Neural Tube Defects
Neural Tube Defects are conditions that arise from failure of the developing neural tube to close during foetal life, which usually occurs during the first 28 days after conception. They vary in severity: spina bifida occulta is a condition where there is failure of fusion of the bony arch covering the spinal cord in the small of the back. It often causes no symptoms, and may simply be seen on X-ray as an incidental finding. Sometimes there is an overlying skin dimple with accompanying hair growth. A meningocoele means that not only has the vertebral arch failed to fuse to protect the spinal cord, but its lining - the meninges - is protruding to produce a bulge containing CSF, the fluid that bathes the central nervous system; a meningomyelocoele is the name given to the situation where there is no skin covering the nervous tissue, which lies exposed at the bottom of the back at birth. The degree of disability depends on the level at which the abnormality arises, but may involve muscle, bladder and bowel paralysis. Failure of fusion of the top of the neural tube, rather than the bottom, produces either an encephalocoele, where there is protrusion of brain tissue through the middle of the skull, or anencephaly, which is the lack of development of the brain and most of the head - usually leading to stillbirth.
These defects can often be detected by ultrasound scanning during pregnancy, and there is a blood test available performed at about 16 weeks of pregnancy, which might indicate a foetus at risk. Their cause is unknown, but the incidence is declining, indicating that one contributory factor might be maternal nutrition.
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