The cauda equina is a collection of peripheral nerves in the common dural sheath within the lumbar spinal canal. Cauda equina syndrome, also known as bilateral acute radicular syndrome, usually is caused by a large, sequestered acute disc rupture at L3-4, L4-5, or L5-S1 that produces partial or complete lesions of the cauda equina–lower motor neuron lesions associated with flaccid paralysis, atrophy, and other conditions. Patients usually present with a history of back symptoms that have worsened precipitously. The syndrome includes back pain, bilateral leg pain, saddle anesthesia, bilateral lower extremity weakness, urinary bladder retention, and lax rectal tone. Cauda equina syndrome is rated using Diagnosis-related estimates (DRE) lumbosacral categories VI or VII. Category VI, Cauda Equina–like Syndrome Without Bowel or Bladder Signs, is used when there is permanent bilateral partial loss of lower extremity function but no bowel or bladder impairment. Category VII, Cauda Equina Syndrome with Bowel or Bladder Impairment, is similar to Category VI but also includes bowel or bladder impairment. The AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) uses the term cauda equina syndrome with reference to both the thoracolumbar and cervicothoracic spine regions; this usage is unique to the AMA Guides but maintains the internal consistency of the Injury Model, which is the best approach to date for assessing spine impairment.