Microcephaly, which has always been a relatively unusual and poorly understood problem in the general population, has recently gained much notoriety 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, related to several distinct 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 MICROCEPHALY?
The size of the children’s head is directly related to the size of the brain. If the baby’s brain grows, his skull expands in the same proportion.
Our skull is composed of six bones that at birth are separated by fontanelles (molleiras). This separation allows the skull to expand as the brain grows.
The brain literally pushes the bones of the skull, causing them to expand. This rate of expansion is higher in the first few months and gradually decreases over time as the fontanelles close and limit the capacity of skull expansion.
If for some reason the fetus does not properly develop the brain inside the uterus, it will be born with a smaller sized 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 your skull, making your 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. In about 15% of patients, however, microcephaly is mild and the child may have a normal or near-normal intelligence level.
As already mentioned, microcephaly itself is not a disease, it is a sign of disease. When a child has microcephaly, one must try to identify the cause behind this change.
We will speak specifying the causes later.
CRITERIA FOR MICROCEPHALY
The definition of microcephaly used in the introduction of this article is as simple as possible: a head whose circumference is smaller than the circumference expected for children of the same size and age.
In practice, however, we need a somewhat more detailed definition, involving numbers or percentages so that this comparison with the rest of the population can be made.
Historically, the scientific definition of microcephaly has always been somewhat complex and difficult to understand for the lay public. The two most commonly used settings are:
- Occipitofrontal circumference (COF) less than 2 standard deviations below the mean or lower than the 3rd percentile (mild microcephaly).
- Occipitofrontal circumference (COF) 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 various ages, taking into account the characteristics of the population in question.
With the emergence of Zika cases in pregnancies, the incidence of microcephaly increased sharply, and the diagnosis needed to be simplified, at least for newborns.
With a view to facilitating and increasing the detection of cases of microcephaly, the World Health Organization (WHO) has started to recommend microcephaly as a simple measurement with a head circumference measuring tape (skull circumference), as shown in the photo that opens the article.
Boys with cephalic perimeter less than or equal to 31.9 cm or girls with cephalic perimeter less than or equal to 31.5 cm are considered microcephalic.
It is important to emphasize that this criterion only applies to newborn and full-term children, that is, 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 MICROCEPHALY
Several diseases can cause microcephaly, from genetic problems, to drugs or drugs during pregnancy, to infections and to 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 leading to lack of oxygen to the baby’s brain (hypoxic encephalopathy).
- Craniosynostosis (early fusion of skull bones).
- Infections during pregnancy, such as rubella, cytomegalovirus, toxoplasmosis, syphilis, varicella, HIV or Zika.
- Use of teratogenic medicines during pregnancy.
- Maternal malnutrition.
- Consumption of alcohol in pregnancy.
- Drug use in pregnancy, such as heroin, marijana, or ocaine.
- Smoking during pregnancy.
- Radiation exposure.
- Maternal folate deficiency.
- Maternal metabolic diseases, such as phenylketonuria.
- Maternal poisoning by lead or mercury.
- Diabetes mellitus poorly controlled during pregnancy.
- Stroke in the newborn.
Although the above list is large and not complete, many cases of microcephaly end up being left unidentified. This usually occurs because they are caused by genetic abnormalities whose research is not available at their place of residence, or by inadvertent exposure to harmful substances or by prenatal infections that were not diagnosed during pregnancy.
SYMPTOMS OF MICROCEPHALY
The signal present in all cases of microcephaly is a small head, of a size disproportionate to the body. Microcephaly capable of causing retardation in intellectual development is often quite obvious on physical examination.
Some patients with mild microcephaly do not have any other signs or symptoms other than a head that is less than the average of the population. In these cases, called isolated microcephaly or microcephaly vera, intellectual capacities may be almost or completely preserved.
In most cases, however, microcephaly is accompanied by other signs and symptoms, whether they stem from poor brain development or from the syndromes themselves that have impeded proper growth of the brain and skull.
Depending on the severity of the accompanying syndrome, children with microcephaly may have:
- Late intellectual development.
- Delay in speech development.
- Delay in baby developmental milestones (sit, stand, crawl, walk… )
- Motor incoordination.
- Muscular rigidity (spasticity).
- Facial distortions.
- Physical changes typical of the genetic syndrome of which the patient is a carrier (such as Down’s syndrome, for example).
- Convulsive crisis.
- Visual or auditory deficits.
DIAGNOSIS OF MICROCEPHALY
The diagnosis can be made even during pregnancy through fetal ultrasound, which is able to measure the size of the fetal skull. The best time for this evaluation is at the end of the 2nd trimester, during the exam that is usually called “morphological ultrasound”.
Even though fetal ultrasonography is normal, the baby’s head circumference should be measured 24 hours after birth. If you are normal, your pediatrician should keep measurements during routine appointments until the child is two years old and your 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 magnetic resonance imaging, can provide important information about the baby’s brain structure, helping to confirm microcephaly, and give tips on its possible causes.
TREATMENT OF MICROCEPHALY
Although there is no cure, there are treatments that help minimize the problems caused by microcephaly.
As already mentioned, infants with mild microcephaly generally present no other problems than a small head. These cases only need monitoring, and no specific treatment is required.
For babies with craniosynostosis, there are surgeries that help detach the bones from the skulls, allowing the brain to grow without restrictions.
In children with more severe cases, the treatment aims at controlling the 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 severe genetic syndromes or infections during pregnancy.