Neural Tube Defects

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, have 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

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

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, can lead to severe physical and mental disabilities, but occasionally there are no symptoms or only minor disabilities. Health issues will vary for each individual. With the right care, babies born with spina bifida can grow up to reach their full potential.

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 deformities such as scoliosis. 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. Additional problems such as learning disabilities may arise later.

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 complications and constipated bowels 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.

There are several types of neural tube defects (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 mental 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.

Cases of spina bifida are generally classified as either "closed," where the skin covers the defect, or as "open," where the skin is not intact. Different types include:

Closed Neural Tube Defects

• 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 and may never know that it exists unless it is identified during testing that is 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, lump, or skin opening. 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 screening tests.

Open Neural Tube Defects

• 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 those with 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.

According to the Spina Bifida Association, approximately 70-90% of those affected by 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. Left untreated, this condition can cause mental retardation and learning disabilities and can, in some cases, be fatal.

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 (CDC) estimates that about 1 in 4,800 babies born every year in the U.S. will be born with anencephaly. Those who are born alive are usually unconscious, unable to feel pain, deaf, and blind. Most of those affected 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:

• Encephaloceles – in those affected, part of the brain and its membranes bulge out through openings in the skull; newborns with this condition may have microcephaly (small head) and develop hydrocephalus. Prognosis depends on severity.
• Iniencephaly – in this condition, the head is bent back at a severe angle and the baby does not usually have a neck; associated with other abnormalities, most affected infants do not survive.

The goals of testing are to detect and diagnose neural tube defects (NTDs) 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:

• Maternal serum screen (triple screen or quad screen) – this group of tests is performed on the mother during her second trimester to screen for a variety of problems and includes an AFP (alpha-fetoprotein) test. 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 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 followed by or performed with a fetal ultrasound.

A variety of laboratory and non-laboratory tests may be performed by a urologist after birth to help evaluate a newborn's kidney and bladder function.

Non-Laboratory Tests

Imaging tests may be used to help detect defects in a developing baby. These may include:

• Fetal ultrasound – to help diagnose NTDs prior to birth (for more on this, see RadiologyInfo.org: Obstetrical Ultrasound)
• 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

Regular clinical examinations of both the mother and baby are performed to detect and address complications as they arise.

Treatment

There is no cure for NTDs, and any nerve damage or loss in function is permanent. Monitoring is initiated as soon as a neural tube defect is detected. Those with a mild NTD may not require treatment, but many of those affected require one or more surgical interventions with needs that begin at birth and change over time. New options are constantly emerging and parents should work with their healthcare providers to determine which treatments are right for their child.

Children with hydrocephalus are typically treated by implanting a shunt that allows excess cerebrospinal fluid to drain into the abdomen.

Usually, a baby born with spina bifida requires surgery to close the spinal defect and protect exposed nerves from further damage. The surgery is typically performed immediately following delivery or during the first few days of life.

However, a study sponsored by the Eunice Kennedy Shriver National Institute of Child Health and Human Development suggests that there are better health outcomes when prenatal surgery is performed between 19 and 26 weeks of pregnancy as opposed to waiting until the baby is born. The study showed that covering the neural tube defect with layers of the fetus's tissue resulted in better motor function at 30 months age than in babies who received surgery post-delivery. Babies who received prenatal surgery also showed a reduced need for shunt placement. There are increased risks to the mother and baby with prenatal surgery, however. The mothers required follow-up monitoring and cesarean deliveries, and many of the babies were born prematurely. These specialized surgeries are being performed in a few centers, and research into the use of this type of surgery to address NTDs is continuing. 

Prevention

Adequate folate, also called folic acid, is the primary prevention tool. Recent evidence suggests that folic acid supplementation could reduce the incidence of neural tube defects (NTDs) by up to 70%, but the protection it provides must be in place at the time of conception. A woman should begin taking folate a month before becoming pregnant and continue throughout her pregnancy. To ensure this, it is generally recommended that all women of childbearing age get at least 400 micrograms of folate a day. 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.

Women who have spina bifida, or who already have a child with spina bifida, or who are otherwise considered at an increased risk of having a baby with an NTD may be given a prescription for about 10 times the recommended dose for several months before becoming pregnant. This higher dose is not recommended for the general population.