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Stephen J. Falchek

, MD, Nemours/Alfred I. duPont Hospital for Children

Last full review/revision Apr 2019| Content last modified Apr 2019

Microcephaly is an abnormally small head. Often the head is small because the brain is small and abnormally developed.

  • Microcephaly can be caused by many disorders including genetic abnormalities, infections, and brain defects.
  • Newborns with severe microcephaly usually have symptoms of brain damage.
  • Diagnosis is made before birth by doing ultrasound tests or after birth by measuring the head circumference.
  • Doctors usually do imaging tests to look for brain abnormalities and sometimes blood tests to look for a cause.
  • Because microcephaly can range from mild to severe, treatment options can range as well.
  • Early intervention may be especially helpful.

(See also Overview of Brain and Spinal Cord Birth Defects.)

The size of the head is typically determined by the size of the brain. Thus, decreased growth of the brain, or part of the brain, is the cause of microcephaly. Microcephaly can occur alone or in combination with other major birth defects and can be present at birth or develop later in infancy.

Microcephaly is uncommon. It occurs in an estimated 2 to 12 of 10,000 live births in the United States. However, the normal head size for a given age varies in different parts of the world, so it is difficult to estimate the true incidence of microcephaly worldwide.

Causes of Microcephaly

Microcephaly can be caused by a number of disorders, including

Symptoms of Microcephaly

Symptoms depend on how severe the brain is damaged or underdeveloped. Some of the problems that babies with severe microcephaly can have include seizures, developmental delays, feeding problems, hearing or vision problems, problems with movement or balance, hyperactivity, and intellectual disabilities.

Diagnosis of Microcephaly

  • Before birth, ultrasound
  • After birth, physical examination and sometimes imaging tests and blood tests

Before birth, the diagnosis of microcephaly sometimes is made with a routine prenatal ultrasound test done late in the 2nd trimester or early in the 3rd trimester.

After birth, doctors measure a baby's head circumference (the measurement of the head around its largest area) during routine physical examinations. They diagnose microcephaly when the head circumference is significantly smaller than the normal range for babies of the same sex, age, and ethnic group in the region where the baby lives. Occasionally, the diagnosis is made when the baby's head circumference began in the normal range but is not appropriately increasing as the baby ages. When making the diagnosis, doctors also take into account the head circumference of the baby's parents because a slightly small head size may run in the family (a condition called benign familial microcephaly).

If microcephaly is present, doctors usually do computed tomography (CT) or magnetic resonance imaging (MRI) of the head to look for brain abnormalities. Doctors also evaluate the newborn and parents to look for possible causes of microcephaly and then test for any causes they suspect. Sometimes the doctor may request blood tests to help determine the cause.

Treatment of Microcephaly

  • Treatment of symptoms
  • Intervention for physical and intellectual problems

Microcephaly is a lifelong condition, and there is no cure or standard treatment.

Symptoms resulting from brain damage are treated. Some disorders causing microcephaly can be treated.

Regular check-ups and follow-ups by a care team are very important. Developmental services, known as early intervention, often help babies with microcephaly maximize their physical and intellectual abilities.

More Information about Microcephaly

  • March of Dimes

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