Macrocephaly

Excerpt

Measurement of head circumference, or OFC (occipital frontal circumference), is a reflection of head growth and is a useful tool in tracking and monitoring childhood growth and development. On average, head circumference increases by 2 cm per month in 0 to 3 months of age and 1 cm/month in 3 to 6 months of age. During the last six months of infancy, head circumference increases by 0.5 cm/month. During the first year of life, there is a 12 cm average increase in head circumference. After one year of age, only 1 cm gain occurs per 6 months in head circumference until three years of age and only 1 cm every year between 3 to 5 years of age (average 5 cm total gain in head circumference occurs during 1 to 5 years of age).

Accurate measurement of head circumference can be challenging in restless young infants, especially in the presence of thick hair, and particular attention needs to be paid for correct placement of the tape on the anatomical landmarks. Serial measurement of head circumference during every health supervision visit is necessary up to 24 to 36 months of age to assess head growth velocity. It is also critical to monitor head size frequently in high-risk cases such as preterm infants and those in the active phase of bacterial meningitis, subdural hematoma, and hydrocephalus. Abnormal readings should always be double-checked.

Macrocephaly is described as a head circumference more than two standard deviations above the mean for gestational age and sex, which falls above the 97th percentile. Although erroneously used interchangeably with macrocephaly, megalencephaly is a distinct term to suggest increased growth of cerebral structure. Macrocephaly is a broader term to encompass megalencephaly and other causes of increased head size without cerebral overgrowths, such as subdural fluid collection.

It is important to understand that there are different etiologies of macrocephaly. This understanding is needed to differentiate benign macrocephaly from conditions that require acute investigation and intervention to prevent long term neurological deficits and developmental delays.