A newborn's head is usually about 2 cm larger than the chest size. Between 6 months and 2 years, both measurements are about equal. After 2 years, the chest size becomes larger than the head.

Measurements over time that show an increased rate of head growth often provide more valuable information than a single measurement that is larger than expected.

Increased pressure inside the head (increased intracranial pressure) often occurs with increased head circumference. Symptoms of this condition include:

• Eyes moving downward
• Irritability
• Vomiting

Increased head size may be from any of the following:

• Benign familial macrocephaly (family tendency toward large head size)
• Canavan disease (condition that affects how the body breaks down and uses a protein called aspartic acid)
• Hydrocephalus (buildup of fluid inside the skull that leads to brain swelling)
• Bleeding inside the skull
• Disease in which the body is unable break down long chains of sugar molecules (Hurler or Morquio syndrome)

The health care provider usually finds an increased head size in a baby during a routine well-baby exam.

A careful physical exam will be done. Other milestones for growth and development will be checked.

In some cases, a single measurement is enough to confirm that there is a size increase that needs to be tested further. More often, repeated measurements of the head circumference over time are needed to confirm that the head circumference is increased and the problem is getting worse.

Diagnostic tests that may be ordered include:

• Head CT scan
• MRI of the head