Anencephaly is a malformation of the nervous system in which the fetus lacks large hemispheres of the brain, underdeveloped bones of the cranial vault, soft tissues of the head. The anomaly occurs under the influence of chemical, biological or physical teratogenic factors. Most fetuses with anencephaly die in the prenatal period, and even with live birth, the life span of the child does not exceed several hours. Diagnosis is performed prenatally using ultrasound, MRI, amniocentesis, biochemical screening. In such a situation, termination of pregnancy is indicated, if the parents refuse an abortion, palliative care is provided to the child.
ICD 10
Q00.0 Anencephaly
General information
According to WHO, CNS malformations occupy the first place among congenital anomalies in the fetus (25%). Anencephals should be distinguished from acephals (acephals), who do not have a brain at all. Anencephaly occurs in the USA with a frequency of 1 per 10,000 newborns, in the UK — 5:10000, in China — 8:10000. The disease is more often observed in female fetuses. The risk of recurrence of anencephaly in the next pregnancy is up to 5%, and when a woman gives birth to two children with this central nervous system defect, it increases to 10%. The probability of an anomaly in blood relatives is no more than 3%.
Causes
The defect is formed by violations of the intrauterine laying of neurostructures in the embryonic period of fetal formation. It is considered multifactorial, the exact causes of this condition have not been definitively established. Scientists suggest that the appearance of anencephaly is associated with the effects of negative factors in the early stages of pregnancy. Typical teratogenic influences are:
- Toxins. Heavy metal salts, industrial emissions in ecologically unfavorable regions, some medications, for example, used for the treatment of diabetes mellitus, can be a prerequisite for CNS malformation. Important teratogenic factors are alcohol, tobacco resins.
- Infections. Anencephaly is characteristic of infection with cytomegalovirus, toxoplasmosis, rubella. To form a gross defect, infection of the embryo must occur before the 28th day of intrauterine life.
- Lonizing radiation. Radioactive isotopes have a direct damaging effect on the genetic apparatus of the fetus, in addition, they provoke indirect toxic reactions.
Predisposing factors on the part of parents include genetic ones — the presence of various gene mutations, frequent cases of related marriages and incest. The risk of abnormalities in the development of the central nervous system in a child increases if the mother’s body has low levels of iodine, folate and other vitamins of group B. The probability of anencephaly increases with severe gestation, the presence of extragenital pathologies in a pregnant woman: diabetes mellitus, heart failure, hypothyroidism.
Pathogenesis
The formation of anencephaly occurs in the period from the 21st to the 28th days of intrauterine development of the child. At the same time, the neural tube, which normally closes by the 4th week, forming the rudiment of the brain and spinal cord, remains open. The fetus completely lacks the cortex of the cerebral hemispheres, as a rule, the structure of other parts of the central nervous system is disrupted. Brain tissue is underdeveloped, partially sclerosed. Some infants retain a primitive brain stem responsible for vital functions.
Pathomorphologically, the brain of a fetus with anencephaly is a hemorrhagic mass, mainly made in the form of underdeveloped vascular tissue, with elements of glia, single nerve cells. Histologically, abnormal vessels, choroidal plexuses, randomly located fibroblasts, cystic cavities with medullary epithelium are determined. The brain stem and spinal cord usually have pathological structural changes, but they are not so pronounced.
Symptoms
In live-born infants with anencephaly, the cerebral part of the skull is sharply reduced, there are no flat bones, soft tissues are underdeveloped. There is abnormal vascular tissue in place of the brain, which may be covered with skin.
Such children are unconscious, they are blind and deaf, they do not respond to any external stimuli. Often there are concomitant defects: spinal hernias, pathology of the adrenal glands, cleft palate.
Although most live-born patients die almost immediately, at least three cases have been described in medicine when children were able to live for more than 2 years. The girl Stephanie Keen (better known by the nickname Baby Kay), who lived for 2.5 years and died of cardiac arrest, is considered to be a long-lived anencephalic. She had breathing problems that required a ventilator. Jackson Buell from Boston and Victoria de Cristo from Brazil also overcame the two-year milestone.
However, prolonging the life of anencephals is possible only with constant cardiorespiratory support, filling nutritional needs. Due to the absence of most of the brain, the condition of infants remains stably severe until death. The volume and necessity of palliative care for such newborns raises important questions of biomedical ethics.
Complications
Anencephaly is recognized as a 100% fatal defect. In 75% of cases, fetal death occurs prenatally, which is fraught with a frozen pregnancy. If this condition is not detected in time, there is a risk of septic complications in a woman. The casuistic consequences of intrauterine fetal death today include litopedion, fetal mummification. In the remaining 25% of cases, the death of an infant is observed during the first days after birth due to life-incompatible disorders.
Diagnostics
The anomaly is detected antenatally during routine ultrasound pregnancy screenings. Such a diagnosis is an absolute indication for termination of pregnancy regardless of the age of the fetus, therefore, obstetricians and gynecologists have a great responsibility – it is necessary to establish a diagnosis as early as possible in order to reduce the risks for a woman. The following methods are used to detect the defect:
- Prenatal ultrasound. Ultrasound scanning is the main method of diagnosis, which in anencephaly demonstrates an irregular shape of the head, underdevelopment of the musculoskeletal structures of the skull, the absence of large hemispheres. However, the rest of the body structures are usually developed normally. Ultrasound allows you to identify pathology from 11-12 weeks of gestational age.
- Fetal MRI. Magnetic resonance imaging is the safest and most informative method of clarifying the anatomical features of the central nervous system, if the ultrasound results give a dubious picture. The study is conducted from 14-15 weeks of pregnancy.
- Amniocentesis. Invasive diagnostics with amniotic fluid sampling is necessary to determine biochemical parameters, perform differential diagnostics with congenital syndromic diseases caused by gene or chromosomal mutations.
- Biochemical screening. It is possible to suspect pathology by increasing the level of chorionic gonadotropin and alpha-fetoprotein, reducing the amount of protein-A in the first trimester of pregnancy.
Women who plan to terminate pregnancy with detected fetal anencephaly require an extended diagnosis. A standard gynecological examination is prescribed, as well as a set of tests: a clinical blood test, tests for viral hepatitis, HIV infection. Subsequently, the patients were recommended medical and genetic counseling in order to assess the risks of birth defects in subsequent pregnancies.
Treatment
The decision to terminate pregnancy should be made by parents. The only exception is a dead fetus, when a woman needs emergency surgery. Only palliative care can be provided to live-born children with anencephaly. About 66% of such children live a few hours after birth, the rest die in the first minutes. The main directions of medical care for anencephaly:
- Respiratory support. Children have crises in the work of the respiratory system, requiring the appointment of a ventilator for adequate oxygenation of body tissues.
- Nutritional support. Parenteral nutrition is used using glucose solutions, special amino acid mixtures for newborns.
An important component is psychological assistance to parents at all stages from the moment of diagnosis of an anomaly in the fetus, since this becomes a difficult test for the family, women often have depression, apathy, suicidal thoughts. Psychologists, psychiatrists provide assistance (in case of serious violations of the psycho-emotional state), believers can be recommended to contact representatives of religion.
Prognosis and prevention
The prognosis is unfavorable, since anencephaly ends with intrauterine fetal death or death shortly after a live child is born. Modern medical capabilities make it possible to provide such a baby with a decent end of life if the parents have decided not to terminate the pregnancy.
Given the variety of predisposing factors, effective measures to prevent this condition have not yet been developed. Positive for the prevention of severe fetal abnormalities is taking vitamin supplements with folic acid salts, supplementing the diet with green leafy vegetables, beans, orange juice containing folates, as prescribed by a gynecologist.