Neural (pronounced NOOR-uhl) tube defects are abnormalities that can occur in the brain, spine, or spinal column of a developing embryo and are present at birth (birth defects).
Very early in the development of an embryo, certain cells form a tube (called the neural tube) that will later become the spinal cord, the brain, and the nearby structures that protect them, including the backbone (also called the spinal column or vertebra). As development progresses, the top of the tube becomes the brain and the remainder becomes the spinal cord. A neural tube defect occurs when this tube does not close completely somewhere along its length, resulting in a hole in the spinal column or another type of defect. These defects occur in the first month of pregnancy, often before a woman even knows that she is pregnant.
There are several types of neural tube defects:
Spina bifida (pronounced SPY-nuh BIF-i-duh) is the most common type of neural tube defect. It occurs when the neural tube does not close completely. An infant born with spina bifida usually has paralysis of the nerves below the affected area of the spine, which can cause lifelong problems with walking and other difficulties. Because bladder and bowel control are controlled by the lowest spinal nerves, bowel and urinary dysfunction are common. Many infants who are born with spina bifida will have normal intelligence, but some will have learning or intellectual disabilities. There are several common types of spina bifida:
Spina bifida occulta (pronounced o-CULT-tuh) is the mildest form, and most experts do not consider it to be a true neural tube defect. There is a small gap in the spine but no opening or sac on the back. The nerves and spinal cord are not damaged, and the defect usually does not cause any disability. Consequently, spina bifida occulta sometimes is called "hidden" spina bifida.Anencephaly (pronounced an-en-SEF-uh-lee) is a more severe, but less common, type of neural tube defect. This condition occurs when the neural tube fails to close at the top. The fetus has little or no brain matter and also may be lacking part of its skull. Infants born with this condition are usually unconscious as well as deaf and blind and unable to feel pain. They may have reflex actions, such as breathing and responding to touch. All infants with anencephaly are stillborn or die soon after birth.
Encephalocele (pronounced ehn-SEF-o-low-seel), another rare type of neural tube defect, occurs when the tube fails to close near the brain and there is an opening in the skull. The brain and membranes that cover it can protrude through the skull, forming a sac-like bulge. In some cases, there is only a small opening in the nasal or forehead area that is not noticeable. The infant may have other problems as well, such as hydrocephalus, paralysis of the arms and legs, developmental delays, intellectual disabilities, seizures, vision problems, a small head, facial and skull abnormalities, and uncoordinated movements (ataxia). Despite the various disabilities and developmental effects, some children with this condition have normal intelligence.
Iniencephaly(pronounced in-ee-ehn-SEF-ah-lee), another rare but severe type of neural tube defect, is diagnosed when the infant's head is bent severely backward. The spine is exceptionally distorted. Often, the infant lacks a neck, with the skin of the face connected to the chest and the scalp connected to the back. Other abnormalities may exist as well, such as a cleft lip and palate, cardiovascular irregularities, anencephaly, and malformed intestines. Infants born with this condition usually do not live longer than a few hours
The symptoms associated with neural tube defects vary widely depending on the type of defect. Symptoms range from physical and intellectual disability to paralysis, urinary and bowel control problems, blindness, deafness, lack of consciousness, and in many cases, death. Most children with neural tube defects die or experience serious disability.
The exact causes of neural tube defects are not known. Many
different factors are likely to play a role, including genetics,
nutrition, and environmental factors. Research studies have found that getting enough folic
(pronounced FOH-lik) acid (also known as folate
or vitamin B9) before and during pregnancy can
greatly reduce the risk of spina bifida and other neural tube defects. Well-established evidence shows that women who are obese, have
poorly controlled diabetes, or take certain antiseizure medications,
such as phenytoin (Dilantin), carbamazepine (Tegretol), and valproic
acid (Depakote), or anti-folate (such as aminopterin) are at greater
risk than are other women of having an infant with spina bifida or
anencephaly. Some studies suggest that neural tube defects and
miscarriage are more common among fetuses of women who experience high
temperatures (such as using a hot tub or sauna or having a fever)
during the first 4 to 6 weeks of pregnancy. Women who may become
pregnant or who are pregnant should avoid using hot tubs or saunas.
In the United States, about 1,500 infants are born each year
with spina bifida. The other types of neural tube defects are less common. About
340 infants are born in the United States each year with an
encephalocele, and about 860 are born with anencephaly. Iniencephaly is
estimated to occur in 0.1 to 10 per 10,000 births. Anencephaly and
iniencephaly are more common in females. Many pregnancies that involve
anencephaly end in miscarriage. These conditions are more common in infants born to Hispanic
women than those born to non-Hispanic white and non-Hispanic black
women. Parents who have already had a child with spina bifida or
another neural tube defect have a 4% risk of having a second child with
spina bifida. Parents who already have two children with spina bifida
have about a 10% chance of having another child with this condition.
When one parent has spina bifida, there is about a 4% chance that his
or her child also will have it.
Women who have had one pregnancy with anencephaly have a 2% to 3% risk
of having a second neural tube defect in later pregnancies. To help
prevent recurrence, health care providers recommend that these women
take 4 mg of folic acid supplements a day starting 3 months before
conception. This dosage is 10 times the 400 mcg normally recommended.
Neural tube defects are usually diagnosed before the infant is
born, through laboratory or imaging tests. Prenatal laboratory tests include: Prenatal ultrasound imaging usually detects almost all types
of neural tube defects. When an infant with a diagnosed or suspected neural tube
defect is born, the health care provider will perform tests to assess
its severity and complications. These tests might include X-ray,
magnetic resonance imaging, computed tomography scan to look for spinal
defects or excess fluid, and measuring the head circumference;
assessing the infant's vigor, motor, and sensory functioning; and
observing the infant's urinary stream. In some people who have milder spina bifida, the condition may
not be diagnosed until later in childhood or in adulthood.
Infants born with anencephaly or iniencephaly are usually stillborn or die soon after birth.
Infants born with neural tube defects that are not immediately fatal may have other conditions that need treatment. Such conditions vary from one infant to another, and some conditions develop or must be addressed over time or later in life.
The most severe issues tend to develop in those who have myelomeningocele, the most severe form of spina bifida, in which the spinal cord is exposed.
Many infants born with spina bifida get extra fluid in and around the brain, a condition called hydrocephalus, or water on the brain. The extra fluid can cause swelling of the head, which may lead to brain injury.
The brains of most children with myelomeningocele are positioned abnormally. The lower part of the brain rests farther down than normal, partially in the upper spinal canal. The cerebrospinal fluid can get blocked and cause hydrocephalus. Although most affected children have no other symptoms, a few may have upper-body weakness and trouble breathing and swallowing.
Typically, the bottom of the spinal cord floats freely in the spinal canal, but for many people with spina bifida, the spinal cord is actually attached to the spinal canal. Thus, in these cases the spinal cord stretches as a person grows, and this stretching can cause spinal nerve damage. The person might have back pain, scoliosis (crooked spine), weakness in the legs and feet, bladder or bowel control problems, and other conditions.
People with spina bifida high on the back (near the head, for instance) might not be able to move their legs, torso, or arms. People with spina bifida low on the back (near the hips, for example) might have some leg mobility and be able to walk unassisted or with crutches, braces, or walkers.
People with spina bifida often cannot control their bladder or their bowel movements. They also can develop urinary tract infections.
Many people with spina bifida-possibly three-quarters of those with the condition-are allergic to latex, or natural rubber. Although researchers still do not entirely understand why this rate is so high, some experts believe such an allergy can be caused by frequent exposure to latex, which is common for people with spina bifida who have shunts and have had many surgeries.
Some studies have shown that up to 50% of children with myelomeningocele have a pattern of characteristics and deficits consistent with nonverbal learning disabilities syndrome. This syndrome shares some of its characteristic features with Asperger syndrome.
Some people with myelomeningocele have additional physical or psychological conditions, including digestive, vision, sexual, social, and emotional problems; obesity; and depression.
Encephaloceles are sometimes treated with surgery. During the surgery, the bulge of tissue is placed back into the skull. Surgery also may help to correct abnormalities in the skull and face.
Treatment for spina bifida depends on the severity of the condition and the presence of complications. For some people, treatment needs may change over time depending on the severity or complications.
There is no treatment for anencephaly or iniencephaly. These conditions are usually fatal shortly after birth.
-NIH
