Table 1. Definitions and features of masses and proposed nonmass lesions in ACR BI-RADS ultrasound.

Classifications	Definition*	Major features	Associated features
Masses	Three-dimensional and occupying space; should be seen in 2 different planes	Shape, margin, orientation, echo pattern, and posterior features	Calcifications, architectural distortion, duct changes, skin changes, edema, vascularity, and elasticity
Nonmass lesions	Discrete finding distinctly different from normal tissue; lacks the margination of a mass and cannot be assigned a specific shape; often subtle and may be visualized primarily in 1 plane only	Distribution and echo pattern	Calcifications, architectural distortion, duct changes, posterior features, vascularity, and elasticity

^*Definitions and features of masses are based on the 5th edition of BI-RADS [1], and those of nonmass lesions are based on presentations at the Society of Breast Imaging symposium in May 2023 [23]. In the BI-RADS lexicon, calcifications are not in “associated features” category and are a separate major category after mass. Modified from Choi et al. J Breast Imaging 2023 [24].

ACR = American College of Radiology, BI-RADS = Breast Imaging Reporting and Data System