Spina bifida is a developmental congenital disorder caused by the incomplete closing of the embryonic neural tube. Some vertebrae overlying the spinal cord may not be fully formed and remain unfused and open. If the opening is large enough, this allows a portion of the spinal cord to protrude through the opening in the bones. There may or may not be a fluid-filled sac surrounding the spinal cord.
Spina bifida malformations fall into three categories:
spina bifida cystica with meningocele
Meningocele is less severe than myelomeningocele and is characterized by the herniation of the meninges, but not the spinal cord, through the opening in the spinal canal.
spina bifida cystica with myelomeningocele
Myeolomeningocele also involves herniation of the meninges as well but also involves the spinal cord through the opening and can be considered serious due to the involvement of the spinal cord.
Spina bifida occulta
In this type of neural tube defect, the meninges do not herniate through the opening in the spinal canal like that which occurs in meningocele and myelomeningocele. By definition, spina bifida occulta means hidden split spine and the most frequently seen form of spina bifida occulta is when parts of the bones of the spine, called the spinous process, and the neural arch appear abnormal, usually shown on a radiogram, but is generally harmless and causes no impairment. Most times the spinal cord and spinal nerves are not involved in this birth defect. The risk of recurrence in those who have a first degree relative (e.g. parent, sibling) is five to ten times greater than that of the general population.