The skull is not a single bone like a crash helmet, but is made up of “plates” of bone that are joined together by seams (sutures) similar to what you might find in clothing.
The sutures are there to help with the moulding of the head during delivery, but they also have a role in the general shaping of the head as it grows. They are not in fact essential for head growth, the head will grow even when all the sutures have fused together, but if there is a problem with them, then the shape of the head can be affected.
Sutures normally fuse after all head growth has finished. However, they can sometimes fuse before birth and this is the condition known as craniosynostosis. It may affect a single suture or several. When it affects a single suture it is often referred to as ‘simple’ craniosynostosis. When it affects multiple sutures then it is often associated with a particular syndrome. In other words, the child may have other areas, particularly the facial bones and fingers affected as well.
Syndromic and the other complex forms of craniosynostosis usually involve the two coronal sutures which run from the anterior fontanelle region down the side of the head to the temple area. When these fuse prematurely, they produce a flattening of the forehead, which is particularly obvious where it meets the upper border of the eye sockets. Sometimes only the two coronal sutures are involved, sometimes all the sutures of the skull are affected. In addition to changing the child’s appearance, complex forms of synostosis can be associated with several other problems. If the bones of the upper jaw fail to grow forward normally, this produces obstruction to the child’s airway that can lead to difficulty breathing. If the bones both above and below the eye sockets have failed to grow properly, the eyes themselves may be left in a protruding position and when this is severe the child may have difficulty closing his or her eyes.
Frequently Asked Questions
Another possible complication for children with complex syndromic forms of craniosynostosis is raised pressure inside the head (raised intracranial pressure – ICP). This can be due to several different causes. The bones of the skull may just not be able to expand sufficiently to accommodate the growing brain and there is therefore a mismatch between the size of the brain and the bone of the skull that can lead to a rise in ICP. Some children also have obstruction to the flow of ‘brain water’ (cerebrospinal fluid – CSF), which normally circulates through various cavities (the ventricles) within the brain and then over the surface of the brain.
Obstruction to the circulation leads to a build-up of CSF under pressure, a condition we call hydrocephalus. Finally, raised ICP can be due to obstruction of the veins of the head as they pass through the bones at the base of the skull (venous hypertension). As you can see, children with complex and syndromic forms of craniosynostosis may have little wrong with them except for a change in their appearance, but some are much more severely affected and have problems related to eye exposure, difficulty breathing and raised intracranial pressure. It is for this reason that it is our usual policy to admit these children to our unit for a few days of formal assessment that may include brain scanning (usually computerised tomographic – CT) and examination by a variety of different specialists including ophthalmology (eyes), ear nose and throat, orthodontics (teeth), plastic surgery, genetics, speech and language, psychology and any other specialties that appear appropriate.
This assessment allows the craniofacial team to decide whether the child has any problems that require immediate attention (raised intracranial pressure or difficulty breathing for example) or, if all is well at present, what sort of future supervision by the craniofacial team is required. Most children who do not require any early form of intervention are then looked after according to a protocol that determines how often they are seen and at what intervals further assessments are required.
Our general policy with regard to the management of children with complex and syndromic forms of craniosynostosis can be summarised as follows;
Most of these conditions are caused by a single disordered gene (see section on genetics below), which continues to exert its effects upon the growth of the head and face, for as long as growth continues, often up until the late teenage years. This means that if any form of reconstruction is carried out before growth has ended, subsequent growth will tend to produce a degree of relapse (or reversion) of whatever has been achieved by the operation.
From this, it can be seen that unless surgery is required for some pressing functional reason (difficulty breathing, raised ICP, for example), the best final cosmetic result may not be achievable until the child is nearly grown up. Once again, this depends very much upon the severity with which the child has been affected and the syndrome involved (some have comparatively minor effects, some more major).
During a child’s early years therefore, we tend to reserve surgical intervention for such problems as raised intracranial pressure, difficulty breathing, eye exposure etc. The timing of surgery for ‘purely’ cosmetic reasons varies from child to child and from syndrome to syndrome. The earlier such surgery is carried out, the more likely it is that either all or some element of it may need to be repeated. However, children who look unusual may be bullied at school and therefore there are often compelling reasons for operating earlier (just prior to a change of school, for example).
There is premature closure of both coronal sutures, but in more severe cases, other skull sutures may be involved as well. There is failure to grow forward of the upper jaw and cheekbones and the nose may have a ‘beaked’ appearance. There is a large variation in the extent to which children may be affected, ranging from very mild with few complications and normal development, to children who require frequent surgical interventions.
Premature closure of at least both coronal sutures and recession of the upper jaw and cheekbones produces a characteristic facial appearance with a tendency for the outer part of each eye to slope downwards. The characteristic feature of Apert syndrome is that the children are born with their fingers and toes matted together (syndactyly). Learning difficulties (developmental delay) is common, as are problems with breathing (airway obstruction) and in severe cases, raised intracranial pressure.
There is (at least) premature closure of both coronal sutures together with impaired development of the upper jaw and cheekbones. In addition, children with Pfeiffer Syndrome have a characteristic appearance of their thumbs and big toes; they tend to be broad and slightly apart from the other toes. The most severely affected children with Pfeiffer Syndrome have hydrocephalus and an abnormal head shape that can take on a clover-leaf appearance.
Both coronal sutures fuse early, but the effect can often be asymmetrical. The nose may be rather prominent but abnormal development of the upper jaw and cheekbones is uncommon as is raised intracranial pressure. A characteristic feature is often drooping of one or both eyelids (ptosis). A minor abnormality of one or more fingers is often seen.
Muenke (P250A) Syndrome
This syndrome has only been described since the advent of DNA testing. It causes premature closure of a single coronal suture or sometimes both. In either case it is entirely compatible with normal intellectual development, although some children do have learning difficulties. Facial problems, airway obstruction and eye exposure do not usually occur in this syndrome. In other words, its implications tend to be entirely cosmetic.
In this syndrome, there is a characteristically wide separation between the eyes (hypertelorism). There is usually premature fusion of one coronal suture. Other features include a prominent gap between the two front teeth and ‘unruly hair’. It is rare for it to be associated with eye exposure, airway obstruction, raised intracranial pressure or any other facial deformity. Treatment is therefore only required for cosmetic reasons.
All the conditions listed above are due to a particular disordered gene and can be inherited/passed on in a distribution that is termed ‘autosomal dominant’. This means that if one parent is affected, half his or her children (and all these conditions can affect boys as well as girls) are likely to be affected also. Many of these conditions however occur in children whose parents who are not obviously affected. In this situation, the gene mutation is a new one, and most geneticists assess the risk of the same parents having a similarly affected child at approximately 2% (as opposed to the 50% if one parent is already affected).
Further information can be found in this publication;
The Clinical Management of Craniosynostosis
Edited by Hayward, Jones, Dunaway and Evans
MacKeith Press 2004