Craniosynostosis (say "kray-nee-oh-sih-noh-STOH-sus") is a problem with the skull that causes a baby's head to be oddly shaped. In rare cases it causes pressure on the baby's brain, which can cause damage. It is also called craniostenosis.

A baby's skull is not just one bowl-shaped piece of bone. It is made up of five thin, bony plates that are held together by fibrous material called sutures. The sutures let the skull expand as the brain grows. Over time, the sutures harden and close the skull bones together.

When a baby has craniosynostosis, one or more of these sutures close too soon. How the problem affects your baby depends in part on how many of the sutures close too soon:

• If only one suture closes too soon, the baby's brain usually develops normally, but the head has an odd shape. This is what happens in most cases.
• If more than one suture closes too soon, the baby's brain may not be able to grow as fast as it should. If severe pressure builds up around the brain, it may cause brain damage, seizures, blindness, and developmental delays. But this severe pressure is rare.