A baby’s head has several “soft spots,” known medically as fontanelles, which are spaces where the skull bones have not yet fused. The most noticeable is the anterior fontanelle, located on the top-front of the head. This unique anatomical feature serves two important purposes: it allows the skull bones to overlap and compress slightly, facilitating the baby’s passage through the narrow birth canal. Additionally, these soft spots accommodate the rapid growth of the baby’s brain during the first years of life.
The Purpose and Anatomy of Soft Spots
A newborn’s skull consists of several bone plates joined by fibrous tissues called sutures. Fontanelles are gaps between these developing skull bones, covered by a durable membrane. This design allows the skull to mold during birth and expand as the brain undergoes rapid growth. The brain reaches approximately 50% of its adult size by one year, and open fontanelles permit this development.
The soft spot’s subtle pulsation is due to blood flow through vessels surrounding the brain, reflecting the baby’s heartbeat. This pulsation indicates normal intracranial pressure within the skull. It is a physiological sign that the circulatory system is functioning as expected within the developing brain.
Why Pulsation May Not Be Visible
While a visible pulsation of the fontanelle is a normal sign, it is also common for it not to be visibly pulsating all the time. The visibility of this pulsation can vary due to several normal factors. It is often subtle and may not always be easily seen, especially if the baby is calm, sleeping, or if the viewing angle or lighting conditions are not optimal.
A baby’s position and activity level can also influence whether pulsation is noticeable. The pulsation might be more apparent when the baby is crying or straining, due to temporary increases in intracranial pressure, but it should return to normal when the baby calms. When a baby is quiet or relaxed, the pulsation may become less discernible.
Individual differences among babies also play a role; some infants naturally have less noticeable fontanelle pulsation than others, which is healthy. A sunken fontanelle where pulsation might not be seen can be a sign of dehydration. However, a sunken fontanelle is typically accompanied by other obvious symptoms of dehydration, such as lethargy, dry mouth, reduced urination, and a lack of tears when crying. If the absence of pulsation is the only observation without these other symptoms, it is less likely to be a cause for concern.
When to Seek Medical Advice
While a non-pulsating soft spot alone is often not a concern, certain changes in the fontanelle’s appearance, especially when combined with other symptoms, warrant immediate medical attention. A bulging or swollen fontanelle, particularly if it does not return to normal when the baby is calm and upright, can indicate increased pressure inside the skull. This can be a sign of serious conditions such as fluid buildup in the brain (hydrocephalus), infections like meningitis, or bleeding in the brain. Additional symptoms accompanying a bulging fontanelle that require urgent evaluation include fever, vomiting, unusual irritability, excessive sleepiness, or a high-pitched cry.
Conversely, a significantly sunken fontanelle is often a sign of dehydration. This is especially concerning if it occurs alongside other signs of severe dehydration, such as a dry mouth and lips, a reduced number of wet diapers, lack of tears, sunken eyes, or unusual drowsiness. If the fontanelle feels unusually tense or hard, or if the baby exhibits any other concerning symptoms like poor feeding or changes in behavior, it is advisable to consult a pediatrician promptly. Parents should always seek professional medical advice if they have any lingering worries about their baby’s health or the appearance of their fontanelle.
Normal Development and Closing of Soft Spots
Babies are born with multiple fontanelles, but the two most prominent are the anterior and posterior fontanelles. The posterior fontanelle, located at the back of the head, is smaller and typically closes much earlier than the anterior one. It usually fuses within the first 1 to 3 months after birth.
The anterior fontanelle, the larger soft spot at the top of the head, remains open for a longer period to accommodate the brain’s rapid growth. It generally closes between 9 and 18 months of age, though the range can vary. Some sources indicate closure can occur as early as 7 months or as late as 26 months. This variation in timing is normal, and pediatricians routinely monitor fontanelle size and closure during well-child visits.