Cauda equina syndrome (CES) is a surgical emergency.
Caused by compression of nerve roots L1–S5, most commonly due to L4/L5 disc herniation.
Presents with back pain, sciatica, bladder dysfunction, saddle anaesthesia, and lower limb weakness.
Emergency MRI spine, and urgent surgical decompression within 24–48 hours.
🧬 Pathophysiology
The cauda equina refers to the bundle of peripheral nerves (L1–S5) in the lumbar canal below the spinal cord.
Compression reduces blood flow and CSF diffusion, leading to intraneural compartment syndrome and nerve root ischaemia.
Most common cause: Acute lumbar disc herniation at L4/L5 (e.g. after lifting a heavy object).
👀 Clinical Features
Symptoms
Severe lower back pain
Sciatica – unilateral or bilateral, burning/shooting pain radiating into legs
Lower limb weakness
Bladder dysfunction - disruption of the autonomic nervous system supply to the bladder leads to:
Urinary retention
Overflow incontinence (due to loss of sensation of bladder filling)
Saddle anaesthesia (numbness in perianal/perineal area)
May also have bowel or erectile dysfunction
Examination findings:
Lower limb weakness, hyporeflexia (LMN)
Sensory loss in legs and perianal area
Reduced anal tone and absent perianal pinprick (S2–S4 dermatomes)
🧪 Investigations
MRI spine is 1st line and gold standard
Should be arranged within 1–2 hours of presentation if CES is suspected
Imaging will show compression of the thecal sac and nerve roots
💊 Management
Emergency referral to spinal surgery service if any red flags present
Urgent MRI lumbar-sacral spine
Emergency surgical decompression ideally within 24–48 hours to prevent permanent neurological damage
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
