By Mr Ahmed-Ramadan Sadek, Neurosurgeon · Last reviewed October 2026 · 6 min read

What is cauda equina syndrome?

The spinal cord itself ends near the top of the lower back. Below that point, the nerves continue downwards inside the spinal canal as a loose bundle that resembles a horse’s tail, which is what cauda equina means in Latin. These nerves supply the legs and also control the bladder, the bowel, sexual function and feeling in the skin around the bottom.

If something presses hard on this bundle, the signals running through it can be disrupted. When this produces problems with the saddle area, bladder, bowel or sexual function, it is called cauda equina syndrome. Because the damage can become permanent if the pressure is not relieved, spinal surgeons treat it as an emergency.

CES is uncommon. the British Association of Spine Surgeons (BASS) patient information puts the frequency at somewhere between 1 in 33,000 and 1 in 100,000 people, and its web guidance quotes a figure of 6 to 10 per million. According to the BASS booklet, it accounts for only around 2 to 6% of lumbar disc problems that need an operation.

Symptoms

CES does not look exactly the same in everyone. Typical features include:

• Changed or reduced feeling in the buttocks, inner thighs, genitals or around the anus.
• Back pain and leg pain, sometimes in both legs, with or without numbness or weakness.
• Bladder changes: being unable to pass urine, losing the sensation of needing to go, or leaking (incontinence).
• Bowel changes, including loss of control or reduced sensation.
• Reduced sexual sensation or function.

Symptoms can appear within hours or creep on gradually, especially if the canal is already narrowed. Never dismiss slow changes as simply “getting older”.

What causes it?

The most frequent cause is a large disc prolapse, where a big piece of disc material bursts backwards into the middle of the spinal canal. This is different from the more common situation in which a slipped disc presses on a single nerve to one leg, causing sciatica.

Other, rarer causes include:

• A smaller disc bulge in someone who already has marked lumbar spinal stenosis (narrowing of the canal).
• A tumour within the spine.
• Infection, bleeding, cysts, fatty deposits or inflammation in the spinal canal.
• Major spinal injury such as a fracture or penetrating wound.
• Abnormal blood vessels present from birth (arteriovenous malformation).

How is it diagnosed?

If CES is suspected, an A&E doctor or GP will refer you urgently to the spinal team. You will be examined carefully, including your leg strength, reflexes and sensation. The doctor will also need to test feeling around your bottom with a light pin-prick and check the muscle tone of your back passage with a gloved finger. It can feel awkward, but it is essential.

A quick ultrasound of the bladder after you have been to the toilet shows whether urine is being left behind. The BASS booklet notes that if roughly 200 ml or more remains, a catheter (a thin tube) is usually placed to drain the bladder. The diagnosis is confirmed with an urgent MRI scan; occasionally a CT scan is used instead.

Treatment

When the cause is a disc prolapse, the treatment is an urgent operation to remove the disc fragment and free the nerves. BASS web guidance states that the published evidence points to better results when decompression is carried out within 48 hours of symptoms starting, and surgeons generally aim to operate as soon as it is safe.

Under general anaesthetic, through a midline cut in the lower back, the surgeon removes some bone from the back of the spine, either a whole section (laminectomy) or a smaller window on one or both sides (laminotomy), then takes out the disc fragment, often using an operating microscope. Other causes such as infection or a tumour may need a different approach. You can read more in our guide to lumbar discectomy and decompression.

Risks and complications

Any operation carries risks. The figures below come from the BASS patient booklet on cauda equina syndrome surgery and are approximate.

Risk	Approximate frequency (BASS)
Nerve root injury (first operation)	Less than 1 in 100
Nerve root injury (repeat surgery)	Up to 10 in 100
Tear in the nerve lining (dura), first operation	5 to 15 in 100
Dural tear, repeat surgery	Up to 25 in 100
Return to theatre to repair a leaking dural tear	Less than 0.05%
Leg pain returning or worsening (scarring or another disc prolapse)	More than 5 in 100 (days to years later)
Superficial wound infection	Up to 4 in 100
Deep wound infection	Fewer than 1 in 100
Injury to a major blood vessel during disc surgery	About 1 in 4,000
Blood clot in the leg (DVT) or lung (PE)	Fewer than 1 in 700
Death from damage to major vessels or organs	About 1 in 10,000
Death from anaesthetic complications	About 1 in 250,000

Other possible problems include pressure or eye injuries from positioning on the operating table (very rarely, loss of sight), stroke, heart attack, and, very rarely, further nerve damage leading to paralysis, for instance from bleeding inside the spinal canal after surgery. Infection is more likely with diabetes, steroids or a weakened immune system. Tell your team about any blood-thinning medicines, as these may need to be stopped or reversed.

Recovery and outlook

Surgery cannot repair nerves that have already been damaged; its job is to prevent further harm and give them the best chance of healing. Leg pain often improves first, sometimes straight away, though it can take 8 to 12 weeks or more to settle. Numbness, weakness and bladder or bowel function recover more slowly; the BASS booklet notes improvement can continue for up to two years, and recovery is not always complete.

• Before your catheter is removed, the nurses will check that you can empty your bladder. Some people need to learn to pass a catheter themselves a few times a day for a while.
• Ongoing bladder, bowel or sexual problems should be referred to specialist continence, urology or sexual health services. Please do not feel embarrassed to raise them.
• Most people stay off work for around four weeks, or longer for physical jobs or if recovery is incomplete.
• BASS advises that you must inform the DVLA after CES, and should only drive when you can safely do an emergency stop.

Living with lasting effects can be isolating. Support groups such as Cauda Equina UK can put you in touch with others who understand.

• BASS patient information: Cauda equina syndrome
• BASS patient booklet: Cauda equina syndrome
• NHS: Cauda equina syndrome
• Cauda Equina UK (patient charity)
• Spinemathema guide: Acute back pain

This guide is general information and is not a substitute for advice about your own situation. Please speak to your GP or specialist.