Microcephaly--no small deal.

Anatomic shortening of the fetal frontal lobe seems to precede microcephaly. Brain size determines the size of the calvarium. The report by Pilu and colleagues provides a physiological basis for recent anatomical observations made regarding microcephaly. Biometry of the frontal lobe of the fetal brain may be a valuable tool for the identification of the fetus at risk for microcephaly. A thorough investigation of the subtle brain anatomy of the developing fetus is necessary in suspicious cases. Prenatal studies have suggested that abnormalities of neurocranial architecture occur in approximately two-thirds of cases. Steinlin and colleagues found a much higher incidence in children (90%) affected by microcephaly. Either the progressive nature of the condition or the improved sensitivity of childhood magnetic resonance imaging (used in their study) over prenatal ultrasonography for the detection of subtle brain abnormalities may account for this difference. However, high-resolution ultrasonographic instruments should allow for the detection of many accompanying neuroanatomic abnormalities, possibly before the markedly small calvarium is seen. Finally, Pilu and colleagues have shown that the underlying conditions that may predispose to brain atrophy may be recognizable with Doppler ultrasonography.