Determining Parental Cause of Large Head Circumference in Infants

Diagnostic Approach

The American Academy of Pediatrics recommends measuring the head circumference of both parents to assess for macrocephaly (>98th percentile or >+2 SD) if the infant has a large head circumference, as this can indicate benign familial megalencephaly 1
The American Journal of Kidney Diseases suggests using a firm, non-stretchable measuring tape to measure head circumference, applying sufficient tension to compress hair against the skull, and recording the measurement to the nearest 0.1 cm 2
Serial measurements of the infant's head circumference are valuable for assessing growth trajectory, according to the American Academy of Pediatrics 3

The presence of macrocephaly in one or both parents, normal fontanels, normal motor development, and absence of signs of increased intracranial pressure are indicative of benign familial megalencephaly, as recommended by the American College of Medical Genetics 1
A structurally normal brain on MRI is also a key diagnostic feature of benign familial megalencephaly, according to the American Academy of Neurology 1

MRI is mandatory to confirm benign familial megalencephaly and exclude other causes, such as hydrocephalus or structural abnormalities, as recommended by the American Academy of Neurology 1, 4, 5, 6

If parental cause is confirmed (benign familial megalencephaly), no treatment is required, and reassurance to parents is recommended, according to the American Academy of Pediatrics 1
Serial head circumference measurements should be continued to ensure a stable growth trajectory, as recommended by the American Academy of Pediatrics 3