Imaging of Microcephaly.

One of the most common definitions of microcephaly cited is that of an occipitofrontal circumference (OFC) of the head that is less than two standard deviations below the average for age (or gestational age, if identified prenatally) and sex. Similarly, severe microcephaly is defined as an OFC that is less than three standard deviations below the average. Microcephaly is not a diagnosis, but rather, a finding that is secondary to a multitude of etiologies that can be categorized as prenatal versus postnatal, genetic versus environmental, and congenital versus acquired.