AKT · Musculoskeletal/Spine & back

Cauda equina syndrome

Compression of the lumbosacral nerve roots below the conus (usually a large central disc prolapse)

Overview

Compression of the cauda equina nerve roots below the conus medullaris — most often by a large central lumbar disc prolapse, but also tumour, abscess or haematoma. It is a surgical EMERGENCY: delayed decompression risks permanent bladder, bowel and sexual dysfunction and leg weakness. Any back pain with bladder/bowel or saddle symptoms mandates immediate MRI.

Recognise

Bilateral sciatica/leg pain and weakness; saddle (perineal) anaesthesia; reduced anal tone
Bladder dysfunction — early loss of sensation/poor stream, later painless RETENTION with overflow incontinence; faecal incontinence
Often on a background of low back pain; sexual dysfunction

Red flags

Urinary retention/incontinence, saddle anaesthesia, bilateral leg symptoms or reduced anal tone → IMMEDIATE MRI and emergency decompression — never 'watch and wait'
Time to decompression determines recovery — treat as a true emergency

Differentials & how to tell them apart

Mechanical sciaticaunilateral, no saddle/bladder/bowel involvement, normal anal tone

Conus medullaris lesionmixed UMN/LMN signs, early bladder involvement — also needs urgent imaging

Peripheral neuropathyno acute retention/saddle anaesthesia or back pathology

Investigations

EMERGENCY whole-spine MRI (the immediate investigation); post-void bladder scan (retention); assess perineal sensation and anal tone (PR); urgent spinal surgical referral in parallel — do not delay MRI.

Management

Immediate MRI + emergency surgical decompression

1Suspect from bladder/bowel dysfunction, saddle anaesthesia, bilateral leg symptoms or reduced anal tone on a background of back pain. Arrange EMERGENCY whole-spine MRI and an urgent spinal surgical referral simultaneously.Gate: Never 'watch and wait' — the time to decompression determines whether bladder/bowel/sexual function recovers; treat as a true emergency.
2Emergency surgical decompression (discectomy or as dictated by the cause); catheterise for retention; rehabilitate and treat the underlying lesion (tumour/abscess/haematoma).

Emergency surgical decompression — the definitive treatment — urgency determines outcome; arrange immediately

Urgent MRI + spinal referral — in parallel; catheterise if in retention

Treat the cause — discectomy for disc prolapse; tumour/abscess/haematoma managed accordingly

Analgesia / supportive care — alongside definitive management

Key points

Back pain + bilateral sciatica + saddle anaesthesia + urinary retention/incontinence + reduced anal tone = cauda equina syndrome → EMERGENCY MRI and surgical decompression. Speed determines recovery. Also carded on neurology — same emergency, do not delay.

Monitor & prognosis

Neurological/bladder recovery post-decompression; rehabilitation.

Outcome hinges on time to decompression; established deficits may be permanent.

Source: NICE; cross-ref neurology