What Are Neural Tube Defects?

Neural tube defects (NTDs) are among the most common congenital anomalies in the United States, second only in frequency to congenital heart defects.

Efforts to reduce the prevalence of these devastating abnormalities demonstrates the effectiveness of the translation of basic science and population research to health care practices, and from practice to public policy.

NTDs are congenital abnormalities that result from the failure of the normal development of brain and spinal cord. The Centers for Disease Control and Prevention (CDC) estimate that, in 2005, the rates for spina bifida and anencephaly, the two most common forms of NTDs, were 18 and 11 cases per 100,000 live births, respectively.1 An estimated 3000 children are born each year in the United States with an NTD.

Normally, the tissue that is to become the central nervous system (the brain and the spinal cord) forms as a flat plate of cells that later folds over on itself to form a closed tube. This normally occurs within four weeks after conception. In children with NTDs, one or both ends of the tube fail to fully close. The result is one or more congenital defects that affect the cranium or the spine.

One common NTD is anencephaly in which the large portions of the brain fail to develop. In other cases, parts of the skull may not form and portions of the brain may extend or herniate through the opening.

Another form of NTD is spina bifida, in which the vertebral column fails to completely surround the spinal cord and the spinal nerves. The meninges (the tissue that surrounds the central spinal cord) may herniate through the opening to form a meningocele. If portions of the spinal cord herniate through the gap, to form a myelomeningocele, the spinal cord and the spinal nerves may be severely and permanently damaged.

These defects are often associated with other congenital neurologic defects. Hydrocephalus (a condition in which excess fluid collects in the brain, compressing normal brain tissue) occurs in 70-90% of cases, and a significant malformation in which a portion of the brain is displaced downward into the neck (the Chiari II malformation) occurs in one-third of children with spina bifida. Each of these causes additional clinical disability depending upon the specific parts of the nervous system that are affected.

Clinical consequences are severe, debilitating, and irreversible. Anencephaly is incompatible with life. Spina bifida with myelomeningocele formation leads to paralysis and loss of sensation with associated urologic, orthopedic, and neurologic consequences requiring multiple operations and life-long medical care.

References: 

Centers for Disease Control: Racial/Ethnic Differences in Birth Prevalence of Spina Bifida – United States, 1995-2005. MMWR 2009; 57:1409-1413.

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