A newborn's head is usually about 2 cm (0.78 inch) 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 to break down long chains of sugar molecules (Hurler or Morquio syndrome)

Your 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
• Cranial ultrasound

Treatment depends on the cause of the increased head size. For example, for hydrocephalus, surgery may be needed to relieve the buildup of fluid inside the skull.

Macrocephaly

Bamba V, Kelly A. Assessment of growth. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 27.

Mitchell AL. Congenital abnormalities. Disorders in head shape and size. In: Martin RJ, Fanaroff AA, Walsh MC, eds. Fanaroff and Martin's Neonatal-Perinatal Medicine. 11th ed. Philadelphia, PA: Elsevier; 2020:chap 30.

Updated by: Charles I. Schwartz, MD, FAAP, Clinical Assistant Professor of Pediatrics, Perelman School of Medicine at the University of Pennsylvania, General Pediatrician at PennCare for Kids, Phoenixville, PA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.