The cauda equina () is a bundle of spinal nerves and spinal nerve rootlets, consisting of the second through fifth lumbar nerve pairs, the first through fifth sacral nerve pairs, and the coccygeal nerve, all of which arise from the lumbar enlargement and the conus medullaris of the spinal cord. The cauda equina occupies the lumbar cistern, a subarachnoid space inferior to the conus medullaris. The nerves that compose the cauda equina innervate the pelvic organs and lower limbs to include motor innervation of the hips, knees, ankles, feet, internal anal sphincter and external anal sphincter. In addition, the cauda equina extends to sensory innervation of the perineum and, partially, parasympathetic innervation of the bladder.
Structure
In adulthood, the cauda equina is made of lumbosacral spinal nerve roots.
Development
In humans, the spinal cord stops growing in infancy. At birth the end of the spinal cord is about the level of the third lumbar vertebra, or L3. Because the bones of the vertebral column continue to grow, by about 12 months of age the end of the cord reaches its permanent position. Typically this is at the level of L1 or L2 (closer to the head), Cauda equina syndrome occurs when the nerve roots in the lumbar spine are compressed, disrupting sensation and movement. Nerve roots that control the function of the bladder and bowel are especially vulnerable to damage. It can lead to permanent paralysis, impaired bladder and/or bowel control, loss of sexual sensation, and other problems if left untreated. Even with immediate treatment, some patients may not recover complete function. A disc herniation occurs when one of the soft flexible discs that functions as an elastic shock absorber between the bones of the spinal column displaces from its normal position. The herniation occurs after the disc begins to break down with aging and can be precipitated by stress or a mechanical problem in the spine. The result is that the softer, center portion of the disc pushes out and causes pressure on the nerve roots in the lumbar spine. Other causes include spinal lesions and tumors, spinal infections or inflammation, lumbar spinal stenosis, trauma to the lower back, birth abnormalities, spinal arteriovenous malformations (AVMs), spinal hemorrhages (subarachnoid, subdural, epidural), narrowing of the spinal canal, postoperative lumbar spine surgery complications or spinal anesthesia.
Radiculopathy
The cauda equina is vulnerable to being compressed, causing a radiculopathy.