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

Abstract

OBJECTIVE: Fronto orbital advancement (FOA) requires the removal of the fronto-orbital bandeau via an anatomically challenging osteotomy that passes from the anterior cranial fossa to the middle fossa. During the intracranial portion of the osteotomy, visualization of the saw blade is lost as it passes through the fronto-orbito-sphenoid junction, prior to entering the middle cranial fossa. This places the temporal lobe dura and parenchyma at risk of injury. The aim of this study is to provide a 3-dimensional analysis of the space surrounding this osteotomy, and determine differences amongst different types of craniosynostosis. METHOD: 18 head CT scans of patients from ages 2 to 24 months with craniosynostosis (6 Metopic, 6 nonsyndromic Bicoronal, and 6 Unicoronal) were reconstructed to 3D skulls using Mimics 24.0 (Materialise NV, Lueven, Belgium). Unicoronal skulls were mirrored as necessary to be right sided. These skulls were landmarked with 47 cephalometric points. Measurents and volumetric analysis was performed to determine differences in sphenoid anatomy between the 3 craniosynostoses. RESULTS: For the 3 craniosynostosis groups, metopic, bicoronal and unicoronal, the average distance from the lateral orbital rim to temporal lobe tip was significantly different (17.37mm, 10.15mm, 14.76mm, respectively (p<0.05)). The mean depth of the temporal lobe tip from the edge of the sphenoid was also significantly different (16.23mm, 27.5mm, 22.8 mm respectively, p<0.05). The thickness of the fronto-orbito-sphenoid junction at the level of the supraorbital rim was significantly different between the three groups as well (7.75mm, 3.60mm, 8.04mm; p=0.01). Distances from the cornea to the lateral orbital rim, anteroposterior depth of the lateral orbit, and overhang of the lesser sphenoid wing over the middle cranial fossa were not significant between groups. CONCLUSION: Sphenoid shape and the zone of the fronto-orbital-sphenoid junction differs between types of craniosynostosis. Bicoronal craniosynostosis has the most unfavorable anatomy in this area, with minimal distance between the orbit and the anterior portion of the temporal lobe, a vertically deep middle cranial fossa, and thin bone at the fronto-orbital sphenoid junction, all of which make retraction and protection of the temporal lobe more challenging. Careful understanding of the patient’s specific anatomy is necessary to perform this osteotomy safely.