Progress in Ultrasound Research on Non-Mass Breast Lesions: Definition, Classification, and Differential Diagnosis

Non-mass lesions in breast ultrasound refer to abnormalities that exhibit different echogenicity from surrounding tissues but lack a distinct mass shape. Malignant breast lesions may also present as non-mass lesions on ultrasound, making accurate detection and diagnosis crucial for resolution. Currently, “non-mass breast lesions” are not included in ultrasound terminology of the 5th Edition Breast Imaging Reporting and Data System (BI-RADS). Although multiple classification systems have been proposed in the literatures, there remains no standardized ultrasound definition or malignant risk grading for non-mass lesions. The ultrasound features of benign and malignant non-mass breast lesions are often subtle and partially overlapping, complicating differential diagnosis and impacting clinical evaluation and management. The authors reviewed definitions and classification systems for non-mass breast lesions in the literatures, summarized their ultrasound features, and introduced the diagnostic applications and value of ultrasound technologies. This aims to enhance the diagnostic proficiency of sonographers in evaluating non-mass breast lesions. This paper reviews the ultrasound definitions and classifications of non-mass breast lesions, exploring the correlation between their ultrasound features and pathological histology as well as malignant risk. It also discusses the diagnostic values of conventional ultrasound, automated breast ultrasound, ultrasound elastography, and contrast-enhanced ultrasound for non-mass breast lesions. Finally, it compares the diagnostic accuracy of various ultrasound-guided needle biopsy techniques for non-mass lesions. Through deepening their understanding and mastery of non-mass breast lesions, sonographers can enhance diagnostic accuracy and improve their capabilities in image analysis and clinical interpretation.