Involvement of the sphenosquamosal suture for unilateral coronal synostosis.

The etiology of the clinical entity commonly known as unilateral coronal synostosis is often described as the unilateral fusion of the coronal ring. However, recent theories have poorly explained the basis of the deformities associated with unilateral coronal synostosis. We retrospectively analyzed computed tomographic data sets from 18 patients who presented with unilateral coronal synostosis and arrived at our hospital between 1985 and 2010. Using three-dimensional reconstructions of the computed tomographic images, analyses of the cranial base and measurements of each cranial bone were performed. As a result, the ipsilateral and contralateral basion-clinoid-pterion angles did not differ significantly (P = 0.49) and were almost identical in each case. However, the ipsilateral basion-partis-petrosae angle was wider than the corresponding contralateral angle (P < 0.001). In addition, the ipsilateral nasion-clinoid-pterion angle and the sphenoid, zygomatic, and temporal bones on the ipsilateral side were significantly shorter than those on the contralateral side (P < 0.001). Based on a shortening ratio, the sphenoid bone was smaller (42.0% ± 10.9%) than the temporal (68.9% ± 7.58%) and zygomatic bones (71.1% ± 8.38%). This difference was significant (P < 0.001). In conclusion, restricted growth potential of the central portion of the ipsilateral sphenoid bone was identified. We propose that the coronal ring, which includes the frontoparietal and frontosphenoidal sutures, and the sphenosquamosal suture are involved in unilateral coronal synostosis. Using our findings and the theory of Delashaw et al, the deformity observed in unilateral coronal synostosis can be explained more adequately and/or completely.