Craniosynostosis

A birth defect which results in a misshapen head, craniosynostosis is more than a cosmetic problem. With skull bones that close prematurely the head is distorted which consequently can lead to brain abnormalities and associated complications within the skull region.

Summary

A baby’s brain requires sufficient room to develop and grow, and the joints between the plates in an infant’s skull provide the flexibility to allow this. However, in some cases one or more of these soft joint areas closes too early, before the brain has fully developed, leaving insufficient room for normal growth.

The outcome of this early bone fusion is a head which is distorted, a symptom which may be apparently visually, but there could be underlying abnormalities present too. Learning difficulties, headaches, visual defects and other symptoms may all appear in childhood as a manifestation of craniosynostosis.

Presenting features

One of the defining features of craniosynostosis is the abnormal skull shape; the extent of the deformity depends on the form of craniosynostosis.

In a baby’s head, there is a strong elastic tissue which stretches between the seven plates of bone: these are called cranial sutures. And these sutures are what provides the skull with the flexibility to be able to allow the brain room to grow. This flexibility is absolutely vital because a human brain doubles in size in the first three years, and the skull needs to expand to be able to accommodate this.

By the time the individual matures and the skull no longer needs to continue to expand, the sutures permanently fuse creating a continuous covering of bone rather than the mosaic effect that the plates of a baby present.

In craniosynostosis, a hard ridge grows along the sutures far too soon and the fontanelle either disappears or feels changed. Parents may start to notice that their child’s head is no longer growing proportionally to the rest of the body.

As a result of these changes within the skull plates, raised intracranial pressure (ICP) can develop. This condition worsens as pressure rises due to the misshapen effect.

ICP doesn’t always rise; in cases of craniosynostosis where just one suture is affected, just 15% of infants suffer raised ICP. However in cases where there are multiple sutures which are involved, up to 60% of infants will also suffer from raised ICP.

Depending on the severity of the condition, the craniosynostosis may not be identified immediately, and can take several months to be identified. In cases which are particularly mild, it may remain undiagnosed until the raised ICP starts to become more symptomatic, typically between the ages of 4-8 years old.

The initial presenting features of ICP usually are visual defects such as blurring or double vision, chronic headaches and an inexplicable reduction in the academic performance of the child.

What makes later diagnosis particularly difficult is that these symptoms are vague and may well be attributable to another, less serious cause. In some circumstances they may be ignored or disregarded as fatigue or overwork. The majority of children presenting with these symptoms will not have craniosynostosis but it’s important to get the diagnosis ruled out.

If medical attention is not sought, raised ICP can ultimately lead to:

1. Breathing problems
2. Auditory difficulties
3. Difficulty tracking an object visually
4. Swollen eyes
5. Vomiting
6. Irritability

Diagnosis
Craniosynostosis is typically diagnosed by a consultant paediatrician and is based on a combination of visual observation and confirmatory tests and investigations. In many cases, a visual assessment is often sufficient to more or less confirm the diagnosis. This is because the distinctive ridges along the suture lines will be evidence, and this combined in some cases with displacement of the ears can be more than adequate signs.

To aid with the diagnosis, the paediatrician is likely to ask about the following:

1. The length of time the child spends lying on their back
2. When the changes were first identified
3. The sleeping position
4. Whether there have been any seizures
5. Whether the developmental milestones are being met
6. If there is any documented family history of either craniosynostosis or genetic variations such as Crouton or Apert Syndrome.

If there is any doubt over the diagnosis, or if information is required to establish the extent of the condition and the amenability for surgical correction, investigations such as a CT scan or plain X-ray may be carried out.

In some cases there may be concerns that the craniosynostosis is part of a wider condition; if this is the case then saliva, hair and blood may be taken to check for genetic mutations. 

Classification

Craniosynostosis can be subdivided into a number of separate categories, differentiated by the sutures which are involved in the deformity. The shape of the skull and any consequent defect will be a direct result of the sutures which have been affected.

Sagittal synostosis (scaphocephaly)
This is one of the most frequently seen types of craniosynostosis, presenting in around 50% of all the cases.

The suture which lies at the topmost part of the skull, the sagittal suture, is affected and fuses as a result. The prevents the head growing in width, instead forcing it into a long and thin shape.

Coronal craniosynostosis  (anterior plagiocephaly)
This subcategory accounts for approximately a quarter of all cases, second only to sagittal synostosis.

In this presentation, either one or both of the sutures which stretch to the top of the ears from the peak of the skull are affected. These sutures are known as the coronal sutures.

Where fusion has only occurred on one side, there will be a flattening of the forehead, but only on the affected side. The eye socket may also be raised and crooked nose.

In cases where there is a two-sided fusion (known as bicoronal synostosis or brachycephaly), there will be a flattening of the forehead all the way across and there may also be a prominence of the brow too.

Metopic synostosis
A far less common type of craniosynostosis, metopic synostosis occurs in less than one in ten cases. The metopic synostosis is the suture which runs from the top of the head through to the nose.

Infants who are affected by this type of craniosynostosis will have a scalp which develops a point and also appears to be triangular.

Lambdoid synostosis
The rarest presentation of all, lambdoid synostosis only occurs in just 2-4% of all instances of craniosynostosis. The lambdoid suture stretches along the rear of the head and when this is affected, the infant will have a characteristically flattened head.

However, it’s important to note that not all infants with a flattened head at the back will have a diagnosis of lambdoid synostosis. Because of the length of time that babies spend lying on their backs, some flattening of the head can occur. This is particularly the case now that the majority of infants are put to sleep lying on their back. It can also be the result of trauma during birth.

When this occurs it is referred to as positional plagiocephaly and is unrelated to lambdoid synostosis or any other kind of craniosynostosis. Positional plagiocephaly typically resolves spontaneously within the first 12 months. In severe cases a custom-made helmet may be fitted to help gently encourage the head to regain a normal shape.

Epidemiology and aetiology

Craniosynostosis is a condition which is caused by the bones fusing too early, thus preventing the skull from expanding to accommodate the skull as required.

However, when one part of the skull is fixed and unable to grow, another part may try to compensate for the lack of movement, growing excessively in order to try and release some of the pressure which inevitably builds around the brain.

This lop sided growth means that the skull will have extra growth in some areas and reduced growth in others, and it’s this unevenness which leads to the unusual shape.

Craniosynostosis is either idiopathic and presents in isolation without any other defects at birth or is considered to be syndromic, where it’s part of a rare condition, and just one of the features of such. Syndromic causes are typically but not exclusively genetic. Craniosynostosis has an incidence of just one case in every 1700-3000 live births. Three quarters of those affected are males.

Nonsyndromic is far more common, with up to 95% of cases arises from no definable cause. Of the small percentage which are syndromic, there are around 150 known syndromes which could result in the deformity. All are very rare and include:

1. Apert Syndrome. The incidence is approximately 1 in every 100,000 and manifests with a disruption of normal bone growth antenatally, resulting in birth defects to the face, hands, feet and head
2. Crouzon Syndrome. The incidence is 1 in every 60,000 with the bone deformity limited to the face and skull. Although the bone growth abnormalities are confined to one area, the extent of the facial disfigurement can be extremely severe.
3. Pfeiffer Syndrome. The incidence is roughly 1 in every 100,000 and alters bone growth at various sites within the body resulting in deformities of the head and face with broad thumbs and large toes and webbing in the feet and hands.
4. Saethre-Chotzen. The incidence is 1 in every 50,000 and the bone disfigurements can be widespread with many body parts affected, including the face.

Treatment

The only effective treatment for craniosynostosis is surgery and when this should be carried out is very much an individual decision which will be determined depending on the extent, placement and severity of the deformity.

Where possible, the surgery will be postponed for as long as possible so that the likelihood of having to repeat surgery is reduced. However, this won’t always be viable, particularly if the deformity is causing complications inside the skull, or with the jaw or eyes. In some cases early surgical correction is desirable for cosmetic purposes.

The decision about whether to operate will be reached jointly between the parents and the treating physicians.

At present, there are four NHS hospitals within the UK who have the expertise to be able to carry out this type of surgery. These are:

1. Alder Hey Hospital in Liverpool
2. Birmingham Children’s Hospital
3. Great Ormond Street Hospital in London
4. John Radcliffe Hospital in Oxford

When surgery is carried out, two teams are usually involved, one for the neurosurgeon and the other for the craniofacial surgeon.

Surgical options

When surgery is performed to correct the defects associated with craniosynostosis, there are two possible routes: open surgery or endoscopic.

Open surgery
A far more common procedure, open surgery requires a general anaesthetic which means that the child will be unconscious throughout the operation which is likely to take several hours.

An incision will be made across the scalp and the parts of the skull which have been affected will be removed. This part of the surgery is performed by the neurosurgeon.

The craniofacial surgeon and their team then takes over to reshape the fragments of skull bone before being placed back into a more normal position. The incision will be stitched and the resulting scar usually covered by the hair in due course. Plates may be used to screw the bone plates into position. These are usually made from a material which can be gradually reabsorbed by the body.

Further surgery may be required to correct any severe facial deformities at a later date.

Endoscopic surgery
When surgery is carried out on younger children, usually babies aged under six months, because their skull is far softer and hasn’t yet fully hardened, endoscopic surgery may sometimes be considered as an alternative.

With endoscopic surgery, a general anaesthetic is not required. An endoscope is inserted through a small inclusion in the scalp from which the suture can be re-opened to allow normal growth of the skull to resume.

There are benefits to proceeding with endoscopic surgery such as a far quicker procedure, typically around an hour, and a shorter, easier recovery.

Prognosis

Following surgery, a full recovery is typically made and the skull will often adopt a more uniform shape. Of course, the first few days must be approached carefully and it’s normal procedure to keep the child on a high dependency ward for 24-48 hours, particularly for open surgery. Most children are discharged from hospital within five days of surgery.

Recovery is normally uncomplicated with only mild pain experienced although swelling around the eyes may be severe. In some cases the child may not be able to open their eyes. This is only a temporary effect and will quickly resolve within a matter of days. Although distressing to the child, it does not represent any danger and is a common side effect.

After surgery for craniosynostosis, the child will be kept under regular follow up to monitor the future growth of their skull. By the age of six these routine follow-ups will typically be no more frequent than once per year.

Approximately a fifth of children develop further problems with their skull as they mature, which may require a second bout of surgery.