FFinalistSouthampton · 2027
Neurology
AKT · Neurology/Cord & peripheral

Cauda equina syndrome

Compression of the lumbosacral nerve roots below the cord (LMN)

Overview

Compression of the cauda equina (lumbosacral nerve roots below the cord, ~L1/L2 down) — a surgical EMERGENCY. Usually a large central disc prolapse. The red-flag features (saddle anaesthesia, bladder/bowel dysfunction, bilateral sciatica) mandate emergency MRI and decompression to prevent permanent incontinence.

Recognise

  • SADDLE anaesthesia (perineal numbness), BLADDER dysfunction (retention with overflow incontinence, loss of sensation), bowel incontinence/reduced anal tone
  • Bilateral sciatica/leg weakness, LMN signs (reduced reflexes, areflexia)
  • Usually a large central lumbar disc prolapse; also tumour, abscess, haematoma

Red flags

  • Urinary retention/incontinence, saddle anaesthesia, reduced anal tone, bilateral leg symptoms → emergency MRI + surgery

Differentials & how to tell them apart

Spinal cord compressionUMN signs + sensory level (above L1/L2) — cauda equina is LMN + saddle/sphincter
Mechanical back pain / sciaticano saddle anaesthesia, no bladder/bowel or bilateral signs
Conus medullaris lesionmixed UMN/LMN at the transition

Investigations

URGENT MRI lumbosacral spine; post-void bladder scan (retention); assess perineal sensation and anal tone (PR).

Management

Emergency MRI + urgent surgical decompression

  1. 1Suspect on red flags (saddle anaesthesia, bladder/bowel dysfunction, bilateral sciatica, reduced anal tone) → EMERGENCY MRI lumbosacral spine.Gate: Do not wait — the longer the delay to decompression once sphincter function is affected, the more likely permanent incontinence; this is a same-day surgical emergency
  2. 2Urgent surgical decompression; treat the underlying cause; bladder/bowel rehabilitation.
No drug — surgical decompression — urgent neurosurgical/spinal decompression is the treatment

Key points

Saddle anaesthesia + urinary retention/overflow + bilateral sciatica + reduced anal tone = cauda equina → emergency MRI + surgery. It is the LMN, lumbosacral counterpart of cord compression.

Monitor & prognosis

Bladder/bowel and perineal function, post-op recovery.

Time-critical — early decompression preserves continence.

Source: NICE NG59 (low back pain); spinal surgery guidance