Spina bifida, which literally means "cleft spine," is characterized by the incomplete development of the brain, spinal cord, and/or meninges (the protective covering around the brain and spinal cord). It is the most common neural tube defect in the United States, affecting 1,500 to 2,000 of the more than four million babies born each year.
Understanding the Neural Tube
The human nervous system develops from a small, specialized plate of cells along the back of an embryo. Early in development, the edges of this plate begin to curl up toward each other, creating the neural tube, which is a narrow sheath that closes to form the brain and spinal cord of the embryo. As development progresses, the top of the tube becomes the brain and the remainder of the tube becomes the spinal cord. This process is usually complete by the 28th day of pregnancy. However, if problems occur during this process, they can result in brain disorders called neural tube defects. Spina bifida is a neural tube defect that is caused by the failure of the fetus's spine to close properly during the first month of pregnancy.
The three most common types of spina bifida are:
- Myelomeningocele, the most severe form, in which the spinal cord and its protective covering (the meninges) protrude from an opening in the spine (see Myelomeningocele)
- Meningocele, in which the spinal cord develops normally but the meninges protrude from a spinal opening (see Meningocele)
- Spina bifida occulta, the mildest form, in which one or more vertebrae are malformed and are covered by a layer of skin (see Spina Bifida Occulta).
Spina bifida may also cause bowel and bladder complications, and many children with spina bifida will have hydrocephalus
, which is an excessive accumulation of cerebrospinal fluid in the brain.