Non-Mass Lesions on Breast Ultrasound

A non-mass lesion on breast ultrasound (US) is described as a distinct, identifiable area of altered echotexture compared to the surrounding breast tissue without forming a typical mass shape.The incidence of non-mass lesions in screening breast US was reported to be between 1.0% and 5.3%.The Japan Society of Ultrasonics in Medicine has classified non-mass abnormalities into five subtypes: hypoechoic areas in the mammary gland, ductal abnormalities, architectural distortion, multiple small cysts, and echogenic foci without hypoechoic areas.Non-mass lesions are most commonly observed when US is used to evaluate mammographic focal asymmetries or non-mass enhancement seen on magnetic resonance imaging.These lesions can be associated with calcifications, ductal abnormalities, posterior shadowing, hypervascularity, and architectural distortion.Non-mass lesions must be distinguished from normal fibroglandular tissue.While often associated with benign conditions, they may also be indicative of malignant lesions.Nevertheless, there are no standardized classifications or approaches for non-mass lesions.Hence, further research is necessary to improve the interpretation of non-mass lesions in screening and diagnostic breast US and ensure accurate application in clinical practice.This review aims to enhance the accuracy of breast cancer diagnosis in clinical practice by examining the definition, characteristics, classification, correlation with other imaging studies, and histological features of non-mass lesions on breast US.