Neural tube defects involve abnormal closure of the neural tube, which usually causes abnormal development of the spine, spinal cord, skull, or the brain. Neural tube defects involving the spine are also called spina bifida. Spina bifida may be asymptomatic, with only a small malformation of the spine that spares the spinal cord, which is called spina bifida occulta. The most severe kind of spina bifida is called myelomeningocele, in which part of the spinal cord is outside of a defect in the spine, usually causing a severe myelopathy syndrome of that area. Neural tube defects may also involve the skull, with variable severity, the most severe being anencephaly, in which the cerebrum does not form, although brainstem and spinal cord functions may be present. The most severe type of neural tube defect involves little or no development of central nervous system tissue, which is not compatible with life.
The cause of most neural tube defects is unclear, but there is an association with low intake of the vitamin folate by the mother during neurulation. The disorder is congenital since neurulation occurs early in development, but the resulting syndrome may gradually become apparent in the first few years of life with delays in milestones. The course usually consists of stable abnormalities from the malformed tissue after development.