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:
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
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