Suture formation, premature sutural fusion, and suture default zones in Apert syndrome.

On the basis of our studies, we postulate that suture formation in Apert syndrome is related to the relative maturity of abutting calvarial bones. The fused coronal suture, a consistent manifestation at birth, develops first because the ossification centers of the frontal and parietal bones are in intimate contact early during intrauterine life. Calvarial immaturity and the megalencephalic brain characteristic of the Apert syndrome appear to work in concert to produce a widely patent midline calvarial defect extending from the glabella to the posterior fontanelle. Because sagittal growth in the coronal sutures cannot take place, the megalencephalic brain grows upward and laterally, and bulges forward through the midline defect. The defect fills in by coalescence of bony islands without proper suture formation because the gap to be bridged is so great that the time window for developing sutural interdigitations may have closed. Other sutures, such as the lambdoid, squamosal, and sphenotemporal, develop with normal interdigitations because abutting bone margins are in close enough proximity to permit suture formation.