What is craniosynostosis?
The skull is formed by several bones that are connected to one another by specialized structures called cranial sutures. The cranial sutures are the seams between the skull bones as can be seen below. The purpose of the skull is to protect the brain so it must have the exact shape of the brain and be able to grow at the same rate as the brain grows. The cranial sutures are growth centers for the skull bones that respond to growth of the brain by making more bone. The brain grows very quickly in the first year of life, tripling in size during this time. As the brain grows it stretches the sutures which signals the sutures to make new bone. This growth mechanism allows the skull to enlarge and create exactly the right amount of space for the brain.
Normally, the cranial sutures remain open until we reach adulthood, long after the brain and skull has stopped growing. The only suture that normally closes before adulthood is the metopic suture which closes at 6-9 months of age. Craniosynostosis is present when one or more cranial sutures close prematurely. The brain continues to grow at the same rate whether one or more sutures have closed. The closed sutures cannot generate bone to make room for the growing brain, so the remaining open (functional) cranial sutures must make up the difference by creating more bone to have enough room for the brain to grow. This extra growth at open sutures and lack of growth at the closed suture(s) causes the skull to grow into an abnormal shape because the remaining open sutures can only grow in one direction. In addition to causing an abnormal appearance, craniosynostosis can have negative effects on intellectual development and learning so early diagnosis is important.
The image above illustrates how growth is restricted at the closed sagittal suture and the extra growth, called compensatory growth, at the remaining open sutures can only grow perpendicular to the open sutures which causes an abnormal head shape. In the case of sagittal synostosis a long and narrow head shape occurs. The head shape that results from craniosynostosis in one or more sutures is predictable and consistent enough that experienced craniofacial surgeons can usually make the diagnosis from physical examination alone. This abnormal head shape can cause significant appearance concerns later in childhood. In some cases, the remaining open sutures can’t grow fast enough to keep up with the brain’s growth causing an abnormally high pressure in the skull, which can have negative effects on brain health. This is called elevated intracranial pressure (ICP). The chronic effects of elevated ICP include learning delays, blindness, and death, if untreated.
Two types of craniosynostosis:
Craniosynostosis can affect children in two different ways. The closing of only one suture with no other associated health problems is the most common kind of craniosynostosis. This is called isolated craniosynostosis or non-syndromic craniosynostosis. Isolated craniosynostosis occurs in about 1 in 2,500 newborns. The most common types of isolated craniosynostosis are:
A different and much more rare form is called syndromic craniosynostosis. Syndromes are predictable and well-recognized collections of medical conditions. When craniosynostosis is part of a syndrome there are usually two or more sutures that close abnormally early. Patients with craniosynostosis syndromes have multiple other medical problems that range in severity and depend on the syndrome. In addition to having craniosynostosis, these patients often have abnormal growth potential of the skull and facial bones which makes their treatment much more complicated than the treatment of patients with isolated craniosynostosis. Craniosynostosis syndromes occur at different rates ranging from 1 in 25,000 to 1 in 150,000, depending on the syndrome. The most common of the rare craniosynostosis syndromes include:
Because of these extra medical problems, patients with syndromic craniosynostosis usually need more surgeries. The needs of the two groups of craniosynostosis patients are so different that I think of them as completely different problems and discuss them in separate sections of this website to avoid confusion.
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