Craniosynostosis (craniostenosis) is a condition that affects the skull development of a fetus or newborn. In craniosynostosis, one or more of the connections (sutures) between plates in a fetus's or baby's skull close too soon, and the bony plates of the skull fuse too early.

As a result of early fusion of the plates, the affected area of the skull does not expand normally with the growing brain, causing a misshapen head. In severe cases, usually when craniosynostosis affects more than one suture, pressure builds on the brain and may cause long-term complications.

Some babies develop craniosynostosis because they inherited certain genetic traits from one or both parents. Other causes are not fully understood but may be related to fetal growth or position or to other conditions during pregnancy.

An irregularly shaped head is the most noticeable feature of craniosynostosis, and it is usually noticed at birth or shortly thereafter. Imaging tests (such as a skull X-ray, CT scan, and MRI) may be done to confirm a diagnosis.

Craniosynostosis is treated with surgery to allow the skull to return to its normal shape, grow normally, and prevent further complications. Generally, no permanent disfigurement occurs, especially when surgery is done early, often within the first 6 months of life.