Cauda Equina Syndrome: Etiology and Pathophysiology
Cauda equina syndrome is most commonly caused by massive midline disc herniation, occurring in approximately 0.04% of patients with low back pain. 1, 2
Primary Causes
Mechanical Compression (Most Common)
- Massive midline lumbar disc herniation is the predominant cause, representing the majority of cauda equina syndrome cases 1, 2
- Spinal cord or nerve root compression from tumors (malignancy) can cause cauda equina syndrome 2
- Spinal stenosis with severe narrowing can lead to cauda equina compression 1
Infectious Etiologies
- Spinal infections including epidural abscess or discitis can compress the cauda equina 2
- Tuberculosis of the spine can cause cauda equina syndrome 3
Traumatic Causes
- Vertebral fractures or dislocations from trauma can acutely compress the cauda equina 1
- Penetrating injuries to the lumbar spine may directly damage cauda equina nerve roots 1
Pathophysiological Mechanism
The cauda equina consists of the bundle of lumbar and sacral nerve roots that descend from the conus medullaris (typically at L1-L2 level). When these nerve roots are compressed, they lose their ability to transmit signals, resulting in the characteristic pattern of bilateral radiculopathy, bladder/bowel dysfunction, and saddle anesthesia. 1, 2
Progressive Neurological Damage
- Early compression causes reversible nerve dysfunction if decompression occurs within 12-72 hours 1
- Prolonged compression leads to irreversible nerve damage, particularly once complete urinary retention develops 1
- The progression from incomplete to complete cauda equina syndrome represents advancing ischemia and mechanical injury to nerve roots 1
Clinical Pitfall
The critical error is waiting for complete urinary retention before initiating evaluation, as this represents a late sign indicating likely irreversible damage. 1, 2 Bilateral radiculopathy and new difficulties with micturition while control is still preserved are the red flag symptoms requiring immediate MRI and neurosurgical consultation. 1, 2