Neural tube defects affecting the spinal cord

Dysraphias of the spinal cord are also called spina bifida. It is assumed that the earlier the defect takes place, the more severe the disturbance. The following section discusses several forms of spina bifida in increasing degrees of severity. In spina bifida occulta, a gap in only one or more vertebral arches is present. Both the spinal cord and the meninges are located within the vertebral canal and are generally normal. The skin above the vertebral arches is usually closed. Occasionally, the area that is affected has a tuft of hair.
The severe forms are called spina bifida aperta. In meningocele, more than two vertebral arches exhibit a defect. The meninges protrude outwards like a hernial sac covered by skin. Meningomyelocele is the form in which the hernial sac includes both meninges and spinal cord tissue. In most cases, it occurs in the lumbar or lumbosacral region. The most severe  but rarest form of spina bifida aperta is myeloschisis. In this case, the neural tube fails to close. Nerve tissue is exposed at the surface and can develop tumours. Myeloschisis may occur in the cervicothoracic as well as in the thoracolumbar region.