Pediatrics · Craniosynostosis and Microcephaly

Is a Small Head Size the Same as Craniosynostosis?

At a Glance

No, a small head size is not the same as craniosynostosis. Microcephaly happens when the brain fails to grow, leaving the skull small. Craniosynostosis occurs when the skull bones fuse prematurely, which can trap a normally growing brain and cause an abnormally shaped head.

No, a small head size (microcephaly) is not the same thing as craniosynostosis. While both conditions involve an unusual head size or shape in infants, the underlying reasons for them are completely different.

Understanding the fundamental difference comes down to the relationship between the brain and the skull. Under normal circumstances, an infant’s brain grows very rapidly during the first few years of life ^[1]. The skull is made up of several separate plates of bone held together by flexible expansion joints called cranial sutures ^[2]. These open sutures allow the skull to expand seamlessly in response to the growing brain ^[1].

Microcephaly: A Primary Brain Growth Issue

In microcephaly, the primary issue is that the brain itself is not growing or developing as it normally should ^[3]^[4]. Because the expansion of the infant skull is directly driven by the outward pressure of the growing brain, a brain that does not grow will not prompt the skull to expand. As a result, the skull remains small, leading to a significantly reduced overall head circumference ^[5]^[6]. In this scenario, the skull plates and sutures are typically normal and remain open; they simply aren’t being forced to grow.

Craniosynostosis: A Primary Skull Fusion Issue

Craniosynostosis, on the other hand, is fundamentally an issue with the skull, not the brain. It occurs when one or more of the cranial sutures fuses closed prematurely ^[7]^[2]. The brain inside the skull is usually healthy and trying to grow normally, but it becomes physically restricted by the fused, rigid section of the skull ^[8]^[9].

Because the brain continues its normal growth trajectory and needs space, it will push outward against the areas of the skull where the sutures are still open ^[8]^[9]. This leads to compensatory growth, where the head may become noticeably elongated, wide, or asymmetrical, depending on which specific suture closed too early ^[10].

If the brain is severely restricted by the fused skull, it can lead to increased pressure inside the head (intracranial pressure). Doctors actively monitor for this pressure because, if left untreated, it can potentially lead to issues such as developmental delays or vision problems ^[11]^[12]. However, craniosynostosis is highly treatable. Surgical procedures (such as cranial vault remodeling) are routinely performed to release the fused sutures, reshape the skull, and ensure the brain has the adequate space it needs to grow safely ^[13]^[14].

The Key Takeaway

To summarize:

Microcephaly is caused by a lack of brain growth, which results in a small skull ^[5]^[3].
Craniosynostosis is caused by early fusing of the skull, which can physically restrict and confine an otherwise healthy, normally growing brain ^[7]^[8].

While the two conditions are distinct, it is very rare, though possible, for a child to have both conditions at the same time ^[15]. Sometimes, a severe lack of brain growth can cause the sutures to fuse early because they aren’t being stretched open (this is known as secondary craniosynostosis).

Pediatricians routinely track head circumference and shape at every well-child visit, which is typically how these conditions are initially flagged. Because both affect the head’s shape or size, a specialist will use physical examinations, a history of head circumference measurements, and imaging tests (like cranial ultrasound, MRI, or CT scans) to determine the exact cause of a child’s specific condition and outline the best path forward ^[16]^[17].

Common questions in this guide

Is a small head size always a sign of craniosynostosis?

No, a small head size is not always craniosynostosis. It is often caused by microcephaly, a condition where the brain itself does not grow properly. Because the brain isn't growing to push the skull outward, the head remains small.

What is the main difference between microcephaly and craniosynostosis?

Microcephaly is primarily an issue with brain development, where a lack of brain growth results in a small skull. Craniosynostosis is an issue with the skull itself, where premature bone fusion traps and restricts a healthy, actively growing brain.

What happens if craniosynostosis causes increased pressure in the head?

If a child's brain is severely restricted by fused skull bones, it can cause increased pressure inside the head. If left untreated, this pressure can lead to vision problems or developmental delays.

How is craniosynostosis treated?

Craniosynostosis is highly treatable. Surgeons routinely perform procedures like cranial vault remodeling to release the fused skull sutures, reshape the head, and ensure the brain has enough space to grow safely.

How do doctors diagnose microcephaly or craniosynostosis?

Pediatricians track head circumference and shape at regular well-child visits. If an unusual size or shape is flagged, specialists may use physical exams and imaging tests like a cranial ultrasound, MRI, or CT scan to confirm the diagnosis.

Curated prompts to bring to your next appointment.

1.Which specific suture or sutures are suspected to be fused in my child?
2.Are there any current signs of increased intracranial pressure, such as changes in my child's eyes or development?
3.What imaging tests, if any, do you recommend at this stage to confirm the diagnosis and why?
4.What specific signs of increased pressure or changes in head shape should I watch for at home?

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Related questions

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This page provides educational information on the differences between microcephaly and craniosynostosis. Always consult a pediatrician or pediatric neurosurgeon regarding your child's head shape, growth, or development.

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