Sunken fontanelles are an obvious curving in of the "soft spot" in an infant's head.

See also: Fontanelles - bulging

The skull is made up of many bones. There are 7 bones in the skull itself and 14 bones in the facial area. They join together to form a solid, bony cavity that protects the brain and supports the structures of the head. The areas where the bones join together are called the sutures.

The bones are not joined together firmly at birth. This allows the head to get through the birth canal. The sutures gradually gain minerals and harden, firmly joining the skull bones together. This process is called ossification.

In an infant, the space where two sutures join forms a membrane-covered "soft spot" called a fontanelle (fontanel). The fontanelles allow for the skull to grow during an infant's first year.

There are normally several fontanelles on a newborn's skull, mainly at the top, back, and sides of the head. Like the sutures, fontanelles ossify over time and become closed, solid, bony areas. The fontanelle in the back of the head (posterior fontanelle) usually closes by the time an infant is 1 or 2 months old. The fontanelle at the top of the head (anterior fontanelle) usually closes within 7 - 19 months.

The fontanelles should feel firm and should curve inward slightly to the touch. A noticeably sunken fontanelle is a sign that the infant does not have enough fluid in his or her body.

• Dehydration
• Malnutrition
• Normal variant