What Are Neural Tube Defects?

Neural tube malformation, also known as neural tube defect, is a serious malformed disease. The neural tube is the central nervous system of the fetus. From the 15th to the 17th day of the embryo, the nervous system begins to develop. By the 22nd day of the embryo, the two sides of the neural fold begin to move closer to each other to form a tube, called the neural tube. Its front end is called the anterior neural tube hole. The caudal end is called the posterior foramen of the neural tube. On the 24th, 25th, and 26th days, the anterior foramen and the posterior foramen are closed successively. Fetal neural tube defects are mainly manifested as anencephaly, cerebral bulge, cerebrospinal membrane bulge, spina bifida / recessive spina bifida, cleft lip and palate. According to the birth defect monitoring data of 29 provinces, municipalities and autonomous regions from 1986 to 1987, the incidence of neural tube defects in China is about 2.74 , and it is higher in the north than in the south and higher in the rural than in the cities. Babies born in autumn and winter are more likely to be born in spring and summer.

Basic Information

nickname

Neural tube defects

English name

neural tube defects

Visiting department

Pediatrics

Common causes

Genetic factors, vitamin B12 and folic acid, severe vomiting in early pregnancy

Common symptoms

Developmental deformities such as anencephaly, encephalocele, cerebrospinal meningocele, spina bifida / recessive spina bifida, cleft lip and palate

Causes of neural tube defects

1. Genetic factors: anencephaly children and spina bifida are polygenic, and those with a history of childbirth of this disease have an increased risk of recurrence in the next child. The expression or mutation of many types of genes are related to the development of the nervous system and neural tube defects: development regulatory genes and transcription factor genes; proto-oncogenes and tumor suppressor genes; growth factors and their receptor genes; protein kinase C related Genes; homocysteine metabolism-related genes; other genes: cytoskeleton and cell junction genes.

2. Reduced chorionic gonadotropin production in early pregnancy or embryonic recipient cells are not sensitive to this hormone can cause neural tube defects. Female embryos have higher requirements for this hormone than males, so women with brainless children account for about 70% of total brainless children, and women with spina bifida account for 55% to 60%.

3. Vitamin B ₁₂ and folic acid deficiency can affect neural tube closure.

4. Severe vomiting during early pregnancy or pregnancy with diabetic ketoacidosis and other internal environment abnormalities can affect neural tube closure.

5. Others: Those with high fever above 38.5 in early pregnancy and lasting for more than one week, the incidence of fetal neural tube malformations in pregnant women who work in high temperature environment for a long time increases; improper medication in early pregnancy can also cause neural tube insufficiency.

Clinical manifestations of neural tube defects

The central neural tube is where the embryo develops into the brain, spinal cord, back of the skull, and spine. If the central neural tube fails to develop properly, defects may occur in these areas when the baby is born.

Anencephaly and spina bifida are deformities that occur during the development of the fetus. The so-called "neural tube malformation" refers to anencephaly, cerebral bulge, cerebrospinal membrane bulge, spina bifida / recessive spina bifida, cleft lip and Developmental deformities such as cleft palate.

Neural tube malformations in fetuses are caused by excessive amniotic fluid during pregnancy because the fetus cannot swallow amniotic fluid before birth.

Anencephaly is an incomplete head. Children with anencephaly deformities have not fully developed their heads, and their skin, craniums and even their brains have not developed well. Such fetuses usually die in the womb before birth, forming a "stillbirth" or "stillbirth". Even if they are born, they will die within a short period of time, and almost no case survives.

Spina bifida means that the spine bones are not well developed, causing the spinal cord, which should have been protected by spinal bones, to protrude or be exposed to the body surface. Spina bifida can be completely open and can be recognized by the naked eye as soon as the baby is born; it can also be recessive. As the child gets older, it produces different symptoms. At this time, X-ray diagnosis is needed. The most common defect is spina bifida, which can affect one or more spines. Symptoms of this disease include: weak or paralyzed legs, deformed legs, incontinence of the urine, no pain in the skin below the lesion level, sometimes hydrocephalus, and in some cases, learning disabilities.

Neural tube malformation

Prenatal diagnostic tests:

1. Non-invasive method

(1) Fetal morphological observations such as ultrasound, X-rays, and magnetic resonance can detect anencephaly and spina bifida deformities.

(2) Biochemical and fetal tissue analysis Maternal serum biochemical indicators, such as alpha-fetoprotein, chorionic gonadotropin, free estradiol, and pregnancy-related proteins. Analysis of embryo cell enrichment in maternal blood. Analysis of embryo cell enrichment in cervical lavage fluid.

2. Intrusive methods

Amniocentesis, villus biopsy, fetal blood analysis, fetal skin, liver, and muscle biopsy.

Diagnosis of neural tube defects

1. The disease is diagnosed before birth

For pregnant women with the following factors, prenatal genetic counseling and necessary prenatal diagnosis should be strengthened to prevent the birth of severely congenital defective fetuses:

(1) Older pregnant women (age 35 years).

(2) Pregnant women with a history of poor fertility: such as children who have had congenital malformations, anencephaly, congenital stupidity and other chromosomal abnormalities

(3) Pregnant women with recurrent miscarriages, difficult pregnancy, and unexplained perinatal stillbirths.

(4) The spouse is a carrier of chromosomal balance shift.

(5) Pregnant women who have a history of familial genetic disease or a couple who have a genetic disease.

(6) Pregnant women with suspected viral infection during pregnancy.

(7) Pregnant women who use teratogenic drugs during pregnancy, such as anti-tumor drugs and progestin.

(8) Excessive doses of radiation and harmful substances in early pregnancy.

(9) Pregnant women with chronic diseases, such as insulin-dependent diabetes mellitus, epilepsy, hyperthyroidism, autoimmune disease, chronic heart disease, kidney disease, etc.

2. Prenatal diagnostic tests

(1) Ultrasound examination of the fetus during pregnancy can accurately detect anencephaly and spina bifida deformities; X-ray examination of the fetus during pregnancy can find no skull.

(2) Serum and amniotic fluid increase in pregnant women during pregnancy.

(3) The concentration of estriol in the plasma and urine of pregnant women during pregnancy is significantly reduced, which is due to fetal adrenal hypoplasia and reduced corticosteroids.

Neural tube deformity treatment

1. Once the fetus is diagnosed as a neural tube malformation, the pregnancy should be terminated immediately.

2. No treatment is required for asymptomatic recessive spina bifida.

3. The general principles of spinal fissure surgery are mass removal, nerve release, decompression of the spinal canal and return of bulging nerve tissue into the spinal canal, repairing soft tissue defects, and avoiding permanent involvement of the nerve tissue to aggravate symptoms. Postoperative bandaging is required to be tight, and prone or lateral position should be used within 2 to 3 days after surgery and suture removal to prevent wet stools and contamination of the incision.

Prognosis of neural tube defects

Recessive spina bifida and nerveless cysts do not hinder health after removal. Secondary infection of the cyst can cause meningitis. Patients with neurological symptoms have a poor prognosis, and the symptoms are difficult to improve after removal of the cyst, and often worsen.

Prevention of neural tube defects

1. For pregnant women with high-risk factors, prenatal genetic counseling and necessary prenatal diagnosis should be strengthened to prevent the birth of severely congenital defective fetuses.

2. Folic acid and vitamin B ₁₂ supplementation, pregnant women in the first month of pregnancy to 4 months after pregnancy, oral oral folic acid 0.4 mg once a day, can reduce the incidence of fetal neural tube defects 70%, but should not take more, Just in case there are side effects.

3. Active and reasonable treatment of diseases during pregnancy.

4. Strengthen perinatal health care and avoid high heat environment.