Neural tube defects (NTDs) are one of the most common birth defects, occurring in approximately one in 1,000 live births in the United States. An NTD is an opening in the spinal cord or brain that occurs very early in human development.
There are two types of NTDs: open, which are more common, and closed. Open NTDs occur when the brain and/or spinal cord are exposed at birth through a defect in the skull or vertebrae.Open NTDs are anencephaly, encephaloceles,hydranencephaly, iniencephaly, schizencephaly,and spina bifida. Rarer types of NTDs are called closed NTDs. Closed NTDs occur when the spinal defect is covered by skin.Common examples of closed NTDs are lipomyelomeningocele, lipomeningocele, and tethered cord.
Spina Bifida is further divided into two subclasses, Spina Bifida Cystica and Spina Bifida Occulta.
Spina Bifida Cystica includes meningocele and myelomeningocele. Meningocele is less severe and is characterized by herniation of the meninges, but not the spinal cord, through the opening in the spinal canal. Myeolomeningocele involves herniation of the meninges as well as the spinal cord through the opening.
In Spina Bifida Occulta the meninges do not herniate through the opening in the spinal canal.