Fontanel

Fontanel refers to soft, membranous gaps between the bones of an infant’s skull. These gaps are covered by tough connective tissue and lie between growing skull bones that are not yet fully fused by sutures. At birth there are typically four fontanels: anterior, posterior, and two anterolateral (sphenoidal) and posterolateral (mastoid) fontanels. The fontanels allow the skull to be molded during birth and to expand rapidly as the brain grows in infancy.

The anterior fontanel is the largest, diamond-shaped, located at the junction of the frontal and two parietal bones; it is usually palpable and may be mildly pulsatile and slightly raised. It generally closes between 18 and 24 months of age. The posterior fontanel is triangular, at the junction of the parietal and occipital bones; it typically closes by about 2 to 3 months. The anterolateral (sphenoidal) fontanel lies on the side of the skull where several bones meet and usually closes by 3 to 6 months. The posterolateral (mastoid) fontanel is located behind the ear region and tends to close between 12 and 18 months.

Clinical significance includes monitoring fontanel size and tension. A bulging fontanel can indicate increased intracranial pressure, crying, or other conditions, while a sunken fontanel may suggest dehydration or malnutrition. Abnormalities in fontanel size or delayed closure can reflect cranial or metabolic issues and warrant medical evaluation.

In adulthood, all fontanels have closed and are replaced by sutures and bone.