Trauma & Orthopaedics

Cauda Equina Syndrome

Acute or rapidly progressive compression of the lumbosacral nerve roots below the spinal cord, threatening permanent loss of bladder, bowel, sexual and lower-limb function unless decompressed urgently.

Definition

Cauda equina syndrome is acute or rapidly progressive compression of the lumbosacral nerve roots in the spinal canal. It is diagnosed clinically, from back or radicular leg pain together with new or deteriorating sacral symptoms or a severe bilateral neurological deficit, supported by MRI. No single symptom, sign or scan finding is pathognomonic.

Epidemiology

CES is very rare, at 1 to 3 per 100,000 population, and a large lumbar disc prolapse is the commonest cause. Haematoma, trauma, infection, tumour and spinal or epidural anaesthesia account for the rest. Missed or treated late, it causes permanent bladder, bowel, sexual and lower-limb disability.

Pathophysiology

Central compression in the lumbosacral canal affects several nerve roots at once. Because those roots carry the leg myotomes and dermatomes as well as bladder, bowel, sexual and saddle innervation, the deficit mixes radicular pain, lower motor neurone weakness and sacral dysfunction. Sustained compression impairs root perfusion and conduction, which is why function lost for long enough may not return.

First principles

The cauda equina is a bundle of lumbosacral roots below the end of the cord

The spinal cord ends in the upper lumbar spine, and the lumbar and sacral roots then run free in the canal before leaving at their own foramina. A single central lesion can therefore compress several roots at once. That produces a mixture of radicular pain, lower motor neurone leg weakness and sacral dysfunction rather than one dermatomal radiculopathy.¹

The emergency is triggered by suspicion, and documented suspicion is medicolegal

The national document is called the suspected cauda equina syndrome (CES) pathway for a reason. Getting It Right First Time (GIRFT) states that CES is a collection of symptoms and signs, and that MRI alone cannot diagnose it. No single symptom or sign is pathognomonic. Negative physical tests do not rule it out when compatible symptoms are reported. GIRFT's foreword records that 23% of litigated spinal surgery claims in England relate to CES, which is why the pathway prescribes exactly what a referral must record.¹

Recent onset within 14 days is half the rule, and the five symptoms are the other half

The emergency rule has two halves. Leg pain and/or back pain is the first. The second is recent onset, 14 days or fewer, or deterioration of any one of five named symptoms. Recency matters because a static deficit present for months is handled differently from one that started last week or is worsening. Note precisely what the bowel symptom is: loss of the sensation of rectal fullness, not incontinence.^1,2

Sacral sensation is asked about as well as tested

GIRFT records that the altered area may be small or as big as a horse's saddle, and that it may be subjectively reported or objectively tested. It states twice that a digital rectal examination is not necessary but that subjective perianal sensation must be recorded. The pathway prescribes no sensory technique. In practice, ask whether wiping with toilet paper feels normal, compare left with right, then test light touch and pinprick over perianal, perineal and genital skin.¹

The commonest cause is a large disc prolapse, but the pathway is cause-agnostic

GIRFT's pathway is written around a large lumbar disc prolapse, but haematoma, trauma, infection, tumour and spinal or epidural anaesthesia can all compress the roots. The immediate job is the same: find the compression and get the patient to a spinal surgical service. Only the definitive operation and the additional treatment change with the cause. Known cancer plus cord or cauda equina signs is metastatic spinal cord compression (MSCC), a separate oncological emergency.^1,3

Presentation

Back or leg pain plus a new or deteriorating sacral symptom, typically within the last 14 days. That combination is the emergency, whatever the examination shows.^2,1

Cardinal features

Leg pain and/or back pain: the background against which every other symptom counts
Difficulty initiating micturition, or impaired sensation of urinary flow, which may lead to incontinence
Altered perianal, perineal or genital sensation in the S2 to S5 dermatomes, subjectively reported or objectively tested
Severe or progressive neurological deficit of both legs, such as major motor weakness of knee extension, ankle eversion or foot dorsiflexion
Loss of the sensation of rectal fullness, which is the bowel symptom, not faecal incontinence
Sexual dysfunction: inability to achieve an erection or to ejaculate, or loss of genital sensation

Red flags

Recent onset, 14 days or fewer, or deterioration of any one of the five symptoms: refer as an emergency now
Painless urinary retention with overflow incontinence, or a patient who cannot void at all
Sudden bilateral sciatica, or unilateral sciatica that has progressed to bilateral, as a warning that CES may follow
Fever, immunosuppression, known cancer, anticoagulation, trauma, or recent spinal or epidural anaesthesia
Any deterioration while waiting for an urgent musculoskeletal (MSK) appointment: convert it to an emergency referral
Do not be reassured by normal anal tone, a normal examination or a post-void residual under 200 mL

Investigations

Focused emergency history and neurological examination

Record onset, duration and progression of the urinary, bowel, sexual and perineal symptoms, then power and sensation in both legs. GIRFT names the movements to test as knee extension, ankle eversion and foot dorsiflexion. The examination sets a baseline and supports triage; it cannot exclude CES.

Expected finding: Findings may include bilateral or progressive weakness, root-pattern sensory loss, altered perineal sensation or reduced reflexes. A completely normal examination does not rule out CES when compatible symptoms are reported. A digital rectal examination (DRE) is not necessary; record subjective perianal sensation instead.

^2,1

Bladder scan, as an adjunct only

Ask about urinary flow, initiation, sensation of filling and emptying, and incontinence, then scan. GIRFT is explicit that bladder scans must not be used in isolation, or as a discriminator in deciding whether to request MRI or to operate.

Expected finding: If the patient cannot void, scan; above 600 mL, catheterise, document whether the bladder is sensate and perform a catheter tug. If the patient can void, document the pre-void volume and the post-void residual volume (PVR). A PVR under 200 mL cannot exclude CES. A PVR over 200 mL makes CES 20 times more likely. A PVR over 600 mL means catheterise, to avoid bladder distension injury. GIRFT cites Woodfield et al 2023: 60% of patients who had emergency decompressive surgery for CES had a PVR under 200 mL.

Emergency MRI for suspected CES

A sagittal T2-weighted sequence, typically 2D turbo spin echo, is the single sequence that screens for cauda equina compression. GIRFT sets the target as soon as possible and certainly within four hours of the request to radiology. MRI at the presenting hospital is best practice in and out of hours. A transferred patient is scanned within four hours of the receiving unit's own request.

Expected finding: A large central disc prolapse or another compressive lesion may be seen. If compression is identified, axial T2-weighted and sagittal T1-weighted images are added. If it is not, a single sagittal T2 sequence covering the cervical and thoracic spine follows. The report should reach the referring clinician within one hour. CT or CT myelogram is used only where there is an absolute contraindication to MRI.

Assessment for cancer, infection, bleeding and trauma

Ask about known or past cancer, fever, immunosuppression, recent procedures, anticoagulation and trauma. Past or current cancer with symptoms or signs of cord compression is metastatic spinal cord compression (MSCC), an oncological emergency in its own right.

Expected finding: NICE NG234 recommendation 1.3.2 says to contact the MSCC coordinator immediately and treat it as an oncological emergency. Recommendation 1.5.2 requires MRI as soon as possible and always within 24 hours. The differential also includes epidural abscess, discitis, haematoma and fracture, and none of it delays the emergency CES pathway.

^3,1

Management

Step	Detail	Source
Apply the emergency-referral rule and refer now	The rule: leg and/or back pain, plus recent onset (14 days or fewer) or deterioration of any one of the five CES symptoms. That patient attends the nearest hospital with emergency MRI now. NICE NG127 recommendation 1.7.3 requires the same referral for severe low back pain radiating into the leg with new bladder, bowel or sexual dysfunction or perineal numbness.^2,1	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, sections Symptoms and Making an emergency referral; NICE NG127 recommendation 1.7.3
Document the referral against the pathway's own list	Time and date, examination findings, power and sensation in both legs. The CES symptoms present, with duration, frequency and progression. Who it was referred to in secondary care, and when. Any advice received, and from whom, if referral was thought unnecessary. Give the patient their clinical summary to take. Telephone assessment is acceptable if face-to-face review would delay referral.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, section Emergency referral documentation
Request the emergency MRI immediately	Discuss with a senior decision maker (ST4 or equivalent or above, or a consultant), then request. Target: within four hours of the request to radiology. Nil by mouth from the request, because emergency surgery may follow. GIRFT says prior discussion with the on-call spinal service is not required and causes delay.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, section Imaging
Know what the scan covers and who reports it	A sagittal T2-weighted sequence, typically 2D turbo spin echo, screens for compression. If compression is seen, axial T2 and sagittal T1 are added. If not, a single sagittal T2 of the cervical and thoracic spine follows. The report reaches the referring clinician within one hour. Emergency MRI takes precedence over routine and elective scans.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, sections MRI protocol and MRI reporting
Refer confirmed compression to spinal surgery immediately	Confirmed cauda equina compression goes straight to the spinal surgical service. Keep the patient nil by mouth. If transfer is needed, GIRFT specifies a Category 2 blue-light ambulance, and the bed manager is informed once the referral is accepted. The surgical team makes a time-stamped review of history and examination before surgery, and consents the patient.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, section When to refer to the spinal surgical team
Understand the two urgency categories	Incomplete symptoms (CESI) are decompressed as quickly as possible. NCEPOD, the National Confidential Enquiry into Patient Outcome and Death, classes this as an E1/E2 emergency: time-sensitive and life-changing, not life-threatening. Painless urinary retention with overflow incontinence (CES-R) is timed by the operating surgeon, but within 24 hours of MRI. Any delay is documented.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, section Surgical timing
Catheterise before surgery, then trial without catheter after it	Catheterise as soon as the decision to operate is made, and before surgery starts, to avoid bladder distension injury. After surgery, mobilise on the first post-operative day and record any motor or sensory deficit before discharge. Trial without catheter (TWOC) as soon as possible, with pre-void and post-void bladder scans.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, sections Surgical technique and Urinary function and catheterisation
Run the post-operative bladder protocol by the numbers	Pre-void scan over 500 mL with no sensation to void, or no void for six hours: re-catheterise with a long-term catheter and flip/flow valve. Post-void residual under 100 mL: no catheter at discharge. Over 100 mL, or no void after six hours: re-catheterise and teach intermittent self-catheterisation (ISC). Do not TWOC again.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, section Urinary function and catheterisation
Use flip/flow correctly and hand over bladder care	Open a flip/flow valve at least every four hours, including overnight, aiming for a bladder volume under 500 mL. Never rely on sensation or urge to void as the trigger. Anyone who fails TWOC goes to the regional spinal cord injury (SCI) service or an agreed urology service, not a second TWOC.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, section Urinary function and catheterisation
Bowel, sexual and psychological care before discharge	Prescribe a stimulant laxative and a stool softener in the acute post-operative phase, for example senna and docusate sodium; take doses from the BNF. Teach digital rectal stimulation followed by digital rectal evacuation. Signpost the Spinal Injuries Association and the Cauda Equina Champions Charity. Reassess bladder, bowel and sexual function at the surgical outpatient appointment.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, sections Bowel function, Psychological support and Sexual function
If MRI shows no compression, safety-net and redirect	Neural compression explaining radicular pain: advise that the pain usually improves, and refer to the musculoskeletal (MSK) interface or triage service. No cause found: consider alternative diagnoses. Sudden bilateral sciatica without CES symptoms is an urgent MSK referral, to be seen within two weeks. Any new or worsening CES symptom converts it to an emergency referral.^4,1	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, sections Warning signs, Making an urgent referral and When to refer to the spinal surgical team; NICE NG59 Context
Safety-net: the sensory warnings the patient must know	Give the MACP (Musculoskeletal Association of Chartered Physiotherapists) warning card and video, available in 35 languages. The sensory warnings are pins and needles or loss of feeling between the inner thighs or genitals. Also numbness in or around the back passage or buttocks, and altered feeling when using toilet paper to wipe.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, section Safety netting
Safety-net: the bladder, bowel and sexual warnings	Increasing difficulty passing urine, difficulty stopping or controlling flow, or loss of sensation when passing urine. Leaking urine, needing pads, or not knowing when the bladder is full or empty. Inability to stop a bowel movement or leaking, and loss of sensation when passing a bowel motion. Change in erection or ejaculation, or loss of genital sensation during intercourse.¹	GIRFT National Suspected Cauda Equina Syndrome Pathway, March 2026, section Safety netting

Illustrations

Cauda equina anatomy within the lumbar spinal canalDiagram of the spinal cord terminating above the cauda equina nerve roots, with the lumbosacral roots descending in the canal before exiting at their foraminae.PassFinals · original

Cauda-equina compression from a spinal epidural abscessSagittal T2-weighted lumbar MRI showing a posterior epidural collection that severely compresses the thecal sac and cauda equina.Jing Jing Chan and Jen Jen Oh, Wikimedia Commons · CC-BY-4.0

Saddle sensory distribution and emergency symptom pathwayDiagram outlining the perianal, perineal and genital S2-S5 distribution alongside the urinary, bowel, sexual and bilateral-leg symptoms that require emergency assessment.PassFinals · original

Differentials

Lumbar radiculopathy or severe sciatica without CES

Radicular pain with no new urinary, bowel, sexual or perineal symptom and no severe or progressive bilateral deficit. Still needs safety-netting.

Metastatic spinal cord compression

Past or current cancer, severe progressive or night-time back pain, neurological signs or sphincter symptoms. Follow the NICE MSCC emergency pathway.

Spinal epidural abscess or discitis

Back pain with fever, injecting drug use, indwelling lines, immunosuppression or systemic illness, with or without neurological deficit.

Spinal epidural haematoma

Abrupt severe spinal pain then rapid neurological decline, typically after a procedure, spinal anaesthesia, trauma or on anticoagulation.

Conus medullaris or higher cord lesion

Earlier, more symmetrical sphincter dysfunction, a sensory level, and mixed upper and lower motor neurone signs rather than pure lower motor neurone.

Non-neurological urinary or bowel dysfunction

Urinary tract infection, stress or urge incontinence, constipation or pelvic pathology. Sensation of urinary flow and saddle sensation are preserved.

Complications

Permanent urinary retention or incontinence, with long-term catheter or intermittent self-catheterisation
Neurogenic bowel dysfunction and faecal incontinence
Persistent saddle anaesthesia and sexual dysfunction
Lower-limb weakness, foot drop, chronic neuropathic pain and reduced mobility
Psychological distress and loss of independence, employment and driving
Complications of the underlying lesion, including sepsis, malignancy or bleeding

Prognosis

Some patients remain significantly disabled despite prompt treatment. GIRFT states that treating CES before symptoms become severe can reduce the risk of permanent disability. Around 70% of patients presenting with painless retention and overflow incontinence still benefit from decompression, so established retention is not a reason to withhold surgery. Ongoing bladder, bowel, sexual or motor deficits need spinal cord injury service follow-up.

Guidelines

Spinal Surgery: National Suspected Cauda Equina Syndrome (CES) Pathway (NHS England Getting It Right First Time (GIRFT), co-badged with UK spinal, urological, radiology, physiotherapy and patient organisations, 2026)
Suspected neurological conditions: recognition and referral (NG127) (NICE, 2023)
Spinal metastases and metastatic spinal cord compression (NG234) (NICE, 2023)
Low back pain and sciatica in over 16s (NG59), which explicitly excludes cauda equina syndrome (NICE, 2020)

References

Evidence checked: 2026-08-07

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.