The skull consists of 5 thin, curved, bony plates that are held together by fibrous material called sutures. These sutures allow the baby's skull to expand with the growing brain. Usually a baby's brain and skull double in size in the first 6 months of life and double again by age 2 when some sutures begin to close. The skull and brain continue to grow throughout early life but at a much slower rate.

Sutures close and fuse into bone at different ages according to their location. For example, the sagittal suture normally closes between 12 and 24 months of age.

If any of the sutures close too early, it may affect normal skull development, sometimes resulting in a misshapen head or other problems.