Macrocephaly is the term for an unusually large head. An infant with macrocephaly will have a larger head than most other infants of the same age and sex.

In many cases, this condition is benign or harmless. In other cases, it may indicate an underlying medical condition, such as a genetic syndrome or a brain tumor.

In this article, learn about the causes of macrocephaly and how doctors diagnose and treat the potential underlying medical conditions.

a mother stood up holding a baby in one arm, and looking at a phone in their free handShare on Pinterest
Maskot/Getty Images

Macrocephaly is the name for a condition in which an infant has an unusually large head size.

A doctor will diagnose macrocephaly if the measurement of the head around its widest part is bigger than 97% of infants of the same age and sex.

Macrocephaly may sometimes be a sign of an underlying condition that requires treatment.

In other cases, it is harmless and occurs due to genetics.

Genes are responsible for many cases of macrocephaly. A doctor may diagnose benign familial macrocephaly in an infant if they have a large head and a family history of larger-than-average head sizes.

Infants with benign familial macrocephaly will not experience symptoms other than a large head.

Other causes of macrocephaly may require investigation and treatment in order to prevent long-term neurological problems and developmental delays.

These causes include:

  • megalencephaly, an unusually enlarged brain
  • hydrocephalus, fluid buildup in the brain
  • bleeding in the brain
  • thickened bone in the head
  • increased intracranial pressure
  • brain tumors
  • certain metabolic conditions
  • some types of infection
  • Alexander disease
  • Greig cephalopolysyndactyly syndrome
  • Sotos syndrome
  • chronic hematomas and other lesions

The primary sign of macrocephaly is an unusually large head. This is the only symptom in cases of benign familial macrocephaly.

If macrocephaly results from an underlying condition, an infant may have additional symptoms. Depending on the condition, these may include:

  • delays reaching developmental milestones
  • comorbidity with other conditions, such as autism
  • mental disorders

A doctor will typically continue to monitor the infant after the diagnosis. They also may ask parents or caregivers to watch for signs, including:

  • excessive sleepiness
  • unusual eye movement
  • trouble feeding
  • vomiting
  • a bulging soft spot
  • excessive irritability

The potential health complications of macrocephaly vary based on the condition causing the enlarged head.

Some specific conditions and possible complications are as follows:

  • In cases of megalencephaly, where an infant has an atypically large and usually malfunctioning brain, complications may include delayed development, partial paralysis, seizures, and dysfunction of the brain cortex and spinal cord.
  • In cases of hydrocephalus, where cerebrospinal fluid builds up in the brain, complications may include delayed intellectual development and physical disabilities.
  • In cases of neurocutaneous disorders, a rare group of disorders involving the nervous system and skin, complications may include an increased risk of seizures and an increased risk of developing certain kinds of tumors.
  • In cases of Sotos syndrome, complications may include developmental delays and problems with coordination.

Doctors often diagnose macrocephaly during a routine physical examination.

As part of a physical examination for an infant, a doctor will measure their head circumference by wrapping a measuring tape around their head, aligning it just above the eyebrows.

To meet the criteria for macrocephaly, the infant’s head circumference must be at or above the 97th percentile for their age and sex. This means that the head circumference is larger than 97% of similar infants.

If a doctor thinks an infant has macrocephaly, they will take a careful medical history to determine if it is due to an underlying condition and will often order imaging tests, such as a CT scan, ultrasound, or MRI.

These tests will help the doctor determine if there is fluid buildup in the brain, which could cause increased pressure and other complications.

Some symptoms of increased pressure on the brain include:

The treatment for macrocephaly will vary depending on the underlying cause. An infant with benign familial macrocephaly will not usually require any treatment other than monitoring the head’s size.

Infants whose macrocephaly stems from a genetic condition may require lifelong treatment and support, including:

An infant who has a fluid buildup or bleeding in the brain will often require referral to a neurosurgeon and prompt surgery to prevent further complications and decrease intracranial pressure.

Doctors may use a variety of methods to treat a brain tumor, including:

The outlook largely depends on the underlying condition causing the macrocephaly. Infants with benign familial macrocephaly have a good outlook and will not usually experience complications.

An infant who has macrocephaly due to an underlying condition, such as a brain tumor or a genetic syndrome, will require an individualized treatment plan.

Macrocephaly describes infants who are born with or who begin to develop an atypically large head shortly after birth.

It is often benign and passed down through genetics, but it can also indicate problems such as fluid buildup in the brain or a genetic disorder.

Testing for macrocephaly involves measuring and tracking the growth of an infant’s head. In some cases, a doctor may order radiological imaging.

While infants with benign macrocephaly will not require treatment and typically outgrow the condition by early childhood, treatment may be necessary in other cases.