Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Identify evolving sacral nerve and terminal cord dysfunction, use a low threshold for emergency MRI and coordinate decompression without relying on any single symptom, examination or bladder volume.
The adult spinal cord usually ends around the L1 vertebral level as the conus, below which lumbar and sacral roots descend in the thecal sac. Compression of these mobile roots creates cauda equina syndrome, often with severe radicular pain, asymmetric lower-motor-neurone weakness, reduced reflexes and patchy saddle or leg sensory loss. A lesion of the conus is more compact, so bilateral sacral dysfunction, saddle anaesthesia and mixed long-tract or root signs may occur together.
CES is a clinical suspicion followed by MRI, not a checklist diagnosis. The patient may initially retain the ability to void but lose normal sensation or need to strain. Progression from incomplete CES to painless retention worsens prognosis. Conversely, pain, medicines, anxiety and constipation commonly alter bladder function without compression. Because neither symptoms nor examination are perfectly discriminating, a credible new sacral syndrome deserves emergency imaging rather than reassurance based on one negative sign.
Assessment should be respectful and specific. Ask about urinary sensation and control, bowel fullness and continence, genital sensation, erection or ejaculation and bilateral motor change. Test lower-limb myotomes, reflexes and sensation plus perianal sensation when it will inform the pathway, with consent and a chaperone. Digital rectal tone has limited discriminatory value and must not be used as the sole reason to avoid MRI.
A large lumbar disc or severe degenerative canal narrowing can compress several lumbosacral roots, sometimes after preceding back pain or sciatica.
Metastasis, primary spinal tumour or pathological collapse can compress the terminal cord or roots, often with progressive, nocturnal or mechanical pain.
Spinal epidural abscess or inflammatory tissue can narrow the canal, particularly after bacteraemia, spinal procedures, injected drug use or immunosuppression.
Epidural haematoma, fracture or dislocation may produce abrupt compression, with anticoagulation, coagulopathy and recent neuraxial intervention increasing haemorrhagic risk.
Disc, bone, tumour, pus or blood occupies the canal and mechanically deforms mobile cauda-equina roots or the compact terminal spinal cord.
Continuing pressure impairs venous drainage and microvascular perfusion, producing oedema, conduction failure and eventually irreversible axonal or cord injury.
Damage to sacral sensory, motor and autonomic fibres disrupts saddle sensation, bladder awareness and emptying, bowel control and sexual function.
Involvement of lumbar and sacral roots causes radicular pain, patchy weakness, sensory loss and reduced reflexes; conus injury may add upper motor-neurone signs.
Back or bilateral radicular pain accompanies altered urinary sensation, impaired initiation, need to strain or reduced stream awareness while voluntary voiding remains possible, often with saddle change.
Painless urinary retention and overflow occur with marked saddle or genital sensory loss and possible faecal or sexual dysfunction, indicating advanced sacral-root compromise.
Early symmetrical bladder, bowel and sexual dysfunction with saddle anaesthesia and relatively modest leg weakness combines absent ankle reflexes with possible brisk knees or extensor plantars.
Severe bilateral or asymmetric sciatica, flaccid myotomal weakness, reduced knee or ankle reflexes and dermatomal loss accompanies evolving sacral autonomic symptoms.
Fever, immunosuppression, injecting drug use, cancer, weight loss or unremitting night pain broadens the emergency beyond disc prolapse and affects contrast imaging and treatment.
Single-root pain and weakness without new saddle, bladder, bowel or sexual dysfunction supports radiculopathy, but evolving bilateral symptoms lower the threshold for emergency MRI.
A clear truncal sensory level, brisk legs and extensor plantar responses favour cord disease above the conus rather than isolated mobile-root compression.
Symmetrical ascending weakness and areflexia without a structural sensory level favour polyradiculoneuropathy; early bladder paralysis and severe local pain suggest an alternative.
Pain, medicines and anxiety can alter bladder emptying and effort, but positive inconsistency cannot safely exclude compression when a credible new sacral syndrome is evolving.
Pain-related voiding difficulty, medication effects, urinary infection, pelvic disease, diabetic neuropathy and functional symptoms can resemble elements, but are concluded only after proportionate emergency exclusion of compression.
Prolonged sacral injury may leave retention, overflow, incontinence, recurrent urinary infection, constipation and the need for lifelong catheter or bowel programmes.
Genital numbness, erectile or ejaculatory dysfunction and loss of sexual sensation may persist and can profoundly affect identity, relationships and fertility planning.
Irreversible root damage can cause foot drop, gait disability, muscle wasting and persistent radicular pain despite technically adequate decompression.
Loss of mobility and continence increases pressure injury, thrombosis, dependence, depression and occupational disruption, requiring coordinated rehabilitation and support.
Waiting for painless overflow misses the earlier incomplete stage when altered urinary sensation or initiation may be the only autonomic clue.
Residual volume helps manage retention and probability but cannot safely veto emergency MRI in a convincing evolving sacral syndrome.
Technique and subjective interpretation reduce sensitivity, so a normal digital examination must never be used as the sole exclusion.
Terminal cord injury can combine brisk knees or plantar responses with absent ankles and sacral lower-motor-neurone dysfunction.
Mobile roots are compressed unevenly, so unilateral-dominant sciatica or weakness does not remove concern when sacral symptoms evolve.
Most suspected cases lack compression, but they still require explanation, complication treatment and safety-netting rather than invalidation.
Asking only about incontinence and missing altered flow sensation, initiation, filling awareness and sexual function.
Using normal rectal tone or a low post-void residual as a standalone reason not to image.
Delaying MRI until weakness becomes bilateral or painless retention develops.
Assuming every sacral syndrome is a disc and overlooking abscess, tumour, haematoma or trauma.
Quoting an arbitrary decompression time threshold as permission to postpone urgent surgical discussion.
Discharging an MRI-negative patient without treating retention, considering alternatives or giving progression advice.
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A 39-year-old with acute back pain and bilateral sciatica can still pass urine but now must strain and cannot feel the urinary stream normally. Perianal sensation feels altered. What is the best next step?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes
Opioids can cause retention, constipation and sedation that complicate assessment; analgesic response neither confirms nor excludes CES.
A catheter can conceal subsequent voiding function and introduce infection; it treats retention but does not treat neural compression or replace MRI.
Do not give a generic regimen divorced from allergy, renal function, source and local resistance; sampling must not cause harmful delay.
Balance thrombosis, last dose and renal clearance; licensed and commissioned reversal options differ by agent and bleed site. Document when and how the original anticoagulant indication will be reconsidered.