The process by which the infants soft skull becomes harder after birth is known as:

Anatomy of the Newborn Skull

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Although the skull appears to be 1 large bone, there are actually several major bones that are connected together. The major bones that compose the skull of a newborn include the following:

• 2 frontal bones

• 2 parietal bones

• 1 occipital bone

These bony plates cover the brain and are held together by fibrous material called sutures.

What are sutures?

Sutures allow the bones to move during the birth process. They act like an expansion joint. This allows the bone to enlarge evenly as the brain grows and the skull expands. The result is a symmetrically shaped head. Some sutures extend to the forehead, while others extend to the sides and back of the skull. One suture in the middle of the skull extends from the front of the head to the back. The major sutures of the skull include the following:

• Metopic suture. This extends from the top of the head down the middle of the forehead, toward the nose. The 2 frontal bone plates meet at the metopic suture.

• Coronal suture. This extends from ear to ear. Each frontal bone plate meets with a parietal bone plate at the coronal suture.

• Sagittal suture. This extends from the front of the head to the back, down the middle of the top of the head. The 2 parietal bone plates meet at the sagittal suture.

• Lambdoid suture. This extends across the back of the head. Each parietal bone plate meets the occipital bone plate at the lambdoid suture.

If any of the sutures close too early (fuse prematurely), there may be no growth in that area. This may force growth to happen in another area or direction. This results in an abnormal head shape (craniosynostosis).

What are fontanelles?

There are 2 fontanelles (the space between the bones of an infant's skull where the sutures intersect) that are covered by tough membranes that protect the underlying soft tissues and brain. The fontanelles include:

• Anterior fontanelle (also called soft spot). This is the junction where the 2 frontal and 2 parietal bones meet. The anterior fontanelle remains soft until about 18 months to 2 years of age. Doctors can assess if there is increased intracranial pressure by feeling the anterior fontanelle.

• Posterior fontanelle. This is the junction of the 2 parietal bones and the occipital bone. The posterior fontanelle usually closes first, before the anterior fontanelle, during the first several months of an infant's life.

Cranial sutures are fibrous bands of tissue that connect the bones of the skull.

An infant's skull is made up of 6 separate cranial (skull) bones:

• Frontal bone
• Occipital bone
• Two parietal bones
• Two temporal bones

These bones are held together by strong, fibrous, elastic tissues called sutures.

The spaces between the bones that remain open in babies and young children are called fontanelles. Sometimes, they are called soft spots. These spaces are a part of normal development. The cranial bones remain separate for about 12 to 18 months. They then grow together as part of normal growth. They stay connected throughout adulthood.

Two fontanelles usually are present on a newborn's skull:

• On the top of the middle head, just forward of center (anterior fontanelle)
• In the back of the middle of the head (posterior fontanelle)

The posterior fontanelle usually closes by age 1 or 2 months. It may already be closed at birth.

The anterior fontanelle 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 sutures allows the bones to overlap so the baby's head can pass through the birth canal without pressing on and damaging their brain.

During infancy and childhood, the sutures 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 could not grow enough. The child would develop brain damage.

Feeling the cranial sutures and fontanelles is one way that health care providers 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, providers may need to use imaging techniques to see the brain structure, such as CT scan or MRI scan. Surgery may be needed to relieve the increased pressure.

Sunken, depressed fontanelles are sometimes a sign of dehydration.

Fontanelles; Sutures - cranial

Goyal NK. The newborn infant. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 113.

Varma R, Williams SD. Neurology. In: Zitelli BJ, McIntire SC, Nowalk AJ, eds. Zitelli and Davis' Atlas of Pediatric Physical Diagnosis. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 16.

Updated by: Neil K. Kaneshiro, MD, MHA, Clinical Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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