Relationship between head circumference and brain volume in healthy normal toddlers, children, and adults

Objective: To quantify the relationship between brain volume and head circumference from early childhood to adulthood, and quantify how this relationship changes with age. Methods: Whole-brain volume and head circumference measures were obtained from MR images of 76 healthy normal males aged 1.7 to 42 years. Results: Across early childhood, brain volume and head circumference both increase, but from adolescence onward brain volume decreases while head circumference does not. Because of such changing relationships between brain volume and head circumference with age, a given head circumference was associated with a wide range of brain volumes. However, when grouped appropriately by age, head circumference was shown to accurately predict brain volume. Head circumference was an excellent prediction of brain volume in 1.7 to 6 years old children (r = 0.93), but only an adequate predictor in 7 to 42 year olds. Conclusions: To use head circumference as an accurate indication of abnormal brain volume in the clinic or research setting, the patient's age must be taken into account. With knowledge of age-dependent head circumference-to-brain volume relationship, head circumference (particularly in young children) can be an accurate, rapid, and inexpensive indication of normalcy of brain size and growth in a clinical setting.