Merck Manual

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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
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Macrocephaly is the technical term for a large head.

  • Macrocephaly can be normal or caused by genetic disorders or other disorders.

  • Diagnosis is made before birth through routine 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.

  • Treatment for macrocephaly depends on the cause, and sometimes, if no problems are found, no treatment is necessary.

Infants with macrocephaly have a head circumference that is considerably larger than others of the same age.

Macrocephaly can be classified as

  • Disproportionate: The head is larger than appropriate for the child's overall size.

  • Proportionate: The head appears appropriately sized for the body (in other words, the child has a large body and a large head).

Many people with large heads or large skulls are healthy.

Abnormal macrocephaly may be due to an enlarged brain (megalencephaly), water on the brain (hydrocephalus), overgrowth of the bones of the skull (cranial hyperostosis), or other conditions. These conditions may be the result of genetic disorders or disorders the child acquired before or after birth.


  • Before birth, ultrasound

  • After birth, physical examination, including measurement of head circumference and sometimes imaging tests and blood tests

Before birth, the diagnosis of macrocephaly 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 macrocephaly when the head circumference is significantly larger than the normal range for babies of the same sex, age, and ethnic group in the region where the baby lives. When making the diagnosis, doctors also take into account the head circumference of the baby's parents and grandparents because a slightly larger head size may run in the family.

If macrocephaly 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 macrocephaly and then test for any causes they suspect. Sometimes the doctor may request blood tests to help determine the cause.


  • Depends on the cause

Treatment of macrocephaly depends on the cause. Sometimes, no treatment is necessary. If the cause is an abnormality, such as hydrocephalus, treatment, including surgery, may be necessary.

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