sections include: spina bifida occulta, overt spina bifida, prevention and treatment
Spina bifida is a birth defect in which one or more of the vertebrae (the small bones that form the spine) fail to form properly in the fetus during the first trimester of pregnancy. Spina bifida is one of the more common birth defects; in different parts of the world, it occurs between 1 and 5 live births per 1,000.
There are several causes of spina bifida, including:
- low levels of folic acid in pregnant women
- chromosomal abnormalities
- an unusually high body temperature during pregnancy
- some drugs, such as valproic acid, taken during pregnancy
The disorder affects girls more often than boys, and there seems to be a slight genetic factor. If you have had a child with spina bifida, the risk that a subsequent baby will have the disorder is 5 percent, climbing to 10 percent to 15 percent for a baby with two older siblings affected. Mothers who had spina bifida have a 3 percent chance of giving birth to a child with the condition. The effects of this disorder can range from no disability at all to permanent and serious disability.
The disorder is traditionally divided into two main types: spina bifida occulta and overt spina bifida.
Spina Bifida Occulta
Spina bifida occulta is the more common of the two types; it is often very mild and rarely causes disability. For most infants, it involves a failure of one vertebra in the lower back to fuse properly. Spina bifida occulta is often either largely or completely hidden from sight (hence the term occulta). Frequently it is not even discovered until doctors take an X ray of the child’s lower back for an unrelated problem.
For a very few infants, however, spina bifida occulta is much more serious. This form can be marked by a visible sign on the skin, such as a red or brown birthmark, a very deep dimple or sinus (a tiny opening in the skin that extends deeply toward the spinal canal), a tuft of hair, or a soft lump or mass of fatty tissue (lipoma) under the skin, which may extend toward the spinal canal. In rare cases, the spinal membranes and cord will protrude through the gap in the vertebra; this can cause the same problems as overt spina bifida, described below.
In other infants, spina bifida occulta is associated with the spinal cord being tethered to the backbone. When this happens, the cord does not slide up as the child grows, as it normally should, because it is held in place by surrounding tissue. This can sometimes result in nerve damage. Symptoms may not appear until adolescence or even early adulthood. They commonly include an inversion of the feet (usually one before the other), and impaired bladder and bowel control.
A skin “marker,” an X ray, or an early change in foot posture or bladder function should alert a physician to the possibility that a child has one of the complicating anomalies of spina bifida occulta. X ray, ultrasound, computed tomographic (CT) scanning, magnetic resonance imaging (MRI), and at times myelography (in which an opaque material is injected into the cerebrospinal fluid to outline the spine structures for X rays) are all used to confirm the diagnosis. Doctors should scrupulously examine infants and children with meningitis for small sinus defects in their skin; these may have served as pathways for the bacteria that have invaded the children’s bodies.
Overt Spina Bifida
Overt spina bifida, which used to be called spina bifida cystica, is much more apparent than spina bifida occulta because of the presence of a sac or cyst on the infant’s back. There are two forms of overt spina bifida. The first, called meningocele, occurs in about 10 percent of cases. It involves a defect in the vertebra, and in the soft tissues overlying that portion of the spine, so that the coverings of the spinal cord protrude through the opening in the vertebrae but are nevertheless well covered by skin.
The second, more common type of overt spina bifida is called myelomeningocele. Here the sac or cyst includes not just the coverings of the spinal cord but also the cord’s nerve roots, and often the cord itself, the whole bulging out and often not covered by skin. In these cases the children are virtually never able to control their bladder and bowel and often suffer loss of sensation or paralysis below the damaged vertebrae. If those vertebrae are very low, sometimes only the feet and bladder are affected, and the child will be able to walk. The higher up the spinal cord the problem appears, the more of the body it affects.
The larger majority of infants and children with meningomyelocele also suffer hydrocephalus, a condition in which cerebrospinal fluid (CSF) does not drain properly from the head. That symptom is usually apparent shortly after birth, but occasionally appears in early childhood. This is particularly true when a simple myelomeningocele has been surgically repaired—presumably because the cyst that doctors removed was serving as a reservoir for the CSF and thus reducing the pressure inside the head. In infancy, hydrocephalus is made apparent by a rapidly growing head, while in childhood, symptoms include headache, unsteadiness, vomiting, and lethargy.
Virtually all children with myelomeningocele and hydrocephalus have a problem known as the Arnold-Chiari malformation, in which the brain stem, cerebellum, and lower cranial nerves are pushed downward through the opening of the skull (the foramen magnum) into the upper neck region (the cervical region). This compression of neural tissue can cause its own symptoms: difficulty swallowing, respiratory problems and stridor (a harsh, high-pitched sound made while breathing in or out), and abnormal eye or facial muscle movements. Timely surgery can relieve hydrocephalus and all of the symptoms of the Arnold-Chiari malformation.
Prevention and Treatment
Women of childbearing age should take a daily dose of 400 micrograms (mcg) of folic acid to prevent spina bifida beginning before they become pregnant. Taking folic acid after you have missed your first menstrual period does not prevent spina bifida, because the problem arises so early in pregnancy.
Pregnant women are routinely offered a prenatal test that screens their blood for alphafetoprotein (AFP), a protein from a fetus with an open neural tube defect that leaks into the amniotic fluid and thence into the mother’s blood. AFP detects spina bifida with 90 percent accuracy. Two additional tests, ultrasound and amniocentesis, are usually recommended to confirm any AFP test that suggests a fetus has spina bifida.
Spina bifida occulta usually requires no treatment. If a child has a tethered cord and surgery is performed shortly after the symptoms begin, he or she will often recover.
Children with overt spina bifida may need the cooperative efforts of neurosurgeons, orthopedists, genitourinary specialists, pediatricians, and pediatric neurologists to address the various potential complications of the disorder. Meningocele can be repaired surgically by replacing the sac internally and using skin grafts to cover it. There are usually no lasting effects.
If a baby has the most severe form of spina bifida, doctors usually operate shortly after birth to reposition the spinal cord and cover it with muscles and skin. This surgery helps prevent infection and additional nerve damage but cannot reverse the nerve damage that has already occurred. For children who have some degree of paralysis, physical therapists can assist with leg braces, crutches, or, in the most severe cases, wheelchairs. With treatment, children with spina bifida can usually become active individuals. With early treatment of hydrocephalus, most children with myelomeningocele have average cognitive function and survive well into late adult life.
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