Cauda equina syndrome
Back pain with sciatica in both legs, numbness in the saddle area, or a change in bladder or bowel control is cauda equina until proven otherwise. Examine, bladder scan, emergency MRI, and spinal surgery the same day.
A 38-year-old man with known back pain has had pain going down both legs for 2 days. Today he noticed tingling "where he sits" and found it hard to start passing urine. He can walk. Leg power is normal.
He can walk and his power is normal. Can he go home with painkillers?
- Ask the red flag questionsEvery patient with back pain or sciatica.
- ExamineFull lower limb neurology, saddle and perianal sensation, anal tone (with a chaperone).
- Bladder scan after passing urinePost-void residual volume.
- Emergency MRI lumbar spineSame day, including out of hours. Transfer if not available.
- Call spinal or neurosurgery on callAs soon as cauda equina is suspected.
- Pain reliefAs for back pain.
- Document carefullySymptoms, examination, times, who you spoke to.
- Safety-net if not admittedWritten advice: return immediately if red flags appear.
- Sciatica in both legs
- Saddle or perianal numbness
- New difficulty passing urine or reduced feeling of passing it
- Painless retention or overflow incontinence
- Loss of bowel control
- Cauda equina syndrome
- Spinal cord compression
- Spinal epidural abscess
- Spinal TB
| Red flags | Sciatica in both legs, saddle numbness, new bladder or bowel change, sexual dysfunction |
| Bladder scan | Post-void residual over about 200 mL is concerning |
| MRI | Emergency, same day. Do not wait until morning or next week |
| Treatment | Surgical decompression, urgently |
| Normal power | Does not rule out cauda equina |
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On this page
What it is
The cauda equina is the bundle of nerve roots below the end of the spinal cord (around L1–L2). A large central disc prolapse, tumour, abscess, TB, haematoma or fracture can compress it. The roots control the bladder, bowel, sexual function, and saddle sensation. Once these are lost, they may not recover. Delay causes permanent incontinence and disability, so the diagnosis is made early and acted on fast.
Ask every patient with back pain
- Pain, numbness or weakness in both legs?
- Numbness or tingling in the saddle area: between the legs, around the back passage, when wiping?
- Bladder: difficulty starting, weak stream, needing to strain, reduced sensation of passing urine, leaking?
- Bowel: loss of control, not feeling when the bowels are full?
- Sexual: new numbness of the genitals or loss of function?
Patients often do not volunteer these symptoms out of embarrassment. Ask directly and privately.
Examination
- Full lower limb neurology: power, tone, reflexes (knee and ankle), sensation by dermatome.
- Saddle and perianal sensation (light touch and pinprick).
- Anal tone and squeeze on rectal examination, with a chaperone.
- Palpate the bladder.
- Normal leg power and reflexes do not exclude cauda equina.
Categories
- Red flag symptoms such as bilateral sciatica or subjective saddle change
- Bladder function still normal
- Emergency MRI
- This is where the best outcomes are
- Objective loss of saddle sensation, altered bladder sensation or reduced stream
- Still has voluntary control
- Emergency MRI and surgery
- Painless retention with overflow, no voluntary control
- Saddle anaesthesia
- Emergency surgery, but outcomes worse
Bladder scan
- Ask the patient to pass urineThen scan the bladder straight away.
- Residual under about 100 mLReassuring, but does not exclude early cauda equina.
- Residual over about 200 mLConcerning for retention. Catheterise and get the MRI.
- Painless retentionLate sign. Emergency.
MRI and surgery
- MRI lumbar spine is an emergency. Same day, including at night and weekends. If your hospital has no MRI available, arrange urgent transfer.
- Call the spinal or neurosurgical team as soon as you suspect cauda equina. Do not wait for the MRI to call.
- Treatment: urgent surgical decompression (for example discectomy).
Causes to consider in Pakistan
- Central lumbar disc prolapse (most common).
- Spinal TB (Pott's disease): back pain for weeks, fever, night sweats, weight loss, a gibbus. Needs anti-TB treatment and often surgery.
- Epidural abscess: fever, severe back pain, diabetics, injecting drug users, recent spinal procedures.
- Tumour or metastases, fracture, haematoma (on anticoagulants or after spinal anaesthesia).
Common mistakes
- Not asking about saddle sensation and bladder in every patient with sciatica.
- Reassured by normal leg power.
- No bladder scan, or scanning without asking the patient to pass urine first.
- Booking a routine MRI or waiting until Monday.
- Missing spinal TB or abscess in a patient with fever and back pain.
- Sending home without written advice on red flags.
Frequently asked questions
What are the symptoms of cauda equina syndrome?
Sciatica in both legs, numbness in the saddle or perianal area, new difficulty passing urine or reduced bladder sensation, loss of bowel control, and sexual dysfunction.
How urgent is an MRI for suspected cauda equina?
It is an emergency: the MRI should be done the same day, including out of hours, with transfer if needed.
Does normal leg power exclude cauda equina?
No. Leg power and reflexes may be normal, especially early. Saddle sensation and bladder symptoms matter most.
How urgent is cauda equina syndrome?
It is a surgical emergency. Suspected cauda equina needs examination, a bladder scan and an emergency MRI the same day, with spinal surgery if confirmed, to prevent permanent bladder, bowel and sexual dysfunction.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A 40-year-old has bilateral sciatica, saddle tingling and urinary hesitancy. Power is normal. What is the best management?
Answer: Emergency MRI. Suspected cauda equina syndrome needs emergency MRI and spinal surgical review, even with normal power.
- Physiotherapy referral: Delay is harmful.
- Steroid injection: Not indicated.
- Analgesia and home: Red flags for cauda equina.
- Routine MRI in 6 weeks: Must be emergency.
2. A patient has saddle numbness, no urge to pass urine and a post-void residual of 450 mL. What is this?
Answer: Cauda equina with retention. Painless retention with saddle anaesthesia indicates CES-R: catheterise, emergency MRI and surgery.
- Simple back pain: No.
- UTI: Not this picture.
- Prostatic obstruction: Saddle numbness suggests cauda equina.
- Incomplete cauda equina: Retention has developed.
3. A man has weeks of back pain, night sweats, weight loss and a gibbus deformity. What is the likely diagnosis?
Answer: Spinal tuberculosis. TB spine is common in Pakistan. MRI, TB tests and anti-TB treatment with surgical review.
- Ankylosing spondylitis: Different pattern.
- Mechanical back pain: Night sweats and weight loss are red flags.
- Osteoporotic fracture: Doesn't explain night sweats.
- Disc prolapse: No.
4. A 40-year-old with back pain has bilateral sciatica, perineal (saddle) numbness and new urinary retention. What is needed?
Answer: Emergency MRI and decompression. Cauda equina syndrome (usually a large central L4/5 or L5/S1 disc prolapse; also tumour, abscess, haematoma) is a surgical emergency: bilateral sciatica, saddle anaesthesia, bladder dysfunction (retention with overflow), bowel dysfunction, sexual dysfunction, reduced anal tone. Urgent MRI and surgical decompression (ideally < 48 h; earlier better) to save sphincter function.
- Analgesia and physiotherapy: Analgesia and physio miss a surgical emergency.
- Outpatient MRI in 6 weeks: Delay causes permanent deficits.
- Epidural steroid injection: Epidural steroids do not treat cauda equina syndrome.
5. A 40-year-old man with back pain for a week now has pain down both legs, numbness around his anus and genitals, and has not passed urine for 10 hours. What is the immediate management?
Answer: Emergency MRI, then decompression. Cauda equina syndrome is compression of the lumbosacral nerve roots below the conus, usually by a large central disc prolapse. Red flags: bilateral sciatica, saddle anaesthesia, bladder dysfunction (retention or incontinence), bowel and sexual dysfunction. It is a surgical emergency: emergency MRI and decompression to preserve bladder and bowel function.
- Analgesia and physiotherapy referral: Saddle anaesthesia and urinary retention mean cauda equina syndrome; analgesia and physiotherapy would miss a surgical emergency.
- Outpatient MRI: An outpatient MRI risks permanent bladder, bowel and sexual dysfunction; cauda equina needs emergency imaging and decompression.
- Epidural steroid injection: Injections don’t relieve cauda equina compression; urgent MRI and decompression are needed.
6. A man with a large central lumbar disc prolapse has bilateral sciatica, saddle anaesthesia, urinary retention and reduced anal tone. What is the diagnosis and the immediate action?
Answer: Cauda equina; urgent MRI, surgery. Cauda equina syndrome is compression of the lumbosacral nerve roots below the conus, most often from a large central disc prolapse (L4/5, L5/S1), tumour, haematoma or abscess. Features: bilateral or alternating sciatica, saddle (perineal) anaesthesia, bladder dysfunction (retention with overflow; check post-void residual), bowel dysfunction, sexual dysfunction and reduced anal tone; lower motor neurone signs (absent reflexes). It is a surgical emergency: urgent MRI and decompression to preserve bladder and bowel function. Conus lesions give a more symmetrical, mixed UMN/LMN picture with early sphincter loss.
- Simple sciatica; analgesia: Red flags make this an emergency.
- Conus tumour; elective review: Conus lesions differ and still need urgent imaging.
- Neuropathy; nerve conduction: Not this picture.
- Spinal shock; observe only: Not trauma-related here.
7. Which condition typically produces a loud first heart sound (S1)?
Answer: Mitral stenosis with mobile cusps. S1 is closure of the mitral and tricuspid valves. It is loud when the cusps are still wide open as the ventricle contracts: mitral stenosis with pliable leaflets, a short PR interval and fast heart rates (exercise, fever, thyrotoxicosis, anaemia). It is soft with a long PR interval, mitral regurgitation, a calcified immobile valve and poor ventricular function.
- Long PR interval: Cusps drift closed before systole: soft S1.
- Mitral regurgitation: Incomplete closure: soft S1.
- Calcified, rigid mitral valve: Rigid cusps barely move: soft S1.
- Severe heart failure: Weak contraction: soft S1.
References and dose sources
- GIRFT National Suspected Cauda Equina Syndrome pathway (NHS England)
- NICE NG59: Low back pain and sciatica
- GIRFT — national suspected CES pathway
- British Association of Spine Surgeons — CES standards
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.