What is microcephaly?
Microcephaly is a neurological
disorder in which the circumference of the head (the measured
distance around the top) is smaller than average for an
infant's size and age. The disorder can be present at birth
or acquired during the first few years of a child's life.
Microcephaly is often associated with some degree of mental
retardation. However, in 15 percent of the cases, the child has
normal intelligence. Microcephaly is rare, occurring from 1 per
6200 to 8500 births.
What causes microcephaly?
The growth of the skull is
determined by the expansion of the brain. Microcephaly occurs most
often because the brain fails to grow at a normal rate. This can be
caused by a variety of conditions or exposure to harmful substances
during fetal development. Some of these causes include:
- Chromosomal disorders such as Down's syndrome, Cri du
chat syndrome, Trisomy 13, and Trisomy 18
- Maternal viral infections such as rubella (German measles),
toxoplasmosis, and cytomegalovirus
- Maternal alcoholism or drug abuse
- Maternal diabetes
- Mercury poisoning
- Uncontrolled maternal PKU
- Maternal malnutrition
Acquired microcephaly might occur after birth due to various
brain injuries such as lack of oxygen or infection.
What are the symptoms of microcephaly?
Aside from a
noticeably smaller head, the following are the most common symptoms
of microcephaly.
- High-pitched cry
- Poor feeding
- Convulsions
- Increased movement of the arms and legs (spasticity)
- Hyperactivity
- Developmental delays
- Mental retardation
As the child grows older, his or her face continues to grow
while the skull does not. This causes the child to develop a
disproportionately large face, a receding forehead and a loose,
often wrinkled scalp. The rest of the body is often underweight and
proportionately smaller than normal.
How is microcephaly diagnosed?
Microcephaly can
sometimes be diagnosed before birth by prenatal ultrasound. In many
cases, however, it might not be evident by ultrasound until the
third trimester, and therefore might not be seen on ultrasound
performed earlier in pregnancy.
Most of the time, the diagnosis will not be made until birth or
later in infancy. Along with noting that the baby's head
circumference is much smaller than normal, the doctor will perform
a complete physical examination and obtain a complete prenatal and
birth history of the child. In the case of later development of the
disorder, the doctor might ask the parents about developmental
milestones such as crawling and walking, since microcephaly is
frequently accompanied by mental retardation.