Neural Tube Defects and Spina Bifida

Spina bifida is a neural tube defect. Although spina bifida can be serious, people who have it may live a long life.

Spina bifida results when the neural tube fails to close completely and remains an open channel. In spina bifida, the bones of the spine (vertebrae) do not close over the spinal cord. It most commonly affects the spine in the lower back. One or more of the vertebrae may be involved.

Spina bifida occulta is the mildest form of spina bifida. Typically, only the bone at the back of the vertebra (one of the bones that make up the backbone) is affected and the spinal cord and meninges are unaffected.

This common defect is called "occulta" because it is hidden (covered) by a layer of skin. This skin layer typically appears normal, but sometimes it is a different color than the surrounding skin, or there may be a small tuft of hair overlying the defect.

Spina bifida occulta usually causes no symptoms but can be associated with other birth defects or with abnormalities of the spinal cord (occult spinal dysraphism).

Occult spinal dysraphism is a form of spina bifida in which the spinal cord is affected. In occult spinal dysraphism, newborns may have visible abnormalities on their lower back. These include birthmarks, overly pigmented areas (hemangiomas and flame nevus [stork bite]), tufts of hair, openings in the skin (dermal sinus), or small lumps (masses). The underlying spinal cord may have a defect, such as a fatty tumor (lipoma), or the band that anchors the spinal cord (filum terminale) may be thickened and short, causing the cord to be stretched and unable to move normally within the spinal canal. As the child grows, the spinal cord must be able to move freely inside the spinal canal. If not treated, this problem with the cord can lead to nerve damage that results in a loss of bladder and bowel control, leg weakness, and spasm of leg muscles, which can eventually lead to an inability to walk.

Spina bifida cystica is the most serious form of spina bifida. In spina bifida cystica, tissues of the meninges, spinal cord, or both protrude through the opening in the vertebrae. A thin membrane of skin may cover the tissues, or they may not be covered by skin.

Spina bifida cystica has the following categories:

• A meningocele: Only the meninges protrude

• A meningoencephalocele: The meninges and brain tissue protrude

• A meningomyelocele: The meninges and spinal cord tissue protrude

• An encephalocele: Only brain tissue protrudes

• A myelocele: Only spinal cord tissue protrudes

Damage to brain or spinal cord tissue is much more likely when tissue protrudes outside the normal contour of the back, especially if there is no normal skin covering the protruding tissue. Also, when spinal cord tissue or meninges are fully exposed, they may become infected by bacteria, causing meningitis.

Spina Bifida: A Defect of the Spine

In spina bifida, the bones of the spine (vertebrae) do not form normally. Spina bifida can vary in severity. In occult spinal dysraphism, one or more vertebrae do not form normally, and the spinal cord and the layers of tissues (meninges) surrounding it may also be affected. There are several types with differing neurologic severities. The diagnosis is sometimes suggested by symptoms in the lower back, such as a tuft of hair, a dimpling, or a pigmented area on the skin over the defect. In a meningocele, the meninges protrude through the incompletely formed vertebrae, resulting in a fluid-filled bulge under the skin. The spinal cord is in its normal location. The most severe type is a meningomyelocele, in which the meninges and spinal cord protrude. The affected area appears raw and red, and the infant is likely to be severely impaired.

There are many causes of neural tube defects.

Deficiency of a B vitamin, folate, during pregnancy is a significant factor.

Genetic factors and use of certain medications during pregnancy (such as valproate) can make neural tube defects more likely. The defect often develops before the mother knows she is pregnant.

Many children who have minor neural tube defects have no symptoms.

Most symptoms caused by neural tube defects result from brain or spinal cord damage.

Neural tube defects can cause brain damage, including water on the brain (hydrocephalus), learning disabilities, and difficulty swallowing.

Spinal cord damage can cause severe problems, typically involving the bowels, bladder, and legs. Problems include

• Weakness and paralysis: Walking can be difficult or impossible, unused muscles shrink and stiffen up

• Decreased sensation of the skin

• Urinary problems: Inability to pass urine (urine retention) or urinary incontinence and frequent urinary tract infections (severe urinary problems sometimes lead to kidney failure)

• Bowel problems: Loss of control over bowel movements or constipation

Other problems, such as clubfoot, arthrogryposis (joints, usually ankles, that become frozen and cannot bend), a dislocated hip, or an abnormally curved spine that causes a humpback (kyphosis), may also be present at birth. Scoliosis may develop later in some children.

• Before birth, blood tests or amniocentesis to measure alpha-fetoprotein levels or prenatal ultrasonography

• After birth, physical examination and additional imaging tests

Many neural tube defects can be detected before birth with prenatal screening tests.

A high level of alpha-fetoprotein in a pregnant woman's blood or in amniotic fluid may indicate a neural tube defect in the fetus. So during the second trimester, blood tests or amniocentesis (removing a sample of fluid from around the fetus) may be done to measure these levels.

Prenatal ultrasonography may show the defect or characteristic abnormalities.

After birth, some defects are obvious during the physical examination. If newborns have abnormalities that suggest occult spinal dysraphism, ultrasonography or magnetic resonance imaging (MRI) is done to check for defects in the spine. X-rays of the spine, hips, and sometimes the legs are done.

After spina bifida is diagnosed, tests to evaluate bladder function are done. They include urinalysis, urine culture, blood tests, and ultrasonography.

• Surgery

Health care professionals, usually a team of specialists (including a neurosurgeon, a urologist, a pediatrician, a pediatric rehabilitation medicine specialist, an orthopedic surgeon, a physical therapist, a nurse practitioner, and a social worker), evaluate the type and severity of the defect and talk to the family about how treatment and care can be implemented.

Neural tube defects are usually closed surgically. Certain defects, such as a myelomeningocele, are typically repaired soon after birth. A shunt (a plastic tube that creates a permanent alternate drainage path for cerebrospinal fluid) may be placed to treat hydrocephalus.

Problems with the bladder, bones, or muscles and other problems are treated as needed.

With appropriate care, most children do well.

However, complications, such as loss of kidney function and problems with shunts needed to treat hydrocephalus, may occur and sometimes cause death in older children.

• Folate

Folate reduces the risk of neural tube defects.

All women of childbearing age who have notfolate) beginning 3 months before getting pregnant and continuing through the first 3 months of pregnancy.

Women who have had an infant with a neural tube defect are at high risk of having another affected infant and should take high doses of folate supplements beginning 3 months before getting pregnant again and continuing through the first 3 months of pregnancy. Folate supplements may not prevent all cases of neural tube defects but can reduce the risk of neural tube defects substantially.

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

1. Spina Bifida Association: An organization providing support, education, and research resources and information about how to live with or care for someone who has spina bifida

2. March of Dimes: An organization for pregnant people and babies that provides support and information about how to prevent maternal health risks, premature birth, and mother and infant deaths