Tethered Spinal Cord Syndrome Health Article

Definition

Tethered spinal cord syndrome (TSCS), also known as occult spinal dysraphism sequence, is a congenital condition that causes the spinal cord, before or after birth, to become attached to the spinal column at some point along its length, most often in the lower (lumbar) portion. TSCS is related to spina bifida, since both disorders arise from a failure of the neural tube to close completely during embryonic development. There are differing forms and degrees of severity of TSCS, including tight filum terminale, lipomeningomyelocele, split cord malformations, and dermal sinus tracts.

Description

The normal spinal cord, a cable of nerves, extends vertically from the base of the brain to the lumbar region, or lower back, contained within the hollow cylinder formed by the bony vertebrae and soft tissues of the spinal column. The spinal cord hangs freely within the spinal column, cushioned by cerebrospinal fluid, and is attached at its lower end to a strand of elastic tissue, the filum terminale, which is in turn attached to the lower end of the spinal column and which secures the lower end of the cord but allows it to be stretched without injury. Beyond the lower end of the cord proper, the major afferent and efferent nerves for the muscles of the legs, lower bowel, and bladder, the cauda equina, continue down the spinal canal and branch to those areas.

TSCS is initiated by incomplete closure, during embryonic development, of the neural tube, the early embryonic foundation of the spinal cord and column, resulting in malformations of the spinal column and cord. One disorder brought about by the malformation is spina bifida, in which the spine is open on its dorsal surface, somewhere along its length. Spina bifida can range in severity from not being visible externally, or spina bifida occulta, to a visible, open cavity with major impairment of the spinal cord at and below that spot. Among these extremes, tethered spinal cord may occur in the invisible forms, or spina bifida occulta.

In cases of relatively mild spina bifida that result in TSCS, the flaw occurs most often along the lower (lumbar) portion of the spinal column and cord. Cases of tethered cord in the cervical and thoracic regions of the spinal column are known but are extremely rare.

The developmental flaw causes soft tissues of the spinal column to grow into the hollow containing the spinal cord and to attach to the spinal cord, anchoring it at that spot. Since the spinal cord grows more slowly than the spinal column, a tethered spinal cord becomes stretched and stressed over time, causing neurological damage in the cord and the nerves of the cauda equina that results in physical problems that manifest in a range of diagnostic symptoms and signs. Bending or stretching movements of the body put additional tension on the tethered cord.

As the cord is stretched, circulation of blood to the lower portion and cauda equina may be reduced as the blood vessels there are compressed by the tension in the cord. This in turn results in hypoxia, or loss of oxygen, delivered in the blood to that part of the cord, eventually causing damage and loss of function in the neurons.

If left untreated, the stress induced in the tethered cord can cause permanent damage and malfunction to the nerves and muscles that control movements of the legs, feet, bowel and bladder. Severe consequences can be deformed feet and legs, paralysis and incontinence.

Other forms of tethered cord include tight filum terminale syndrome, in which malformations in the embryonic neural tube at its lowermost point result in a defective filum terminale, the normally flexible anchor of the cord's lower end. A defective filum terminale is short and fibrous, with reduced elasticity or none, thus tethering the spinal cord at its lower end.

A lipomeningomyelocele is an abnormal growth of fatty tissue at the base of the developing spinal cord that entangles the lower end of the cord and thus tethers it.

In diastematomyelia, or split cord syndrome, an abnormal growth of bony or fibrous tissue forms a spur within the spinal canal, parting longitudinally (not severing) the nerves of the spinal cord, which rejoin into a single tract below the spur. The spinal cord can become tethered at the location of the split.

A dermal sinus tract is a canal lined with epithelial (skin) tissue, one end of which shows as an opening in the lumbar skin, the other end connecting with the tissues of the spinal cord or canal, or with adjacent tissues. Tumors form in the internal end of the sinus in about half of all cases, the tumors often bringing about spinal cord tethering.

TSCS may also develop following surgery for spina bifida, when scar tissue resulting from surgery grows and snags the spinal cord, thus tethering it.