Alterations in Sphenoid anatomy in Craniosynostosis: Implications for Fronto-orbital Advancement

Abstract

Background: Fronto-orbital advancement requires removal of the fronto-orbital bandeau via extra- and intra-cranial osteotomies. During this transitional osteotomy, visualization of the saw blade is lost as it passes through the fronto-orbital-sphenoid junction. This places the dura and parenchyma of the temporal lobe at risk of injury. We aim to provide a three-dimensional analysis of the space surrounding this osteotomy to determine differences amongst different types of craniosynostoses. Method: We reconstructed 3D skulls from head CT scans of 30 patients with 6 different types craniosynostosis (4 with Apert sydrome, 3 Crouzon syndrome, 2 Muenke syndrome, 6 metopic, 6 nonsyndromic bicoronal, and 6 unicoronal), and landmarked them with 47 cephalometric points using Mimics 24.0 (Materialise NV, Lueven, Belgium). Statistical analyses were performed to determine differences in the linear and volumetric measurements among the 6 groups. Results: Multiple significant differences were found amongst groups. The mean distance from the lateral orbital rim to cornea was significantly different among the 6 groups, with Apert syndrome having the largest (16.1± 2.3mm) value. The average distance of the middle cranial fossa from the frontozygomatic suture was significantly different with Apert (10±3.4mm), Muenke (10.4±2.0) and bicoronal (9.5±1.6mm) having the smallest values. The mean cephalocaudal depth of the temporal lobe tip from the edge of the sphenoid was significantly different, with Apert having the largest average depth (38±11.6mm). The thickness of the fronto-orbito-sphenoid junction at the level of the supraorbital rim was significantly different among the groups, with smallest values for the Apert (3.6±3.1mm) and bicoronal (3.7±1.3mm) groups. The mean distance from the cornea to the supraorbital rim, overall orbital depth, and overhang of the lesser sphenoid wing over the middle cranial fossa did not show significant difference among the groups. Conclusion: Patients with Apert syndrome have the most unfavorable morphology of the anterior and middle cranial fossae. They have the highest corneal overhang beyond the lateral orbit, a large projection of the middle cranial fossa anteriorly, the most vertically deep middle cranial fossa and the thinnest bone at the fronto-orbital-sphenoid junction, all of which make retraction and protection of the temporal lobe more challenging during fronto-orbital advancement.