What You Should Know About Macrocephaly

Medically Reviewed by Sabrina Felson, MD on May 05, 2023
4 min read

Parents of new babies expect that pediatricians will check their length and weight. But they may not expect that doctors will pull out a tape measure to check the size of a new baby's head. Baby head measurements are just as important for tracking growth as height and weight are. But what does it mean when a baby has a head that is larger than average?‌

The medical term for a large head is "macrocephaly." Most of the time, it isn't a serious condition, so parents don't need to worry about it. In rare cases, however, it can be an indication that your baby has other health conditions. 

Learn more about macrocephaly and what it means. 

The simple definition of the word macrocephaly is "large head." Doctors apply that diagnosis when a baby's head size is in the 98th percentile. This means that the baby's head is bigger than 98% percent of other babies of the same age.

Sometimes, doctors detect macrocephaly during an ultrasound before the baby is born. In other cases, it's something that they notice when they measure the baby at routine exams during the baby's first year of life. Your pediatrician may have you see a neurologist if your child has macrocephaly.

Not all cases of macrocephaly are a sign that something is wrong. One of the most common reasons for macrocephaly is something that doctors call "benign familial macrocephaly." In other words, big heads run in your family.

A doctor might determine that a baby's big head is inherited by measuring the heads of the parents. The doctor will also check the baby's head, particularly the fontanelles (soft spots that are normal for babies). If everything is fine, there is nothing you need to do. The doctor will probably ask you to come back in a few months or if any other symptoms arise. 

If your baby has specific physical or behavioral symptoms, the doctor may be more concerned. Causes for concerns include:

  • Tightness or bulging of the soft spot 
  • Unusual eye movements 
  • Unexplained projectile vomiting
  • Irritability that gets worse over time
  • High-pitched cry like the baby is in pain or discomfort
  • Developmental delays

If something is wrong, doctors will first need to determine if the size of the head is due to an enlarged brain, excess fluid in the skull, or an overgrowth of the skull bones. They will use imagining tests such as an MRI or CT scan to answer these questions. After that, they may need to do blood tests or genetic testing to reach a final diagnosis.

Hydrocephalus is sometimes called "water on the brain." It refers to a build of excess cerebrospinal fluid around the brain. Sometimes, when this happens to babies, it's not a problem. Doctors call it "benign extra-axial collections of infancy" or "benign external hydrocephalus." Children typically outgrow the condition by early childhood. Still, your doctor will want to follow up with you regularly to keep an eye on your baby. 

There are times when hydrocephalus is dangerous. The pressure of the fluid can lead to brain injuries. Your baby may need surgery to relieve the pressure and reduce the risk of lasting brain damage. 

Sometimes, macrocephaly is a symptom of an underlying genetic condition. Some of the conditions include:

Sotos syndrome. This condition causes rapid physical growth before birth and for the first several years of life. In addition to macrocephaly, the shape of the head is longer than is typical. People with this condition also tend to have developmental delays.

Cowden syndrome. This condition results in non-cancerous growths that appear on a person's body. People with Cowden syndrome may have a high risk of certain cancers later in life. 

Gorlin syndrome. Also known as basal cell nevus syndrome, this condition results in a large head, distinctive facial features, and pitted skin on the hands and feet. Gorlin syndrome causes benign tumor growth. People who have it have a significant risk of basal cell skin cancer as young adults.

Fragile X syndrome.Fragile X syndrome happens because a person's body doesn't produce a particular protein needed for brain development. It causes developmental delays, learning and intellectual disabilities, and social-emotional difficulties.

Genetic conditions like this don't have a cure. Instead, your doctor will help you manage the symptoms that your child has. This might include medical treatment as well as therapy to help with physical or developmental delays. You and your doctor can make a plan to serve your child's particular needs best. ‌