Cauda Equina Disorders

ANATOMY The spinal cord tapers to its end, the conus medullaris, usually at the lower edge of the first lumbar vertebra. The continuation of the spinal cord is a strand of connective tissue, the filum terminale. The ventral and dorsal lumbar and sacral nerve roots that arise from the conus medullaris form a bundle, the cauda equina (Figure 1). These lumbar and sacral spinal nerve roots separate in pairs to exit laterally through the nerve root foramina. The main destinations for these roots are the lumbar and sacral plexuses. Nerves from these plexuses provide the motor and sensory innervation of the lower limbs and pelvic organs. The cauda equina, like the spinal cord, is invested by the meninges. The arachnoid membrane envelops it loosely as the thecal sac.