What Is Cauda Equina Syndrome

Overview

Cauda equina syndrome is a rare condition involving compression of nerves in the lumbosacral region of the spine (the lower section of the backbone just before the pelvis). These nerves pass messages between the brain and the lower limbs and pelvic organs. When pinched, the function of these spinal nerves can be affected.¹ 

The spinal cord begins at the brainstem, runs down through the spinal canal (the bony tunnel formed by the vertebral bones), and stops at the top of the lumbar spine area. At the point where the spinal cord ends, a bundle of nerves and nerve root fibres emerge, descending towards the coccyx (tailbone). This is called the ‘cauda equina’ - Latin for ‘horse’s tail’ - due to its resemblance to a bundle of horse tail hair.¹

The nerves of the cauda equina innervate (supply) the legs, perineum (the area between the anus and genitals) and pelvic organs. The messages they send and receive govern sensation and movement in these areas and control bladder, bowel, and sexual function.² Compression of these nerves can damage them and reduce, or even eliminate, their function. This can cause pain and result in significant neurological deficits.

Causes of cauda equina syndrome

The most common cause of compression in cauda equina syndrome is lumbar disc herniation (also called a lumbar disc prolapse, a disc bulge or a slipped disc), which accounts for 45% of all cases.² This most frequently occurs at the lumbar spine vertebral levels L4/5 or L5/S1.³ 

The spinal column is made up of a series of stacked vertebral bones, with intervertebral discs between each bone. Levels of the spinal column are numbered according to the number order of the vertebral bones. A spinal disc herniation involves damage to the tough, fibrous exterior of an intervertebral disc that allows its soft inner centre to protrude and bulge outwards. This protrusion of the disc can put pressure on components of the nervous system running close by through the spinal canal. In the lower lumbar and sacral regions, the cauda equina nerves run through it. 

In addition to disc herniation, there are a number of other, less common causes of cauda equina compression. These include:^{2, 4}

• Spinal epidural abscess – a spinal infection
• Spinal epidural haematoma – an accumulation of blood in the spine
• Discitis – an infection of a vertebral disc
• Tumour – caused by a primary cancer or metastatic (secondary) cancer
• Spinal stenosis – narrowing of the spinal canal 
• Aortic obstruction – obstruction in the aorta (the largest artery in the body, transporting oxygenated blood from the heart to the rest of the body)
• Birth abnormalities
• Trauma resulting in spinal injury – such as falls, motor vehicle accidents, weight-lifting, and in rare instances, spinal manipulation
• Placement of interspinous devices (instruments used in spinal stabilisation surgery)
• Inferior vena cava thrombosis – a blockage in one part of the vena cava (the largest veins in your body, transporting deoxygenated blood back to the heart) due to a blood clot
• Complications from ankylosing spondylitis
• Sacral fractures – fracture of the triangular sacral bone at the base of the spine 

Signs and symptoms of cauda equina syndrome

Patients with Cauda equina syndrome may experience the following signs and symptoms: ¹

• Lower back pain and leg pain 
• Tingling, numbness or weakness in the buttocks, back of legs, feet and toes
• Saddle anaesthesia – numbness of the inner thighs, perineum (area between the anus and scrotum or vulva), buttocks, anal area
• Changes to bladder and bowel function include:
  • Urinary retention (inability to fully empty the bladder)
  • Urinary incontinence (inability to control the holding of urine and emptying of the bladder, leading to unintentional passing of urine)
  • Loss of sensation of the fullness of the bladder and the awareness of the need to urinate
  • Difficulty initiating urination
  • Bowel incontinence (inability to control bowel movements leading to unintentional leaking of stool) or severe constipation
• Sexual dysfunction – including impotence (inability to achieve an erection) and loss of sensation in the genital area, or conversely, priapism – defined as a persistent erection in the absence of sexual stimulation
• Abnormal reflex response 
• Reduction/loss of (muscle) tone of the anal sphincter

Diagnosis

The following techniques are commonly used to diagnose cauda equina syndrome and provide details on the cause, location and extent of the condition:

• History taking, which includes:
  • Details of symptoms, including duration, pattern, onset
  • Potentially related trauma
  • Previous relevant medical history such as anticoagulation therapy, spinal surgery
• Physical examination – including sensation, reflexes, stability, ability to carry out specific movements
• MRI scan (Magnetic Resonance Imaging) – to provide detailed, 3-dimensional images of the spinal cord
• Myelography – CT (Computerised Tomography) or X-ray after contrast material injection⁴ to help show areas of pressure on the spinal nerves and nerve roots

Many of the symptoms of cauda equina are also found in other conditions, and these must be excluded through the diagnostic process. 

In particular, lower back/leg pain, altered sensation and muscle weakness can be found in patients with lumbar disc herniation without cauda equina involvement. Lumbar disc disease and herniation are common conditions, and only 2% of these cases result in cauda equina complications.⁴ 

However, the presence of saddle anaesthesia and bladder/bowel control problems alongside symptoms of pain, altered sensation and muscle weakness are strongly indicative of potential cauda equina compression and considered ‘red flags’ (indicators of serious medical conditions). As cauda equina compression constitutes a medical emergency, patients should have these red flag symptoms investigated immediately because the delay of surgical intervention, if it is required, can potentially cause permanent neurological damage and loss of function.

Types of cauda equina syndrome

Cauda equina syndrome can be acute or chronic in nature.⁴ 

Acute symptoms appear suddenly and with severity. Chronic symptoms come on more slowly and gradually, often starting with low back pain and progressing to other symptoms such as changes to bladder function and reduction in bowel control.¹

Classification of cauda equina syndrome

Cauda equina syndrome can be classified into:

• Incomplete cauda equina syndrome (sometimes abbreviated to CESI): involving sensory and motor changes but no complete retention or incontinence of bladder and/or bowel
• Complete cauda equina syndrome or cauda equina syndrome with true retention (sometimes abbreviated to ‘complete CES’ or CESR): involving sensory and motor changes and full retention or incontinence of bladder and/or bowel⁴

Management and treatment for cauda equina syndrome

Treatment of cauda equina syndrome aims to remove the pressure on the nerves to allow them to recover and regain their function. This usually requires emergency spinal surgery. The type of surgical decompression technique selected will be decided by the spinal surgeon, depending on the needs of the individual case.

If a  lumbar disc herniation is the cause, a discectomy is commonly recommended. This is a surgical procedure to remove the soft inner section of the disc, which has bulged out of the disc’s fibrous exterior and is putting pressure on the cauda equina nerves.

If appropriate, treatment may also address other causes of the nerve compression, such as cancer, infection or inflammation.

Cauda equina syndrome is considered a medical emergency and should be treated as quickly as possible for the best outcomes. However, even those treated early may still not achieve full recovery from symptoms and may be left with residual numbness, weakness, incontinence or sexual dysfunction. Left untreated, permanent paralysis and loss of bowel, bladder and sexual function can result.^1,2

FAQ

How can I prevent cauda equina syndrome?

Cauda equina syndrome is caused by compression of nerves in the lumbar spine area. The most common cause of this pressure is a herniated lumbar disc. Although disc disease and herniation cannot always be prevented, it may be possible to reduce the risk of their development. Further information on disc herniation and its prevention can be found at the Cleveland Clinic website and the Mayo Clinic website.

How common is cauda equina syndrome?

Cauda equina syndrome is a rare condition, with an estimate of between 0.3 and 7 occurrences in 100,000 people per year (depending on the population group sampled), according to a systematic review carried out in 2020.⁵

Who is at risk of cauda equina syndrome?

The most common cause of cauda equina syndrome is a herniated lumbar disc. People are at greater risk of developing a lumbar disc herniation as they get older due to the normal processes of degeneration associated with ageing. 

In addition, the following are also risk factors, according to the Mayo Clinic: 

• Having a sedentary lifestyle
• Being overweight
• Having a physically demanding job that involves lifting, twisting, pushing, pulling, bending 
• Smoking 
• Frequent driving 
• A genetic predisposition

When should I see a doctor?

Cauda equina syndrome is considered a medical emergency and requires urgent evaluation. The sooner that treatment to decompress the cauda equina nerves is carried out, the better the outcome. If you experience severe pain in the lower back and/or legs along with numbness or weakness in your legs, numbness in your groin/saddle area or changes to your bladder or bowel control, seek urgent advice at a hospital accident and emergency department.

Summary

Cauda equina syndrome is a rare condition involving compression of the bundle of nerves located in the lumbar and sacral regions of the spine. This compression can lead to pain, altered sensation and muscle weakness in the legs and pelvic area, sexual dysfunction and loss of bladder and bowel control. Cauda equina syndrome is a medical emergency and requires urgent attention to reduce the risk of long-term complications. Treatment usually involves surgery to reduce compression on the nerves.