Contrast-enhanced ultrasound for indeterminate adnexal masses on IOTA simple rules: an exploratory single-center pilot study

To investigate the diagnostic accuracy of contrast-enhanced ultrasound (CEUS) in differentiating among benign, borderline, and malignant adnexal masses classified as indeterminate by the International Ovarian Tumour Analysis (IOTA) simple rules, and to explore its advantage in identifying the microcystic pattern (MCP). This single-center retrospective pilot study included 90 patients with IOTA-indeterminate adnexal masses evaluated using CEUS between April 2019 and May 2026. With postoperative histopathology as the reference standard, cases were classified as benign ( n = 44), borderline ( n = 26), and malignant ( n = 20). The DeLong test was applied to compare the diagnostic performance of two-dimensional microcystic pattern (2D-MCP) and CEUS-derived microcystic pattern (CEUS-MCP) for borderline ovarian tumors (BOTs) diagnosis. Based on sonographic features with significant between-group differences, nested firth penalized logistic models were built for three binary outcomes, and AUCs of 2D and 2D+CEUS models were compared to explore the incremental value of CEUS. CEUS-MCP exhibited significantly higher diagnostic performance for BOTs than 2D-MCP (DeLong test, P = 0.024). Adding CEUS features to 2D features significantly increased AUCs for all three binary outcomes: 0.664 to 0.849 for benign vs. non-benign (ΔAUC = 0.185, P = 0.0003), 0.727 to 0.846 for borderline vs. non-borderline (ΔAUC = 0.119, P = 0.016), and 0.672 to 0.815 for malignant vs. non-malignant (ΔAUC = 0.143, P = 0.015). Significant positive NRI and IDI were consistently observed, and CEUS-MCP yielded a higher interobserver kappa value than 2D-MCP (0.450 vs. 0.345). In this single-center pilot study of adnexal masses indeterminate by IOTA simple rules, CEUS delivers incremental diagnostic value, with significantly improved discrimination across benign, borderline and malignant lesions after adding CEUS features. CEUS-MCP outperforms 2D-MCP for BOTs detection and has higher interobserver reproducibility. As exploratory findings, CEUS may act as a supplementary tool for IOTA-indeterminate cases, pending further validation in large multicenter prospective trials.