Craniosynostosis is a birth defect in which the bones in a babys skull join together too early, before the babys brain is fully formed. As the babys brain grows, the skull can become more misshapen. The spaces between a typical babys skull bones are filled with flexible material and called sutures. These sutures allow the skull to grow as the babys brain grows. Around two years of age, a childs skull bones begin to join together because the sutures become bone.

Craniosynostosis usually involves premature fusion of a single cranial suture, but it can involve more than one of the sutures in a babys skull (multiple suture craniosynostosis) . In rare cases, craniosynostosis is caused by certain genetic syndromes (syndromic craniosynostosis) . The term given to each type of craniosynostosis depends on what sutures are affected. Types of craniosynostosis include:

• Sagittal (scaphocephaly): premature fusion of the sagittal suture that runs from the front to the back at the top of the skull forces the head to grow long and narrow. This head shape is called scaphocephaly.
• Coronal: premature fusion of one of the coronal sutures (unicoronal) that run from each ear to the top of the skull may cause the forehead to flatten on the affected side and bulge on the unaffected side. When both coronal sutures fuse prematurely (bicoronal), the head has a short and wide appearance, often with the forehead tilted forward.
• Nonsyndromic craniosynostosis: the most common type of craniosynostosis.

Craniosynostosis can affect a childs brain and development. The degree of the problems depends on the severity of the craniosynostosis, the number of sutures that are fused, and the presence of brain or other organ abnormalities. The most apparent sign of craniosynostosis is typically an abnormally shaped head. Other signs may include no "soft spot" on the babys skull, a raised firm edge where the sutures closed early, and slow growth or no growth in the babys head size over time. Many types of craniosynostosis require surgery to relieve pressure on the brain, correct the craniosynostosis, and allow the brain to grow properly. When needed, a surgical procedure is usually performed during the first year of life, but the timing of surgery depends on which sutures are closed and whether the baby has one of the genetic syndromes associated with craniosynostosis.