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Cauda Equina Syndrome

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Last updated: May 27, 2020
Revisions: 13

Last updated: May 27, 2020
Revisions: 13

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Cauda equina syndrome (CES) is a surgical emergency caused by a compression of the cauda equina. If untreated, patients can develop debilitating complications, hence a high level of suspicion and rapid intervention is required.

The condition has peak onset between 40-50 years of age. Approximately 4 in every 10,000 patients presenting with lower back pain are ultimately diagnosed with the syndrome.

In this article, we shall look at the pathophysiology, clinical features, and management of cauda equina syndrome.

The Cauda Equina

The cauda equina is a bundle of nerves situated inferior to the spinal cord.

The spinal cord tapers to an end (known as the conus medullaris), approximately at the first lumbar vertebra, with nerve roots L1-S5 leaving from at this region to pass down the spinal canal (as the cauda equina) to exit at their respective formaina.

Consequently, the cauda equina is formed by lower motor neurones, containing motor and sensory impulses to the lower limbs, motor innervation to the anal sphincters, and parasympathetic innervation for the bladder.

Figure 1 – The expanded sub-arachnoid space, forming the lumbar cistern


Cauda equina syndrome is caused by compression of the cauda equina:

  • Disc herniation – most common at L5/S1 and L4/L5 level
  • Trauma – including vertebral fracture and subluxation
  • Neoplasm – either primary or metastatic
    • The most common cancers that spread to spinal vertebrae are thyroid, breast, lung, renal and prostate
  • Infection – e.g. discitis or Potts disease
  • Chronic spinal inflammation – e.g. ankylosing spondylitis
  • Iatrogenic – e.g. haematoma secondary to spinal anaesthesia

Clinical Features

Cauda equina syndrome results in lower motor neurone signs and symptoms.

Symptoms include reduced lower limb sensation (often bilateral), bladder or bowel dysfunction, lower limb motor weakness, severe back pain, and impotence.

Figure 2 – The distribution of saddle anaesthesia

An important feature to assess is bladder dysfunction, specifically the presence of retention. Confirmed retention or reduced ability to void (loss of desire, reduced urinary sensation) suggests complete or incomplete CES respectively.

On examination, features include perianal (the lower sacral dermatomes, termed “saddle” anaesthesia) or lower limb anaesthesia, loss of anal tone, urinary retention, and lower limb weakness and hypoflexia.

If no obvious cause is evident, a thorough history and examination may reveal the pathophysiology, such as weight loss as a sign of metastatic disease or living in an area of endemic tuberculosis.

As part of the examination for suspected CES, regardless of symptoms, patients will require a PR examination and a post-void bladder scan.


Cauda Equina Syndrome can be classified into 3 groups:

  1. Cauda Equina Syndrome with retention (CESR) – Presents as back pain with unilateral or bilateral sciatica, lower limb motor weakness, sensory disturbance in the saddle region, loss of anal tone, and loss of urinary control
  2. Incomplete Cauda Equina Syndrome (CESI) – As above, however only altered urinary sensation (e.g. loss of desire to void, diminished sensation, poor stream, and need to strain); painful retention may precede painless retention in some cases
  3. Suspected Cauda Equina Syndrome (CESS) – Cases of severe back and leg pains with variable neurological symptoms and signs, and a suggestion of sphincter disturbance

Most cases will be progressive in nature and will not immediately cause complete compression on the cauda equina. This is important for the management, as incomplete cauda equina syndrome has a greater potential for neurological recovery.

Differential Diagnosis

  • Radiculopathy – presents with radiating back pain, however there will be no faecal, urinary, or sexual dysfunction in these patients
  • Cord compression – a surgical emergency with a similar pathophysiology to CES, however is characterised by upper motor neurone signs


For suspected cases of cauda equina syndrome, an emergency whole spine MRI is the gold standard investigation. However, only 60% of patients suspected to have CES from clinical assessment have an abnormality found on MRI.

Further imaging may be required dependent on the underlying cause, however if CES is confirmed, then urgent surgical intervention is the priority.


An early neurosurgical review for urgent decompression must be initiated, especially for those with incomplete CES as the prognosis is potentially more favourable.

Most patients will be initially started on high-dose steroids (such a dexamethasone) to reduce any localised swelling, and in cases of trauma immobilisation is often employed.

For cases deemed suitable for surgical intervention, the neurosurgical team will discuss plans for surgical decompression. In cases caused by malignancy, radiotherapy and/or chemotherapy can be used (especially if the patient is not suitable for surgery).


The prognosis of cauda equina syndrome is variable depending on both aetiology and the time taken from symptom onset to surgery.

Indeed, a retrospective study examined the case for early surgery and found that patients who were in theatre within 24 hours from onset of autonomic dysfunction had reduced bladder problems at long-term follow up.

Key Points

  • Cauda equina syndrome is a surgical emergency caused by a compression of the cauda equina
  • CES results in lower motor neurone signs and symptoms
  • Any suspected cases requires an urgent whole spine MRI scan
  • An early neurosurgical review for urgent decompression is required for confirmed cases