Anterior and Posterior Fontanelle Closures

Your baby has two places where their skull bones don’t fully fuse together in the first several months of life. These “soft spots” are fontanelles, a normal part of your baby’s development.

Issues with fontanelles, such as bulging or sinking, can be signs of other health concerns. Additionally, babies in the Neonatal Intensive Care Unit (NICU) or those with ongoing health conditions will have additional considerations related to their fontanelles.

Children’s Hospital Colorado neonatal experts explain how your baby’s fontanelles should feel and develop and when to seek care.

What are fontanelles?

Fontanelles are the soft spaces on your baby’s head where their skull bones have not yet fused together. These spaces allow for the skull bones to shift as needed during birth and for your baby’s brain to grow. They will close as your baby grows. You should keep your eye on two fontanelles:

• Anterior fontanelle is located near the front, top of your baby’s head. This is the larger of the fontanelles.
• Posterior fontanelle is located near the back of the head.

It’s OK to lightly touch your baby’s fontanelles. A healthy fontanelle should feel soft and flat. A bulging or sunken fontanelle may be a sign of a health issue.

When do fontanelles close?

Typically, fontanelles close by the time your baby is 18 months old. The posterior fontanelle usually closes first — within 2 months of birth. The anterior fontanelle closes between 7 and 18 months. If you feel your baby’s fontanelles are closing too soon or haven’t closed in 18 months, consult your pediatrician.

Fontanelle closure for babies with medical conditions

Premature babies or babies with ongoing medical conditions might have fontanelles close on a different schedule. Conditions like hydrocephalus and brain bleeds commonly affect when fontanelles close, although other conditions can have the same effect.

Your baby’s care team can tell you when to expect your baby’s fontanelles to close based on their condition.

Premature closure of the anterior fontanelle

Sometimes, the anterior fontanelle closes too early. This is known as craniosynostosis and can limit brain growth or create an abnormal head shape. If your baby’s doctor suspects craniosynostosis, they may recommend seeing pediatric craniofacial specialists or pediatric neurosurgeons. Contact your baby’s pediatrician if you feel their fontanelle has closed too early.

Delayed closure of the anterior fontanelle

Just as fontanelles can close too early, fontanelles that close late can also be a sign of medical issues. The most common causes of fontanelles closing outside the normal time range are:

• Achondroplasia: A genetic disorder that affects cartilage and bone growth
• Hypothyroidism: An issue in the thyroid gland that affects hormone production
• Down syndrome
• Increased pressure in the brain

What does a bulging fontanelle mean?

Sometimes when a baby cries or lies down, their fontanelle will bulge above the skull bone. This is normal, as long as the fontanelle returns to its regular position when the baby sits up or stops crying.

A bulging fontanelle when not crying or lying down, it may indicate a more serious medical issue, such as:

• Hydrocephalus: A buildup of fluid in the brain
• Encephalitis: Swelling of the brain usually caused by infection
• Meningitis: Swelling of the membranes that cover the brain and spinal cord
• Bleeding or pressure in the brain

A fontanelle that bulges when your baby is not crying, vomiting or lying down is a medical emergency. Call 911 or go to the nearest emergency room.

What does a sunken fontanelle mean?

A fontanelle that is sunken into the skull can also signal certain medical issues, including:

• Dehydration: When your baby isn’t getting enough fluid; this is the most common cause of sunken fontanelles
• Failure to thrive: Babies who are not gaining enough weight for their age
• Malnutrition: Not getting enough food or having a very imbalanced diet

If your baby has a sunken fontanelle, contact their doctor immediately and seek care as soon as possible.

Fontanelle considerations for babies with medical conditions

Babies born early or with certain medical conditions may have different sized fontanelles than babies born at full term. A larger fontanelle can be a sign of various medical conditions. Your baby’s NICU care team will diagnose such a condition and arrange the right care. If you feel your baby’s fontanelle is larger than typical, talk to your care team.

Babies born prematurely also have a higher rate of bleeding in the brain, which can lead to hydrocephalus. If your baby had bleeding in their brain, pay close attention to their fontanelles and their head circumference. Talk to your baby’s care team if you have any concerns.