Beyond Hounsfield Units: A Comparative Study of Semiquantitative Morphological Features for Differentiating Silicone from Autologous Costal Cartilage Nasal Implants on CT Imaging

Introduction: Identifying the type of existing nasal implant is crucial for preoperative planning of revision rhinoplasty in patients with secondary cleft lip nasal deformity. However, patients often lack accurate information. Although Hounsfield Units (HUs) on computed tomography (CT) offer a potential solution, their discriminatory power remains uncertain. This study evaluated the efficacy of a novel three-dimensional (3D) density measurement method and compared it with semiquantitative morphologic assessment for differentiating silicone from autologous costal cartilage implants. Materials and Methods: A retrospective study enrolled nine patients undergoing secondary rhinoplasty (4 with costal cartilage implants, 5 with silicone implants). Preoperative CT scans were analyzed using Mimics software to create 3D models of the implants and calculate the average HU value of their entire volume. Interobserver and intraobserver reliability were assessed using the intraclass correlation coefficient (ICC). The Mann-Whitney U test was used to compare density values and semiquantitative scores for morphologic features (implant boundary clarity and heterogeneous calcification) between groups. Results: The novel 3D measurement method demonstrated excellent reliability (ICC > 0.98). The median HU values showed no significant difference between the costal cartilage and silicone implant groups (265.96 HU versus 118.17 HU, P = 0.754). In contrast, semiquantitative morphologic assessment revealed significant differences. The costal cartilage group had significantly higher (worse) scores for boundary clarity (median: 2.5 versus 0, P < 0.05) and heterogeneous calcification (median: 1.75 versus 0, P < 0.05), indicating blurrier boundaries and more frequent calcification compared with silicone implants. Conclusion: Although CT density values alone are insufficient for reliable implant differentiation, specific morphologic features—particularly implant boundary clarity and heterogeneous calcification—serve as highly discriminatory radiologic markers when assessed semiquantitatively. We recommend prioritizing semiquantitative morphologic evaluation over density measurement in the CT assessment of these patients to enhance preoperative planning for revision surgery.