A baby’s skull has 6 major cranial sutures:
- The metopic suture
- Two coronal sutures
- The sagittal suture
- Two lambdoid sutures
The baby’s growing brain is what makes their skull grow. The growing brain does this by mechanically triggering growth signals in the sutures that leads to new bone formation and enlargement of the skull bones. This keeps the skull just large enough for the brain to fit perfectly. The brain more than triples in size during a child’s first 2 years of life. To make room for the brain, the skull must grow rapidly during this time, reaching 80% of its adult size by the age of 2 years. By age 5, the skull has grown to over 90% of the adult size. All sutures remain open until adulthood, except for the metopic suture which usually closes between 6 and 12 months of age.
A baby will have a misshapen head when one or more of the sutures closes too early. This usually happens prenatally, before the child is born. Again, the brain is growing very quickly at this age. The remaining open sutures must grow faster to create the space inside the skull that the closed suture was supposed to accommodate. This extra growth at the open sutures causes a misshapen head. The abnormal head shape created by craniosynostosis depends on which sutures are closed. Craniofacial surgeons can usually determine which suture(s) is closed when they examine the patient because the abnormal head shape that the closure of each suture produces is characteristic. In about 15 out of 100 cases, one closed suture results in the skull not growing fast enough to keep up with the rapid growth of the brain. This can be harmful to the health of the brain. The more closed sutures there are, the higher the likelihood that the skull will not be able to grow fast enough.