The relationship between scaphocephaly at the skull vault and skull base in sagittal synostosis

The skull vault is scaphocephalic in sagittal synostosis but little is known about the deformity at the skull base. If differential progressive deformity occurs between the vault and base, this might affect decision making regarding the timing of surgical intervention. We used 3-dimensional CT (3DCT) scans to compare deformity at the vault, base and posterior fossa in sagittal synostosis. Cephalic index (CI) was measured in 34 consecutive cases of isolated sagittal synostosis and 16 controls using predefined landmarks on the 3DCT volume data set. Planes were generated by a Vitrea™ workstation. Data were analysed by Student's t-test and Pearson coefficient.

Ratios of CI between the vault and base, and the vault and posterior fossa were significantly reduced in sagittal synostosis (p < 0.0001 and p = 0.0031) demonstrating a milder deformity at the base and posterior fossa. However there was strong positive correlation between CI at the vault and base (r = 0.77, p < 0.0001). We have therefore shown for the first time that the deformity at the base is less severe, but is still closely correlated with the vault in unoperated sagittal synostosis. This study provides a basis for future work analysing the progression of these deformities before and after surgery.