What Is the Skull Structure Influence of Squamosal Suture Synostosis in Nonsyndromic and Syndromic Crouzon Craniosynostosis?

Background: The morphologic effect of squamosal synostosis has not been clarified, due to its low occurrence rate, and its inclination to be combined with premature closure of other major sutures, especially in syndromic synostosis. This study's goal is to explore the morphological influence of squamosal synostosis in both syndromic and nonsyndromic craniosynostosis patients. Methods: Twenty-five computed tomography (CT) scans from nonsyndromic squamosal synostosis (NSS), Crouzon syndrome with squamosal synostosis (CSS), Crouzon syndrome without squamosal synostosis, and normal controls were included. Three-dimensional (3D) cephalometry, entire cranial volume and cranial fossa volume were measured using Materialise software. Results: The entire cranial volume of all groups was similar. The NSS developed a gradual reduction in the severity of reduced segmental volume from the anterior cranial fossa, to the middle cranial fossa, and to the unaffected volume of posterior cranial fossa. The CSS developed the most severe volume reduction of middle cranial fossa (12608.30 +/- 2408.61 mm(3) vs 26077.96 +/- 4465.74 mm(3), 52%), with proportionate volume reduction of the anterior (7312.21 +/- 2435.97 mm(3) vs 10520.63 +/- 2400.43 mm(3), 30%) and posterior cranial fossa (33487.29 +/- 5598.93 mm(3) vs 48325.04 +/- 14700.44 mm(3), 31%). The NSS developed a narrower anterior cranial fossa, a clockwise rotated Frankfort horizontal plane, and a retracted chin (pogonion). Conclusion: Squamosal synostosis may alter the development of cranial fossa volume, especially the volume of middle cranial fossa. However, the development of cranial base, and related facial features are determined largely by major vault sutures and associated syndromic conditions, rather than the squamosal suture alone.