Merck Manual

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Stephen J. Falchek

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

Reviewed/Revised Jul 2023

Macrocephaly is the technical term for a large head.

  • Macrocephaly can be caused by genetic disorders or other disorders or can run in families.

  • Diagnosis is made before birth through routine ultrasound tests or after birth by measuring the head circumference.

  • Doctors usually do an imaging test to look for brain abnormalities and genetic testing to look for a cause.

  • Treatment for macrocephaly usually includes surgery.

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.

The most common cause of macrocephaly is familial macrocephaly, in which a larger head size runs in the child's family because of features of the skull and brain growth.

Abnormal macrocephaly may be caused by an enlarged brain (megalencephaly), water on the brain (hydrocephalus Hydrocephalus Hydrocephalus is an accumulation of extra fluid in the normal spaces within the brain (ventricles) and/or between the inner and middle layers of tissues that cover the brain (the subarachnoid... read more 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.

Children may also have complications, for example, lazy eye (also called amblyopia Amblyopia Amblyopia, a common cause of vision loss in children, is a decrease in vision that occurs because the brain ignores the image received from an eye. Vision loss may be permanent if the disorder... read more ), misaligned teeth, and/or speech difficulties related to effects on the mouth and jaw.

Diagnosis of Macrocephaly

  • Before birth, ultrasound

  • After birth, physical examination, including measurement of head circumference and sometimes magnetic resonance imaging (MRI)

  • Genetic testing

After birth, doctors measure a baby's head circumference Head Circumference Physical growth refers to an increase in body size (length or height and weight) and in the size of organs. From birth to about age 1 or 2 years, children grow rapidly. After this rapid infant... read more (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 MRI Magnetic Resonance Imaging (MRI) Magnetic resonance imaging (MRI) is a type of medical imaging that uses a strong magnetic field and very high frequency radio waves to produce highly detailed images. During an MRI, a computer... read more Magnetic Resonance Imaging (MRI) of the brain to look for 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.

A baby who has this birth defect may be evaluated by a geneticist. A geneticist is a doctor who specializes in genetics (the science of genes and how certain qualities or traits are passed from parents to offspring). Genetic testing of a sample of the baby's blood may be done to look for chromosome and gene abnormalities. This testing can help doctors determine whether a specific genetic disorder is the cause and rule out other causes.

Treatment of Macrocephaly

  • Depends on the cause

Many children with macrocephaly do not require treatment.

In children who have familial macrocephaly, treatment is not possible or necessary. Likewise, some genetic disorders that are associated with a larger-than-normal head size also are not treatable, and the head size by itself is not a cause of illness.

Regardless of the cause, children who have macrocephaly may have developmental delays. Developmental services, known as early intervention, often help babies with macrocephaly maximize their physical and intellectual abilities. Regular check-ups and follow-ups by a care team are very important.

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