Aetiology

CES is caused by a large space-occupying lesion within the canal of the lumbosacral spine. This is most commonly due to disc herniation, usually at the L4/5 or L5/S1 level. Other causes include spinal stenosis (the most common cause of thecal sac compression in older people), traumatic injury, spinal tumour (metastatic or primary), spinal epidural haematoma, and spinal epidural abscess.[6]

Spinal surgery is a risk factor for CES as injury may occur during the surgery itself, or postoperatively due to haematoma. Patients on anticoagulation therapy are at higher risk of haematoma, particularly after neuraxial anaesthesia or surgery.[6]

Pathophysiology

The cauda equina comprises a bundle of spinal nerves (L1 to S5) in a common dural sac that begins at the end of the spinal cord (the spinal cord normally terminates between T12 and L2, most commonly at L1).[6] These nerves are involved in bladder, bowel, lower limb muscle, and sexual function. In CES, the nerve roots are compressed within the lumbosacral spinal canal, resulting in a variety of symptoms. However, not all symptoms are observed in all patients.[6][8][11]

Classification

CES can be classified as follows:[1][2][3][4]

  • Incomplete CES (CESI): thecal sac compression with subjective symptoms (e.g., difficulty urinating or a loss of desire to urinate, but no retention) and objective signs of CES.

  • CES with retention (CESR): thecal sac compression with established neurogenic urinary retention and overflow incontinence.

  • Complete CES (CESC): complete loss of all cauda equina function, absent perineal and perianal sensation, and a patulous anus.

However, evidence suggests that classifying individual patients into these subcategories is unreliable, with poor inter-observer agreement between clinicians.[5]​ Caution is therefore required in clinical practice.

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