Fontanelles - excessively large Health Article

Alternative Names

Soft spot - large

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 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.

Common Causes

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

Call your health care provider if

If you think that the fontanelles on your baby's head are excessively large, talk to your health care provider. Most of the time, this sign will have been seen during the baby's first medical exam.

What to expect at your health care provider's office

The health care provider will perform a physical exam and ask questions about the patient's medical history, including:

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

Note: An excessively large fontanelle is usually discovered by the health care provider, and the parents may not have been aware of its presence.

The health care provider may check the size of the fontanelles and the head over several months. This can help determine problems of the fontanelle and head growth.

Diagnostic tests may include:

• 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
• Blood tests for suspected causes such as a serum thyroxin (T3 and T4) for suspected hypothyroidism