Fontanelles - excessively large

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Fontanelles

Large fontanelles

Large fontanelles (lateral view)

Skull of a newborn

Soft spot - large

The skull of the newborn is made up of boney plates (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 sutures.

The bones are not joined together firmly at birth (this allows the head to pass through the birth canal). The sutures gradually harden by a process called ossification, which firmly joins the skull bones together.

In an infant, the spaces where sutures come together, but are not completely joined, is called the soft spot. It is covered by a membrane. The medical term for such spaces is fontanelle (fontanel or fonticulus). The fontanelles allow for growth of the skull during an infant's first year.

Two fontanelles are usually seen on a newborn's skull: one on the top in the middle, just forward of center; and one in the back in the middle. Like the sutures, fontanelles gradually 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, or may already be closed at birth. The anterior fontanelle (at the top of the head) usually closes sometime between 9 months and 18 months.

A wide fontanelle occurs when the fontanelle is larger than expected for the age of the baby. Slow or incomplete closure of the skull bones is most often the cause of a wide fontanelle.

Delayed closure (larger-than-normal fontanelles) is most commonly caused by:

• Intrauterine growth retardation (IUGR)
• Prematurity
• Hydrocephalus
• Down syndrome
• Achondroplasia

Rarer causes:

• Hypothyroidism
• Rickets
• Osteogenesis imperfecta
• Congenital rubella (seldom seen since immunization begun with MMR -- measles, mumps, rubella -- vaccine)
• Apert syndrome
• Cleidocranial dysostosis

Review Date: 05/10/2006
Reviewed By: Daniel Rauch, MD, FAAP, Director, Pediatric Hospitalist Program, Associate Professor of Pediatrics, NYU School of Medicine, New York, NY. Review provided by VeriMed Healthcare Network.