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Health condition · Surgical emergency

Cauda equina syndrome, the red flags, the emergency MRI, the urgent decompression.

Rare but catastrophic if missed. Bilateral sciatica, saddle numbness or new bladder change with back pain is a same-day A&E problem, day or night.

See the red flags
A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE, BASS (British Association of Spine Surgeons) and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice for suspected cauda equina - emergency MRI, urgent decompression and long-term rehabilitation.

Key facts

Cauda equina syndrome at a glance.

Rare, but a genuine emergency - the essentials on what it is, what causes it, and how it is treated in the UK.

  • What it is

    A surgical emergency caused by compression of the cauda equina, the bundle of L1 to S5 nerve roots below the conus medullaris.

  • How rare

    Rare, at around 2 in 100,000 people per year, but catastrophic and often permanent if missed.

  • Common cause

    A large central lumbar disc prolapse at L4/L5 or L5/S1 accounts for most cases in adults.

  • Red flag pentad

    Bilateral sciatica, saddle anaesthesia, bladder change, bowel change and sexual dysfunction - any of these needs emergency review.

  • Gold-standard test

    Urgent MRI of the whole spine within hours, day or night, at a unit with on-call spinal or neurosurgical cover.

  • Definitive treatment

    Surgical decompression, ideally within 24 to 48 hours of onset, to give the best chance of neurological recovery.

Why this guide matters

Time is neurology.

Missed or delayed cauda equina syndrome is one of the most serious avoidable harms in spinal medicine. Three principles run through this whole page.

  • Any red flag deserves emergency review

    Bilateral sciatica, saddle numbness, new bladder or bowel change or new sexual dysfunction alongside back pain is an A&E problem, not a GP one.

  • MRI is the gold standard

    A same-day whole-spine MRI - not an X-ray, not a CT - is what confirms or excludes compression of the cauda equina.

  • Decompression within 24 to 48 hours

    Where CES is confirmed, urgent surgical decompression gives the best chance of preserving bladder, bowel, sexual and leg function.

How the diagnosis is made

From first red flag to the operating theatre.

The steps a UK emergency department, spinal service or neurosurgical unit will normally follow when cauda equina syndrome is suspected.

  1. 01

    Assessing

    Focused red-flag history

    Bilateral leg pain, numbness in the saddle area, difficulty passing urine, loss of bowel control or new sexual dysfunction - each is a red flag.

  2. 02

    Assessing

    Targeted examination

    Perineal sensation, anal tone on PR, anal reflex, lower-limb power and reflexes - a normal exam does not exclude CES on its own.

  3. 03

    Assessing

    Bladder scan and residual

    A bedside ultrasound bladder scan and post-void residual volume help identify painless retention with overflow, which is a major warning sign.

  4. 04

    Confirming

    Emergency MRI whole spine

    The definitive test. Performed within hours of suspicion, at any time of day or night, at a centre with on-call spinal or neurosurgical services.

  5. 05

    Confirming

    CT if MRI contraindicated

    Reserved for people with pacemakers or other MRI contraindications - a CT myelogram can substitute in select cases.

  6. 06

    Acting

    Bloods and coagulation

    Full blood count, CRP, coagulation and group and save - especially where infection, malignancy or haematoma are suspected.

  7. 07

    Acting

    Urgent spinal referral

    Direct transfer to a neurosurgical or spinal surgical unit for decompression, tumour biopsy, abscess drainage or haematoma evacuation as appropriate.

Typical timeline: A&E to MRI in hours, decompression within 24 to 48 hours of onset.

Symptoms

What cauda equina syndrome feels like.

The classic pentad of red flags, plus the two important sub-categories - CES incomplete and CES retention - that shape urgency.

  • Bilateral sciatica

    Pain, tingling or weakness running down both legs is a major red flag, particularly when it is new or rapidly worsening.

  • Saddle anaesthesia

    Numbness or altered sensation in the perineum, genitals and inner thighs - the S3 to S5 dermatomes.

  • Urinary retention

    Difficulty starting to pass urine, reduced awareness of a full bladder, or leaking small amounts with a full bladder (overflow incontinence).

  • Bowel dysfunction

    Faecal incontinence, reduced anal tone or loss of anal sensation - often noticed only on direct questioning.

  • Sexual dysfunction

    New erectile difficulty, loss of ejaculation or reduced perineal sensation during intimacy.

  • Leg weakness

    Progressive weakness in the legs or feet, unsteady gait, or difficulty climbing stairs.

  • CES incomplete (CES-I)

    Altered urinary or perineal sensation with preserved bladder function - the earlier stage where prompt surgery gives the best outcome.

  • CES retention (CES-R)

    Painless urinary retention with overflow - a later stage with a worse prognosis if decompression is delayed beyond 48 hours.

Treatment

How cauda equina syndrome is treated.

The primary treatment is urgent surgical decompression. Cause-specific options - tumour, infection or haematoma - and long-term rehabilitation sit alongside it.

  • Emergency spinal referral

    The first step in any suspected case - direct transfer to a neurosurgical or spinal surgical unit for MRI and definitive management.

  • Lumbar decompressive surgery

    Discectomy, laminectomy or wider decompression, aiming to relieve pressure on the nerve roots within 24 to 48 hours of onset where possible.

  • Tumour-directed treatment

    Decompression with biopsy, followed by radiotherapy, oncology review and spinal metastasis MDT input where malignancy is confirmed.

  • Infection management

    IV antibiotics, surgical drainage of an epidural abscess and specialist microbiology input for pyogenic or tuberculous causes.

  • Haematoma evacuation

    Urgent surgical evacuation and reversal of anticoagulation for spontaneous or post-procedural spinal epidural haematoma.

  • Steroids in malignancy

    Dexamethasone can reduce oedema around a spinal tumour while surgery, radiotherapy or oncology treatment is arranged.

  • Bladder and bowel care

    Urgent catheterisation, formal urodynamics later, intermittent self-catheterisation where retention persists and a structured bowel programme.

  • Rehabilitation and support

    Physiotherapy, occupational therapy, specialist spinal rehab, pain management and links to the Cauda Equina Champions Charity for peer support.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards for suspected cauda equina syndrome, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

If you have any of the red-flag symptoms described here, do not wait. Go to A&E the same day or call 999.

  • NICE. Low back pain and sciatica in over 16s: assessment and management (NG59).

  • British Association of Spine Surgeons (BASS) and Society of British Neurological Surgeons. Standards of care for investigation and management of cauda equina syndrome.

  • Getting It Right First Time (GIRFT). Spinal services national report - cauda equina pathway.

  • Royal College of Radiologists. Guidance on emergency MRI for suspected cauda equina syndrome.

Red flags

When back pain becomes a 999 call.

Any single feature on this list, with new or worsening back or leg pain, warrants same-day emergency assessment. Do not wait to see if it settles.

  • Bilateral sciatica

    New or worsening leg pain or weakness on both sides - go to A&E the same day, do not wait for a routine appointment.

  • Saddle anaesthesia

    Numbness or pins and needles in the perineum, genitals, buttocks or inner thighs - treat as an emergency.

  • Urinary retention or overflow

    Inability to pass urine, reduced sensation of a full bladder, or leaking small amounts while the bladder feels full.

  • Bowel incontinence or loss of anal tone

    New difficulty controlling bowels, or a feeling that the anus is numb - both are red flags for cauda equina.

  • New sexual dysfunction with back pain

    Sudden erectile problems, loss of ejaculation or reduced sensation during intimacy alongside back or leg pain.

  • Post-spinal-anaesthesia deficit

    New leg weakness, saddle numbness or bladder change after a spinal or epidural procedure - contact the treating team urgently.

  • Anticoagulation with new deficit

    People on warfarin, DOACs or heparin who develop back pain plus new neurological symptoms need urgent imaging for haematoma.

  • Fever, back pain and neurology

    Consider spinal epidural abscess, especially with IV drug use, diabetes or immunocompromise - needs urgent MRI and antibiotics.

  • Known cancer with back pain

    A patient with breast, lung, prostate, kidney or myeloma malignancy and new back pain needs urgent spinal imaging to exclude cord or cauda equina compression.

Living with it

Recovery, rehab and the long tail.

Nerve recovery after cauda equina syndrome is slow and often incomplete. Bladder, bowel, sexual and mobility outcomes vary widely - specialist rehabilitation matters as much as the surgery itself.

A quiet reminder

Ask about specialist follow-up.

Urodynamics, uro-neurology, spinal rehab and psychological support are all part of a good recovery pathway. If a service was not offered, it is fair to ask.

  1. 01 Act fast

    Trust the red flags

    If any red-flag symptom develops - saddle numbness, bladder change, bilateral sciatica - go straight to A&E. Timing changes outcomes.

  2. 02 After surgery

    Recovery takes months

    Nerve recovery is slow and incomplete for many. Rehab, urodynamic follow-up and a bowel programme are part of normal care.

  3. 03 Bladder

    Intermittent self-catheterisation

    Many people learn to self-catheterise if the bladder does not fully recover. It protects the kidneys and gives control back.

  4. 04 Support

    You are not alone

    The Cauda Equina Champions Charity, spinal rehab teams and psychological services all support people through the long tail of recovery.

Frequently asked

Everything we get asked about cauda equina syndrome.

Quick answers on red flags, timing, MRI, surgery and long-term recovery.

  • What is cauda equina syndrome?

    Cauda equina syndrome (CES) is a surgical emergency caused by compression of the cauda equina - the bundle of L1 to S5 nerve roots that runs below the end of the spinal cord. Compression can cause bladder, bowel and sexual dysfunction, leg weakness and permanent nerve damage if not decompressed promptly.

  • What are the red flag symptoms I should not ignore?

    Bilateral sciatica, saddle anaesthesia (numbness in the perineum, genitals or inner thighs), difficulty passing urine or urinary retention, faecal incontinence or loss of anal sensation, and new sexual dysfunction alongside back pain. Any of these need same-day emergency assessment at A&E.

  • How quickly should I be seen?

    Immediately. Suspected cauda equina syndrome is a same-day A&E problem, day or night. The gold standard is an emergency MRI of the whole spine within hours and, if confirmed, surgical decompression ideally within 24 to 48 hours of symptom onset.

  • What causes cauda equina syndrome?

    The most common cause is a large central lumbar disc prolapse, usually at L4/L5 or L5/S1. Other causes include spinal stenosis, spinal tumours (primary or metastatic), spinal epidural abscess, spinal trauma or fracture, spinal epidural haematoma (particularly in people on anticoagulants) and post-surgical scarring.

  • What happens during treatment?

    You will have an urgent MRI, a bladder scan and often a urinary catheter. If the scan confirms compression, you will be transferred to a neurosurgical or spinal surgical unit for decompressive surgery - typically a lumbar discectomy or laminectomy. Tumour, infection and haematoma each have their own additional treatments.

  • Will I fully recover?

    Outcomes vary widely. People operated on early, before urinary retention sets in (CES incomplete), tend to do best. Persistent bladder, bowel or sexual dysfunction is common where treatment is delayed. Long-term care involves specialist rehabilitation, urodynamic assessment, a bowel programme, physiotherapy and psychological support.

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