Spina bifida (Latin: "split spine") is a developmental birth defect involving the neural tube: incomplete closure of the embryonic neural tube results in an incompletely formed spinal cord. In addition, the bones of the spine (vertebrae) overlying the open portion of the spinal cord do not fully form and remain unfused and open. This allows the abnormal 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 open spinal cord. Other neural tube defects include anencephaly, a condition in which the portion of the neural tube which will become the cerebrum (front of the brain) does not close, and encephalocele, which results when other parts of the brain remain unfused.
Spina bifida malformations fall into three categories: spina bifida occulta, spina bifida cystica (myelomeningocele), and meningocele. The most common location of the malformations is the lumbar and sacral areas of the spinal cord. Myelomeningocele is the most significant form and is that which leads to disability in most affected individuals. The terms spina bifida and myelomeningocele are usually used interchangeably.
Spina bifida can be surgically closed after birth, but this does not restore normal function to the affected part of the spinal cord and an individual with this condition will have dysfunction of the spinal cord and associated nerves from the point of the open defect and below. Intrauterine surgery for spina bifida has also been performed and the safety and efficacy of this procedure is currently being investigated with an NICHD-funded grant. The incidence of spina bifida can be decreased up to 70% when daily folic acid supplements are taken prior to conception.