Cystic Breast Lesions: Diagnostic Approach and US Assessment

Various cystic breast lesions are encountered during screening and diagnostic breast imaging. According to the Breast Imaging Reporting and Data System (BI-RADS) from the American College of Radiology, cystic breast lesions can be classified into the following categories based on sonographic findings: simple cysts, complicated cysts, clustered microcysts, and complex cystic and solid masses. With appropriate technique, simple cysts can be diagnosed easily by satisfying the diagnostic criteria, which include anechoic round or oval lesions with circumscribed margins and posterior enhancement on US images. Simple cysts are categorized as BI-RADS category 2, benign. Complicated cysts contain debris and satisfy all other sonographic criteria for simple cysts, except they are not anechoic. Clustered microcysts are defined as lesions comprising a cluster of small anechoic masses without a solid component. Based on recent investigations, complicated cysts are categorized as BI-RADS category 3, probably benign, whereas clustered microcysts are categorized as BI-RADS category 2. Complex cystic and solid masses contain fluid and solid components and include those with a thick wall, thick septations, an intracystic or mural mass, and both cystic and solid components. They usually are considered BI-RADS category 4, suspicious, and are accompanied by a biopsy recommendation. Radiologists must evaluate cystic lesions carefully, with meticulous technique, and provide appropriate assessment and management recommendations, thereby reducing unnecessary follow-up and biopsies while preventing cancers from being missed or dismissed. ^©RSNA, 2025 Supplemental material is available for this article.