When a child is born with problems in the fusion of the skull plates, he or she has a condition called craniosynostosis. Normally, a child is born with a skull that has not quite closed over by the time of birth, but in some cases the skull plates have closed over abnormally quickly. Babies with this condition can have noticeably unusual face or head shapes, but mild cases can display little symptoms. Four major types of craniosynostosis are possible; coronal craniosynostosis is the second most common, and the different conditions are divided by the way the skull has fused.
In the womb, a baby grows in size and completes the growth of various parts of the body. The skull gives support to the head and the face, and it also protects the brain from accidental injury. It first appears as separate plates of bone, which eventually come together to give a normal closed-up skull. Two main issues can arise, however, during the baby's development that can give rise to craniosynostosis.
The individual plates can fuse together earlier in the pregnancy than usual, potentially causing the child's skull to be smaller in that area than normal. As the bone plates continue to grow, despite the closure of the gap between them, the new bone can then develop into ridges. Another possible cause of craniosynostosis, which typically affects the whole head, is that the brain does not grow at the usual rate. Pressure from the brain getting bigger underneath the skull plates helps to drive the bony growth and fusion, and if the brain is not as large as normal, then the plates may grow abnormally.
Each gap between the plates of the skull is called a suture, and different types of craniosynostosis are described by the specific sutures they affect. The most common example is the sagittal synostosis, which displays abnormal closure of the suture that runs along the top of the head from forehead to the back of the head. If a child has coronal craniosynostosis, then he or she has problems with the sutures that form a line between the ears and the top of the head. Less common is a synostosis of the suture that runs from the child's nose to the top of the forehead, and the least common craniosynostosis affects the suture that passes horizontally across the back of the child's head.
Coronal craniosynostosis can affect one side of the baby's head, or both sides. If one side only has a problem, then the child can have a flattening of the forehead on that side only, along with an abnormally high eye socket. His or her nose can also be bent to one side. If both the coronal sutures are involved in the condition, then the child usually has both eye sockets higher than usual and a flattening of the entire forehead.
Medical issues that can arise with coronal craniosynostosis include abnormally high pressure inside the skull itself. Operations can help reduce the pressure, and can also help give the child's skull a more normal appearance. Children with coronal craniosynostosis may also have developmental problems relating to the brain, but this does not affect all babies with the condition. Some cases are due to genetic mutations, but others appear to happen randomly.