neural tube defect
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What is a neural tube defect?
A neural tube defect is a congenital disability of the brain and spinal cord that occurs very early in embryonic development. It happens when the neural tube, which develops into the central nervous system, doesn't close properly, is missing parts, or is blocked.
Examples of neural tube defects include anencephaly (absence of the brain), spina bifida (where the spinal cord doesn't close completely), meningocele (a fluid-filled sac protrudes through the vertebral defect), and myelocele (where the spinal cord is exposed).
Taking folic acid during early pregnancy can lower the risk of neural tube defects.
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How does the neural tube form during early development?
During early prenatal development, the neural tube, which becomes the brain and spinal cord, forms through a series of crucial steps. Around 18 days after conception, a neural plate develops from a thickening of the ectoderm on the embryo's dorsal midline. This plate folds, creating a neural groove, and further growth causes these folds to meet and fuse, forming the neural tube. The tube's walls then differentiate into the ependymal, gray, and white matter. Neural tube defects happen if this closure is incomplete, missing, or blocked.
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What happens if the neural tube doesn't close properly?
If the neural tube doesn't close properly during early embryonic development, neural tube defects (NTDs) can occur, often accompanied by defects of the vertebral column or skull. These malformations arise because the neural tube fails to close completely, parts are missing, or there's a blockage.
Examples of NTDs include anencephaly (absence of brain) and spina bifida, where the spinal cord is not fully enclosed. Spina bifida can manifest in varying degrees of severity, from spina bifida occulta, which has no effect on body functions, to more serious forms like meningocele or meningomyelocele, which can result in paralysis and impaired bladder and bowel function.
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What are some common types of neural tube defects?
Neural tube defects are congenital disabilities of the brain and spinal cord that occur during embryonic development. These defects arise from the incomplete closure of the neural tube.
Common types include:
* Spina bifida: Incomplete closure of the vertebrae, potentially leading to nerve damage and functional impairments.-
Anencephaly: Absence of major portions of the brain and skull, typically resulting in death at or shortly after birth.
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Meningocele: Protrusion of the meninges through a vertebral defect, forming a fluid-filled sac.
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Myelocele: Exposure of nerve tissue on the back's surface without skin or meninges.
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Meningomyelocele: A sac containing nervous tissue protrudes through the vertebral defect.
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Encephalocele: A sac with brain tissue protrudes from the skull.
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How can neural tube defects affect a person's body and health?
Neural tube defects, arising from incomplete closure during early fetal development, can lead to various health issues. Spina bifida, a common defect, occurs when the vertebrae don't fully form around the spinal cord, potentially causing nerve damage.
Different types of spina bifida vary in severity. Spina bifida occulta may have no noticeable impact, while more severe forms can result in paralysis and impaired bladder and bowel function. Myelocele involves exposed nerve tissue, meningocele features a fluid-filled sac, and meningomyelocele includes both. Encephalocele, another defect, involves a sac of brain tissue protruding from the skull, with outcomes varying based on the amount of tissue involved. Hydrocephalus, fluid accumulation in the brain, can also occur, potentially causing brain and skull enlargement.
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What factors can increase the risk of developing neural tube defects?
Neural tube defects, congenital disabilities of the brain and spinal cord, arise from incomplete neural tube closure during early embryonic development.
Several factors can elevate the risk of neural tube defects:
* Folic acid deficiency Insufficient folic acid intake during early pregnancy increases the risk of neural tube defects. Supplementation is recommended for women who may become pregnant.
* Alcohol Consumption Heavy alcohol consumption during pregnancy can cause fetal alcohol syndrome and may increase the risk of neural tube defects.
* Diabetes Untreated diabetes in pregnant women is associated with a higher incidence of fetal defects. Gestational diabetes also poses risks to the fetus.
* Weight Being underweight or overweight before pregnancy can increase the risk of complications and birth defects.3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
neural tube defect, any congenital defect of the brain and spinal cord as a result of abnormal development of the neural tube (the precursor of the spinal cord) during early embryonic life, usually accompanied by defects of the vertebral column or skull. In normal development a plaque of nerve tissue forms along the surface of what will become the back of the fetus; this tissue folds into a closed tube that develops into the structures of the central nervous system. Malformations occur because the tube fails to close properly, because parts of it are missing, or because part of the tube is blocked.
Failure of the tube to close in some degree is the basic defect underlying spina bifida, meningocele, myelocele, and meningomyelocele. Spina bifida is caused by the failure of the vertebrae to form over the back of the spinal cord, leaving the nerve unprotected. It usually occurs in the sacral or lumbar regions at the base of the spine, the final section of the neural tube to close. All the other neural tube defects in this group are particular forms of spina bifida.
In spina bifida occulta, or hidden spina bifida, the vertebrae fail to completely enclose the spinal cord, but the latter is normal in form and is covered by the skin of the back. This form of the defect has no effect on body functions and may go undetected for life.
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In more serious forms of spina bifida, part of the spinal cord is left uncovered by the skin or actually protrudes from the spinal column. In myelocele, the spinal cord is exposed so that nerve tissue lies exposed on the surface of the back without even a covering of skin or of the meninges, the membranous tissue surrounding the brain and spinal cord. Meningocele occurs when these meninges protrude through the vertebral defect, forming a fluid-filled sac. Meningomyelocele is a compound defect in which the protruding sac contains some nervous tissue as well. If any of these defects communicate with the central canal of the spinal cord, the prefix syringo- is added to the name; hence, a syringomyelocele is an open defect containing nerve tissue and opening into the spinal cord.
Children born with the more serious forms of spina bifida experience paralysis in those parts of the body below the site involved. The legs may be completely paralyzed, and bladder and bowel functions may be absent or impaired. Spina bifida defects can be treated surgically early in life; success is greatest with meningocele, because paraplegia or other disabilities associated with myelocele can complicate therapy.
Another form of open neural tube defect, encephalocele, occurs when a meningeal sac containing brain tissue protrudes from the skull. The outlook for affected individuals depends on the amount of nervous tissue involved.
Hydrocephalus, an accumulation of fluid within the brain, occurs when normal passages for the cerebrospinal fluid that fills the neural tube are partially or completely blocked. The brain and skull are greatly enlarged because of the fluid pressure. Hydrocephalus occurs in one or two of every 1,000 live births and was routinely fatal until surgical techniques for shunting the excess fluid out of the central nervous system were developed; today it need not cause any intellectual impairment if recognized and treated promptly.
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