Pathophysiology

  • Compression of the nerve roots in the thecal sac of the lumbar spine. 
  • The cauda equina is the collection of peripheral nerves (L1-S5) in the lumbar canal
  • Compression decreases blood flow/CSF diffusion resulting in reduced nutrient delivery, and intraneural compartment syndrome - this leads to nerve root ischaemia 
  • Most common cause is acute lumbar disc herniation at L4/L5 - might be triggered by lifting a heavy object etc. 
  • Lower motor neuron lesion

Clinical Features

  • Back pain
  • Sciatica - unilateral or bilateral - shooting/burning radiating pain into legs and feet
  • Lower limb weakness
  • Bladder dysfunction - disruption of the autonomic nervous system supply to the bladder leads to urinary retention (due to inability to initiate bladder muscle contraction), and overflow incontinence (no sensation of bladder filling) 
  • Saddle anaesthesia
  • More rarely - bowel dysfunction or erectile dysfunction 
  • Examination
    • Lower limb weakness - for example knee extension, ankle eversion or foot dorsiflexion
    • Sensory loss - absent/reduced sensation in legs
    • Reduced anal tone and absent pinprick sensation in perianal region (S2-S4) 
    • Hyporeflexia of knee/ankle jerks -(remember, CES causes a LMN lesion) 

Management

  • If any of the above red flags, arrange emergency referral to spinal surgery service 
  • Imaging - 1st line: MRI - ideally obtained within 1-2 hours of presentation 
  • Management - emergency surgical decompression within 24-48 hours 
MRI lumbar-sacral spine- Cauda equina syndrome
Figure 122: MRI lumbar-sacral spine- Cauda equina syndrome. MRI of the lumbar spine of a A 57-year-old woman: The collection in the posterior epidural space and the posterior disc bulge is seen compressing the thecal sac and the cauda equina. Jing Jing Chan and Jen Jen Oh, MRI of the lumbar spine with abscess in the posterior epidural space, causing cauda equina syndrome, CC BY 4.0