Neural Tube Defects

There are several types of NTDs that vary in their severity. Depending on the type of defect and the location, the symptoms can range from mild to severe and the complications can vary from minor to serious, including intellectual and physical disabilities, and/or be life-threatening. The two most common types of neural tube defects are spina bifida and anencephaly.

Spina bifida

Spina bifida, which literally means "cleft spine," is the most common type of NTD. According to the National Institute of Neurological Disorders and Stroke, spina bifida affects about 1,500 to 2,000 of the babies born in the United States each year. It occurs when the neural tube does not close completely somewhere along the spine.

Different types of spina bifida include:

• Occulta. Spina bifida occulta is often called hidden spina bifida. A small gap may exist in one or more of the vertebrae, but the spinal cord and tissues are normal. Many people with this condition do not have any symptoms, although it can lead to back pain or bladder function issues, and may never know that it exists unless it is identified during imaging tests done for another reason.
• Closed neural tube defects are frequently grouped with spina bifida occulta. They consist of a wide variety of spinal defects with malformed bone, tissue, and/or fat deposits at the location of the defect. Often, there is a visible sign on the outside of the baby's skin. This may be a tuft of hair, a dimple, a birthmark, or lump. Many with this condition will have few symptoms, but some may have nerve damage that affects normal bowel or urinary function and/or can cause lower body weakness and pain. Closed neural tube defects are often not detected by prenatal screening tests.
• Meningocele. With this type of spina bifida, cerebrospinal fluid and meninges have ballooned out of the spinal opening to form a bulge or sac, but the spinal cord is usually in its normal location. This bulge may or may not be covered with a layer of skin. This bulge will be noticeable on the back of the baby. Symptoms of this type are variable.
• Myelomeningocele. This is the most severe type of spina bifida. It develops when the cerebrospinal fluid, meninges, and the spinal cord protrude through the opening in the spine. It leaves the spinal cord vulnerable to damage and can cause paralysis in those parts of the body below the opening. Those affected with a myelomeningocele frequently have bowel and urinary dysfunction. Some will require assistance to walk and others will require a wheelchair. Newborns with this condition are at an increased risk of developing meningitis.

Approximately 15% to 25% of children with myelomeningocele will develop hydrocephalus. This complication occurs when the flow of cerebrospinal fluid is obstructed and accumulates in the brain. The child's head becomes larger and the fluid applies pressure on the brain. Approximately 80% to 90% of those with hydrocephalus will require shunting, or placement of a tube to allow draining of the excess cerebrospinal fluid. Left untreated, this condition can cause varying degrees of intellectual disability and can be fatal in some cases.

Those with myelomeningocele may also have a Chiari malformation. This is a structural defect in which the cerebellum, the portion of the brain that sits just above the spinal cord, protrudes down into part of the space normally occupied by the spinal cord. The cerebellum controls balance. People with a Chiari malformation may experience a range of symptoms, including sensory disturbances, vision problems, headaches, neck pain, and dizziness.

Anencephaly

Anencephaly occurs when the neural tube fails to close properly at the head. The result is the lack of development of a large portion of the brain and skull. The Centers for Disease Control and Prevention estimates that about 3 in 10,000, or 1,206, pregnancies in the U.S. have anencephaly. Most of those affected are stillborn or die within a few hours or days.

Rare Forms

There are varieties of other, rarer forms of NTDs. All are associated with a lack of proper neural tube formation. Examples of these include:

• Encephalocele – protrusion of membranes and brain tissue through a bony defect of the skull; this can occur anywhere along the center of the skull, in the front or back; newborns with this condition may have microcephaly (small head) and develop hydrocephalus. Prognosis depends on the location and severity of the defect.
• Iniencephaly – severe defect where the spine joins the skull; the head is bent back at a severe angle and the baby does not usually have a neck; associated with other abnormalities and most affected infants do not survive.

Some factors that increase the risk of having a baby with an NTD include:

• Personal history—people who have an NTD or a child diagnosed with NTD
• Family history—people who have family members with an NTD
• Use of some anti-seizure medications, such as valproic acid, has been associated with an increased risk. A woman should discuss her medications with her healthcare provider before becoming pregnant.
• Certain diseases in the mother, such as diabetes or obesity
• High body temperature in the mother early in the pregnancy
• Use of opioids in the first two months of pregnancy

Risk can be reduced but not eliminated by ensuring that the mother has adequate folate, also called folic acid, at the time of conception. See the section on Prevention below.

Signs and symptoms of neural tube defects vary from person to person and can change over time. Spina bifida, one of the two most common neural tube defects, may have no symptoms or only minor disabilities but can also lead to severe physical and intellectual disabilities in some cases. Health issues will vary for each individual.

Between 20% and 50% of people with spina bifida may develop tethered cord syndrome. This occurs when the spinal cord becomes attached to bone or skin (such as scar tissue) and is unable to flex and move. The cord becomes stretched and can lead to nerve damage. In children, it can lead to spine issues such as scoliosis (curvature of the spine). Surgery to untether the cord can prevent further damage but is not likely to correct nerve or tissue damage that has already occurred.

Babies born with myelomeningocele (a form of spina bifida) may experience hydrocephalus, an accumulation of fluid in the brain. These children may also develop meningitis, an infection in the tissues surrounding the brain. Usually, a surgeon will implant a shunt to drain the fluid as needed. Children with hydrocephalus are at increased risk for developmental and learning disabilities.

People with spina bifida in the upper portion of the spine may be paralyzed, but those who have a defect in the lower portion of the spine may be able to walk or stand on their own or with the aid of crutches or braces. Urinary tract dysfunction and constipation are common among people with spina bifida, and skin problems can arise due to a lack of sensitivity in the lower extremities. Children with spina bifida may also have latex allergies as well as higher rates of depression and obesity.

Life expectancy for babies born with anencephaly, a neural tube defect where the forebrain or cerebrum does not form, is typically very short.

The goals of testing are to detect and diagnose neural tube defects in a developing baby and/or in a newborn and to evaluate severity and complications. Very mild cases of NTDs may never be detected or may be detected later in life when testing is performed for other reasons.

Laboratory Tests

Laboratory tests are generally used to screen for neural tube defects during pregnancy. They may include:

• Alpha-fetoprotein (AFP) or maternal serum screen (triple screen or quad screen) – AFP is a protein produced by fetal tissue. During development, AFP levels in fetal blood and amniotic fluid rise until about 12 weeks, and then levels gradually fall until birth. Some AFP crosses the placenta into the mother's blood. An AFP test is used to screen for neural tube defects such as spina bifida. An increased level of AFP in the mother's blood has been associated with an increased risk of an open NTD in the baby.
  • AFP may be performed by itself when risk for chromosome disorders, such as Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18), have already been assessed using non-invasive prenatal screening (NIPS) or first trimester Down syndrome screening.
  • AFP may be performed as part of the triple or quad screen, a group of tests performed on the mother during her second trimester. These tests screen for NTDs as well as chromosome disorders.
• AFP and acetylcholinesterase in amniotic fluid (see Amniotic Fluid Analysis) – if the AFP is elevated in the mother's blood, AFP and acetylcholinesterase can be measured in amniotic fluid, as confirmatory tests. 
• An evaluation of a baby's chromosomes (fetal karyotype test) may also be done on amniotic fluid at the same time to rule out chromosomal abnormalities as a cause of abnormal AFP. These tests are performed with or after a fetal ultrasound.

A variety of laboratory and non-laboratory tests may be performed after birth to help evaluate and monitor the health of various organs, such as the kidneys and bladder.

Non-Laboratory Tests

Fetal ultrasound may be used to help detect defects in a developing baby and help diagnose NTDs prior to birth. For more on this, see RadiologyInfo.org: Obstetric Ultrasound.

Scans done after a baby is born may include:

• X-ray, MRI (magnetic resonance imaging), and/or CT scan (computed tomography) of the spine and vertebrae after birth to look for defects and deformities
• X-ray or CT scans of the head to detect excess fluid when hydrocephalus is suspected

It is generally recommended that all women of childbearing age get at least 400 micrograms (mcgs) of folate a day to prevent NTDs. This helps ensure that pregnant women or women who are planning a pregnancy get enough folate (folic acid). Recent evidence suggests that folic acid supplementation could reduce the incidence of neural tube defects by up to 70%, but the protection it provides must be in place at the time of conception. Ideally, a woman should begin taking folate a month before becoming pregnant and continue throughout her pregnancy.

Women at a high risk for NTDs (such as women who have or have a child with spina bifida) should take 4,000 micrograms of folic acid each day through week 12 of pregnancy, but this is not recommended for the general population.

Since folic acid is a water-soluble vitamin, it must be constantly replenished. In addition to supplements, folic acid can be found in dark green vegetables and some fruit. Most grain products in the U.S. are good sources because they have been fortified with added folic acid.