Understanding the heterogenicity of unicoronal synostosis - A morphometric analysis of cases compared to controls

Background: Preoperative severity of unicoronal synostosis varies greatly and involves the frontal bone, skull base and orbits. Degree of deformity affects long-term morphological and functional outcomes after surgery. The aim of this study was to describe the morphological heterogenicity and investigate its relation to patient-specific factors.

Materials and methods: In this retrospective cohort study, non-syndromic unicoronal synostosis patients treated between 2006 and 2022 at Necker Hospital, France or Uppsala University Hospital, Sweden, were included and matched to controls. Severity of skull base, orbital and posterior skull asymmetry, degree of anterior plagiocephaly and Harlequin deformity, lateralisation, head circumference, age, timing of metopic fusion and fusion of peri-pterionic sutures were investigated.

Results: Ninety-five patients and ninety-three controls were included. Skull base asymmetry was linearly related to orbital asymmetry (p < 0.001), correlated with earlier CT scans (p = 0.004) and anterior (p < 0.001) and posterior (p = 0.03) plagiocephaly. Posterior plagiocephaly was more common in patients (31%) compared with controls (5%) (p < 0.001). A patent metopic suture above nine months of age was associated with severe Harlequin deformity (p = 0.04) and a lower head circumference when fused (p = 0.03). Fronto-sphenoidal suture fusion was associated with later CT scans (p < 0.001) and less skull base asymmetry (p = 0.002). Spheno-parietal fusion was correlated with decreased skull base asymmetry (p = 0.03). Right lateralisation was more common in females.

Conclusions: Heterogenicity of unicoronal synostosis seems to be predominantly explained by variability in skull base morphology. Peri-pterionic fusions might limit deformity.