Tracing craniosynostosis to its developmental stage through bone center displacement

In metopic and coronal suture synostosis, the involved bone centers are abn ormally situated just next to the affected suture. Bone centers are the sta rting point of ossification during embryogenesis from which bone growth spr eads radially. In this paper, we describe a similar observation for sagitta l suture synostosis, with both parietal bone centers located almost complet ely cranially. The (reduced) distance between the bone centers of a synosto tic suture reflects the time during embryogenesis at which fusion took plac e. We suggest that in craniosynostosis the bone centers arise in their norm al position, and initial outgrowth is undisturbed until the bone fronts mee t. It is during this developmental stage that fusion occurs instead of sutu re formation. Due to the fusion, growth can only occur at the free bony rim s from then on. The bone centers remain located at a fixed distance from on e another in the middle of the fused bones, becoming relatively more displa ced with time. This implies that the distance between the involved bone cen ters directly indicates the developmental period during which sutural growt h was arrested. The same phenomenon of bone center displacement is found in types of craniosynostosis with and without fibroblast growth factor recept or (FGFR) or TWIST gene mutations.