Tethered spinal cord syndrome

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.

Demographics

TSCS is a relatively rare disorder. Its exact frequency is unknown, mostly because of a general lack of research on the disorder, and because the mildest forms may never be detected. TSCS in all forms affect both sexes and all races and ethnic groups.

Causes and symptoms

Congenital TSCS is initiated by incomplete closure of the neural tube during embryonic development. During the eighteenth to twenty-second day of embryonic development, the beginning structure of the neural tube, which will become the spinal column and cord, is formed by ectodermal tissue on the back of the embryo that forms a groove, which deepens and forms into a hollow tube, still open dorsally along its length. The tube begins to close itself, starting in the thoracic region, then moving on toward the head and lumbar regions. During the twenty-eighth to forty-eighth day of development, ectodermal tissue in the tail area of the embryo forms a separate, short length of neural tube, the conus medullaris, whose anterior end meets and fuses with the main neural tube while the posterior forms the filum terminale. The conus medullaris also produces the cauda equinae nerves.

Symptoms of TSCS may be visible at birth or appear later, even in adulthood, but most often in childhood. The symptoms may be visible or behavioral. Various visible signs on the skin of the lower back, along and near the spinal cord, are:

• lipomas, or fatty tumors below the skin
• hairy patches
• spots of increased pigmentation
• dimples that may indicate dermal sinus tracts
• skin lesions
• skin tags or outgrowths
• angiomas, or port-wine stains

Behavioral symptoms manifest as:

• chronic lower back pains
• progressive scoliosis, or curvature of the spine
• foot deformities
• numbness and loss of sensation in the legs or feet
• awkward gait and stumbling
• weakness in legs or feet
• unequal growth in the legs or feet
• progressive loss of control over bladder and bowel functions (incontinence)
• urinary tract infections

Diagnosis

The initial indicators of TSCS are the physical and behavioral ones listed above. A newborn that carries any of the symptomatic skin defects should be diagnosed further for possible TSCS. Among the behavioral signs, a child will likely complain to parents of lower back pains, while other behavioral symptoms will become obvious to parents. An adult who shows any of the physical or behavioral symptoms should bring these to the attention of his family physician, who should suspect TSCS as the cause. Symptoms, physical or behavioral, may not appear until many years after birth, including well into adulthood, depending on the time of tethering, degree of stretching of the spinal cord, and severity of damage to the nerves of the cord.

The next steps in diagnosis of TSCS are taking x-ray images of the spine to detect bone abnormalities, followed by the application of diagnostic neuro-imaging by means of MRI (magnetic resonance imaging ) to produce three-dimensional images of the spinal column and spinal cord. Since a defect in the spinal cord or column makes it likely that there are other defects in the cord, column, or brain, an entire imaging of the brain and spinal column are recommended. Electromyography (EMG) can be used to check for or assess damage to nerve conduction in the spinal cord and the nerves of the cauda equinae. Ultra-sound imaging can be used to monitor unborn infants for evidence of TSCS, should there be a reason to suspect it.

Since the muscles of the bladder are often affected by TSCS, urodynamics testing is recommended to discover the extent of the damage.

Treatment team

A family doctor is probably the person most likely to first link symptoms in a child or adult to TSCS, when parents bring in a child for a routine health check or because of the physical and behavioral signs and problems. Following the tentative diagnosis, the patient will be sent to neurologists, MRI imaging technicians, EMG technicians, urologists, surgeons and neurophysiologists if surgery is called for, and the personnel monitoring recovery.

Treatment

TSCS is corrected by surgery to detach the cord at its place of tethering. Follow-up examinations are necessary because the freed spinal cord sometimes becomes re-tethered to growing scar tissue.

In the case of tight filum terminale, the filum terminale is severed, allowing the cord to float freely.

Surgery for TSCS generally takes four to six hours, and is conducted according to the form of TSCS in the patient. The spinal column is opened from behind to reach the site of tethering. Neurophysiologists are present to monitor spinal cord and nerve functioning to reduce the risk of damage to nerves and other tissues.

Recovery and rehabilitation

The degree of recovery is based on the amount of damage induced by the TSCS and the success of the surgery. Nearly all patients improve or at least show no worsening of signs. A successful operation leaves 2% or less possibility of the symptoms getting worse, and a 50% like-lihood of sensation and movement problems becoming normal. Back pain usually is reduced or eliminated and strength to the lower part of the body improves. On the other hand, bladder dysfunction usually does not improve.

Ongoing monitoring of a patient following surgery for TSCS is required, in case the spinal cord should retether.

Prognosis

The prognosis for tethered spine syndrome is favorable, since skin symptoms may be visible at birth or later, allowing early detection and treatment, while behavioral symptoms manifest slowly enough for diagnosis and treatment before the condition becomes severe.

Special concerns

Spinal surgery is always risky because of possible damage to the nerves of the spinal cord. The patient may also have to deal with permanent damage caused by TSCS that surgery cannot improve.

Resources

BOOKS

Parker, James N. and Philip M. Parker. The Official Patient's Sourcebook on Tethered Spinal Cord Syndrome (Revised and Updated). ICON Health Publications, San Diego, CA, 2002.

Weinstein, Stuart L. Pediatric Spine Surgery. Philadelphia: Lippincott Williams & Wilkins Publishers, 2001

PERIODICALS

Baskaya, M. K., J. A. Menendez, and B. K. Willis. "Late presentation of tethered spinal cord in a 73-year-old patient." Journal of the American Geriatric Society 49, no. 5 (May 2000): 682–683.

Ratliff, J., P. S. Mahoney, and D. G. Kline. "Tethered cord syndrome in adults." Southern Medical Journal 92, no. 12 (December 1999): 1199–1203.

Witkamp, T. D., W. P. Vandertop, F. J. Beek, et al. "Medullary cone movement in subjects with a normal spinal cord and in patients with a tethered spinal cord." Radiology 220, no. 1 (July 2001): 208–212.

WEBSITES

NINDS Tethered Spinal Cord Syndrome Information Page. National Institute of Neurological Disorders and Stroke. <http://www.ninds.nih.gov/health_and_medical/disorders/tethered_cord.htm>.

ORGANIZATIONS

National Organization for Rare Disorders (NORD). P.O. Box 1968 (55 Kenosia Avenue), Danbury, CT 06813-1968. 203-744-0100 or 800-999-NORD (6673); Fax: 203-798-2291. [email protected]. <http://www.rarediseases.org>.

Spina Bifida Association of America. 4590 MacArthur Blvd. NW, Suite 250, Washington, DC 20007-4266. 202-944-3285 or 800-621-3141; Fax: 202-944-3295. [email protected]. <http://www.sbaa.org>.

Kevin Fitzgerald