Pyriform, nasal base, and nasal deformity: A mediation analysis evaluating the mechanisms of secondary cleft lip nasal deformity.

Abstract

The biomechanical relationship between maxillary defects and secondary cleft nasal deformities in adult patients remains unelucidated. This study aimed to investigate the pathophysiology of cleft lip nasal deformity by comprehensively measuring parameters using preoperative computed tomography (CT) records. Retrospective analysis of 56 adult patients with unilateral cleft (24.2±6.2 years) using CT data. Patients were stratified by alveolar cleft involvement with pyriform margin (type I/II) and with or without palate involvement. Parameters were categorized into the maxillary, nasal base, and nasal tip and analyzed using linear regression. Additionally, mediation analysis was used to evaluate nasal base's intermediary role in transmitting skeletal effects. Results demonstrated preserved nasal base projection on the cleft side despite pyriform depression. Compensatory subcutaneous soft tissue thickening was significantly greater at cleft-side landmarks (p < 0.01). Additionally, cleft-side nostril sill height (p = 0.032) and mucosal surface area (Δ = 106.08 mm², p = 0.048) showed significant reductions. Linear regression revealed several significant associations between pyriform and nasal tip deformities; however, mediation analysis showed most nasal base parameters did not statistically mediate this relationship. Notably, cleft alveolar defects exhibited indirect effects on columellar tilt through nostril sill mediation (p = 0.048). Skeletal displacement in cleft deformities minimally influences nasal morphology. Compensatory soft tissue adaptations maintain nasal base projection despite the underlying bony discrepancies, making nasal base augmentation unbeneficial for nasal deformity. However, the nostril sill emerges as a critical mediator of columella deviations while mucosal lining could possibly impact tip projection.