Relative CT Number as a Quantitative Imaging Biomarker for Differentiating Sinonasal Polyp, Inverted Papilloma, and Squamous Cell Carcinoma: A Preliminary Retrospective Study

Background/Objectives: Unilateral sinonasal lesions may be difficult to characterize on non-contrast computed tomography (CT) because inflammatory polyps, benign neoplasms, and malignant tumors can appear as similar unilateral soft-tissue masses. Non-contrast CT is widely available, but the diagnostic performance of relative CT number across inflammatory, benign neoplastic, and malignant sinonasal lesions within a single cohort remains insufficiently characterized. This study aimed to provide additional evidence regarding the diagnostic performance of relative CT number on non-contrast CT by comparing its values among sinonasal polyp (SP), inverted papilloma (IP), and squamous cell carcinoma (SCC), and by evaluating predefined binary diagnostic comparisons. Methods: This retrospective single-center study included 92 patients with histopathologically confirmed unilateral or unilateral-dominant sinonasal lesions: 49 SP, 24 IP, and 19 SCC. Preoperative non-contrast paranasal sinus CT images were reviewed. Relative CT number was calculated as the ratio of mean lesion attenuation to mean pontine attenuation. Group differences were analyzed using non-parametric tests, and diagnostic performance was assessed with receiver operating characteristic (ROC) curve analysis. Age-adjusted binary logistic regression analyses were also performed for the predefined binary comparisons. Sensitivity analyses were additionally adjusted for lesion ROI area. Results: Relative CT number differed significantly among the three groups (overall p < 0.001). ROC analysis showed an AUC of 0.815 (95% CI, 0.704–0.904) for SP versus IP, 0.667 (95% CI, 0.498–0.826) for IP versus SCC, 0.869 (95% CI, 0.792–0.932) for SP versus IP+SCC, and 0.937 (95% CI, 0.866–0.986) for SP versus SCC. After age adjustment, relative CT number was associated with the positive diagnostic category in all four comparisons; however, the IP–SCC association was no longer significant after ROI-area adjustment (p = 0.073). The highest diagnostic performance was observed for distinguishing SP from SCC. Conclusions: These preliminary findings suggest that relative CT number may serve as an adjunctive quantitative CT parameter for differentiating unilateral inflammatory sinonasal lesions from neoplastic lesions, with the strongest diagnostic performance observed for SP versus SCC. However, its standalone discrimination between IP and SCC was limited, and the age-adjusted association remains hypothesis-generating.