Defining and Correcting Asymmetry in Isolated Unilateral Frontosphenoidal Synostosis: Differences in Orbital Shape, Facial Scoliosis, and Skullbase Twist Compared to Unilateral Coronal Synostosis

Introduction: Isolated frontosphenoidal synostosis (FS) is a rare cause of fronto-orbital plagiocephaly that can be challenging to distinguish from isolated unicoronal synostosis (UC). The purpose of this paper is to analyze differences in fronto-orbital dysmorphology between the 2 conditions, to describe approaches for surgical correction, and to report surgical outcomes between FS and UC patients in a casecontrol fashion. Methods: Patients treated for craniosynostosis over a 12-year period at our institution were retrospectively evaluated under institutional review board approval. Frontosphenoidal synostosis patients who underwent bilateral fronto-orbital correction of anterior plagiocephaly with minimum 2-year follow-up, adequate pre-, and minimum 2-year postoperative computed tomography scans were included in the case-control portion of the study. These patients were randomly age-matched to UC patients meeting the same inclusion criteria. Preoperative and postoperative orbital shape and volumetric analysis was performed using Mimics software. Results: Twelve FS patients were treated during the study period. Seven of these patients met casecontrol inclusion criteria with average follow-up of 47.5 months. The characteristic FS orbit was a relatively wide, short, and shallow trapezoid, while the characteristic UC orbit was a relatively narrow, tall, and deep parallelogram. Frontosphenoidal synostosis orbits were significantly wider, shorter, shallower, and smaller than UC orbits. Surgical correction tailored to the differential dysmorphologies resulted in statistical equalization of these differences between affected and contralateral control orbits at follow-up, with the exception of UC orbital width, which remained significantly narrower than unaffected contralateral control. One patient in each group required cranioplasty for skull defects at follow-up, while no patient underwent surgical readvancement. Conclusions: Frontosphenoidal synostosis and UC orbital shape differ significantly, and can be normalized using fronto-orbital advancement tailored to the distinct orbital dysmorphologies of these 2 groups.

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