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

The objective of this review is to deepen the understanding and mastery of non-mass breast pathologies, enabling ultrasonographers to enhance diagnostic accuracy and improve their capabilities in image analysis and clinical interpretation. Narrative means have been used to synthesize evidence in this review. 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 literature, 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. 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 the synthesis and summarization of the relevant literature, this paper aims to enhance the diagnostic proficiency of sonographers in evaluating non-mass breast lesions.