Cauda equina syndrome (CES) is a condition that occurs when the bundle of nerves below the end of the spinal cord known as the cauda equina is damaged. Signs and symptoms include low back pain, pain that radiates down the leg, numbness around the anus, and loss of bowel or bladder control. Onset may be rapid or gradual. The cause is usually a disc herniation in the lower region of the back. Other causes include spinal stenosis, cancer, trauma, epidural abscess, and epidural hematoma. The diagnosis is suspected based on symptoms and confirmed by medical imaging such as MRI or CT scan. CES is generally treated surgically via laminectomy. Sudden onset is regarded as a medical emergency requiring prompt surgical decompression, with delay causing permanent loss of function. Permanent bladder problems, sexual dysfunction or numbness may occur despite surgery. A poor outcome occurs in about 20% of people despite treatment. About 1 in 70,000 people is affected every year. It was first described in 1934. Signs and symptoms Signs and symptoms of cauda equina syndrome include: Severe back pain Saddle anesthesia (see diagram), i.e., anesthesia or paraesthesia involving S3 to S5 dermatomes, including the perineum, external genitalia and anus; or more descriptively, numbness or "pins-and-needles" sensations of the groin and inner thighs which would contact a saddle when riding a horse. Bladder and bowel dysfunction, caused by decreased tone of the urinary and anal sphincters. Detrusor weaknesses causing urinary retention and post-void residual incontinence as assessed by bladder scanning the patient after the patient has urinated. Sciatica-type pain on one side or both sides, although pain may be wholly absent Weakness of the muscles of the lower legs (often paraplegia) Achilles (ankle) reflex absent on both sides. Sexual dysfunction Absent anal reflex and bulbocavernosus reflex Gait disturbance Severe back pain, saddle anesthesia, urinary or fecal incontinence and sexual dysfunction are considered "red flags", i.e. features which require urgent investigation. Causes After the conus medullaris (near lumbar vertebral levels 1 (L1) and 2 (L2), occasionally lower), the spinal canal contains a bundle of nerve fibers (the cauda equina or "horse-tail") that branches off the lower end of the spinal cord and contains the nerve roots from L1–L5 and S1–S5. The nerve roots from L4–S4 join in the sacral plexus which affects the sciatic nerve, which travels caudally (toward the feet). Compression, trauma or other damage to this region of the spinal