Fontanelles

Fontanelles are soft membranous gaps between the bones of an infant’s skull. They are remnants of unfused cranial sutures that allow the skull to mold during birth and to accommodate rapid brain growth in the early years of life. In a typical newborn, there are six fontanelles: the anterior fontanelle at the top of the skull, the smaller posterior fontanelle at the back, and two anterolateral (sphenoidal) and two posterolateral (mastoid) fontanelles on the sides. The anterior fontanelle is the largest and is felt as a diamond-shaped soft spot.

Development and closure follow a general timetable. The posterior fontanelle usually closes within two to three months. The anterolateral and posterolateral fontanelles typically close within the first year. The anterior fontanelle generally closes between 12 and 24 months, most often by about 18 months, though there is natural variation among individuals.

Clinically, fontanelles are palpated to assess contour and tension. A slightly pulsatile fontanelle is common in infants. A sunken fontanelle may indicate dehydration or poor intake, while a tense, bulging fontanelle can be seen with fever, crying, or raised intracranial pressure. Persistent enlargement or delayed closure beyond the normal window, or an abnormal contour, may warrant medical evaluation for underlying conditions such as cranial anomalies or hydrocephalus. Fontanelles thus serve as a useful, noninvasive means to monitor skull development and hydration status in infancy.