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.

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

• you think that the fontanelles on your baby's head are excessively large. Quite often this sign will have been detected at the first newborn examination in the hospital.

The medical history will be obtained and a physical examination performed.

Medical history questions documenting the symptom in detail may include:

• time pattern
  • When did you first notice that the fontanelle looked large?
• location
  • Which "soft spots" are affected?
• quality
  • Is it always the same, or does it change in any way?
• other
  • What other symptoms are also present?
  • Have large fontanelles been present with previous babies?

Note: This finding is usually discovered by the health care provider, and the parents may not have been aware of its presence.

The physical examination may include repeated assessment of the size of the fontanelles and the head circumference over several months. This can help determine abnormalities of the fontanelle and head growth. Transillumination of the skull using a bright light may be done to help determine the presence of hydrocephalus, "water on the brain," a relatively common cause of an enlarged fontanelle. Transillumination can also help discern separated sutures.

Diagnostic tests that may be performed are:

• head circumference measurements
• transillumination of the skull (generally in the newborn or infant of only a few weeks)
• ultrasound of the head
• head X-rays , CT scan, or MRI
• specific tests for suspected causes, such as a serum thyroxin (T3 and T4) for suspected hypothyroidism

AFTER SEEING YOUR HEALTH CARE PROVIDER
If a diagnosis was made by your health care provider as to the cause of the large fontanelles, you may want to note that diagnosis in your child's personal medical record. You may also want to document your own findings of the child's head circumference as he or she grows.