Microcephaly
The term Microcephaly literally means "small head". The determination of microcephaly is usually made when the head circumference is more than 2 standard deviations below normal for age, gender, race and gestation. Some physicians prefer to diagnose at the 3 SD mark. There may also be a diagnosis of "relative microcephaly", which means that in relation or comparison to weight and length, the head size is below the expected norm. Microcephaly may be congenital (present at birth) or it may develop in the first few years of life. The disorder may stem from a wide variety of conditions that cause abnormal growth of the brain, and is often a symptom of syndromes associated with chromosomal abnormalities.
The number of microcephalic individuals in the general population ranges from 0.1 to 2.5 percent, depending on whether the head circumference is 2 or 3 standard deviations below normal. Many of normal intelligence and function are included in the larger percentage, which seems to indicate that the 3 SD deviation is more closely related to the incidence of neurologic impairment. There are approximately 1.6 per 1000 single birth deliveries that include a diagnoses of microcephaly, but only 14 percent of all microcephalic infants diagnosed by the first year of age are detected at birth.
Primary and Secondary Microcephaly
Primary Microcephaly can result from a variety of insults that can cause anomalies of induction and migration.
Secondary Microcephaly may result when an infection or disease process, either impairs the growth of a normally developing brain before birth or following.
Microcephaly has a high incidence of mental and physical retardation. Seizures are often, but not always, present.
What causes microcephaly?
Microcephaly is either caused by exposure to harmful substances during the fetal development, or it may be associated with genetic problems or syndromes that may have a tendency to run in families.
Theories suggest that the following may predispose a fetus to problems that affect the normal development of the head during pregnancy:
exposure to hazardous chemicals/substances
exposure to radiation
lack of proper vitamins and nutrients in the diet
infection
prescription or illegal drug and alcohol consumption
maternal diabetes
Microcephaly can occur alone or in association with other health problems, and may occur from inheritance of an autosomal recessive, or rarely, an autosomal dominant gene. Acquired microcephaly may occur after birth due to various brain injuries such as lack of oxygen or infection.
Autosomal recessive and autosomal dominant are two patterns in which genes are inherited in a family. Genes determine our traits, such as eye color and blood type, and can also cause disease. Autosomal means that both males and females are equally affected. Recessive means that two copies of the gene, one inherited from each parent, are necessary to have the condition (in this case, microcephaly). After parents have had one child with autosomal recessive microcephaly, there is a 25 percent chance, or one in four chance, with each pregnancy, to have another child with microcephaly.
What are the symptoms of microcephaly?
The following are the most common symptoms of microcephaly. However, each child may experience symptoms differently. Symptoms may include:
appearance of the baby's head is very small
high-pitched cry
poor feeding
seizures
hypo or hypertonia
developmental delays
mental retardation
The symptoms of microcephaly may resemble other conditions or medical problems. Always consult your child's physician for a diagnosis.
How is microcephaly diagnosed?
Microcephaly may be diagnosed before birth by prenatal ultrasound, a diagnostic imaging technique, which uses high-frequency sound waves and a computer to create images of blood vessels, tissues, and organs. Ultrasounds are used to view internal organs as they function, and to assess blood flow through various vessels.
In many cases, microcephaly may not be evident by ultrasound until the third trimester, and, therefore, may not be seen on ultrasounds performed earlier in pregnancy. The diagnosis of microcephaly may be made at birth or later in infancy. The baby's head circumference is much smaller than normal. During the physical examination, the physician obtains a complete prenatal and birth history of the child. In older babies and children, the physician may also ask if there is a family history of microcephaly or other medical problems. The physician will also ask about developmental milestones since microcephaly can be associated with other problems, such as mental retardation. Developmental delays may require further medical follow up for underlying problems.
A measurement of the circumference of the child's head is taken and compared to a scale that can identify normal and abnormal ranges.
Diagnostic tests that may be performed to confirm the diagnosis of microcephaly and identify abnormalities in the brain include:
head circumference - this measurement is compared with a scale for normal growth and size.
x-ray - a diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.
computed tomography scan (Also called a CT or a CAT scan.) - a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images (often called slices), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including bones, muscles, fat, and organs. CT scans are more detailed than general x-rays.
magnetic resonance imaging (MRI) - a diagnostic procedure that uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.
blood tests
urine tests
