Neural Tube Defects (NTDs)

NTDs occur when the spinal cord, brain, and related structures do not form properly. NTDs are congenital anomalies that are present at birth. They usually occur very early in pregnancy—usually during the first month—and can cause serious problems after birth.

Since NICHD was founded, one of its main focuses has been understanding the causes, treatment, and prevention of congenital anomalies like NTDs.

About Neural Tube Defects (NTDs)

NTDs are abnormalities that can occur in the brain, spinal cord, or spine of a developing fetus.

Very early in the development of a fetus, 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 vertebrae). As development progresses, the top of the tube becomes the brain and the remainder becomes the spinal cord. An NTD occurs when this tube does not close completely somewhere along its length, resulting in a hole in the spinal column or another type of problem.

These anomalies occur in the first month of pregnancy, often before a woman even knows that she is pregnant. Because they are present at birth, they are categorized as congenital anomalies.

There are several types of NTDs, described here.

Spina bifida (pronounced SPY-nuh BIF-i-duh) is the most common type of NTD. 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 spinal cord, which can cause lifelong problems with walking and other difficulties. Because bladder and bowel functions are controlled by the lowest spinal nerves, bowel and urinary dysfunction are common with spina bifida. Many infants with spina bifida have normal intelligence, but some will have learning disabilities or intellectual disabilities.1 There are several common types of spina bifida:

  • Spina bifida occulta (pronounced o-CULT-tuh) is the mildest form. It is so mild, in fact, that most experts do not consider it to be a true NTD. With this condition, 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.2
  • Closed neural tube defect is a malformation of the fat, bone, or membranes in the spinal column. In some people, a closed NTD causes few or no symptoms, but other people might experience partial paralysis or other symptoms. In some cases, the only outward sign of a closed NTD might be a dimple or tuft of hair on the spine.3
  • Meningocele (pronounced muh-NING-guh-seel) describes cases in which a sac of fluid protrudes through an opening in the back, but the spinal cord is not involved or damaged. For this reason, some people with meningocele will have no symptoms, while some people will have more severe problems.2
  • 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 an opening in the back. A person with this condition usually has partial or complete paralysis in the parts of the body below the spinal column problem. Bowel and urinary problems are common. Children with myelomeningocele may also develop hydrocephalus (pronounced hahy-druh-SEF-uh-luhs) (excess fluid on the brain), which can lead to learning and intellectual disabilities. Some infants born with myelomeningocele have severe intellectual disabilities.2

Anencephaly (pronounced an-en-SEF-uh-lee) is a more severe, but less common, type of NTD. This condition occurs when the neural tube fails to close at the top. As a result, most or all of the brain is missing, and parts of the skull may also be lacking. Infants born with this condition usually remain unconscious and are deaf, blind, and unable to feel pain because brain structures related to those functions do not exist. They may have reflex actions, such as breathing and responding to touch. Infants with anencephaly are either stillborn or die soon after birth.4

Encephalocele (pronounced ehn-SEF-o-low-seel), another rare type of NTD, 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 cavity or forehead area that is not noticeable. Infants with encephalocele may have other problems, such as hydrocephalus, limb paralysis, 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.5

Iniencephaly (pronounced in-ee-ehn-SEF-ah-lee), another rare but severe type of NTD, describes a head that 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.6

Citations

  1. Centers for Disease Control and Prevention. (2016). Spina bifida. Retrieved February 23, 2017, from http://www.cdc.gov/ncbddd/spinabifida/facts.html
  2. National Institute of Neurological Disorders and Stroke (NINDS). (n.d.) Spina bifida information page. Retrieved February 23, 2017, from https://www.ninds.nih.gov/Disorders/All-Disorders/Spina-Bifida-Information-Page
  3. McComb, J. G., & Chen, T. C. (1996). Closed spinal neural tube defects. In G. T. Tindall, P. R. Cooper, & D. L. Barrow (Eds.), The practice of neurosurgery (pp. 2754–2777). Baltimore: Williams & Wilkins.
  4. NINDS. (n.d.). Anencephaly information page. Retrieved February 23, 2017, from https://www.ninds.nih.gov/Disorders/All-Disorders/Anencephaly-Information-Page
  5. NINDS. (n.d.). Encephaloceles information page. Retrieved February 23, 2017, from https://www.ninds.nih.gov/Disorders/All-Disorders/Encephaloceles-Information-Page
  6. NINDS. (n.d.). Iniencephaly information page. Retrieved February 23, 2017, from https://www.ninds.nih.gov/Disorders/All-Disorders/Iniencephaly-Information-Page

What are the symptoms of neural tube defects?

The symptoms associated with NTDs vary depending on the specific type of defect. 

Symptoms include physical problems (such as paralysis and urinary and bowel control problems), blindness, deafness, intellectual disability, lack of consciousness, and, in some cases, death. Some people with NTDs have no symptoms. Most children with certain types of NTDs die or experience serious disability.

What causes neural tube defects (NTDs)?

The exact causes of NTDs are not known. Many different factors, including genetics, nutrition, and environmental factors, are known to play a role.

Research shows that getting enough folic acid (also known as folate or vitamin B9) before conception and early in pregnancy can greatly reduce the risk of spina bifida and other NTDs.

In addition, 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 antifolate (such as aminopterin) are at greater risk than other women are of having an infant with spina bifida or anencephaly.1,3

Some studies suggest that NTDs 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.1,2,3 For this reason, health care providers often advise women who may become pregnant or who are pregnant to avoid using hot tubs or saunas.

Citations

  1. Moretti, M. E., Bar-Oz, B., Fried, S., & Koren, G. (2005). Maternal hyperthermia and the risk for neural tube defects in offspring: Systematic review and meta-analysis. Epidemiology, 16(2), 216–219. Retrieved August 6, 2018, from https://journals.lww.com/epidem/fulltext/2005/03000/Maternal_Hyperthermia_and_the_Risk_for_Neural_Tube.10.aspx 
  2. Chescheir, N., & American College of Obstetricians and Gynecologists (ACOG) Committee on Practice Bulletins-Obstetrics. (2003, reaffirmed 2016). ACOG Practice Bulletin: Neural tube defects, Number 44. International Journal of Gynecology and Obstetrics, 83, 123–133.
  3. Centers for Disease Control and Prevention. (2016). Spina bifida. Retrieved February 23, 2017, from http://www.cdc.gov/ncbddd/spinabifida/facts.html

How many people are at risk for neural tube defects (NTDs)?

NTDs are a major cause of death and lifelong disability worldwide. According to the Centers for Disease Control and Prevention, spina bifida is the most common NTD in the United States.1 Anencephaly is the second most common, but it occurs far less often than spina bifida. Other types of NTDs are less common, and some are rare, such as iniencephaly. For additional statistics about NTDs, visit https://www.cdc.gov/folic-acid/about/index.html.

Parents who have already had a child with spina bifida or another NTD have a slightly higher risk (less than 5%) than other parents of having a second child with spina bifida. Families with two children with spina bifida have a 1 in 10 chance of having another child with this condition.2 To help prevent NTDs in later pregnancies, health care providers may recommend a higher amount of folic acid for these women, starting well before conception.

Citations

  1. Centers for Disease Control and Prevention. (2018). Birth defects COUNT. Retrieved May 3, 2018, from https://www.cdc.gov/birth-defects/about/index.html#cdc_disease_basics_risk-risk-factors
  2. Chescheir N., & American College of Obstetricians and Gynecologists (ACOG) Committee on Practice Bulletins-Obstetrics. (2003, reaffirmed 2016). ACOG Practice Bulletin: Neural tube defects, Number 44. International Journal of Gynecology and Obstetrics, 83, 123–133.

How do health care providers diagnose neural tube defects (NTDs)?

NTDs are usually diagnosed during pregnancy, through laboratory or imaging tests.

Prenatal laboratory tests may include:

  • “Triple screen” blood test: One part of the triple screen blood test looks for an elevated level of alpha-fetoprotein (AFP), which is associated with a higher risk of NTDs. The AFP test also can be done by itself. The two other parts of the triple screen involve testing for human chorionic gonadotropin (hCG) and estriol. This test generally is done during the second trimester.1
  • Amniotic fluid tests: Testing amniotic fluid may also show a high level of AFP, as well as high levels of acetylcholinesterase. Health care providers might perform this test to confirm high levels of AFP seen in the triple screen blood test. The amniotic fluid also can be tested for chromosomal abnormalities, which might also be the cause of the abnormal AFP level.2

Prenatal ultrasound imaging usually detects almost all types of NTDs.2

Shortly after the birth of an infant with a diagnosed or suspected NTD, the health care provider will perform tests to assess the severity of the NTD and any complications. These tests might include an X-ray, magnetic resonance imaging (MRI), a computed tomography (CT or CAT) scan to look for spinal defects or excess fluid2; measuring the head circumference; assessing the infant’s strength, motor, and sensory functioning; and observing the infant’s urinary stream.3

Those with milder spina bifida may not be diagnosed until later in childhood or in adulthood.2

Citations

  1. Lab Tests Online. (2018). Maternal serum screening, second trimester. Retrieved August 8, 2018, from https://labtestsonline.org/tests/maternal-serum-screening-second-trimester 
  2. Centers for Disease Control and Prevention. (2016). Spina bifida. Retrieved February 23, 2017, from http://www.cdc.gov/ncbddd/spinabifida/facts.html
  3. Jallo, G. I. (2015). Neural tube defects clinical presentation. Retrieved February 23, 2017, from http://emedicine.medscape.com/article/1177162-clinical#b4 

Are there disorders or conditions associated with NTDs?

Infants born with NTDs 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 infants who have myelomeningocele, the most severe form of spina bifida.1 Associated conditions can include the following.

Hydrocephalus

Many infants born with spina bifida have a buildup of fluid in and around the brain, a condition called hydrocephalus. The extra fluid can cause swelling that pushes some brain structures against the skull or away from where they are usually located, which may lead to brain injury.

Chiari II Malformation

In many children with myelomeningocele, the brain is positioned abnormally. The lower part of the brain rests farther down than normal, partially in the upper spinal canal. This unusual position can block cerebrospinal fluid 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

Unlike a normal spinal cord, which floats freely in the spinal canal, in spina bifida, the spinal cord is attached to the spinal canal. This attachment means the spinal cord stretches as a person grows, which 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 problems.

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 that frequent exposure to latex can cause the allergy. Exposure to latex is common for people with spina bifida who have shunts and have had many surgeries.2

Learning Disabilities

Studies have shown wide variability in deficits associated with learning disabilities among patients with spina bifida. These include intellectual disability, substandard scores on some types of memory tests and tasks related to executive function, and nonverbal learning problems.3 This syndrome shares some of its characteristic features with autism spectrum disorders, specifically what used to be called Asperger syndrome.

Other Conditions

Some people with myelomeningocele have digestive, vision, sexual, social, and emotional problems; obesity; and depression.

Citations

  1. Centers for Disease Control and Prevention. (2016). Spina bifida: Health issues & treatments for spina bifida. Retrieved February 23, 2017, from http://www.cdc.gov/NCBDDD/spinabifida/treatment.html
  2. Spina Bifida Association. (n.d.). Natural rubber latex allergy: People with spina bifida are at high risk for latex allergy. Retrieved February 23, 2017, from https://www.spinabifidaassociation.org/resource/latex-2/ 
  3. Alriksson-Schmidt, A., Thibadeau, J. K., Swanson, M. E., Marcus, D., Carris, K. L., Siffel, C., et al. (2013). The natural history of spina bifida in children pilot project: Research protocol. JMIR Research Protocols, 2(1), e2. Retrieved March 23, 2018, from https://www.ncbi.nlm.nih.gov/pubmed/23612276

What are the treatments for neural tube defects (NTDs)?

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 condition’s severity or complications.1

  • 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 (excess fluid surrounding 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.
  • Encephaloceles. People with encephaloceles—sac-like bulges where the brain and surrounding membranes protrude through the skull—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.
  • Tethered spinal cord. Surgery can separate the spinal cord from surrounding tissue.1
  • Paralysis and limitations in mobility. People with spina bifida use different means to get around, including braces, crutches, walkers, and wheelchairs.
  • Urinary tract infections and lack of bladder and bowel control. People with myelomeningocele often have nerve damage that keeps the bladder from completely emptying. This can cause urinary tract infections and damage to the kidneys. Health care providers may address this problem by using a tube to fully empty the bladder. Medications, injections, and surgery also can help prevent urine from leaking accidentally and keep the kidneys and bladder working for the long term.

There is no treatment for anencephaly or iniencephaly.2 Infants with these conditions usually die shortly after birth.

Citations

  1. National Institute for Neurological Disorders and Stroke. (n.d.). Spina bifida information page. Retrieved February 23, 2017, from https://www.ninds.nih.gov/Disorders/All-Disorders/Spina-Bifida-Information-Page
  2. Centers for Disease Control and Prevention. (2015). Birth defects: Facts about anencephaly. Retrieved February 23, 2017, from http://www.cdc.gov/ncbddd/birthdefects/Anencephaly.html
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