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# Cauda equina syndrome

[Cauda equina](https://durgical.com/en/anatomy/cauda-equina/) syndrome is compression of the nerve roots at the bottom of the spine; it causes numbness, bladder or bowel problems and is an emergency.

Updated 2026-10-29

## Structures involved

Tap one to see what it is and open it in 3D.

- [Cauda equina](https://durgical.com/en/anatomy/cauda-equina/)
- [Conus medullaris](https://durgical.com/en/anatomy/conus-medullaris/)
- [Dura (dural sac)](https://durgical.com/en/anatomy/spinal-dura/)
- [L4–L5 disc](https://durgical.com/en/anatomy/l4-l5/)
- [L5–S1 disc](https://durgical.com/en/anatomy/l5-s1/)
- [S1 nerve root](https://durgical.com/en/anatomy/s1/)
- [Pudendal nerve](https://durgical.com/en/anatomy/pudendal-nerve/)
- [Pelvic floor](https://durgical.com/en/anatomy/levator-ani/)
- [L5 vertebra](https://durgical.com/en/anatomy/lumbar-vertebra-spine-and-pelvis-l5/)

## In the clinical exam

- [Lasègue sign (straight leg raise) and Bragard sign](https://durgical.com/en/clinical-exam/lasegue-sign-and-bragard-sign/)
- [Spinal cord syndromes: complete, Brown-Séquard, central, anterior](https://durgical.com/en/clinical-exam/spinal-cord-syndromes-complete-brown-sequard-central-anterior/)

## In physiology

- [Defecation and continence](https://durgical.com/en/physiology/defecation-and-continence/)
- [Spinal cord reflexes](https://durgical.com/en/physiology/spinal-cord-reflexes/)
- [Micturition and the bladder reflex](https://durgical.com/en/physiology/micturition-and-the-bladder-reflex/)

## Why it happens

- [Upper versus lower motor neuron lesions](https://durgical.com/en/physiology/upper-versus-lower-motor-neuron-lesions/)
- [Peripheral nerve: endoneurium, perineurium, epineurium; myelin](https://durgical.com/en/histology/peripheral-nerve-endoneurium-perineurium-epineurium-myelin/)

## What it is

Compression of several lumbar and sacral nerve roots of the cauda equina, below the end of the [spinal cord](https://durgical.com/en/anatomy/spinal-cord/). It causes saddle anaesthesia, bladder, bowel and sexual dysfunction and leg weakness, and is a surgical emergency.

## Who gets it

Rare, but one of the most important red flags in low back pain. It is most often seen in adults aged 30 to 50 with a large central lumbar disc herniation.

## Causes

- Large central lumbar disc herniation, most often at L4–L5 or L5–S1 (the commonest cause)
- Lumbar spinal stenosis
- Spinal tumours and metastases
- Epidural abscess or haematoma
- Trauma, fractures, or complications of spinal surgery or procedures

## Risk factors

- Known lumbar disc herniation or spinal stenosis
- Cancer with spread to bone
- Anticoagulation or recent spinal procedure (epidural haematoma)
- IV drug use, diabetes or immunosuppression (abscess)

## Pathophysiology

Below the [conus medullaris](https://durgical.com/en/anatomy/conus-medullaris/) the canal holds only nerve roots. A mass in the canal compresses many roots at once, especially the sacral roots S2–S4 that supply the bladder, anal sphincter and perineal [skin](https://durgical.com/en/anatomy/skin/). The roots are lower motor neurones, so findings are flaccid weakness and reduced reflexes. Longer compression makes permanent damage more likely.

## Classification

- Suspected: symptoms without objective deficit
- Incomplete: altered urinary sensation or difficulty voiding, with retained control
- With retention: painless urinary retention and overflow incontinence; worse outcome
- Conus medullaris syndrome: a related lesion of the end of the cord, with mixed signs

## Symptoms and signs

- Saddle anaesthesia: numbness of the perineum, buttocks and inner thighs
- Urinary retention, difficulty starting the stream or overflow incontinence
- Faecal incontinence or loss of anal sensation
- Sexual dysfunction
- Low back pain with sciatica in one or both legs
- Leg weakness and reduced or absent ankle reflexes

## Red flags

- Any new bladder or bowel disturbance with back pain or sciatica
- Saddle numbness
- Bilateral sciatica
- Rapidly progressive leg weakness

## Diagnosis

**Clinical**
High clinical suspicion. Examination includes saddle sensation, anal tone and the bulbocavernosus reflex, the neurological examination of the legs and a check for a palpable bladder.

**Tests**
Bladder ultrasound or catheter for post-void residual volume to detect retention. Blood tests if infection or cancer is suspected.

**Imaging**
Emergency MRI of the lumbosacral [spine](https://durgical.com/en/anatomy/region/spine/) confirms compression and its cause; CT myelography if MRI is not available or contraindicated.

## Differential diagnosis

- Conus medullaris syndrome
- Lumbar disc herniation without cauda equina involvement
- Urinary retention from other causes ([prostate](https://durgical.com/en/anatomy/prostate/), drugs)
- Guillain–Barré syndrome
- Spinal cord compression or transverse myelitis

## Goal of treatment

Decompress the nerve roots as early as possible to protect bladder, bowel, sexual and leg function, and treat the underlying cause.

## Treatment

**Acute**
Urgent referral, emergency MRI and bladder catheterisation for retention.

**Surgical**
Emergency surgical decompression: discectomy, laminectomy or both, depending on the cause; earlier surgery is associated with better recovery.

**Medical**
Antibiotics for abscess; corticosteroids and radiotherapy are options for some tumour compressions; reversal of anticoagulation for haematoma.

**Rehabilitation**
Rehabilitation, bladder and bowel programmes and sexual health support after decompression.

## Complications

- Permanent urinary or faecal incontinence
- Sexual dysfunction
- Chronic pain and persistent leg weakness
- Recurrent urinary tract infections
- Psychological distress and medicolegal disputes from delayed diagnosis

## Prognosis

Patients decompressed before urinary retention develops usually recover better than those with established retention. Some bladder, bowel or sexual dysfunction can remain despite surgery.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the most common cause of cauda equina syndrome?

A large central lumbar disc herniation, usually at L4–L5 or L5–S1.

## What is saddle anaesthesia?

Loss of sensation over the perineum, buttocks and inner thighs (S2–S5), the area that would touch a saddle.

## What is the investigation of choice in suspected cauda equina syndrome, and how urgent is it?

Emergency MRI of the lumbosacral spine, as soon as the diagnosis is suspected.

## Why does cauda equina syndrome give lower motor neurone signs?

Because the cauda equina is made of nerve roots, not spinal cord: weakness is flaccid and reflexes are reduced.

## Which bladder finding marks a worse prognosis in cauda equina syndrome?

Painless urinary retention with overflow incontinence, compared with incomplete loss of bladder sensation or control.

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## Related conditions

- [Lumbar Disc Herniation](https://durgical.com/en/conditions/lumbar-disc-herniation/)
- [Lumbar spinal stenosis](https://durgical.com/en/conditions/lumbar-spinal-stenosis/)
- [Sciatica (Lumbar Radiculopathy)](https://durgical.com/en/conditions/sciatica/)
- [Spinal cord injury](https://durgical.com/en/conditions/spinal-cord-injury/)
- [Mechanical low back pain](https://durgical.com/en/conditions/mechanical-low-back-pain/)
- [Guillain-Barré syndrome](https://durgical.com/en/conditions/guillain-barre-syndrome/)
- [Spondylolisthesis](https://durgical.com/en/conditions/spondylolisthesis/)
- [Spinal epidural abscess](https://durgical.com/en/conditions/spinal-epidural-abscess/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Cauda Equina and Conus Medullaris Syndromes](https://www.ncbi.nlm.nih.gov/books/NBK537200/) (StatPearls (NCBI Bookshelf), 2023).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/conditions/cauda-equina-syndrome/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/cauda-equina-syndrome/