Cranial sutures are fibrous bands of tissue that connect the bones of the skull.
Fontanelles; Sutures - cranial
An infant's skull is made up of six separate cranial bones (the frontal bone, the occipital bone, two parietal bones, and two temporal bones). These bones are held together by strong, fibrous, elastic tissues called cranial sutures.
The spaces between the bones where the sutures are (sometimes known as "soft spots") are called fontanelles. They are a part of normal development. The cranial bones remain separate for about 12-18 months. They then grow together (fuse) as part of normal growth. They stay fused throughout adulthood.
Two fontanelles are usually seen on a newborn's skull: one on the top in the middle, just forward of center; and one in the back in the middle. Like the sutures, fontanelles gradually become closed, solid, bony areas. The posterior fontanelle (in the back of the head) usually closes by the time an infant is 1 or 2 months old, or may already be closed at birth. The anterior fontanelle (at the top of the head) usually closes sometime between 9 months and 18 months.
The sutures and fontanelles are needed for the infant's brain growth and development. During childbirth, the flexibility of the fibers allows the bones to overlap so the head can pass through the birth canal without pressing on and damaging the infant's brain.
During infancy and childhood, the fibers are flexible. This allows the brain to grow quickly and protects the brain from minor impacts to the head (such as when the infant is learning to hold his head up, roll over, and sit up). Without flexible sutures and fontanelles, the child's brain would be constricted in the cranial bones and could not grow enough. The child would develop brain damage.
Feeling the cranial sutures and fontanelles is one way that doctors and nurses follow the child's growth and development. They are able to assess the pressure inside the brain by feeling the tension of the fontanelles. The fontanelles should feel flat and firm. Bulging fontanelles may be a sign of increased pressure within the brain. In this case, doctors may need to use imaging techniques such as CT scan or MRI scan. Surgery may be needed to relieve the increased pressure.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.