Spina bifida refers to incomplete development of the spinal cord, the meninges (the protective covering around the brain and spinal cord) and/or vertebrae with incomplete fusion of these structures such that they do not completely close over the posterior aspect of the lower spine.
The human nervous system develops during the first month of pregnancy. It begins as a small plate of specialized cells along the embryo’s back. As the edges of this sheet begin to curl toward each other, they form the neural tube – a slender sheath that closes to form the embryo’s brain (the top of the tube) and spinal cord (the rest of the tube). This development is generally finished by the fourth week of pregnancy. If any problems arise during this process, the consequence may be a set of disorders known as neural tube defects. One of these defects is spina bifida, the most common kind of neural tube defect. With spina bifida, the tissues that fold to form the neural tube do not close or do not stay entirely closed. This leaves an opening in the vertebrae – the small bones that form the backbone and encircle and protect the nerves of the spinal cord. This defect happens just a few weeks (21 to 28 days) after conception, typically before a woman even knows that she is pregnant. Other neural tube defects include anencephaly, a condition in which the portion of the neural tube that will become the cerebrum does not close, and encephalocele, which results when other parts of the brain remain unfused.
The location and how much spinal column stays open influence the extent of nerve damage. The most common location of the malformations is the lumbar and sacral areas. The defect may result in loss of sensation and major muscle weakness in the lower portion of the body. The degree of paralysis depends on which section of the spinal cord is involved. The higher the defect is found on the body, the more extensive the paralysis.
Abnormal brain development and blockage of the drainage of fluid that circulates around and through the ventricular system of the brain (the cerebral spinal fluid) can be associated with spina bifida. The blockage of CSF drainage can result in a large buildup of pressure in the brain. These factors may cause additional developmental disability.
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Spina Bifida Associaton
March of Dimes