Neural tube defect: an opening in the spinal cord or brain that occurs very early in human development. the neural tube does not close completely.
Spina bifida occulta: a developmental birth defect involving the neural tube: incomplete closure of the
neural tube. The least dangerous form of spina bifida, in which bones in the spine fail to close. However, the skin is intact and there is no sac visable on the back .
Meningocele: a congenital anomaly of the central nervous system in which a sac protruding from the brain or the spinal meninges contains cerebrospinal fluid but no nerve tissue.
Myelomeningocele: a congenital defect of the central nervous system in which a sac containing part of the spinal cord, cerebrospinal fluid and its meninges protrude through a gap in the vertebral column; frequently accompanied by hydrocephalus and mental retardation.
Spina bifida occulta:
Normal closed vertebrae canal and presence of posterior spinous process: