Excessively large fontanelles are larger-than-expected soft spots for the age of a baby. In an infant, the spaces where bones of the skull come together, but are not completely joined, are called soft spots or fontanelle (fontanel or fonticulus).

Fontanelles allows for growth of the skull during an infant's first year. Slow or incomplete closure of the skull bones is most often the cause of a wide fontanelle.

For general information, see fontanelles.

Larger-than-normal fontanelles are most commonly caused by:

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

Rarer causes:

• Apert syndrome
• Cleidocranial dysostosis
• Congenital rubella
• Neonatal hypothyroidism
• Osteogenesis imperfecta
• Rickets

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.

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 does your child have?
• Have you had other babies with large fontanelles?

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:

• Blood tests for suspected hypothyroidism
• Head circumference measurements
• Imaging tests of the head, including x-rays, CT scan, or MRI
• Transillumination of the skull (generally in the newborn or infant of only a few weeks)
• Ultrasound of the head