Sonographic biometry of the frontal lobe in normal and growth-restricted neonates

Assessing the impact of restricted intrauterine growth on neonatal frontal lobe (FL) dimensions is important. We aimed to create a sonographic nomogram of FL dimensions in neonates at different gestational ages (GA) and evaluate the impact of small head circumference (HC) on FL dimensions. We conducted sonographic biometry of the FL at birth. We included 218 newborn infants born at GA of 24-43 wk: appropriate for GA and normal HC (n = 178), and small for GA and small HC (n = 23). Infants with a 5-min Apgar score <7, severe congenital malformations, or chromosomal abnormalities were excluded. Through a coronal ultrasound scan via the anterior fontanelle at the level where the most lateral point of the left Sylvian fissure was best demonstrated, we drew a triangle connecting the most lateral point of the Sylvian fissure, the corpus callosum, and the subcalvarian point of the interhemispheric fissure. We measured the three sides of the triangle, Sylvian-fontanellar distance, Sylvian-callosal distance, and fontanellar-callosal distance, and calculated the frontal triangular area. All four FL dimensions increased significantly between 24 and 43 wk of gestation in both appropriate for GA-normal HC and small for GA-small HC neonates, and were strongly correlated with HC and birth weight. Regression lines of GA against Sylvian-fontanellar distance, Sylvian-callosal distance, fontanellar-callosal distance, and frontal triangular area in the appropriate for GA-normal HC group differed significantly from those of the small for GA-small HC group (p < 0.05). Male neonates had significantly larger Sylvian-fontanellar and Sylvian-callosal distances than females (p < 0.01 and p < 0.015, respectively). In conclusion, FL measures increased significantly between 24 and 43 wk of gestation, and were strongly correlated with HC. We speculate that a sonographically small fetal HC implies growth restriction of the fetal FL.