Spina bifida is a disorder caused by the incomplete closing of the embryonic neural tube. Some vertebrae overlying the spinal cord are not fully formed and remain open. If the opening is large enough it allows a portion of the spinal cord to protrude through the opening in the bones. Spina bifida malformations fall into three categories: spina bifida occulta, meningocele, and myelomeningocele. Myelomeningocele is the most significant and common form.