Ning Zhao, Dehong Che, Xiaokang Hu
BACKGROUND: Ovarian tumours are common among women, with ultrasound serving as the primary diagnostic tool. The O-RADS system classifies tumours into categories 1-5 based on malignancy risk. Category 4 tumours are the most challenging to diagnose, as they may be either benign or malignant, often leading to unnecessary surgery. METHODS: This prospective study enrolled 723 patients with pathologically confirmed adnexal masses from July 2023 to May 2026. A total of 805 masses were included. All underwent standardised ultrasound with dynamic cine loop storage. Category 4 masses were subclassified into 4a (low-risk) and 4b (high-risk) based on locule count (>10 as high-risk) and colour score. Pathological results served as the gold standard. RESULTS: Among 225 O-RADS Category 4 masses, the malignancy rate was 19.1% (43/225). The 4b subclass (86 masses) had a malignancy rate of 45.3% (39/86), significantly higher than the 4a subclass (139 masses, 2.9% (4/139)). Masses with >10 locules showed a 53.3% malignancy rate, while those with colour score 3-4 had a 38.6% malignancy rate. The combined model achieved an area under the curve of 0.956, significantly outperforming single predictors. Decision curve analysis indicated that this model could reduce unnecessary surgeries by approximately 18%. CONCLUSION: The modified O-RADS model effectively stratifies malignancy risk in adnexal masses, improving diagnostic accuracy and potentially reducing unnecessary surgical interventions.