Often called a “soft spot,” a fontanel is an area on the top of baby’s head where the skull bones haven’t yet fused together. Fontanels occur between the bony plates of the skull and are covered with membrane.
Newborn babies actually have six fontanels: the anterior; posterior; two mastoid; and two sphenoid. However, the one most parents are familiar with is the one on top of the head, the anterior fontanel. If touched lightly, the fontanel feels like a soft spot or gap in your baby’s skull. On some babies, the fontanel may even seem to be “pulsing.” This is perfectly normal as it moves with each heartbeat.
Fontanels come in a wide variety of sizes. One baby’s fontanel may be very small; another’s fontanel can seem quite wide. The average size is about 2.1 centimeters (about an inch). However, even 4.5 centimeters falls into the normal range.
The purpose of the fontanel is twofold. First, the fontanels allow your baby easier passage down the birth canal. By not being rigid, fontanels allow slight shifting of the skull plates during delivery as baby navigates through the mother’s pelvis. The second purpose is to give your baby’s brain enough room to grow.
Throughout your child’s early development, every pediatrician well child visit includes a measurement of your baby’s skull. Your doctor is making sure your child’s skull is developing normally. Your baby’s fontanel, for example, should not appear sunken. A sunken fontanel could indicate that baby is dehydrated. If a fontanel bulges, it could indicate abnormal pressure on the brain. When your baby is not crying or stressed, the pediatrician will examine your baby’s fontanel, as the fontanel may appear too full when a baby cries but returns to normal when settled down.
Your baby’s soft spot will usually close by about 18 months of age. Until that time, your pediatrician will keep an eye on the fontanel as a form of assessment. If the fontanel closes too early—in other words, the bony plates fuse together too early in a condition called craniosynostosis—your baby will likely need special medical attention. However, most babies will develop normally, and by 18 months, their skulls will be fused, and the “soft spots” will be gone.
- Joseph Kiesler, and Rick Ricer, “The Abnormal Fontanel,” Am Fam Physician. 2003 Jun 15; 67(12):2547-2552.
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