Neural tube defect

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at September 6, 2016
StartDiseasesNeural tube defect

Neural tube defects (NTD) are abnormalities that occur before birth and affect the spine, spinal nerves, or brain. They occur in the earliest stages of pregnancy.

Contents

Definition & Facts

Soon after conception, the embryo develops cells that form the neural tube. This tube eventually turns into parts of the central nervous system, including the spinal cord, the vertebrae that protect it, and the brain. The top of the tube develops into the brain, while the rest becomes the spinal cord.

Over time, the tube is supposed to close up. If it does not close up completely anywhere along its length, the problem is known as a neural tube defect. About 3,000 pregnancies per year in the United States have embryos with neural tube defects. The consequences range from mild to catastrophic.

The most common manifestation of a neural tube defect is called spina bifida. About 1,500 babies are born every year with this disorder in the United States.

Symptoms & Complaints

A baby who is born with spina bifida is often paralyzed beneath the area where the neural tube didn’t close, which makes it difficult to walk and can cause fecal incontinence and urinary incontinence. Some people born with spina bifida have learning disabilities. Different types of spina bifida include:

  • Myelomeningocele. This is the most common type of spina bifida and the most severe. The baby’s vertebrae are deformed in a way that lets tissue and some of the spinal cord itself protrude through the openings. Hydrocephalus, or fluid on the brain sometimes afflicts babies born with myelomeningocele. This can lead to severe learning disabilities. 
  • Spina bifida occulta. This type of neural tube defect can be so mild that the baby shows no symptoms or obvious abnormalities. There is only a small opening in the spine and no damage to the spinal cord. Because of this, some doctors do not believe that spina bifida occulta is a neural tube defect at all.
  • Closed neural tube defect. This happens when the bone, membranes, or fat around the spinal column are deformed. As with spina bifida occulta, some people have no symptoms, while others experience mild paralysis. The only outward abnormality may be a dimpling or a patch of hair growing on the spine.
  • Meningocele. This presents as a fluid-filled sac that bulges through an opening in the child’s back. Despite this, some people are asymptomatic while others have problems.
  • Encephalocele. This neural tube defect results when the tube doesn’t close around an opening in the skull, usually at the base where the spinal cord connects with the brain, in openings between the nose and the forehead or in the middle of the dome of the skull. As a result, the brain and its protective membranes can bulge through the skull and form a sac. This can lead to hydrocephalus, paralysis, and/or jerky movements of the arms and legs, abnormalities of the face and skull and problems with vision. Despite these burdens, some children with encephalocele have normal intelligence. Around 375 babies are born every year with this condition in the United States.
  • Anencephaly. This type of neural tube defect occurs when the tube doesn’t close at the top. This results in the embryo or fetus having no brain tissue. Parts of the skull may also be missing. Because of this, babies with this problem die before birth, during birth or shortly after birth. About 1,000 babies a year are born with anencephaly in the United States. The majority of them are girls.
  • Iniencephaly. This neural tube defect results in severe and fatal deformities. Babies with this condition do not live long after birth.

Causes

Researchers do not know what causes neural tube defects, though they believe that genetic factors and environmental factors play roles. Couples whose families have histories of neural tube defects are at higher risk for having children with the condition. A woman who is exposed to environmental toxicants during her pregnancy like cigarette smoke, pollution, or toxic chemicals, suffers from obesity or diabetes mellitus or who takes medications for seizures is more at risk for having babies with NTD. Hispanics and whites are more likely to have babies with NTD than other American ethnic groups.

Diagnosis & Tests

A blood test that is taken as part of prenatal testing called a quad screen can find substances in the mother’s blood that points to her being more at risk for having a baby with NTD. This test does not detect signs of encephalocele, though an ultrasound test can. If NTD is suspected, the woman can have further tests such as amniocentesis and a more accurate ultrasound that targets the fetus’ skull and internal organs.

Treatment & Therapy

In some cases, spina bifida can be treated surgically even while the baby is still in the womb. Though the surgery is uncommon, with approximately 400 having been performed, it is more effective than spina bifida surgery performed after birth.

A baby with hydrocephalus can have a shunt inserted into their brain to remove the unwanted fluid. The fluid simply drains into the body, where it is harmless. Mothers can also arrange for a caesarean section, which may place less stress on the baby than vaginal birth. Operations such as meningocele repair can be performed shortly after the child is born.

Prevention & Prophylaxis

One simple way that neural tube defects can be prevented is for the mother to start on a course of folic acid even before she becomes pregnant.

Experts recommend that a woman who plans to become pregnant should take at least 400 milligrams of folic acid a day before she becomes pregnant and to keep taking it throughout her early pregnancy. This folic acid should come in a multivitamin. During pregnancy, a prenatal vitamin with at least 600 micrograms of folic acid should be taken daily.

Women who have already had a baby with a neural tube defect need even more folic acid. They should consult with their doctor as to how much folic acid they need during their pregnancy.

Folic acid can also be taken through enriched foods. Folic acid found naturally in foods is called folate and is abundant in leafy green vegetables and beans. The pregnant woman should still take a vitamin even if she eats these foods.