Sonographic assessment of the fetal frontal lobe: a potential tool for prenatal diagnosis of microcephaly.

A prospective ultrasound evaluation of 150 normal pregnant women was conducted between 15 and 40 weeks' gestation. A variety of biometric measurements were obtained that included measurements of the frontal lobe distance (the anterior edge of the frontal horns of the lateral ventricles to the frontal bone) and the thalamic frontal lobe distance (measured from the posterior edge of the thalami to the frontal bone). Analysis of these data revealed a high degree of correlation between the gestational age and the frontal lobe distance (R2 = 0.89, p less than 0.0001), and between the gestational age and thalamic frontal lobe distance (R2 = 0.93, p less than 0.0001). Similarly, a high degree of correlation was also found between the biparietal diameter and the frontal lobe distance (R2 = 0.95; p less than 0.0001), between the biparietal diameter and the thalamic frontal lobe distance (R2 = 0.90, p less than 0.0001), and between the frontal lobe distance and the thalamic frontal lobe distance (R2 = 0.92, p less than 0.0001). The relationships between femur length and frontal lobe distance (R2 = 0.89, p less than 0.0001) and between the femur length and the thalamic frontal lobe distance (R2 = 0.945, p less than 0.0001) were also evaluated. Nomograms for the relationships between gestational age and frontal lobe distance and thalamic frontal lobe distance were generated and included the mean +/- SD and the percentile distributions. Growth of the frontal lobe was best described by a first-degree linear equation. The results of this study demonstrate the pattern of growth of the frontal lobe and the high rate of correlation between growth of the frontal lobe and the gestational age and the biparietal diameter. These findings offer a potential method by which the decreasing size of the frontal lobe, as shown in three cases described herein, can be evaluated prenatally and thus serve as a useful tool in the prenatal diagnosis of microcephaly.