[Anterior fontanelle as a window to the brain--normal values and timing of closure]

Nowadays an exact examination of the infant's brain is possible through the anterior fontanelle by ultrasonography (US); however for that a certain minimal size of the fontanelle is necessary. In the literature standards for size and timing of closure are scarce. In the Bonn Longitudinal Study of growth and development of preterm infants in comparison with full term infants also the length (anterior-posterior diameter) and width (transversal) of the anterior fontanelle have been measured monthly from birth, and the timing of closure was registered. As a measure of fontanelle size here the width (transversal diameter) is used. For the full term infants the width (50. percentile) at birth is 2.0 cm; it decreases to 0.6 cm until the age of 12 months. The great variability of fontanelle size observed in the Bonn study is also confirmed in the literature. In the appropriate for gestational age (AGA) preterm infants the anterior fontanelle (50. percentile) increases between 32 and 40 postmenstrual weeks from 1.8 to 2.5 cm and is then significantly greater than in the full term infants. At least at the age of 3 months there is no significant difference between the AGA preterm infants and the full term infants, either for the boys or for the girls. For the boys, in spite of their significantly greater head circumference there is a tendency to have a smaller fontanelle than the girls; the difference is at no age significant. For preterm as well as for full term infants timing of closure occurs somewhat earlier in the boys than in the girls.(ABSTRACT TRUNCATED AT 250 WORDS)