Cauda Equina Syndrome: Spinal Level of Occurrence
Cauda equina syndrome occurs below the L2 vertebral level, as the cauda equina consists of nerve roots L2-L5, S1-S5, and the coccygeal nerve that extend below where the spinal cord terminates. 1
Anatomical Basis
The spinal cord normally ends at the L1-L2 disc space by 2 months after birth, with the lowest normal position being the middle third of L2 vertebra. 2 Below this level, the spinal canal contains only nerve roots—not spinal cord—which collectively form the cauda equina (Latin for "horse's tail"). 1
Any compressive lesion from approximately L2 vertebral level downward through the sacral spine can cause cauda equina syndrome. 1
Most Common Levels of Compression
- L4-L5 and L5-S1 are the most frequent sites where disc herniation causes cauda equina syndrome, as more than 90% of symptomatic lumbar disc herniations occur at these levels. 2, 3
- Lumbar disc herniation accounts for 45% of all cauda equina syndrome cases. 1
- The syndrome results from massive midline disc herniation that compresses multiple nerve roots simultaneously within the spinal canal. 2, 3
Critical Distinction from Spinal Cord Injury
Thoracolumbar injuries from T11-T12 to L1-L2 involve the conus medullaris (the terminal end of the spinal cord itself), not the cauda equina. 2 These injuries have different pathophysiology and recovery potential because they involve actual spinal cord tissue containing lower motor neuron cell bodies, whereas cauda equina syndrome involves only nerve root axons. 2
Clinical Implication
The anatomical level matters because:
- Compression at or above L1-L2 may involve both conus medullaris and cauda equina, creating a mixed clinical picture. 2
- Pure cauda equina syndrome occurs with compression below the conus medullaris (typically below mid-L2), affecting only peripheral nerve roots. 2
- Nerve roots have greater regenerative capacity than spinal cord tissue, which influences prognosis and surgical decision-making. 2