The cause of craniosynostosis largely depends on whether it is syndromic (exists with other birth defects) or nonsyndromic (there are no other defects).

Sometimes, the cause is not known.

Causes of nonsyndromic craniosynostosis

The cause of nonsyndromic craniosynostosis is unknown. However, a number of theories have been suggested.

One theory is that nonsyndromic craniosynostosis may be caused by the baby adopting an unusual position in the womb. For example, if the baby’s head is pushed down by their mother’s ribcage, this will place pressure on their skull. This extra pressure may push the plates of bone together, causing the sutures in the skull to fuse too soon.

Other theories suggest that an unidentified defect in the cells that make up the sutures causes them to fuse prematurely, or that a signal from the brain itself results in the abnormal fusion.

Most cases of nonsyndromic craniosynostosis do not appear connected to anything that a mother does during pregnancy. Women who took a medication called valproic acid (sodium valproate), used to treat epilepsy, during pregnancy were thought to be at increased risk of having a baby with craniosynostosis, although recent studies have failed to confirm this.

Causes of syndromic craniosynostosis

Although it is rarer, more is known about the causes of syndromic craniosynostosis.

There are many syndromes that can cause this form of craniosynostosis, including:

• Apert syndrome
• Crouzon syndrome
• Pfeiffer syndrome
• Saethre-Chotzen syndrome

Most cases of syndromic craniosynostosis are caused by one of four genetic mutations. A genetic mutation occurs when instructions carried in certain genes (a unit of genetic material) become scrambled. This means some of the body’s processes do not work in the normal way.

Examples of mutated genes in craniosynostosis are:

• FGFR1, FGFR2 and FGFR3 (three related genes)
• TWIST gene

The FGFR group of genes seem to make a protein called fibroblast growth factor receptor work less effectively. As this protein is involved in regulating cell growth, particularly the growth of bones, it is thought the FGFR mutation disrupts the development of the skull.

The mutated TWIST gene seems to totally block the effects of fibroblast growth factor receptors. There are often a wide range of birth defects associated with this gene.

Craniosynostosis can usually be diagnosed by a paediatrician (specialist in treating children) after a visual examination of your baby’s head. 

Any severe distortions of the skull or face will be apparent, and the existence of ridges over fused sutures or misalignment of the ears will also provide evidence of craniosynostosis.

An X-ray of the skull may be taken to confirm a diagnosis of craniosynostosis.

Computerised tomography (CT) scan

A computerised tomography (CT) scan is the most detailed method of assessing the condition of your child’s skull. A CT scan involves taking a series of X-rays and using a computer to reassemble them into a more detailed image.

CT scans are usually only required to plan some types of surgery or if the diagnosis of craniosynostosis is in doubt.

Read more about CT scans.

If your child has other birth defects that suggest craniosynostosis may be part of a wider syndrome, such as Apert syndrome, a sample of their blood, hair or saliva may be taken and tested for any genetic mutations.

Craniosynostosis is a rare problem with the skull that causes a baby to be born with, or develop, an abnormally shaped head.

The irregular skull shape in craniosynostosis can cause persistent headaches, learning difficulties, eye problems and other symptoms. Most symptoms develop in later childhood.

The symptoms of craniosynostosis usually result from increased pressure within the skull, which is called intracranial pressure (ICP). 

Read more about the symptoms of craniosynostosis.

Craniosynostosis is usually diagnosed after a visual examination of your baby’s head, although further tests may sometimes be necessary.

Read more about diagnosing craniosynostosis.

Why does it happen?

Craniosynostosis is the result of the premature fusion of different sections of the skull. This means the skull is unable to grow in affected areas.

When one area of the skull is prevented from growing, other areas may ‘overgrow’ to compensate and limit the pressure developing around the brain. A lack of growth in some areas and compensatory growth in other areas will result in an altered head shape.

In most cases of craniosyntosis, there are no other birth defects (known as nonsyndromic). When it develops with other birth defects, it is known as syndromic.

The causes of nonsyndromic craniosynostosis are unknown. There are theories about cell defects and the baby’s position in the womb, but these have not been proven.

Syndromic craniosynostosis is the result of one of several possible syndromes. A syndrome is a range of symptoms related to a common cause, which is usually (but not always) genetic.

Some of the syndromes that can lead to craniosynostosis are listed below. 

Read more about the causes of craniosynostosis.

Different types of craniosynostosis can be described based on the areas of the skull affected and the resulting changes in shape (see symptoms of craniosynostosis for more information). 

How common is craniosynostosis?

Craniosynostosis is rare, affecting an estimated one in every 1,800 to 3,000 children. Three out of every four cases affect boys.

Nonsyndromic craniosynostosis is the most common form of the condition, accounting for 80-95% of all cases.

There are more than 150 different syndromes that can cause syndromic craniosynostosis, all of which are very rare. These include:

• Apert syndrome, which affects one in every 100,000 children and disrupts the normal growth of bone before birth, resulting in deformities of the head, hands, feet and face
• Crouzon syndrome, which affects one in every 60,000 children and disrupts the normal growth of bone in both the skull and the face, often resulting in severe facial disfigurement
• Pfeiffer syndrome, which affects one in every 100,000 children and disrupts bone growth, resulting in deformities of the head and face – it also causes big toes, wide thumbs and webbed hands and feet
• Saethre-Chotzen, a genetic condition that affects around in one every 50,000 births and can cause a wide range of disfigurements, including facial defects

Treating craniosynostosis

The main treatment for craniosynostosis is surgery.

This can either be carried out during the first year of your baby’s life, or delayed until later childhood.

The timing of the surgery is decided by doctors, in consultation with you.

Most children with craniosynostosis recover well after surgery and the appearance of their skull improves significantly.

However, around one in 15 children may have further problems with their skull’s development as they get older, which will require further surgery to correct.

Read more about treating craniosynostosis.

Craniosynostosis causes an irregular skull shape. The baby’s skull shape is determined by the type of craniosynostosis they have.

The skull consists of plates of bone connected by strong elastic tissues called sutures. The sutures give the bone plates flexibility so the skull can grow along with the brain.

Skull shapes

Sagittal synostosis

Sagittal synostosis is the most common type of craniosynostosis, accounting for around half of all cases.

It occurs when the suture at the top of the skull (the sagittal suture) fuses. This leads to a lack of growth in width and compensatory growth in length, resulting in a long, narrow skull.

Coronal craniosynostosis

Coronal craniosynostosis is the second most common type of craniosynostosis after sagittal synostosis, accounting for around one in four cases.

In coronal craniosynostosis, the fusion occurs in one or both of the two sutures that run from the top of the ear to the top of the skull. These are known as the coronal sutures.

If only one coronal suture is fused, the infant will develop a flattened forehead on the affected side. They may also have a raised eye socket and a crooked nose. If both coronal sutures are fused, the infant will develop a flat and prominent forehead and brow. 

Metopic synostosis

Metopic synostosis is an uncommon type of craniosynostosis, occuring in 4-10% of cases. The fusion occurs in the metopic synostosis, which is the suture that runs from the nose to the top of the skull. Infants with metopic synostosis will develop a pointed scalp that looks triangular.

Lambdoid synostosis

Lambdoid synostosis is the rarest type of craniosynostosis and occurs in about 2-4% of cases. Fusion occurs in the lambdoid suture, which runs along the back of the head. Infants with lambdoid synostosis will develop a flattened head at the back.

However, not all children with a flattened head at the back have lambdoid synostosis. It is common and normal for babies to have some flatness at the back of their head as a result of lying on their backs for prolonged periods of time. This is known as positional plagiocephaly.

Intracranial pressure (ICP)

Raised intracranial pressure (ICP) is a symptom that may occur in all types of craniosynostosis. ICP increases when pressure builds up inside your child’s skull due to its irregular shape.

When only one suture is involved, raised ICP occurs in less than 15% of children. However, in syndromic craniosynostosis where multiple sutures are involved, raised ICP is more common and may occur in up to 60% of cases.

If your child has mild craniosynostosis, it may not be spotted until they begin to experience problems due to an increase in ICP. This usually occurs when a child is between four to eight years old.

The symptoms of ICP usually begin with:

• a persistent headache, usually worse in the morning and last thing at night
• vision problems, such as double vision, blurred vision or a ‘greying out’ of vision
• an unexplained decline in the child’s academic abilities

If your child complains of any of the above symptoms, take them to see your GP as soon as possible. In most cases, these symptoms will not be caused by raised ICP, but they do require further investigation.

Left untreated, other symptoms of raised ICP can include:

• vomiting
• irritability
• sluggishness and unresponsiveness
• swollen eyes or difficulty following a moving object
• hearing difficulties
• breathing difficulties

Surgery is the main treatment for craniosynostosis, the timing of which depends on your child’s condition and your personal preferences.

Sometimes the surgery is carried out later in childhood to reduce the likelihood of the operation needing to be repeated.

Earlier surgery may be recommended if there are problems inside the head or with the eyes and jaw, or for cosmetic reasons.

You should talk to your child’s doctors to decide when the operation should be carried out.

There are currently four NHS hospitals that have specialist surgical units and teams with experience and expertise in carrying out this type of surgery. They are:

• John Radcliffe Hospital in Oxford
• Great Ormond Street Hospital in London
• Birmingham Children’s Hospital
• Alder Hey Hospital in Liverpool

Surgery for craniosynostosis is usually carried out by a team of two surgeons who each have their own speciality. These are:

• a neurosurgeon – a specialist in the nervous system and brain
• a craniofacial surgeon – a specialist in surgery of the face, head and jaws

The procedure

Surgery for craniosynostosis is carried out under a general anaesthetic, which means your child will be asleep during the procedure and will not feel any pain.

The neurosurgeon will make an incision across the top of your child’s scalp. This will leave a scar, but it will be hidden by their hair. The neurosurgeon will remove affected areas of skull.

The removed pieces of bone are reshaped by the craniofacial surgeon before being returned to a normal position in the skull. The incision will then be sealed using dissolvable stitches.

After the operation

Extra precautions always have to be taken in cases where surgery is carried out on the skulls of very young children.

Therefore, after the operation it is likely your child will be transferred to a high dependency unit (HDU) for one or two days so their condition can be carefully monitored. Most children are well enough to leave hospital around five days after surgery.

Following surgery, most children will only experience mild pain, but it is common for them to develop significant swelling around their eyes. The swelling can often prevent them from opening their eyes. Your child may find this annoying or distressing, but the swelling does not present a health risk and should go down after a few days.

After having surgery for craniosynostosis, it is likely your child will be asked to attend regular check-ups so the future development of their skull can be monitored. The check-ups will be quite frequent at first, such as every six weeks, before becoming less frequent as your child gets older. Most children will only require an annual check-up once they reach the age of six.