Distinguishing Malignant from Benign Causes of Breast Size Changes: A Case-based Primer for the Radiologist.

Changes in breast size, whether enlargement or shrinkage, are a frequent clinical concern. Bilateral size changes are typically associated with benign conditions, while unilateral changes often raise concerns about malignancy, requiring prompt and accurate diagnosis to guide effective management. Through illustrative clinical scenarios, the authors provide a comprehensive review of the evaluation and management of breast size changes and address the spectrum of associated conditions. It is important for radiologists and clinicians to distinguish malignant from benign causes by integrating clinical history, physical examination, and imaging findings, all essential tools in the diagnostic process. Prior imaging, clinical context, and multimodality imaging are explored to provide a structured diagnostic approach. Radiologists are essential in identifying the underlying causes, directing appropriate care, and alleviating patient anxiety. The authors offer a practical framework to guide diagnostic decision making through the synthesis of clinical and imaging data. ©RSNA, 2026 Supplemental material is available for this article.