This study aims to summarize and validate the ultrasonographic features of granulomatous lobular mastitis (GLM) across its various clinical stages.

We have summarized and defined a set of disease-specific ultrasonographic features, including five subtypes of the “track sign,” as well as the “donut sign,” “false burr sign,” abscess formation, ulceration, and fistulous tracts. According to disease progression, GLM was categorized into six stages: Non-Mass Stage, Mass Stage, Abscess Stage, Late Ulceration Stage, Fistula Stage, and Complex Type (the simultaneous presence of ultrasonographic features corresponding to ≥ 2 different GLM stages within the same breast). In this study, a cohort of 273 patients was enrolled to evaluate GLM diagnosis and staging from both clinical and ultrasonographic perspectives. The diagnostic accuracy of ultrasonography was assessed, and the ultrasonographic manifestations of GLM were comprehensively delineated across its various clinical stages—with particular emphasis on the diagnostically challenging Non-Mass Stage.

Ultrasound-based diagnosis of GLM achieved a sensitivity of 98.85%, specificity of 83.33%, and a positive predictive value (PPV) of 99.23%. Stage-specific ultrasonographic features demonstrated statistically significant associations with clinical staging: Track signs were most frequently observed in the Non-Mass Stage (92.86%). The donut sign was prevalent in both the Non-Mass (69.05%) and Abscess (66.67%) stages. The false burr sign was highly characteristic of the Mass Stage (78.69%). The Abscess Stage exhibited large mixed echogenic areas with irregular walls and internal fluid motion (100%). Late Ulceration Stage was marked by hypoechoic areas in the areolar region communicating with dilated ducts (70.37%). Fistula Stage showed duct-like hypoechoic tracts extending to the skin with thickened walls (92.68%). Complex Type cases showed overlapping features of multiple stages. These findings validate the diagnostic utility of stage-specific ultrasonographic signs and support the clinical relevance of the proposed classification system.

GLM exhibits distinct stage-specific ultrasonographic features. When combined with a standardized examination protocol and clearly defined imaging criteria, these features can significantly enhance the early detection and accurate staging of the disease. Additionally, representative images for each stage are provided to support the standardization of ultrasonographic evaluation for GLM.