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.

In a nutshell

Cauda equina syndrome (CES) is compression of the lumbosacral nerve roots and a spinal surgical emergency. Leg and/or back pain plus recent onset (14 days or fewer) or deterioration of a bladder, bowel, sexual or saddle-sensation symptom means emergency referral now.

Classic presentation

A 40-year-old with a week of worsening bilateral sciatica who now cannot tell when urine is flowing and says wiping feels numb.

Key points

CES is rare, 1 to 3 per 100,000, but the Getting It Right First Time (GIRFT) pathway records that 23% of litigated spinal surgery claims in England relate to it.
GIRFT names only two categories: CESI, incomplete symptoms, and CES-R, painless urinary retention with overflow incontinence. Around 70% of CES-R patients still benefit from decompression.
Complication rates in CES decompression are six times higher than in non-CES decompression. Anaesthesia starting between midnight and 07:30 needs consultant on-call sanction.
60% of patients who had emergency decompression for CES had a post-void residual under 200 mL (Woodfield et al 2023, cited by GIRFT).
Sudden bilateral sciatica without CES symptoms is an urgent musculoskeletal (MSK) referral, seen within two weeks, safety-netted with the Musculoskeletal Association of Chartered Physiotherapists (MACP) card and video.
The MACP card is available in 35 languages and includes altered feeling when using toilet paper to wipe: a question worth asking directly.
NICE NG59 explicitly does not cover sciatica with progressive neurological deficit or cauda equina syndrome, so a back-pain pathway is not a CES pathway.
MRI at the presenting hospital is best practice in and out of hours; the report should reach the referring clinician within one hour.

First-line investigation

Emergency MRI: a sagittal T2-weighted sequence screens for compression, as soon as possible and certainly within four hours of the request to radiology.

Management

Refer on suspicion

Leg and/or back pain plus recent onset (14 days or fewer) or deterioration of any of five CES symptoms: emergency referral now to a hospital with emergency MRI.^2,1
The five: impaired initiation or sensation of urinary flow; altered S2 to S5 perianal, perineal or genital sensation. Also severe or progressive deficit of both legs; loss of sensation of rectal fullness; sexual dysfunction.¹
Telephone assessment is enough if face-to-face review would delay referral. Nil by mouth from the moment an emergency scan is requested.¹

Assess without being falsely reassured

Document power and sensation in both legs, testing knee extension, ankle eversion and foot dorsiflexion, plus subjective perianal sensation. A digital rectal examination is not necessary.¹
Record pre-void volume and post-void residual (PVR). PVR under 200 mL cannot exclude CES; over 200 mL makes CES 20 times more likely; over 600 mL, catheterise.¹
Cannot void and bladder over 600 mL: catheterise, document whether sensate, perform a catheter tug. This prevents bladder distension injury.¹

Image within four hours

Request emergency MRI after discussion with a senior decision maker (ST4 or equivalent or above, or a consultant): within four hours of the request to radiology.¹
Sagittal T2 screens for compression. If seen, add axial T2 and sagittal T1; if not, a single sagittal T2 of the cervical and thoracic spine.¹
Do not discuss with the on-call spinal service first. Report to the referring clinician within one hour. CT or CT myelogram only if MRI is absolutely contraindicated.¹

Refer confirmed compression

Immediate referral to the spinal surgical service, nil by mouth, Category 2 blue-light ambulance if transfer is needed, bed manager informed once accepted.¹
Incomplete symptoms (CESI): decompress as quickly as possible, an NCEPOD (National Confidential Enquiry into Patient Outcome and Death) E1/E2 emergency, time-sensitive and life-changing but not life-threatening.¹
Painless retention with overflow incontinence (CES-R): timing is the operating surgeon's, but within 24 hours of MRI. Catheterise before surgery starts.¹

After the operation, work the bladder protocol

Trial without catheter (TWOC) as soon as possible, with pre-void and post-void bladder scans. Mobilise on the first post-operative day.¹
Pre-void over 500 mL with no sensation to void, or no void for six hours: re-catheterise long term with a flip/flow valve.¹
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).¹
Do not TWOC again. Open flip/flow at least four-hourly including overnight, aiming under 500 mL, never triggered by sensation or urge.¹

Safety-net, and follow up what surgery did not fix

No compression: advise pain usually improves, refer to musculoskeletal (MSK) triage. Sudden bilateral sciatica without CES symptoms is an urgent MSK referral, seen within two weeks.^4,1
Safety-net with the Musculoskeletal Association of Chartered Physiotherapists (MACP) card and video (35 languages): new saddle numbness, altered feeling when wiping, urinary or bowel change, sexual change.¹
Failed TWOC goes to the regional spinal cord injury (SCI) or agreed urology service, not a second TWOC. Reassess bladder, bowel and sexual function in clinic.¹
Stimulant laxative plus softener (for example senna and docusate sodium) post-operatively, doses from the BNF. Signpost the Spinal Injuries Association and Cauda Equina Champions Charity.¹

Exam traps

A post-void residual under 200 mL does not exclude CES. A bladder scan must never decide against MRI or surgery.
Urinary incontinence without impaired sensation of urinary flow or saddle anaesthesia: consider urinary tract infection, stress incontinence and urge incontinence first.
The bowel symptom GIRFT names is loss of the sensation of rectal fullness, not faecal incontinence. Incontinence is a later finding.
Digital rectal examination is not necessary and must not delay referral. Record subjective perianal sensation instead.
There is no national rule to decompress within 48 hours of onset. GIRFT sets no hours-from-onset threshold, only urgency categories.
Do not phone the on-call spinal service before requesting the MRI. GIRFT says prior discussion is not required and causes delay.
Whole-spine MRI is not the default. A single sagittal T2 of the cervical and thoracic spine is added only if no compression is found.
Known cancer plus cord or cauda equina signs is metastatic spinal cord compression (MSCC): contact the MSCC coordinator immediately, MRI within 24 hours.

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

Key sources

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.