Contrast-enhanced mammography findings of idiopathic granulomatous mastitis: a retrospective analysis of seventy histopathologically proven cases

PURPOSE This study aimed to characterize the contrast-enhanced mammography (CEM) findings of histopathologically confirmed idiopathic granulomatous mastitis (IGM), compare isolated mass and non-mass enhancement (NME) phenotypes, and explore the cumulative burden of malignancy-mimicking imaging features using an exploratory malignancy-mimicking feature score (MMFS). METHODS This retrospective single-center study included 70 women with histopathologically confirmed IGM who underwent CEM between 2021 and 2024. Imaging findings were reviewed in consensus by two breast radiologists according to the Breast Imaging Reporting and Data System Manual (2025 edition). Lesion morphology, enhancement characteristics, temporal enhancement patterns, conspicuity, and associated imaging findings were recorded. Patients with isolated mass lesions and isolated NMEs were compared. The MMFS was calculated from 12 predefined malignancy-mimicking CEM features, including moderate/high enhancement conspicuity, plateau/washout temporal enhancement patterns, suspicious mass morphology, segmental/linear NME distribution, and associated findings, such as skin thickening and axillary lymphadenopathy. RESULTS The mean patient age was 41.7 ± 8.7 years, and the mean lesion size was 57.3 ± 26.8 mm. NME was the predominant imaging presentation (55.7%), and 14.3% of patients demonstrated both mass and NMEs. Contrast enhancement was present in all lesions, with heterogeneous enhancement (44.3%), high enhancement conspicuity (44.3%), and axillary lymphadenopathy (47.1%) being common findings. Compared with isolated mass lesions, isolated NMEs were significantly larger (median = 70 vs. 50 mm; P = 0.017) and more frequently associated with skin thickening (46.2% vs. 9.5%; P = 0.004). The mean MMFS was 3.41 ± 1.66. All patients demonstrated at least one malignancy-mimicking imaging feature; 90.0% had two or more features, and 65.7% had three or more features. CONCLUSION IGM demonstrates a broad spectrum of CEM findings, including multiple imaging features conventionally considered suspicious for malignancy. NME is the predominant imaging phenotype and is associated with larger lesion size and more frequent skin thickening than isolated mass lesions. The high cumulative burden of malignancy-mimicking imaging features highlights the diagnostic challenge posed by IGM on CEM. CLINICAL SIGNIFICANCE IGM frequently mimics breast cancer on CEM because multiple suspicious imaging features often coexist within the same lesion. Familiarity with the CEM spectrum of IGM may facilitate the appropriate interpretation of suspicious findings and contribute to informed patient management.