What is the normal feel and appearance of the anterior fontanelle?

Normal Appearance and Feel of the Anterior Fontanelle

The normal anterior fontanelle is soft, flat, and slightly concave to the touch, with an average size of 2.1 cm at birth, and typically closes around 13.8 months of age. 1

Anatomy and Normal Characteristics

• The anterior fontanelle is located between the frontal and parietal bones, serving as an important anatomical diagnostic tool for assessing the skull and brain in infants 2
• The normal fontanelle should feel soft and slightly concave or flat when the infant is in an upright position 1
• The fontanelle should not bulge when the infant is quiet and in an upright position 3
• The anterior fontanelle has a diamond shape with the average width (transverse diameter) measuring approximately 2.0 cm at birth in full-term infants 4

Normal Size Variations

• There is considerable normal variation in fontanelle size among healthy infants 4
• In full-term infants, the width decreases from approximately 2.0 cm at birth to about 0.6 cm by 12 months of age 4
• In preterm infants who are appropriate for gestational age (AGA), the anterior fontanelle is typically larger, increasing from 1.8 cm at 32 weeks to 2.5 cm at 40 weeks postmenstrual age 4
• Girls tend to have slightly larger fontanelles than boys, though this difference is not statistically significant 4

Normal Closure Timeline

• The median time for anterior fontanelle closure is 13.8 months 1
• The normal range for closure is between 4 and 26 months 5
• Boys typically experience fontanelle closure slightly earlier than girls 4
• By 3 months of age, there is usually no significant difference in fontanelle size between preterm and full-term infants 4

Abnormal Findings and Their Significance

• A bulging fontanelle (convex or elevated above the surrounding bone) may indicate increased intracranial pressure, intracranial tumors, or meningitis 1, 3
• A sunken fontanelle (significantly depressed below the level of surrounding bone) typically suggests dehydration 1
• An abnormally large fontanelle or delayed closure may be associated with achondroplasia, hypothyroidism, Down syndrome, increased intracranial pressure, or rickets 1
• Persistent open anterior fontanelle beyond 26 months may occasionally be a normal variant once pathological causes have been ruled out 5

Examination Techniques

• The fontanelle should be examined with the infant in both upright and recumbent positions 3
• Gentle palpation should be used to assess the tension and size of the fontanelle 1
• For suspected abnormalities, ultrasonography through the fontanelle provides an excellent window to examine the infant brain without radiation exposure 6
• For anomalies of the cranial sutures and anterior fontanelle, ultrasound examination is often sufficient before considering more advanced imaging 6

Clinical Significance

• The anterior fontanelle serves as a valuable "window to the brain" for both clinical assessment and ultrasonographic examination 4
• Changes in fontanelle appearance, size, or tension can provide important diagnostic clues for various conditions affecting infants 1
• Transfontanellar ultrasound can be used to evaluate newborns or young infants with open fontanelles for various intracranial conditions 6