What Is the Difference in Cranial Base Morphology in Isolated and Syndromic Bicoronal Synostosis?

The association of isolated craniosynostosis and the influence of syndromic forms confound the understanding of craniofacial morphologic development. This study attempts to clarify the individual influences of isolated bicoronal synostosis, Apert syndrome, and Crouzon syndromes on skull base morphology.

One hundred seventeen computed tomographic scans were included (nonsyndromic bicoronal synostosis, n = 36; Apert syndrome with bicoronal synostosis, n = 25; Crouzon syndrome with bicoronal synostosis, n = 11; controls, n = 45). Cephalometric measurements were analyzed using Materialise software.

Nonsyndromic bicoronal synostosis patients developed a shortened cranial base length, with a significantly shortened distance between nasion and sella (p = 0.005). The cranial base angles of nonsyndromic bicoronal synostosis in both the cranial side (N-S-BA) and facial side (N-SO-BA) increased significantly, by 17.04 degrees (p < 0.001) and 11.75 degrees (p < 0.001), respectively. However, both the N-S-BA and N-SO-BA angles of Apert syndrome and Crouzon syndrome were narrowed more than that of nonsyndromic bicoronal synostosis [by 12.11 degrees (p < 0.001) and 12.44 degrees (p < 0.001), respectively, in Apert syndrome; and by 11.66 degrees (p = 0.007) and 13.71 degrees (p = 0.007), respectively, in Crouzon syndrome]. However, there is no statistically significant difference of these two angles between Apert syndrome and Crouzon syndrome, when they were only associated with bicoronal synostosis. Contrary to the relatively normal subcranial space of nonsyndromic bicoronal synostosis, both Apert and Crouzon syndromes developed a reduced subcranial space.

Isolated bicoronal synostosis resulted in a flattened cranial base, whereas Apert syndrome and Crouzon syndrome developed a normal cranial base angle when only associated with bicoronal synostosis. The syndromic skulls had additional significantly reduced subcranial space.