Fontanelles - excessively large

Alternative Names

Considerations

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 accumulate minerals and harden by a process called ossification, firmly joining 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.

There are two fontanelles normally evident 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 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 between 9 months and 2 years.

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

Causes

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

More common causes:

• 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