Question
A 40 year old man presents with severe sciatica in both legs, difficulty passing urine and numbness around his anus.
- What is the diagnosis and what are the main clinical features?
- How would you investigate him?
- What is the management and what affects outcome?
Answer
Diagnosis and clinical features
- Cauda equina syndrome, most often from a large central lumbar disc prolapse at L4 to L5 or L5 to S1
- Bilateral sciatica, saddle anaesthesia, bladder dysfunction, bowel dysfunction and sexual dysfunction
- Incomplete cauda equina syndrome has altered urinary sensation or reduced flow, while retention with overflow is established cauda equina syndrome
- Perform a digital rectal examination for anal tone and perianal sensation, and measure post void residual volume
Investigations
- Emergency MRI of the lumbar spine
- CT myelogram if MRI is unavailable or contraindicated
- Bladder scan for residual volume over about 200 mL
Management
- Urgent surgical decompression with discectomy or laminectomy, ideally as soon as possible after diagnosis
- Outcome is better when surgery is performed before urinary retention develops
- Document the time of onset, examination findings and discussion of consent
- Counsel about possible long term bladder, bowel and sexual dysfunction
Related pages
Author Contributions
Orthofracs team
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.