Q&A: What is craniosynostosis?

Understanding what makes a doctor (or a parent) suspect that a baby has craniosynostosis first requires an understanding of what normally happens to the skull during the first years of a baby's life. While most people tend to think of the skull as one solid, continuous bone, newborns are in fact born with a skull made up of several bony "plates" separated by four main (and several other smaller) sutures. The fact that a newborn's skull is not simply a single bony structure is extremely useful, as it allows the skull to compress and distort enough to make its way through the relatively narrow birth canal. During infancy, the ability for these bony plates to expand also is important in allowing a baby's brain the room it needs to grow, rather than trapping it in a small, rigid space. This is particularly important given that a baby's brain volume typically experiences very rapid growth—increasing in size by as much as four-fold during the first two years of life!

I also find that breaking down the word craniosynostosis is an useful way to better explain what craniosynostosis actually is. Cranio simply refers to the upper portion of the skull (the cranium), syn means "together," and ostosis refers to bone creation or growth. When you put these three terms together, by definition the result is a condition where one or more of the bony plates of the skull (or cranium) fuse together prematurely.

The underlying reason for premature closing, or fusing of the skull's sutures is not clearly understood. What we do know is that one out of every 1800 babies experiences early closure of one or more of the sutures. Because early closure limits normal growth, craniosynostosis causes babies to start to develop abnormally shaped heads. Just what kind of shape the skull takes depends on which (and how many) of the sutures start to close early. In general, craniosynosis usually involves a single suture and occurs by chance, rather than as part of a genetic syndrome.

Knowing that craniosynostosis is potentially serious but also treatable, the current recommendation is for primary care doctors to always be on the lookout for any baby whose head shape is asymmetric or unusual and to refer these children as early as possible to a specialist for further evaluation. The goal of careful assessment is not only to insure that a child with possible signs of craniosynostosis is evaluated, but that when necessary, proper treatment (which typically includes surgery) is discussed and made available.