WHAT IS CRANIOSYNOSTOSIS?
Craniosynostosis is a condition where one or more of the sutures in a child’s skull fuses or closes too early. Sutures are fibrous joints located between the bones in a baby’s skull. Open sutures allow the skull to grow at the same rate as the brain. In the first few years of life this growth is very rapid.
When a suture closes too early, the skull cannot grow normally. This can cause pressure on the growing brain. As the brain continues to grow, it pushes against or expands the areas of the skull that are not fused. This leads to a change in the shape of the head. Depending on which of the four sutures is fused, a typical head shape is produced.
The 4 sutures in the skull are metopic, sagittal, lambdoid and coronal. Only one suture - the metopic - normally closes during the first few years of life, and the others remain open into adulthood.
Most commonly, only one suture is affected. This is called single suture craniosynostosis. With singlesuture craniosynostosis, babies are usually healthy and have no other problems or differences.
Less commonly, two or more sutures can fuse early. In this case, children are more likely to have a craniofacial syndrome, especially when both coronal sutures are affected. The more sutures involved, the higher the level of concern for pressure on the brain.
THERE ARE FOUR TYPES OF SINGLE SUTURE CRANIOSYNOSTOSIS:
1. Sagittal Craniosynostosis (Scaphocephaly)
Sagittal craniosynostosis is the most common form of craniosynostosis, occurring in about 1 in 2000 live births. The sagittal suture runs from the babies soft spot and goes straight back. When it fuses too early, a ridge can often be felt or even seen over this area. The soft spot may be absent or small. As the brain grows, the skull can no longer get wider, so it gets longer and bulges at the front and the back. This is called scaphocephaly. A baby with sagittal craniosynostosis may seem to have a large or prominent forehead.
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2. Metopic Craniosynostosis (Trigonocephaly)
The metopic suture runs from the baby’s soft spot to the forehead. When it fuses too early, a ridge can often be felt or even seen over this area. The soft spot may be absent or small. As the brain grows, the forehead can no longer get wider, and appears pinched. When viewed from above, the head shape looks like a triangle. This is called trigonocephaly. A baby with metopic craniosynostosis may seem to have his or her eyes close together.
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3. Unicoronal Craniosynostosis (Anterior Plagiocephaly)
The coronal suture runs from a baby’s soft spot towards the ear. When it fuses too early, the forehead looks flat of the affected side. The eyebrow can appear higher. As the brain grows, the forehead can appear prominent on the unaffected side. This is called anterior plagiocephaly.
4. Lambdoid Craniosynostosis (Posterior Plagiocephaly)
The lambdoid suture is in the back of the head. When this suture fuses too early, the back of the head is flattened and the ear may be lower on the affected side. This is the rarest type of craniosynostosis.
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HOW COMMON IS CRANIOSYNOSTOSIS?
Craniosynostosis usually occurs while the baby is still in the womb. It is thought to occur in 1 out of every 2000 live births. Babies with this condition typically have an unusual head shape when they are born and it becomes more noticeable as weeks and months pass.
The most common reason for a baby to have an unusual head shape is not craniosynostosis, but a condition called deformational plagiocephaly which does not involved a fused suture. That is why it is important to see a craniofacial specialist for an evaluation.
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WHAT CAUSES SINGLE SUTURE CRANIOSYNOSTOSIS?
The exact cause of craniosynostosis is not yet clear. In about 20 % of children with single suture craniosynostosis, a mutation or change can be identified in one of the genes.
There is scientific evidence that premature fusion occurs when the bones of the skull are restricted in the womb, not allowing for movement from the growing brain. This may be why the incidence of craniosynostosis is higher in twin pregnancies.
Sometimes single suture craniosynostosis is part of a craniofacial syndrome, although this is more common with multiple sutures. Craniofacial syndromes are thought to result from a genetic mutation.
If a couple has a child with single suture craniosynostosis, the chance their next baby will also have craniosynostosis is believed to be less than 2%.
Our center is currently investigating both the molecular mechanisms and the underlying genetic causes of craniosynostosis.
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HOW DO YOU DIAGNOSIS CRANIOSYNOSTOSIS?
If a family or pediatrician notices an unusual head shape, the infant should be referred for evaluation by a craniofacial specialist. Sometimes children are referred based on an unexpected change in head size (circumference) or early closure of the soft spot (fontanel).
An experienced pediatric craniofacial surgeon or pediatric neurosurgeon can make the diagnosis by physical exam. In some cases, a CT scan may be obtained to confirm the diagnosis and assist with the evaluation.
Read more about how craniosynostosis is treated