Spina bifida is the common name for a range of congenital (present at birth) defects caused by problems with the early development of the spine. The main defect of spina bifida is the failure of closure of the vertebral column (the bony column surrounding the spinal cord). Without this closure, the spinal cord is not afforded the usual protection of the vertebrae, and is left open to either mechanical injury or invasion by infection.

Spina bifida is one of a number of neural tube defects. The neural tube is the name for the very primitive structure which is formed during fetal development, and which ultimately becomes the spinal cord and the brain. Other neural tube defects include anencephaly, in which the cerebral hemispheres (sites for all higher intellectual functioning) are absent.

Spina bifida occurs in 1 in 700 births to North American whites, but in less than 1 in 3,000 births to blacks. In some areas of Great Britain, the occurrence is as high as 1 in 100 births, leading to the conclusion that some environmental factor or factors is at work.

Types of defects present in spina bifida

The classic defect of spina bifida is an opening in the spine, obvious at birth, out of which protrudes a fluid-filled sac, and which may include either just the meninges (the membranes which cover the spinal cord) or some part of the actual spinal cord. Often, the spinal cord itself has not developed properly. In spina bifida occulta, the defect may be much more subtle, and may, in fact, be covered with skin, while in rachischisis, the entire length of the spine may be open.

The problems caused by spina bifida depend on a number of factors, including where in the spine the defect occurs, what other associated defects are present, and what degree of disorganization of the spinal cord exists. Certainly, the most severe types of spina bifida (rachischisis) often result in death, either by virtue of greatly increased risk of infection (meningitis) due to the exposed meninges, or due to the extreme compromise of function which occurs.

Types of problems caused by spina bifida

Because different levels of the spinal cord are responsible for different functions, the location of the defect in spina bifida will dictate the type of dysfunction experienced by the individual affected. Most patients with any clinically identifiable spina bifida have some degree of weakness in the legs. This can be so severe as to be actual paralysis, depending on the spinal cord condition.

Because spinal cord functioning is necessary for proper emptying of both the bladder and the bowels, these systems are greatly compromised in people with spina bifida. Difficulty in completely emptying the bladder can result in severe, repeated infections, ultimately causing kidney damage, which can be life-threatening.

There are frequently associated defects which accompany spina bifida. Arnold-Chiari malformations are changes in the architecture and arrangement of brain structures, and can contribute to the occurrence of hydrocephalus (commonly referred to as water on the brain) in people with spina bifida. Hydrocephalus is a condition in which either too much cerebrospinal fluid (CSF-the fluid which bathes the brain and spinal cord) is produced, or the flow of CSF is blocked, resulting in an abnormal accumulation of CSF. This CSF, if left to accumulate, will put pressure on parts of the brain, causing damage.

Many children with spina bifida have other orthopedic complications, including clubfeet and hip dislocations, as well as abnormal curves and bends in their spinal structure, which can result in a hunchbacked or twisted appearance (kyphosis and scoliosis).

Intelligence in children with spina bifida varies widely, and certainly depends on the severity of the defect, and the presence of other associated defects which could adversely affect intellectual ability. Some children have normal intellectual potential, while others may operate at a slightly lower than normal capacity. Extreme intellectual deficits may occur in children with very severe spinal defects with associated Arnold-Chiari malformations and hydrocephalus, as well as in children who have had the misfortune of contracting meningitis.

Interestingly enough, it has recently been noted that children with spina bifida have a greatly increased risk of allergic sensitivity to latex. This allergy may cause minor skin rashes, or more major life-threatening reaction, which compromise breathing. This latex sensitivity is an important issue for these children, who have more than normal need for medical services, which increases the chance for exposure to this substance (which is frequently used to make surgical/exam gloves, as well as other medical supplies).

Treatment

Treatment of spina bifida is aimed first at repairing the spinal defect in order to avoid complications which could be brought on by infection (meningitis). Children with spina bifida also may require orthopedic surgery to repair hip dislocations, clubfeet, kyphosis, or scoliosis. Many children who are able to learn to walk will require braces. Children with hydrocephalus will require the placement of drainage tubes to prevent brain damage from the accumulation of CSF.

Many children with severe spina bifida are unable to completely empty their bladders, and can only do so with the insertion of a catheter tube. Such catheterization may be necessary at regular points throughout every day, in order to avoid the accumulation of urine which could back up, become infected, and damage the kidneys.

Children with significant bowel impairment may have severe constipation, which requires high-fiber diet, laxative medications, enemas, or even removal of stool by hand, to avoid bowel blockage.

Diagnosis

Most types of spina bifida are quite apparent at birth. Diagnostic tools, then, are useful in order to search for hydrocephalus, Arnold-Chiari malformations, and in order to examine the kidneys. Various radiographic techniques are helpful, such as CT (computed tomography) scans, MRI (magnetic resonance imaging), and ultrasonography.

Diagnosis prior to birth is an important area of concern. A particular substance, known as alpha-fetoprotein, is present at greater-than-normal levels in the blood of mothers who are carrying a fetus with a neural tube defect. This can be tested during the sixteenth to eighteenth week of pregnancy. In the case of an elevation of alpha-fetoprotein, other tests can be done to try to diagnose a neural tube defect, such as withdrawal of some of the fluid around the baby (amniocentesis) to test for similarly elevated levels of alpha-fetoprotein, and ultrasound examination of the fetus. Results of amniocentesis, together with the results of careful ultrasound examination, can diagnose over 90% of all neural tube defects. Parents then can decide to terminate the pregnancy, or to use this information to prepare themselves to care for a child who will have significant medical needs.

Prevention

While the medical profession does not yet have the knowledge to guarantee prevention of spina bifida, it is known that women who supplement their diets with folic acid prior to pregnancy and/or during the early weeks of pregnancy, have a lower than usual risk of producing a baby with a neural tube defect.

See also Birth defects; Embryo and embryonic development.

Further Reading

Berkow, Robert, and Andrew J. Fletcher. The Merck Manual of Diagnosis and Therapy. Rahway, NJ: Merck Research Laboratories, 1992.

Hay, William W., et al. Current Pediatric Diagnosis and Treatment. Norwalk, CT: Appleton & Lange, 1995.

Taeusch, H. William, et al. Schaffer and Avery's Diseases of the Newborn. Philadelphia: W.B. Saunders Company, 1991.

Rosalyn Carson-DeWitt

KEY TERMS

Cerebrospinal fluid (CSF)--That fluid which bathes the brain and spinal cord.

Congenital--A condition present at the time of birth.

Fetal--Referring to the period of time of growth and development in the uterus, prior to birth.

Hydrocephalus--An abnormal accumulation of CSF which, if untreated, can put pressure on the brain, resulting in permanent damage. Sometimes referred to as "water on the brain."

Meninges--The three layers of membranes which cover the brain and the spinal cord. The CSF occupies the space between two of the layers.

Vertebrae--The individual bones which together stack up to form the spine.

Record Number: A30438907

SOURCE:
Gale Encyclopedia of Science.  June 2001 pNA.

Full Text: COPYRIGHT 2001 Gale Group