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 defects 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 birth defects.
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
- Centers for Disease Control and Prevention. (2016). Spina bifida. Retrieved February 23, 2017, from http://www.cdc.gov/ncbddd/spinabifida/facts.html
- 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
- 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.
- NINDS. (n.d.). Anencephaly information page. Retrieved February 23, 2017, from https://www.ninds.nih.gov/Disorders/All-Disorders/Anencephaly-Information-Page
- NINDS. (n.d.). Encephaloceles information page. Retrieved February 23, 2017, from https://www.ninds.nih.gov/Disorders/All-Disorders/Encephaloceles-Information-Page
- NINDS. (n.d.). Iniencephaly information page. Retrieved February 23, 2017, from https://www.ninds.nih.gov/Disorders/All-Disorders/Iniencephaly-Information-Page