Normally, during the first month of a pregnancy, the two sides of the spine join together to cover the spinal cord, spinal nerves and meninges. Spina bifida is a developmental congenital disorder caused by incomplete closing of the embryonic neural tube. Some vertebrae overlaying the spinal cord are not fully formed and remained 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 four categories: spina bifida occulta, spina bifida cystica (myelomeningocele, meningocele and lipomeningocele