Development and Validation of the So-RADS: An Ultrasound-Based Risk Stratification System for Soft-Tissue Masses

The accurate diagnosis of soft-tissue masses (STMs) remains challenging due to their heterogeneous histology and the lack of a standardized ultrasound reporting system, which leads to reliance on subjective interpretation. To address this limitation, we developed and validated the soft-tissue radiology reporting and data system (So-RADS), an ultrasound-based risk stratification tool for STMs.

This retrospective study included 858 pathologically confirmed STMs. To enhance clinical applicability for uncertain cases, the model was developed using a cohort of lesions with ambiguous ultrasound features (n = 490). Independent predictors of malignancy, identified through multivariate logistic regression, were assigned points to create a scoring system. This score was then converted into the definitive So-RADS categories.

Seven independent predictors were identified and assigned points: age ≥ 50 y, size ≥ 50 mm, blurred margin, irregular shape, heterogeneous echogenicity, history of malignancy, and rich blood flow. Based on these predictors, the So-RADS system (score range 0-10) demonstrated excellent diagnostic performance, with an area under the receiver operating characteristic (ROC) curve of 0.900. A cut-off score of ≥ 4 points yielded a sensitivity of 78.1% and a specificity of 87.2%. The system employs a two-step classification scheme. First, masses are categorized as typical benign (So-RADS 2). Second, atypical masses are stratified as So-RADS 3 (low risk), 4 (moderate risk), or 5 (high risk), with each category linked to specific management recommendations. Interobserver agreement was substantial (weighted Kappa = 0.784).

The So-RADS system is a robust and reproducible tool that standardizes US reporting for STMs, improves diagnostic accuracy, and provides clear management guidance.