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. 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 a baby's 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. The head doesn't form a normal shape.

How the disease affects your baby depends in part on how many of the skull sutures close too soon:

  • If only one suture closes, the baby's brain usually develops normally, but the head has an odd shape. This happens in most cases of craniosynostosis.
  • If more than one suture closes, 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 delay. But this severe pressure is rare.