Beyond the Mass: A Pictorial Review of Nonmass Lesions on Breast Ultrasound Using BI-RADS v2025.

The BI-RADS v2025 Manual formally incorporates nonmass lesions (NMLs) into the breast ultrasound lexicon, expanding the diagnostic focus of breast ultrasound beyond discrete masses. NMLs can represent a broad spectrum of benign, high-risk, and malignant conditions, with an overall high malignancy rate that warrants tissue diagnosis. However, their identification can be challenging relating to their lack of a discrete margin or specific shape along with technical factors including the gravitational effect related to patient positioning during ultrasound, transducer orientation during dynamic real-time scanning, and operator dependence of handheld acquisition technique. This pictorial review presents a spectrum of illustrative cases of NML, classified by distribution (segmental, linear, focal, or regional NMLs) and encompassing an array of pathologically confirmed benign and malignant diagnoses. The cases demonstrate echo patterns, posterior features, and associated findings based on the BI-RADS v2025 descriptors and highlight the role of multimodality correlation including with mammography, MRI, contrast-enhanced mammography, and [18F]FDG PETCT. Potential pitfalls, particularly relevant in the screening setting, are also addressed. Ultimately, the article aims to facilitate the transition to the new lexicon, foster active recognition of these often-subtle lesions, promote consistent reporting, and lay the groundwork for future systematic data collection and analysis.