Ultrasound non-mass lesions of the breast: imaging features, pathologic risk, and interobserver agreement

PURPOSE: This study aimed to evaluate the sonographic and clinical characteristics of breast non-mass lesions detected on ultrasound, identify factors associated with increasing pathological risk, and assess interobserver agreement among breast radiologists. METHODS: This retrospective study included breast ultrasound examinations performed between January 1, 2021, and August 30, 2025. A keyword search in the picture archiving and communication system identified 2,002 examinations potentially describing non-mass findings. After exclusions, 666 potentially eligible lesions were independently evaluated by three breast radiologists. Lesions were classified as non-mass according to a predefined majority rule (≥ 2 of 3 observers) and assessed using a three-level clinical concern score. Final diagnoses were established by histopathology or ≥ 2 years of imaging follow-up. Associations between imaging and clinical variables and pathological categories were evaluated using univariable analyses and multivariable ordinal logistic regression. Interobserver agreement was assessed using kappa statistics and Gwet's AC1. RESULTS: = 0.015) were independently associated with increasing pathological risk. CONCLUSION: Most breast non-mass lesions detected on ultrasound are benign; however, architectural distortion, posterior acoustic shadowing, and vascularity are independently associated with increased pathological risk. CLINICAL SIGNIFICANCE: Recognizing specific ultrasound features associated with higher pathological risk may help distinguish non-mass lesions requiring more intensive diagnostic evaluation from predominantly benign findings and support more consistent clinical management.