Definition

Sunken fontanelles describe a concave deformity of the "soft spot" in an infant.

Alternative Names

Sunken fontanelles; Soft spot - sunken

Considerations

The skull is made up of many bones, 7 in the skull itself and 14 in the facial area. They join together to form a solid, bony cavity protecting the brain and supporting 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 accommodate passage through the birth canal. The sutures gradually accumulate minerals and harden, firmly joining the skull bones together. This process is called ossification.

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

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

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

Causes

• Dehydration
• Malnutrition
• Normal variant

Review Date: 11/10/2003
Reviewed By: John Goldenring, M.D., MPH, Department of Pediatrics, Children's Hospital, San Diego, CA. Review provided by VeriMed Healthcare Network.