Prespecified Structured CT and MRI Scores for Sinonasal Inverted Papilloma: A Dual-reader Diagnostic Accuracy Study

Rationale and objectives To compare structured computed tomography (CT) and magnetic resonance imaging (MRI) scores for differentiating inverted papilloma (IP) from other benign and malignant causes of unilateral sinonasal opacification.Materials and methods In this retrospective single-center study, 179 patients with histopathologically confirmed unilateral sinonasal opacification were classified as IP spectrum (n = 72) or non-IP (n = 107). Two blinded readers independently assessed CT (n = 172) and MRI (n = 109; both modalities, n = 102) using prespecified IP scores; Reader 1's final assessment served as the primary analysis. Diagnostic performance was compared using area under the curve (AUC) analysis with paired DeLong testing, and independent predictors were identified with multivariable, Firth-penalized, and parsimonious logistic regression.Results In the paired cohort (n = 102), MRI demonstrated a numerically higher, but not statistically superior, performance than CT for distinguishing IP-spectrum from non-IP lesions (AUC 0.915 vs. 0.869; ΔAUC +0.045; p = 0.076). Combining CT and MRI scores did not improve discrimination beyond MRI alone (combined AUC 0.891; cross-validated AUC 0.883). Convoluted cerebriform pattern and bone destruction were the only independent predictors. MRI demonstrated a significant advantage over CT in differentiating IP from unilateral sinonasal polyps (AUC 0.965 vs. 0.811; q Conclusion CT and MRI provide complementary rather than interchangeable information in the evaluation of unilateral sinonasal opacification. Although overall diagnostic performance was comparable and the combined assessment offered no incremental benefit over MRI alone, MRI significantly outperformed CT in distinguishing IP from unilateral polyps. These findings support a structured multiparametric imaging approach, particularly in diagnostically challenging cases, and warrant prospective multicenter validation.