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Neural Tube Defects



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

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.
Closed neural tube defect is a malformation of the fat, bone, or membranes. In some persons, it causes few or no symptoms, but other people might experience partial paralysis or other symptoms. In some cases, the only outward sign might be a dimple or tuft of hair on the spine.
Meningocele (pronounced muh-NING-guh-seel) includes a sac of fluid that protrudes through an opening in the back, but the spinal cord is not involved. Some people will have no symptoms, and some people will have more severe problems.
Myelomeningocele (pronounced MY-uh-low-muh-NING-guh-seel) is the most severe and also the most common form of spina bifida. In this condition, the bones of the spinal column do not form completely, which causes some of the spinal cord and tissues covering the spinal cord to bulge out of the opening. A person with this condition usually has partial or complete paralysis in the parts of the body below the spinal column abnormality. Bowel and urinary dysfunction are common. Children with myelomeningocele may develop hydrocephalus (pronounced hahy-druh-SEF-uh-luhs) (excess fluid on the brain). Hydrocephalus can lead to intellectual and learning disabilities. Some infants born with myelomeningocele have severe intellectual disabilities.

Anencephaly

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

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

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

What are the symptoms of neural tube defects?

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.

What causes neural tube defects?

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.

How many people are affected by or are at risk for neural tube defects?

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.

How do health care providers diagnose neural tube defects?

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.

Is there a cure for neural tube defects?

There is no cure for neural tube defects, and any nerve damage or loss of function present at birth is usually permanent. However, a variety of treatments can sometimes prevent further damage and help with related conditions.

Infants born with anencephaly or iniencephaly are usually stillborn or die soon after birth.

Are there disorders or conditions associated with neural tube defects?

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.

Hydrocephalus

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.

Chiari II Malformation

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.

Tethered Spinal Cord

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.

Paralysis and Limitations in Mobility

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.

Lack of Bladder and Bowel Control

People with spina bifida often cannot control their bladder or their bowel movements. They also can develop urinary tract infections.

Latex Allergy

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.

Learning Disabilities

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.

Other Conditions

Some people with myelomeningocele have additional physical or psychological conditions, including digestive, vision, sexual, social, and emotional problems; obesity; and depression.

What are the treatments for neural tube defects?

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.

  • Open spina bifida. An infant with myelomeningocele, in which the spinal cord is exposed, can have surgery to close the hole in the back before birth or within the first few days after birth.
  • Hydrocephalus. If an infant with spina bifida has hydrocephalus (water on the brain), a surgeon can implant a shunt-a small hollow tube to drain fluid-to relieve pressure on the brain. Treating hydrocephalus can prevent problems such as blindness.
  • Tethered spinal cord. Surgery can separate the spinal cord from surrounding tissue.
  • Paralysis and limitations in mobility.People with spina bifida use different means to get around, including braces, crutches, walkers, and wheelchairs.
  • Urinary tract infections; lack of bladder and bowel control.People with myelomeningocele often have nerve damage that prevents the bladder from completely emptying, a condition that can cause urinary tract infections and kidney damage. Health care providers may address this problem by regularly inserting a catheter into the bladder to allow it to empty fully. Medications, injections, and surgery also can help correct incontinence and preserve kidney and bladder function for the long term.

There is no treatment for anencephaly or iniencephaly. These conditions are usually fatal shortly after birth.

-NIH



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