Investigating the Cause of Late Deformity Following Fronto-orbital Remodelling for Metopic Synostosis Using 3D CT Imaging

Purpose: Late deformity/indentation is well-recognised following fronto-orbital remodelling (FOR) for metopic synostosis. We hypothesise that if damage to temporalis muscle were a contributor, the thickness of soft tissue and bone in the affected area would be reduced.

Materials And Methods: Soft tissues and bone were separately segmented and reconstructed three-dimensionally from computed tomograms of 8 patients 1.5-18 years post-FOR performed at 16 ± 2 months for metopic synostosis and from 8 age-matched controls. Soft tissue (taken as proxy for temporalis muscle) and bone thickness overall and in the indented areas were computed.

Results: Post-FOR, three-dimensional soft tissue thickness maps demonstrated temporalis extending upwards but falling short of the indented area. Overall skull thickness increased with age post-FOR (logarithmic fit R = 0.71) and for controls (R = 0.90). Although immediately post-FOR the future indented area had a thickness of 98% of control, it decreased linearly to 64% 16 years later (Pearson's r = 0.84).

Conclusion: These findings suggest that late post-FOR deformity/indentation is enhanced by limited upward extension (or retraction downwards) of temporalis muscle, while bone thickness in the affected area gradually decreases. This supports the hypothesis that aberrant re-attachment of the temporalis muscle makes a material contribution to late deformity following FOR for metopic synostosis.