Myelomeningocele in spina bifida. Child with a myelomeningocele, the most severe form of the birth defect spina bifida. This condition arises from the incomplete closure of the neural tube during embryonic development, preventing the bones of the spine fusing properly. If the gap in the vertebral column is large enough, part of the spinal cord and its surrounding membranes (meninges) can protrude outwards. The resulting sac (red, centre) is known as a myelomeningocele. It can cause paralysis in limbs and areas below the defect. Treatment involves surgery to correct and repair the defect.