Synopsis
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.
- Cauda equina syndrome is dysfunction from compression of multiple lumbosacral nerve roots below the cord; a large central disc is common, but tumour, abscess, haematoma, stenosis and trauma also cause it.
- Conus medullaris syndrome affects the terminal spinal cord around L1 and often produces more symmetrical deficits, early severe bladder or bowel dysfunction, saddle loss and mixed upper- and lower-motor-neurone signs.
- Early urinary clues are difficulty initiating micturition, impaired awareness of flow or bladder filling, reduced urge and altered urethral sensation; painless overflow retention is a late feature.
- Saddle, perianal or genital sensory change, loss of rectal fullness and new erectile, ejaculatory or genital sensory dysfunction are important even when not volunteered.
- Leg symptoms may be bilateral or progressive and include sciatica, weakness and reduced reflexes, but an asymmetric presentation does not exclude cauda equina compression.
- No individual history item, rectal examination finding or post-void residual has sufficient sensitivity to rule out CES; the decision for MRI integrates the whole evolving syndrome.
- Bladder scanning is a useful adjunct for retention and catheter planning, not a gatekeeper that cancels imaging when red flags persist.
- MRI is the investigation that confirms or excludes compressive CES and should be available as an emergency through the local or regional GIRFT-aligned pathway.
- Decompression timing is an urgent spinal surgical decision based on symptoms, imaging and progression; arbitrary cut-offs must not justify avoidable delay.
- Document exact onset and progression of bladder, bowel, sexual, saddle and leg symptoms, the informed intimate examination and all escalation times because clinical change drives management.
Key red flags
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.
Investigation priorities
Confirm or exclude compression of the cauda equina or conus and define disc, tumour, infection, blood or stenosis for surgery.
Management branches
New back or radicular pain accompanies any credible bladder, bowel, sexual, saddle or severe bilateral motor red flag.
- Record the onset and evolution of urinary initiation, flow sensation, filling awareness, saddle and genital sensation, rectal fullness, sexual function and leg symptoms using clear non-leading language.
- Perform a focused neurological and consented sacral examination, scan the bladder after voiding when feasible and provide analgesia without allowing normal tone or low residual to overrule the syndrome.
- Activate the local GIRFT-aligned emergency MRI pathway and discuss with the spinal service; keep the patient appropriately monitored and nil by mouth if operative compression is plausible.
- Escalate progression immediately, documenting MRI request, reporting, referral and transfer times and communicating any change directly to the receiving surgeon.