Neural Tube Defects

The brain and spinal cord develop as a groove that folds over to become a tube (the neural tube). Layers of tissue that come from this tube normally become the brain and spinal cord and their covering tissues, including part of the spine and the meninges. Sometimes the neural tube does not develop normally, which may affect the brain, spinal cord, and meninges. In the most severe form of neural tube defect, the brain tissue may fail to develop (anencephaly); this defect is fatal. Another type of defect results when the neural tube fails to close completely and remains an open channel. In its mildest form, an open channel defect may affect only bone; for example, in spina bifida occulta (which means hidden spine split in two), the bony spine fails to close, but the spinal cord and meninges are unaffected. This common abnormality causes no symptoms. Sometimes, a meningocele develops in which the meninges and other tissue, such as brain tissue (meningoencephalocele) or spinal cord tissue (meningomyelocele), can protrude out of the opening. Sometimes the meninges are not involved when tissue protrudes from the brain (encephalocele) or spinal cord (myelocele). Damage to brain or spinal cord tissue is much more likely when tissue protrudes than when it does not.