Cauda equina syndrome is a surgical emergency where the nerve roots of the cauda equina at the bottom of the spine are compressed. It requires emergency decompression surgery to prevent permanent neurological dysfunction. However, even with immediate decompression, patients may still not regain full function.
Pathophysiology
The cauda equina (translated as “horse’s tail”) is a collection of nerve roots that travel through the spinal canal after the spinal cord terminates around L2/L3. The spinal cord tapers down at the end in a section called the conus medullaris. The nerve roots exit either side of the spinal column at their vertebral level (L3, L4, L5, S1, S2, S3, S4, S5 and Co).
The nerves of the cauda equina supply:
- Sensation to the lower limbs, perineum, bladder and rectum
- Motor innervation to the lower limbs and the anal and urethral sphincters
- Parasympathetic innervation of the bladder and rectum
In cauda equina syndrome, the nerves of the cauda equina are compressed. There are several possible causes of compression, including:
- Herniated disc (the most common cause)
- Tumours, particularly metastasis
- Spondylolisthesis (anterior displacement of a vertebra out of line with the one below)
- Abscess (infection)
- Trauma
Red Flags
The key red flags to look out for are:
- Saddle anaesthesia (loss of sensation in the perineum – around the genitals and anus)
- Loss of sensation in the bladder and rectum (not knowing when they are full)
- Urinary retention or incontinence
- Faecal incontinence
- Bilateral sciatica
- Bilateral or severe motor weakness in the legs
- Reduced anal tone on PR examination
TOM TIP: A common way people ask about saddle anaesthesia when taking a history is to ask, “does it feel normal when you wipe after opening your bowels?”
Management
Cauda equina is a neurosurgical emergency. It requires:
- Immediate hospital admission
- Emergency MRI scan to confirm or exclude cauda equina syndrome
- Neurosurgical input to consider lumbar decompression surgery
Surgery should be performed as soon as possible to increase the chances of regaining function. Even with early surgery, patients can be left with bladder, bowel or sexual dysfunction. Leg weakness and sensory impairment can also persist.
Metastatic Spinal Cord Compression
When a metastatic lesion compresses the spinal cord (before the end of the spinal cord and the start of the cauda equina), this is called metastatic spinal cord compression (MSCC). This is different to cauda equina, which specifically refers to compression of the cauda equina.
MSCC presents similarly to cauda equina, with back pain and motor and sensory signs and symptoms. A key feature is back pain that is worse on coughing or straining.
MSCC is an oncological emergency and requires rapid imaging and management. There are specialist MSCC coordinators who should be involved early to coordinate the imaging and treatment of patients with MSCC.
Treatments will depend on individual factors. They may include:
- High dose dexamethasone (to reduce swelling in the tumour and relieve compression)
- Analgesia
- Surgery
- Radiotherapy
- Chemotherapy
TOM TIP: Cauda equina presents with lower motor neuron signs (reduced tone and reduced reflexes). The nerves being compressed are lower motor neurons that have already exited the spinal cord. When the spinal cord is being compressed higher up by metastatic spinal cord compression, upper motor neuron signs (increased tone, brisk reflexes and upping plantar responses) will be seen.
Last updated August 2021
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