Cauda Equina Syndrome: Warning Signs and Why Hours Matter

Written by the LSRI clinical team and medically reviewed by Dr Prashant Sankaye, Consultant MSK Radiologist, on 9 October 2026.

Cauda equina syndrome (CES) happens when the bundle of nerves at the bottom of the spinal canal is badly squeezed, most often by a large slipped disc. It is rare, but it is an emergency. If the pressure is not relieved in time, it may cause permanent loss of bladder and bowel function, loss of sexual function, and paralysis of the legs¹.

Most back pain and sciatica is not CES. Back pain usually improves within a few weeks, and sciatica within a few weeks to a few months^2,3. This guide explains the few cauda equina syndrome symptoms that change that, and why acting the same day matters. If you have back or leg pain with any of the warning signs below, stop reading and go to A&E or call 999 now³.

What is cauda equina syndrome?

CES is pressure on the nerve roots in the lower spinal canal. It affects bladder, bowel or sexual function and the feeling around the genitals and back passage^8,12.

In adults the spinal cord ends at around the second lumbar vertebra (L2), in the upper part of the lower back⁶. Below that, separate nerve roots carry on down the spinal canal. Together they look like a horse’s tail, which is what cauda equina means in Latin. These roots supply the legs. They also control the bladder, bowel and sexual function, and the feeling in the “saddle” area: between the legs, around the back passage and genitals, and the inner thighs^1,12.

The most common cause is a large disc prolapse (slipped disc) pressing back into the canal^1,11. Less common causes include tumours, fractures, problems with blood vessels, infection and complications of medical procedures¹². We cover two of these separately: cancer that has spread to the spine and back pain with fever and spinal infection.

How rare is CES? Most back pain is not CES

CES is uncommon, and most people with back pain or sciatica will not get it.

Researchers in Scotland identified, across all centres performing spinal surgery, everyone who needed emergency surgery for CES caused by degenerative disc disease in one year. They found 149 cases in 5.4 million people: about 2.7 new cases per 100,000 people per year, at least four times higher than earlier European estimates. CES was more common in women and in people aged 30 to 49⁴. England’s national pathway quotes 1 to 3 per 100,000¹.

A systematic review (a study that gathers and weighs all the research on a question) pooled four studies and found CES in about 0.27% of people with low back pain who were seen in hospital⁵. Across 18 studies of adults who presented as an emergency with suspected CES, 19% (about 1 in 5) had CES confirmed on examination and scan⁵. The authors judged the evidence limited because studies used different definitions⁵.

So a normal emergency scan is a common and welcome result, not a wasted trip.

What are the warning signs of cauda equina syndrome?

The warning signs are new changes in saddle feeling, bladder, bowel or sexual function, or severe or worsening problems in both legs, in someone with back or leg pain^3,1. The key word is new: England’s national pathway focuses on symptoms that have started, or got worse, recently¹. If you are unsure how long you have had a sign, treat it as new and get checked. You do not need several signs. The NHS advises going to A&E or calling 999 if you have any one of the signs it lists³.

Two stages: why the early signs matter

Specialists usually describe two main stages. The aim is to treat CES in the first stage, before the bladder stops emptying⁷.

• Incomplete CES (CES-I). The nerves are affected but still partly working. People may notice altered feeling when peeing, a weaker urge to go, a poor stream or needing to strain, but they still have control of their bladder and can pass urine, even if it is difficult⁶.
• CES with retention (CES-R). The bladder is no longer under the person’s control and cannot empty properly. Urine builds up and can leak out (“overflow”), and this is painless^6,1.

Stage predicts recovery: people with incomplete CES have a better outlook than those with retention^7,8. One review estimated that 50 to 70% already have retention when they first present, and urged every effort to stop CES-I becoming CES-R⁷. Incontinence is a late sign⁶. Waiting for it means waiting too long.

Why do hours matter? What the evidence on timing shows

Relieving pressure on the nerves early, before retention develops, is thought to give the greatest chance of recovery^7,10. But much of the evidence is observational, so it shows links, not proof^10,11, and the exact time limit is debated¹⁰.

In the UK study, people who needed a catheter before surgery were operated on sooner, and the authors said they could not comment on whether delay leads to worse outcomes¹¹.

The message for patients is still clear. Speed matters because CES can progress from the incomplete stage to retention⁷, symptoms do not follow a set order, and there is no way of predicting who will progress¹⁵. England’s national pathway asks for MRI within four hours of the request and surgery for incomplete CES as quickly as possible. Even with retention, surgery should follow within 24 hours of the MRI¹. Forty-eight hours comes from research, and one review found no strong basis for treating it as a safe time to wait¹⁰. For the wider picture, see why early imaging matters.

Why can cauda equina syndrome be missed or diagnosed late?

CES can be hard to recognise early. The first signs are often subtle and vague, and can come on slowly^15,8.

• No fixed pattern. No single symptom or combination of symptoms is accurate enough to confirm or rule out CES on its own¹, and symptoms do not develop in a set order¹⁵.
• Subtle or slow onset. Early symptoms are often vague, and some people develop them gradually^15,8.
• Embarrassment. People may not mention bladder, bowel or sexual changes because they feel embarrassed⁸.
• Pain takes centre stage. A review that reported patient accounts found some people ignored saddle numbness and put more weight on their pain¹⁵. Yet retention can be painless^1,6.
• Words get in the way. In a patient study described in the same review, people asked about “problems with sexual function” all thought it meant whether they were sexually active¹⁵.
• The bladder can look reassuring. In a large UK study of people who all needed surgery for CES, 59% (216 of 368) of those who had a bladder scan had under 200 ml of urine left after peeing¹¹. Bladder scans should not be used on their own to rule CES in or out¹.
• Services vary. A national review in England found many patients with suspected CES were not being referred, and wide variation in detection¹.

None of this is about blame. It is why clear warning signs and a fast route to MRI matter.

How is cauda equina syndrome diagnosed?

CES is diagnosed by combining a doctor’s assessment with an emergency MRI scan of the lower spine, both arranged by the hospital¹.

The doctor will ask about your symptoms, including bladder, bowel and sexual changes, and check the power and feeling in your legs and the feeling around your back passage¹. MRI (magnetic resonance imaging) uses a strong magnet and radio waves to make detailed pictures of the discs and nerve roots. It is the imaging test of choice for CES⁸. In England, the national pathway says MRI should be done at the hospital where the patient arrives, in or out of hours, and within four hours of the request¹.

A scan alone does not make the diagnosis: doctors put symptoms, examination and scan together¹. Most people scanned for suspected CES do not have it⁵.

Why not book a scan yourself? If you have warning signs, a booked outpatient scan is the wrong route. The national pathway sends people with CES symptoms straight to the nearest hospital with emergency MRI¹. Go to A&E or call 999.

When you do not need an emergency scan

Back pain or sciatica without warning signs is not an emergency and usually improves with time^2,3. Scans also have limits: they often show age-related changes in people with no pain. In a review of CT and MRI studies of people without back pain, disc bulges were seen in 30% of 20-year-olds and 84% of 80-year-olds¹⁶. Our guides to spine MRI for back pain and whether back pain can be a sign of cancer explain when a planned scan helps.

What is the treatment for cauda equina syndrome?

Confirmed CES is usually treated with emergency surgery to take the pressure off the nerves, called decompression¹.

When a disc is the cause, the surgeon removes the disc material pressing on the nerves, which can be harder than routine disc surgery¹⁷. Complication rates are higher than in decompression surgery for other reasons¹, and one review recommends prompt surgery by a suitably experienced surgeon for incomplete CES⁷.

Many people improve, but lasting effects are common. One year after surgery, the UK study of 621 people found¹¹:

Not everyone gave one-year information (284 people returned questionnaires), so these figures describe those who did¹¹.

There was real improvement too. Average disability scores (Oswestry Disability Index, 0 to 100) fell from 63 on admission to 31 at one year, and function improved even in people who presented with retention¹¹. The national pathway estimates that around 70% of people with painless retention benefit from decompression, although they have a poorer outlook than people treated earlier¹.

The national pathway recommends pointing people to support groups¹, so ask your hospital team about the support available to you.

What should you do?

1. Act on the first warning sign, the same day. Go to A&E or call 999³. Do not wait to see if it settles, for the pain to get worse, or for incontinence, which is a late sign⁶.
2. Do not drive yourself. Ask someone to take you, or call 999 and ask for an ambulance³.
3. Do not try to book a scan first. The hospital arranges the emergency MRI and, if needed, surgery¹.
4. Say exactly what has changed, and when. Use plain words, such as “Since yesterday I have numbness around my bottom and genitals.” Mention numbness or bladder changes even if pain bothers you most, and say when each symptom started¹⁵.
5. If your scan is clear, keep watching. Ask what to look out for, and go back straight away if new symptoms appear. The national pathway stresses safety-netting advice (what to watch for and when to return) for people with back pain and other symptoms, and says new or worsening CES symptoms need an emergency referral¹.
6. For back pain without warning signs, get the right level of help. See a GP if it has not improved after a few weeks³. Ask for an urgent GP appointment or contact NHS 111 if you feel hot, cold, shivery or generally unwell, or if severe pain starts suddenly or gets worse quickly².

What LSRI can and cannot do

LSRI is not an emergency service. We cannot arrange emergency MRI or emergency surgery. If you have any warning sign of CES, go to A&E or call 999 rather than contacting us.

We can help with problems that are not urgent:

• Back pain or sciatica that is not improving. Our MRI scans are reported by a Consultant MSK Radiologist within 24 hours. MRI is from £375 per body part, including the scan, a specialist report and access to your images, or from £425 with a consultation.
• A second opinion on an MRI you already have. See our second opinion page.

If warning signs appear while you are waiting for a routine scan with us, go to A&E or call 999.

Reading this from outside the UK?

The warning signs and the need for same-day hospital care are the same everywhere; only the number changes. Call 112 in the EU, 911 in the US and Canada, 000 in Australia, or your local emergency number, or go to the nearest hospital emergency department. In the UK, 999 and 112 both work.

Frequently asked questions

What does saddle numbness feel like?

It is reduced feeling, numbness or pins and needles where a saddle would touch: between your legs and around your back passage and genitals^1,3,12. If it is new and you have back or leg pain, go to A&E or call 999³.

Is sciatica in both legs an emergency?

The NHS advises going to A&E or calling 999 for sciatica on both sides, or for severe or worsening weakness or numbness in both legs³. Most people checked for suspected CES do not have it⁵, but symptoms in both legs can be an early stage⁶.

Is 48 hours the deadline for cauda equina surgery?

No single deadline has been established. A 2000 meta-analysis favoured surgery within 48 hours⁹, but a later review found no strong basis for treating 48 hours as a safe time to wait¹⁰. The advice is to act on the first warning sign^3,7.

Will I fully recover after surgery for cauda equina syndrome?

Many people improve, but lasting effects are common: in a UK study, half of those who replied reported bladder problems one year after surgery¹¹. People who are at the incomplete stage generally do better than those with retention^7,8.

Should I book a private MRI if I am worried about cauda equina syndrome?

Not if you have warning signs: go to A&E or call 999. Hospitals in England are expected to scan within four hours of the request and to treat confirmed CES as an emergency¹.

References

1. Getting It Right First Time (GIRFT), NHS England. Spinal Surgery: National Suspected Cauda Equina Syndrome (CES) Pathway. February 2023, updated March 2026. gettingitrightfirsttime.co.uk
2. NHS. Back pain. Page last reviewed 5 March 2026. nhs.uk
3. NHS. Sciatica. Page last reviewed 3 December 2024. nhs.uk
4. Woodfield J, Lammy S, Jamjoom AAB, Fadelalla MAG, Copley PC, Arora M, et al. Demographics of cauda equina syndrome: a population-based incidence study. Neuroepidemiology 2022;56(6):460-468. doi:10.1159/000527727
5. Hoeritzauer I, Wood M, Copley PC, Demetriades AK, Woodfield J. What is the incidence of cauda equina syndrome? A systematic review. J Neurosurg Spine 2020;32(6):832-841. doi:10.3171/2019.12.SPINE19839
6. Lavy C, Marks P, Dangas K, Todd N. Cauda equina syndrome: a practical guide to definition and classification. Int Orthop 2022;46(2):165-169. doi:10.1007/s00264-021-05273-1
7. Gardner A, Gardner E, Morley T. Cauda equina syndrome: a review of the current clinical and medico-legal position. Eur Spine J 2011;20(5):690-697. doi:10.1007/s00586-010-1668-3
8. Lavy C, James A, Wilson-MacDonald J, Fairbank J. Cauda equina syndrome. BMJ 2009;338:b936. doi:10.1136/bmj.b936
9. Ahn UM, Ahn NU, Buchowski JM, Garrett ES, Sieber AN, Kostuik JP. Cauda equina syndrome secondary to lumbar disc herniation: a meta-analysis of surgical outcomes. Spine 2000;25(12):1515-1522. doi:10.1097/00007632-200006150-00010
10. Chau AMT, Xu LL, Pelzer NR, Gragnaniello C. Timing of surgical intervention in cauda equina syndrome: a systematic critical review. World Neurosurg 2014;81(3-4):640-650. doi:10.1016/j.wneu.2013.11.007
11. Woodfield J, Hoeritzauer I, Jamjoom AAB, Jung J, Lammy S, Pronin S, et al. Presentation, management, and outcomes of cauda equina syndrome up to one year after surgery, using clinician and participant reporting: a multi-centre prospective cohort study. Lancet Reg Health Eur 2023;24:100545. doi:10.1016/j.lanepe.2022.100545
12. Spinal Injuries Association. Cauda equina syndrome. spinal.co.uk (accessed 8 October 2026)
13. DeLong WB, Polissar N, Neradilek B. Timing of surgery in cauda equina syndrome with urinary retention: meta-analysis of observational studies. J Neurosurg Spine 2008;8(4):305-320. doi:10.3171/SPI/2008/8/4/305
14. Mustafa MA, Richardson GE, Gillespie CS, Islim AI, Wilby M, Clark S, et al. Definition and surgical timing in cauda equina syndrome: an updated systematic review. PLoS One 2023;18(5):e0285006. doi:10.1371/journal.pone.0285006
15. Greenhalgh S, Finucane L, Mercer C, Selfe J. Assessment and management of cauda equina syndrome. Musculoskelet Sci Pract 2018;37:69-74. doi:10.1016/j.msksp.2018.06.002
16. Brinjikji W, Luetmer PH, Comstock B, Bresnahan BW, Chen LE, Deyo RA, et al. Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. AJNR Am J Neuroradiol 2015;36(4):811-816. doi:10.3174/ajnr.A4173
17. Gleave JRW, Macfarlane R. Cauda equina syndrome: what is the relationship between timing of surgery and outcome? Br J Neurosurg 2002;16(4):325-328. doi:10.1080/0268869021000032887

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