What are neural tube defects?
Neural tube defects are defects which affect the neural tube and is the most common type of CNS malformation. As the picture alongside demonstrates, the neural tube develops as the baby grows within the womb. The inside portion of the neural tube forms the ventricular system, and the outside portion forms the brain and the spinal cord. In normal circumstances, the neural tube closes and seals itself before birth, but it may either fail to close or may reopen after closing because it is not sealed properly.
What are the types of tissues affected by neural tube defects?
There are several types of tissues which can be affected by neural tube defects: they include neural tissue, bone, soft tissues and the meninges. The most common neural tube defects involve the spinal cord and the type of side effects are dependent on the level at which the defect presents itself. In general, the higher up the spinal cord, the worse the prognosis.
Because the neural tube develops during pregnancy, is there anything that a pregnant woman could do to prevent these defects from happening to their unborn baby?
Yes, there is. The main risk factor for the development of neural tube defects is a lack of folate (vitamin B12) in the diet. Dietary sources of folate include the following:
- Legumes such as lentils as pictured alongside are the richest source
- Foliage such as spinach and collard greens
- Herbs such as parsley
What are the types of neural tube defects?
There are four types of neural tube defects: they include: spina bifida, myelomeningocele, anencephaly and encephalocele.
Spina bifida involves damage to both the brain and the spinal cord. During pregnancy, the vertebrae of the spine do not close and therefore they are left exposed. At birth, the nerve is exposed to the outside environment rather than continuing on down the spinal cord towards the extremities. This can affect organs, muscles and bodily functions such as urination and defecation (passing of urine and faeces) below the exposed site, because the nerve signals become interrupted. The severity of the condition depends on the location of the exposed site: spina bifida becomes more severe the further up the spinal cord.
Spina bifida may present with or without a meningocele or with a myelomeningocele. A meningocele is similar to a herniated muscle, where the meninges pushes out from the spinal cord and it leads to a cyst with cerebrospinal fluid (CSF).
A myelomeningocele is a meningocele with an extension of CSF tissue. This most commonly happens with the lumbosacral region. This location is the junction between the lumbar and sacral spine. The problems that I mentioned above regarding spina bifida are further complicated by infections which can occur on the skin in the exposed area: because the skin is thinner in this area than on the rest of the back, it is therefore more likely to become wounded.
Anencephaly is defined by the absence of a major portion of the scalp, the skull and the brain due to a malformation in the front end of the neural tube. The remaining areas of the brain and the head are left exposed as a result. This condition can develop within the fourth to fifth week of pregnancy, and tragically, most babies end up still-born as a result. For those that survive, they are unable to feel pain, have no conscious awareness of their surroundings, and are blind and deaf.
Encephaloceles are similar to meningoceles, except these protrusions occur through the skull inside of the spine. It most likely occurs within the occipital region of the brain, but it can also happen in the anterior (front) areas.