Microcephaly, which has always been a relatively rare and poorly understood problem in the general population, has recently gained much attention due to its association with Zika virus infection during pregnancy.
In this article we will explain what microcephaly is, what are its main causes, its symptoms, the forms of diagnosis and the treatment options.
Here, let’s talk about microcephaly in general, linked to several different diseases, including Zika. If you are looking for specific information about Zika fever microcephaly, visit the following link: ZIKA FEBRE – Causes, Symptoms, Microcephaly and Treatment.
WHAT IS MICROCEPHALUS?
Children’s head size is directly related to brain size. If the baby’s brain grows, its skull expands in the same proportion.
Our skull is made up of six bones that at birth are separated by fontanels (molleiras). This separation allows the skull to expand as the brain grows.
The brain literally pushes on the bones of the skull, causing them to expand. This rate of expansion is greatest in the first few months and gradually decreases over time as the fontanelles close and limit the skull’s ability to expand.
If for some reason the fetus does not develop its brain correctly in the womb, it will be born with a smaller skull than expected. These cases are called congenital microcephaly.
Microcephaly can also be acquired. A baby may have had normal development in the fetal stage, but the brain may stop growing after birth. Over time, your child’s body will grow faster than her skull, making her head look smaller than expected. These cases that arise after birth are called acquired microcephaly.
Early closure of the fontanelles, called craniosynostosis, is another possible cause of acquired microcephaly. In this case, the brain does not grow because there is a limitation of its physical space.
In most cases, microcephaly is related to a delay in intellectual development. However, in about 15% of patients, microcephaly is mild and the child may have a normal or near normal level of intelligence.
As already mentioned, microcephaly itself is not a disease, it is a sign of disease. When a child has microcephaly, one should try to identify the cause behind this change.
We will talk specifying the causes later.
CRITERIA FOR MICROCEPHALUS
The definition of microcephaly used in the introduction to this article is as simple as possible: a head whose circumference is smaller than the expected circumference for children of the same size and age.
In practice, however, we need a somewhat more detailed definition, involving numbers or percentages to be able to make this comparison with the rest of the population.
Historically, the scientific definition of microcephaly has always been somewhat complex and difficult for the general public to understand. The two most used settings are:
- Occipitofrontal circumference (OFC) less than 2 standard deviations below the mean or less than the 3rd percentile (mild microcephaly).
- Occipitofrontal circumference (OFC) less than 3 standard deviations below the mean (severe microcephaly).
To use the above criteria, one must understand the concept of standard deviation and have a table with the circumferential occipitofrontal circumference curves for the different ages, taking into account the characteristics of the population in question.
With the appearance of Zika cases in pregnancies, the incidence of microcephaly increased considerably and it was necessary to simplify the diagnosis, at least for newborns.
In order to facilitate and increase the detection of cases of microcephaly, the World Health Organization (WHO) has begun to recommend microcephaly as a simple measurement with a tape measure of the head circumference (cranial circumference), as shown in the photo that opens the article.
Boys with a head circumference less than or equal to 31.9 cm or girls with a head circumference less than or equal to 31.5 cm are considered microcephalic.
It is important to emphasize that this criterion only applies to newborns and children born at term, that is, with more than 37 weeks of gestation.
This criterion is not useful for the diagnosis of acquired microcephaly or congenital microcephaly in preterm infants.
CAUSES OF MICROCEPHALUS
Various diseases can cause microcephaly, from genetic problems, medications or drugs during pregnancy, to infections and trauma.
Below we will list some of the possible causes:
- Disorders of genetic or chromosomal origin, such as Down syndrome, Poland, Edward, Patau, Rett, X-linked microcephaly, and several others.
- Complications during childbirth or during pregnancy that cause a lack of oxygen to the baby’s brain (hypoxic encephalopathy).
- Craniosynostosis (early fusion of the skull bones).
- Infections during pregnancy, such as rubelTO, cytomeegalovirus, toxicoplasmosis, siphonillis, varicose veinthere, HIV gold zika.
- Use of teratogenic drugs during pregnancy.
- Maternal malnutrition.
- Consalcohol umption in pregnancy.
- Drug use in pregnancy, such as heroin, husbandAna, gold ocaine.
- Smoking during pregnancy.
- Radiation exposure.
- Myinternal folate deficiency.
- Maternal metabolic diseases, such as phenylketonuria.
- Maternal lead or mercury poisoning.
- diabare mellitus poorly controlled during pregnancy.
- Stroke in the newborn.
Although the list above is large and incomplete, many cases of microcephaly go unidentified. This usually occurs because they are caused by genetic abnormalities for which research is not available where you live, or by inadvertent exposure to harmful substances, or by prenatal infections that were not diagnosed during pregnancy.
SYMPTOMS OF MICROCEPHALUS
The sign present in all cases of microcephaly is a small head, disproportionate in size to the body. Microcephaly capable of causing delayed intellectual development is usually quite obvious on physical examination.
Some patients with mild microcephaly have no other signs or symptoms apart from a head that is smaller than the population average. In these cases, called isolated microcephaly or microcephaly vera, intellectual abilities may be almost or completely preserved.
In most cases, however, microcephaly is accompanied by other signs and symptoms, either resulting from impaired brain development or from the syndromes themselves that have prevented proper growth of the brain and skull.
Depending on the severity of the accompanying syndrome, children with microcephaly may have:
- Late intellectual development.
- Delayed development of speech.
- Delay in baby development milestones (sitting, standing, crawling, walking…)
- Motor incoordination.
- Muscle stiffness (spasticity).
- facial distortions.
- Physical changes typical of the genetic syndrome of which the patient is a carrier (such as Down syndrome, for example).
- Visual or hearing deficits.
DIAGNOSIS OF MICROCEPHALUS
The diagnosis can be made even during pregnancy through fetal ultrasound, which is capable of measuring the size of the fetal skull. The best time for this evaluation is at the end of the second trimester, during what is often called a “morphology ultrasound” exam.
Although the fetal ultrasound is normal, the baby’s head circumference should be measured 24 hours after birth. If it is normal, your pediatrician should keep the measurements during routine appointments until the child is two years old and his fontanelles are closed.
If at any time the pediatrician suspects microcephaly, the child should be referred to a specialized pediatrician.
Some imaging tests, such as MRI, can provide important information about the structure of the baby’s brain, helping to confirm microcephaly and providing advice on possible causes.
TREATMENT OF MICROCEPHALUS
Although there is no cure, there are treatments that help minimize the problems caused by microcephaly.
As already mentioned, babies with mild microcephaly usually have no other problems than a small head. These cases only need monitoring and do not require specific treatment.
For babies with craniosynostosis, there are surgeries that help separate the bones from the skulls, allowing the brain to grow without restriction.
In children with more severe cases, treatment is directed at controlling associated signs and symptoms, such as muscle stiffness, seizures, delayed speech development, etc.
The neurological prognosis is directly related to the degree of microcephaly, being worse in patients with occipitofrontal circumference below 3 standard deviations below the mean and in those with microcephaly caused by more serious genetic syndromes or infections during pregnancy.