Developmental abnormalities of the brain and spinal cord and their protective coverings
- Present from birth
- Sometimes run in families
- Taking certain drugs during pregnancy is a risk factor
- Gender is not a significant factor
Neural tube defects occur during pregnancy as a result of abnormalities in the embryo’s development. The neural tube, which develops along the back of the embryo by about the third week of pregnancy, later becomes the brain and spinal cord and their coverings. If this tube fails to close completely, defects in any of these body parts can result.
Most commonly, the spinal cord and vertebrae are affected, causing a disorder known as spina bifida. The effects of spina bifida vary from dimpling or a tuft of hair at the base of the spine and a minor abnormality of the vertebrae to complete exposure of part of the spinal cord, known as a myelomeningocele. Rarely, the brain and skull are affected. Since the discovery in 1992 that folic acid taken during early pregnancy provides protection against neural tube defects, spina bifida is becoming less common.
The cause of neural tube defects is not fully understood, but they tend to run in families, which suggests genetic factors. Certain types of anticonvulsant drug, such as sodium valproate, are associated with neural tube defects if they are taken during pregnancy.
What are the symptoms?
The symptoms of a neural tube defect depend upon its severity. Often, there are no obvious symptoms, and spina bifida may be diagnosed only if minor conditions, such as backache, occur in adult life. The symptoms of a severe defect will become apparent at varying stages in childhood; they mainly affect the lower body and include:
Paralysis or weakness of the legs.
Absence of sensation in the legs.
Abnormalities in the functioning of the bladder and bowels.
About 8 in 10 children who have severe spina bifida also have a build-up of fluid within the brain (see Hydrocephalus). Occasionally, learning difficulties may develop. In some cases, neural tube defects lead to meningitis, a serious infection of the membranes covering the brain and spinal cord (see Meningitis in children).
How is it diagnosed?
Most neural tube defects are detected during routine antenatal blood tests and ultrasound scanning (see Ultrasound scanning in pregnancy). If a neural tube defect is detected, the implications will be explained to the parents and they may be asked whether they wish to continue with the pregnancy.
What is the treatment?
If the defect is minor, no treatment is necessary. However, if a baby has a serious defect, he or she is likely to require surgery shortly after birth. If hydrocephalus is present, a drainage tube will probably be inserted to release excess fluid and also to prevent further fluid build-up in the cavities of the brain (see Shunt for hydrocephalus).
Even with surgery, children born with severe defects will be permanently disabled and need lifelong care. Practical and emotional support will be provided for the whole family. An affected child will often need regular physiotherapy to keep as mobile as possible, and some children may need a wheelchair. Training in the regular use of a urinary catheter may be necessary for children who cannot pass urine normally (see Bladder catheterization). Some children may need special teaching. Many families find support through joining a self-help group.
Can it be prevented?
You can reduce the risk of your baby having a neural tube defect by taking the recommended dose of folic acid supplements before conception and during the first 12 weeks of pregnancy. Your doctor may recommend that you take a higher dose if you already have an affected child. If a close blood relative has a neural tube defect, a couple who are planning a pregnancy may wish to seek genetic counselling because their children may be at increased risk of the disorder.
What is the prognosis?
Children with only minor defects have a normal life expectancy. If symptoms affecting posture develop, there may be an increased risk of developing osteoarthritis. Children with extensive damage to the brain and/or the spinal cord may have a reduced life expectancy.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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