Which feature is NOT typically associated with malignant breast masses on ultrasound?

• A. Taller-than-wide orientation
• B. Shadowing
• C. Well-circumscribed, smooth margins
• D. Irregular contour

Answer: (C)

A key idea is how ultrasound features differentiate benign from malignant breast masses. Malignant lesions typically disrupt tissue architecture, so they often have irregular, nonuniform, or spiculated margins, may appear taller-than-wide in the transverse view (nonparallel to the skin), and can show posterior acoustic shadowing from dense tissue or fibrotic reaction. In contrast, a mass with smooth, well-circumscribed margins is characteristic of benign processes such as fibroadenomas or simple cysts.

Therefore, the feature that is not typically associated with malignant masses is well-circumscribed, smooth margins. The other features listed—taller-than-wide orientation, shadowing, and irregular contour—are more consistent with malignancy.