What are neural tube defects?
Neural (pronounced NOOR-uhl) tube defects are abnormalities that can occur in the brain, spine, or spinal column of a developing embryo and are present at birth (birth defects).
Very early in the development of an embryo, 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 vertebra). As development progresses, the top of the tube becomes the brain and the remainder becomes the spinal cord. A neural tube defect occurs when this tube does not close completely somewhere along its length, resulting in a hole in the spinal column or another type of defect. These defects occur in the first month of pregnancy, often before a woman even knows that she is pregnant.
There are several types of neural tube defects:
Spina bifida (pronounced SPY-nuh BIF-i-duh) is the most common type of neural tube defect. 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 spine, which can cause lifelong problems with walking and other difficulties. Because bladder and bowel control are controlled by the lowest spinal nerves, bowel and urinary dysfunction are common. Many infants who are born with spina bifida will have normal intelligence, but some will have learning or intellectual disabilities.1 There are several common types of spina bifida:
- Spina bifida occulta (pronounced o-CULT-tuh) is the mildest form, and most experts do not consider it to be a true neural tube defect. 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 some persons, it causes few or no symptoms, but other people might experience partial paralysis or other symptoms. In some cases, the only outward sign might be a dimple or tuft of hair on the spine.3
- Meningocele (pronounced muh-NING-guh-seel) includes a sac of fluid that protrudes through an opening in the back, but the spinal cord is not involved. Some people will have no symptoms, and 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 the opening. A person with this condition usually has partial or complete paralysis in the parts of the body below the spinal column abnormality. Bowel and urinary dysfunction are common. Children with myelomeningocele may develop hydrocephalus (pronounced hahy-druh-SEF-uh-luhs) (excess fluid on the brain). Hydrocephalus can lead to intellectual and learning 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 neural tube defect. This condition occurs when the neural tube fails to close at the top. The fetus has little or no brain matter and also may be lacking part of its skull. Infants born with this condition are usually unconscious as well as deaf and blind and unable to feel pain. They may have reflex actions, such as breathing and responding to touch. All infants with anencephaly are stillborn or die soon after birth.4,5
Encephalocele (pronounced ehn-SEF-o-low-seel), another rare type of neural tube defect, 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 or forehead area that is not noticeable. The infant may have other problems as well, such as hydrocephalus, paralysis of the arms and legs, 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.6
Iniencephaly(pronounced in-ee-ehn-SEF-ah-lee), another rare but severe type of neural tube defect, is diagnosed when the infant’s head 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.5
- Centers for Disease Control and Prevention. (2011). Spina bifida. Retrieved July 23, 2012, from http://www.cdc.gov/ncbddd/spinabifida/facts.html
- National Institute of Neurological Disorders and Stroke. Spina bifida fact sheet. (2012). Retrieved July 23, 2012, from http://www.ninds.nih.gov/disorders/spina_bifida/detail_spina_bifida.htm
- 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.
- National Institute of Neurological Disorders and Stroke. (2010). NINDS Anencephaly Information Page. Accessed July 23, 2012, from http://www.ninds.nih.gov/disorders/anencephaly/anencephaly.htm
- National Institute of Neurological Disorders and Stroke. (2012). Cephalic disorders fact sheet. Accessed July 23, 2012, from http://www.ninds.nih.gov/disorders/cephalic_disorders/detail_cephalic_disorders.htm
- National Institute of Neurological Disorders and Stroke. (2007). NINDS encephaloceles information page. Retrieved on July 23, 2012, from http://www.ninds.nih.gov/disorders/encephaloceles/encephaloceles.htm