Spina Bifida is a neural tube defect, occuring in 1 out of every 1,000 American births, and one out every 750 Canadian babies are born with it. In Australia approximately 1 in 500 pregnancies involves a neural tube defect and about half of these have Spina Bifida.
Spina Bifida occurs within the first four weeks of pregnancy for reasons unknown. The embryo's neural tube, developing into the brain, spinal cord and vertebral column, fails to form properly, resulting in permanent damage to the spinal cord and nervous system . The central nervous system begins to develop from the layer of cells, known as the ectoderm, from which the brain and spinal cord develop in the third week after fertilization, when the embryo is only 15mm long. Prior to this the ectoderm resembles a flat group of cells running down the middle of the embryo. This begins to change and folds to form a groove. The edges eventually come together and form a neural tube, which develops into the spinal cord and brain. Once the neural tube closes it sinks into the embryo becomes covered by a layer of skin. The spinal vertebrae, or bony covering, then begins to form around the tube. Normally the closure of the neural tube occurs around the 30th day of pregnancy. If the neural tube fails to close properly, a neural tube defect occurs.
In Spina Bifida, the outer part of the vertebrae, or bones of the spine, are not completely joined. In more severe forms, the spinal cord and covering, known as the meninges, protrude through the opening. In this case, a few days after birth, surgery is performed at the site of the lesion on the back to ensure a good skin covering, and prevent infection.
SPINA BIFIDA OCCULTA is the least serious type, whereby the outer part vertebrae are not completely joined. The spinal cord and meninges are undamaged, and hair is often at the defected site. It means a hidden split in the spine, where any associated abnormalities are covered by skin. The split in the vertebrae is so small the spinal cord does not protrude, and there is little or no damage. The skin at the site may be normal, or may have some hairs growing from it, there may be a dimple in the skin, or a birthmark. Someone with Spina Bifida Occulta may not have any problems, and would be unaware of its presence unless a back xray was taken.
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