Neural Tube Defects
Abnormal development of the neural tube in the early stages of embryonic development results in various defects of the brain and the spinal cord which originate from the tissues of the neural tube.
- Severe nerve damage, often leading to mental retardation, learning disabilities, lack of bowel control, paralysis and even death may result from neural tube defects.
- A blood test for alpha fetoprotein, amniocentesis and ultrasound scan can diagnose the presence of neural tube defects in the fetus.
- Taking folic acid supplements prior to and in the first three months of pregnancy significantly reduces the risk of neural tube defects.
- Surgical correction of neural tube defects is required in most cases.
During embryonic development, the neural tube develops from the folding over of a groove into a tube-like structure. The brain, spinal cord, and their protective coverings called meninges, develop from the different tissue layers of the neural tube. When abnormalities occur in the development of the neural tube, it affects the development of these structures which originate from it. Complete absence of brain may result from a severe defect in the neural tube development. This condition, known as anencephaly, is always fatal. Incomplete closure of the neural tube may result in abnormalities of various degrees. In mild cases, the open channel may cause only a bone defect such as spina bifida occulta. In this condition, the spinal cord and the meninges covering it are intact, but the bony tissue that makes up the spine does not close completely. It does not cause any symptoms in infants. In some cases of open channel defects, a meningocele may protrude through the opening. If part of the brain tissue protrudes along with the meninges, it is known as a meningoencephalocele. In a similar condition called meningomyelocele, the spinal cord tissue and the meninges protrude. When the brain tissue is exposed without the meninges, it is called an encephalocele and the protrusion of the spinal cord without the meninges is termed myelocele. The protrusion of the brain tissue or the spinal cord tissue through incompletely closed openings results in greater damage to them.
Abnormalities such as tufts of hair, small tissue masses, and openings in the surface of the skin known as dermal sinuses, may be present at the lower back of infants who have a condition called occult spinal dysraphism. Dark pigmented patches known as flame nevus and hemangioma may occur in less serious cases. If the spinal cord is exposed to the outside through an opening, the chances of bacterial infections developing and leading to meningitis are very high. Gradual damage to the spinal cord may occur due to continued exposure. Sometimes, a fatty tumor known as lipoma may develop on the spinal cord, which damages the nerves in the spinal cord. It is essential that any opening exposing the spinal cord tissues or the meninges should be surgically closed to prevent further damage. Infants born with these visible abnormalities should have further investigations such as an ultrasound scan or an MRI scan to examine the defects in the underlying spinal cord and associated tissues.
Some neural tube defects occur due to genetic abnormalities. The defects begin to develop in the very first weeks of pregnancy, even before pregnancy is recognized by the mother. The symptoms of neural tube defects depend on the damage caused to the brain and spinal cord. Meningomyeloceles and meningoencephaloceles are conditions resulting in significant disability in the infant. Fluid accumulation in the brain, known as hydrocephaly, may develop in some cases. Bone and joint defects, lack of sensation of certain body parts and the skin, lack of control over bowel movements and urination, learning disabilities, and even paralysis, may be caused by neural defects.
Prenatal testing of the amniotic fluid or mother’s blood can detect neural tube defects present in the fetus. When alpha-fetoprotein is present in high levels, it is an indication of abnormalities in neural tube development. The defects can be detected by an ultrasound scan done later in pregnancy too. Folic acid supplements taken prior to, and in the first trimester of pregnancy can significantly reduce the risk of neural tube defects in the infants. All women who are likely to conceive should take folate supplements as a precautionary measure. Surgical closure of the defect after birth is the treatment for this condition.
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Yasser Elnahas
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