The conus medullaris is the technical name for the lower end of the spinal cord. Originating at the base of the brain, this thick bundle of nerve tissue passes through the center of the spinal column, penetrating the vertebrae, which protect it from damage. At its terminal end, at the lumbar spine in the lower back, the spinal cord tapers into a cone shape and then into a narrow bundle of fibrous tissue called the filum terminale, which means "terminal thread." This fibrous tissue helps support the spinal cord.

Surrounding the filum terminale is the cauda equina, a group of nerve roots that dangles from the conus medullaris. These nerve roots are referred to collectively as the cauda equina because they dangle from the conus medullaris much like a horse's tail. From the nerve roots of the cauda equina spring nerves that control the lower body, including the bladder, genitals, legs and feet, making the cauda equina the link between the central nervous system of the brain and spinal cord and the peripheral nervous system of the lower body.

Damage to the conus medullaris leads to a collection of symptoms known as conus medullaris syndrome. Common symptoms include pain in the lower back; numbness in the inner thighs, groin, legs or feet; difficulty walking; weakness in the legs; lack of bladder control; rectal incontinence; and impotence. Conus medullaris syndrome usually occurs because of compression of this lower portion of the spinal cord. Compression can occur because of a tumor or hematoma, narrowing of the lumbar vertebra, a spinal cord injury or inflammation of the spinal cord from infection. Other much less common causes include congenital problems that cause the conus medullaris to be malformed, multiple sclerosis or deep vein thrombosis in the veins that serve the spinal cord.

Treatment for conus medullaris syndrome differs based on the underlying cause. If the conus medullaris is compressed by a tumor or hematoma, removing the object causing the compression will ease the symptoms. This could be accomplished through surgery, medication or even radiation therapy, depending on what the foreign body is. Infection causing the conus medullaris to swell might be treated with antibiotics. Some treatments for inflammation might include corticosteroid injections, and congenital problems are most likely to be addressed through surgery.

Conus medullaris syndrome because of spinal cord injury is the most difficult to treat. Immobilizing the spine is crucial immediately after the injury, and surgery likely will be necessary to stabilize the spinal cord. Rehabilitation and physical therapy are common after this type of injury and vital to achieving the highest possible level of recovery.