Fontanels, commonly known as “soft spots,” are normal parts of infant development. These gaps between a baby’s skull bones are covered by a tough, fibrous membrane. They provide skull flexibility, important for both birth and rapid brain growth. Understanding these soft spots helps parents recognize typical development and when to seek medical guidance.
Mapping the Fontanels
A newborn’s skull has six fontanels, but only two are widely recognized. The most prominent is the anterior fontanel, located on the top, front part of the head. This diamond-shaped fontanel is where the two frontal and two parietal bones meet.
Behind the anterior fontanel, at the back of the head, is the posterior fontanel. This smaller, triangular fontanel lies where the two parietal bones meet the occipital bone.
Two smaller, less commonly discussed fontanels are the sphenoid and mastoid fontanels, with one pair on each side. Sphenoid fontanels (anterolateral) are near the temples, where the sphenoid, parietal, temporal, and frontal bones converge. Mastoid fontanels (posterolateral) are behind the ears, at the intersection of the temporal, parietal, and occipital bones. These lateral fontanels are often not easily palpable and close early.
Purpose of Fontanels
Fontanels serve two primary functions important for infant development. First, they allow the baby’s skull to compress and change shape during passage through the birth canal. The unfused skull bones can slightly overlap, enabling a smoother and safer delivery.
Second, fontanels accommodate the rapid growth of the infant’s brain. A baby’s brain grows quickly during the first year, and these soft, membranous gaps provide necessary room for expansion. Without fontanels, the skull would restrict brain growth, potentially leading to complications.
Fontanel Closure and Observation
Fontanel closure follows a typical timeline. The posterior fontanel usually closes first, within two to three months after birth. The anterior fontanel remains open longer, typically closing between 7 and 18 months, though it can vary up to 24 months. Sphenoid fontanels generally close around six months, and mastoid fontanels between six and eighteen months.
A normal fontanel should feel soft and flat, possibly with a slight inward curve. A gentle pulsation, reflecting the baby’s heartbeat, is also common. Healthcare providers regularly check fontanels during routine visits to monitor their size and tension.
Parents should observe their baby’s fontanels for changes. A bulging fontanel, especially if prominent when the baby is calm and upright, could indicate increased pressure inside the skull. This can signal conditions like hydrocephalus, meningitis, or brain inflammation. Conversely, a sunken fontanel often indicates dehydration or, less commonly, malnutrition. If a fontanel closes too early or too late, or if there are other concerns, seeking medical advice is recommended.