; 338: PMID: 19336488

Todd NV. Cauda equina syndrome: the timing of surgery probably does influence outcome. Br J Neurosurg 2005;19:301-6 PMID: 16455534

Korse NS et al. Cauda Equina Syndrome: presentation, outcome and predictors with focus on micturition, defecation and sexual dysfunction. Eur Spine J 2017; 26(3): 894-904. PMID: 28102451