In what way can lumbar disc herniations cause bladder retention?

Cauda Equina : Syndrome when a disc in the lumbar region herniates and compresses the sac of nerves known as the thecal sac or even the end of the spinal cord known as the conus with enough pressure to cause the bladder not to function usually associated with numbness in the region where you would sit on a horse's saddle-saddle anesthesia. This is a true emergency and needs immediate evaluation and surgery.