The relationship in neonates between clinically measured head circumference and brain volume estimated from head CT-scans.

OBJECTIVE: To determine if the frontal-occipital head circumference correlates with brain volume on CT and to investigate correlations between the volumes of different brain subdivisions in live neonates.
METHODS: Records were studied from 27 neonates with anatomically normal head CT-scans which were ordered for clinical reasons, and which were performed at Johns Hopkins Hospital. Clinical data were abstracted from medical records. Brain volumes were estimated by digitizing the structures of interest on each slice of head CT-scans.
RESULTS: In this sample of 27 infants with a mean birth weight of 3000.4 +/- 668 g, mean head circumference of 33.5 +/- 1.8 cm, and mean gestational age of 37 weeks and 4 days +/- 24 days, the mean of total brain volume was 333.0 +/- 78.3 ml. The correlation between clinically measured head circumference and total brain volume was 0.55 (P < 0.003). Regression of total brain volume on head circumference and its second and third powers accounted for 43% of the variation in total brain volume. Other predictor variables, namely infant race, sex, gestational age, and maternal age, were not significant in this regression once head circumference was included. The slope of the cubic function of head circumference as a predictor of brain volume was greatest below the mean head circumference of 33.5 cm. Brain volume leveled off at head circumferences greater than the mean.
CONCLUSION: Head circumference is a powerful predictor of total brain volume in the neonate: below the approximate head-circumference mean of 33.5 cm, smaller head circumference indicates smaller total brain volume.