From the Guidelines
Fontanelles are a normal finding in babies, and their closure is a natural process that occurs as the child grows. The presence of fontanelles allows for the baby's head to compress during delivery and accommodates rapid brain growth in the first year of life. Babies typically have two main fontanelles: the anterior (front) fontanelle, which is diamond-shaped and located on top of the head, and the posterior (back) fontanelle at the back of the head. Some key points to consider about fontanelles include:
- The posterior fontanelle usually closes first, between 1-2 months of age, while the anterior fontanelle typically closes between 9-18 months 1.
- Fontanelles close naturally through a process called ossification, where the edges of the skull bones grow toward each other and eventually fuse.
- Transfontanellar ultrasound may be used to evaluate pediatric patients, including newborn or young infants with open anterior or posterior fontanels, and can be useful in supporting the diagnosis of certain conditions and for ongoing monitoring 1.
- Parents should handle these areas gently but don't need to be overly concerned about injury during normal care.
- If a fontanelle appears sunken, it may indicate dehydration, while a bulging fontanelle could signal increased pressure inside the skull, both requiring immediate medical attention. The timing of closure varies among babies, but significant delays in closure should be evaluated by a healthcare provider. Some diagnostic modalities, such as US Duplex Doppler Head, may be used to evaluate the size and location of hemorrhage, evidence of mass effect, and hydrocephalus in neonates and infants with open fontanels 1.
From the Research
Fontanelles in Babies
- Fontanelles are a regular feature of infant development, with six fontanelles in the human skull, including the anterior fontanelle located between the frontal and parietal bones 2.
- The anterior fontanelle serves as an important anatomical diagnostic tool in the assessment of impairments of the skull and brain and allows access to the brain and ventricles in the infant 2.
Size and Closure of Anterior Fontanelle
- The average size of the anterior fontanelle is 2.1 cm, and the median time of closure is 13.8 months 3.
- Fontanelle size increases up to 2 months of age, and then decreases until closure, with 27.3% of infants having a closed fontanelle at 1 year 4.
- There is great variability in both fontanel size and age at closure, with no significant differences between term and preterm infants or between sexes 5.
Abnormal Fontanelle Development
- A large anterior fontanelle or delayed fontanel closure can be caused by conditions such as achondroplasia, hypothyroidism, Down syndrome, increased intracranial pressure, and rickets 3.
- Abnormal fontanelle dimensions, particularly enlarged fontanelle dimensions, may be associated with certain fetal abnormalities, including chromosomal or non-chromosomal syndromes, primary or secondary cardiac overload, primary skeletal dysplasias, or central nervous system malformations 6.
- A bulging anterior fontanelle can be a result of increased intracranial pressure or intracranial and extracranial tumors, while a sunken fontanel usually indicates dehydration 3.