Is My Baby’s Head Too Big? Macrocephaly Explained

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Your baby’s brain grows quickly during their first year of life. To accommodate the growing brain, your baby’s head has to grow, too. During their first year of life, a baby’s head grows 12 centimeters. That’s three times as much as a child’s head grows between 1 and 5 years old. 

But what happens if their head grows too fast? Could there be something wrong if your baby’s head is too big? Let’s take a look at why some babies have larger heads and what it means for their health and development. 

What is macrocephaly?

Macrocephaly is a medical term for a head size that is large than 97% of the population of the same age and sex. 

Healthcare providers check a baby’s head size at each checkup by wrapping paper measuring tape around the baby’s head. This measures what is called the occipitofrontal circumference (OFC), or head circumference. Your child’s healthcare provider marks this number on a growth chart to track how your baby’s head is growing. 

If a child’s OFC is above the 97th percentile for their age group on the growth chart, they have macrocephaly.     

What are causes of macrocephaly?

There are several reasons why a baby might develop macrocephaly, which are outlined below.

Genetics

Genetics plays a big role in a child’s growth patterns and growth potential. So it’s no surprise that macrocephaly runs in families. A child is likely to have a larger head if their family members also have larger heads. This is one of the most common reasons for macrocephaly in babies. It’s often referred to as benign familial macrocephaly. 

Benign extra-axial fluid collections of infancy

This is a typically harmless condition where a baby has extra fluid around the brain. It goes by many different names, including external hydrocephalus, benign enlargement of the subarachnoid space, extraventricular hydrocephalus, and benign subdural effusion. 

Normally, fluid circulates around the brain and spinal cord, and the body absorbs the same amount of fluid each day. But some babies don’t absorb the brain fluid as well during their first 18 months of life, so their head grows faster. This is another very common cause of macrocephaly. 

Hydrocephalus

Hydrocephalus is a condition that develops when there is too much fluid inside the brain. This causes extra pressure to build up in the brain and makes it swell. Hydrocephalus usually causes a rapid change in a baby’s head size and is a medical emergency. Studies show that most cases of hydrocephalus are detected because of an increase in a baby’s head size.

Brain tumors

A tumor can cause a baby’s head to grow rapidly. But brain tumors are uncommon in babies. Also, studies show that brain tumors in babies are accompanied by other symptoms in addition to macrocephaly. 

Bleeding

Bleeding in and around the brain will put pressure on the brain and cause the head to grow too fast. Bleeding can happen after head trauma and with other rare conditions. LIke brain tumors, this is a very uncommon cause of macrocephaly, and children usually have other symptoms, too. 

Some premature babies may have bleeding in their brain early on, which is called intraventricular hemorrhage. This condition is identified in the neonatal intensive care unit. 

Medical conditions

Children with certain medical conditions are more likely to develop macrocephaly. Children with autism, neurofibromatosis, tuberous sclerosis, achondroplasia, and fragile X syndrome (Sotos syndrome) often develop macrocephaly. Certain inherited metabolic conditions can also cause macrocephaly. Testing for these metabolic conditions is usually part of a newborn screening. 

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How is macrocephaly diagnosed?

Macrocephaly is diagnosed using a growth chart. Your child’s healthcare provider will measure head circumference at every checkup until your child is 3 years old. 

If your child’s head circumference is above the 97th percentile or seems to be growing too fast, your healthcare provider will:

• Take another measurement: Babies are squirmy! They don’t always cooperate for a head circumference measurement. So if the size seems off, your child’s healthcare provider will confirm the measurement. 

• Measure your head circumference: If repeat measurements confirm macrocephaly, it’ll be your turn next. Your child’s provider will measure both parents’ head circumference. There is a tool called the Weaver curve that can be used to determine if your child’s head circumference is large because of genetics.

• Order an ultrasound: If your baby’s macrocephaly isn’t due to benign familial macrocephaly, the next step is a head ultrasound. An ultrasound will show if your baby has benign extra-axial fluid collections or signs of something more serious, like hydrocephalus or a tumor. Studies show that ultrasounds for macrocephaly are very reliable and can safely rule out any serious conditions. (Only about 5% of babies need a CT scan or MRI after an ultrasound.) Plus, ultrasounds don’t use radiation and are quick and painless, making them an ideal first diagnostic study. 

• Order a CT scan or MRI: If your child’s ultrasound shows something concerning, or if their soft spot is already closed, your provider may order a head CT or MRI. (An MRI does not use radiation, so it’s often the preferred imaging option for babies.) These studies will be able to show if your child’s macrocephaly is from something more rare like hydrocephalus, a tumor, or bleeding. 

• Track your child’s development: Ultrasounds, CT scans, and MRIs can’t determine if your child has a medical condition like autism. Your provider will watch your child for any signs of medical conditions associated with macrocephaly. They may also ask you to see a developmental pediatrician or a geneticist. 

What’s the outlook for children with macrocephaly?

Most children who have macrocephaly don’t have any issues with their growth or development. This is especially true if your child’s head is larger because of familial macrocephaly or benign extra-axial fluid collections of infancy.  

Some children with benign extra-axial fluid collections of infancy talk later than other children. But studies show they catch up to their peers by the time they’re 2 years old.   

If your child has macrocephaly because of a medical condition, their overall outlook will be tied to that medical condition. Children who have hydrocephalus, bleeding, and tumors need immediate medical attention. Each child’s course of treatment and outlook will be different.