Neural Tube: What is it? (Causes of Abnormalities and Treatment)

neural tube
Contents

Article reviewed and approved by Dr. Ibtissama Boukas, physician specializing in family medicine

The fertilized egg gives theembryo which then forms the fetus. In fetus form, the baby's body is already made up of different parts with a beating heart and developing brain. the brain development depends on primitive nervous system of the embryo called "neural tube ". This is formed 4 weeks after fertilization. In this article, let's take a look at this structure and the anomalies associated with it.

What is a neural tube?

Le neural tube corresponds to primitive nervous system in chordate embryos. They are biological groups of animals with a backbone. It constitutes the central nervous system in the fetus.

It is formed during the stage of neurulation. This is the phase during which the nervous system appears in the dorsal region of an embryo.

Anatomy and embryology of the neural tube

Le neural tube is the result of the invagination, convergence and fusion of the edges of the neural plate. This plate is obtained from the junction of several cells. It folds in on itself to form the neural tube.

  • On its upper part there is the neural crest which gives rise to different cells such as intestinal neurons and the precursors of melanocytes (cells that pigment the skin).
  • On its anterior end, it widens into 3, then into 5 vesicles to form the brain (brain).
  • The remaining part forms the spinal cord. Subsequently, the ventral roots of the spinal nerves will emerge from the latter. These roots are responsible for the innervation of the muscles. To this end, they pass through the somites and vertebrae, passing through the vertebral openings.

It is thanks to the neural tube cavity that the cerebral canal and ventricles can contain cerebrospinal (or cerebrospinal) fluid. This liquid has the role of protecting the central nervous system and nourishing the nerve cells. the ependymal canal, which contains it, is located in the center of the spinal cord.

The neural tube openings usually close around the sixth week of embryonic development.

What are neural tube defects?

The neural tube defects are due to a failure to close or develop of this structure during pregnancy.

In general, they are rare. However, they represent the majority of abnormalities that affect the brain and spinal cord.

Several factors can be the cause of these malformations. Until now, no factor could be identified with precision.

The risk of neural tube defects may increase especially when the mother:

  • has a vitamin B12 deficiency;
  • is on insulin treatment for diabetes;
  • takes antiepileptic drugs;
  • suffers from obesity.

Neural Tube Malformation: Abnormalities of the Brain

There are different kinds of brain abnormalities.

Encephalocele

THEencephalocele is a malformation that results in a herniation of the brain. Brain tissue sprouts through cracks in the skull. It can be accompanied by various neurological disorders as well as other conditions such as hydrocephalus (critical accumulation of cerebrospinal fluid) or a microcephaly (a head smaller than normal).

Anencephaly

THEanencephalic is the most severe of brain malformations. It corresponds to a non-development of brain tissue. In other words, a large part of the brain is missing. This often results in deafness, blindness (loss of vision), unconsciousness and insensitivity to pain. Usually the child is either stillborn or dies within hours or days of birth.

Hydranencephaly

This brain abnormality is characterized by the absence of the hemispheres of the brain. Instead, there are sacs filled with cerebrospinal fluid. Hydranencephaly can cause seizures and lead to hydrocephalus. A child affected by this anomaly may be blind, deaf or paralyzed. He may also suffer from intellectual and respiratory disorders.

Arnold-Chiari malformation 

They are talking about Arnold-Chiari malformation when part of the brain protrudes into the spinal canal. This causes vomiting, fever, hoarseness, difficulty swallowing and sometimes, hydrocephalus.

To know everything about Arnold-Chiari malformation, see the following article.

Neural Tube Malformation: Spinal Cord Abnormalities

The spinal cord abnormalities are known as " spina bifida ". They result in a abnormal closure of the neural tube at the spine.

In general, the spina bifida is manifested by:

  • paralysis of the lower limbs;
  • hydrocephalus;
  • learning disabilities;
  • epileptic seizures;
  • urinary or faecal incontinence;
  • in the long term, kidney failure that can lead to death.

Depending on its severity, there are 2 different types.

Spina bifida occulta

Le spina bifida occulta is a mild disorder that does not affect the spinal cord or meninges. It only affects the bones of the spine. The breach in the vertebrae hides under a layer of skin, giving a normal appearance.

At birth, the newborn may show no sensory or motor disturbances. However, later in childhood and even in adulthood, minor neurological deterioration may appear gradually.

Spina bifida cystica

Le spina bifida cystica is a serious disorder that affects the tissues of the meninges and spinal cord. The latter are bare in the opening of the vertebrae. This type of spina bifida can cause various malformations:

  • myelocele (protrusion of spinal cord tissue);
  • myelomeningocele (eminence of the meninges and tissues of the spinal cord);
  • meningocele (protrusion of the meninges);
  • an encephalocele;
  • meningoencephalocele (protrusion of the meninges and brain tissue).

To know everything about spina bifida and its treatment, see the following article.

Treatment and prevention of neural tube defects

How to detect neural tube defects?

La detection of neural tube defects can be done both during pregnancy and after birth.

  • During pregnancy: an ultrasound, combined with blood tests, makes it possible to define the probability of damage to the baby. If necessary, amniocentesis (analysis of amniotic fluid) may be necessary.
  • After birth: a clinical examination can detect a neural tube defect. Myelomeningocele and meningocele are very visible. As for spina bifida occulta, it can be detected through a dimple in the skin or a tuft of hair. Additional imaging tests may be needed to clarify the diagnosis.

How to treat neural tube defects?

The neural tube defects corrected only by surgery.

  • For encephaloceles, the intervention consists of replacing the tissues in the skull.
  • For hydrocephalus, the intervention is based on the extraction of excess cerebrospinal fluid using a probe.
  • For spina bifida, it cannot be actually cured. Some complications can be reduced with different surgeries. This is also the case for meningocele and myelomeningocele.

However, some abnormalities are intractable by surgery. This is the case of :

  • anencephaly: it is always fatal;
  • hydranencephaly: most affected babies do not survive. Only a few manage to survive for a few years.

How to prevent neural tube defects?

La prevention of neural tube defects begins 2-3 months before conception. It continues during the first trimester. You can even continue until breastfeeding. This prevention consists of taking folic acid (vitamin B).

  • If you are in good health or suffer from obesity, diabetes or epilepsy: take 0,4 to 1 mg daily.
  • If you have previously given birth to a baby with a congenital malformation (anencephaly, cleft lip, structural heart disease, etc.): take 5 mg per day until 10 to 12 weeks of pregnancy. After that, take a normal dose.

In any case, if you plan to have a baby, it is strongly recommended to consult a gynecologist even before conceiving it.

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