Susceptibility-Weighted Breast MRI Differentiates Abscesses from Necrotic Tumors: A Prospective Evaluation

Background/Objectives: Breast abscesses and necrotic masses often show similar peripheral enhancement and a fluid-containing appearance on breast MRI, leading to diagnostic confusion. Accurate differentiation is critical because biopsies that fail to sample the lesion wall may yield false-negative results, may be misinterpreted as an infectious process, and delay diagnosis. Incorporating SWI into the protocol can provide additional clues to malignancy and, when warranted, prompt a second wall-targeted biopsy, thus reducing the risk of delayed cancer diagnosis. Methods: This single-center prospective diagnostic accuracy study included 42 female patients diagnosed between 2022 and 2025 with either necrotic breast tumors or abscesses, confirmed by histopathology. SWI-based Intralesional Susceptibility Score (ILSS), rim morphology, and mean ADC values were evaluated. Statistical analyses included the Mann–Whitney U test, chi-square test, ROC analysis, DeLong test for comparison of AUCs, and Cohen’s kappa for interobserver agreement. Results: SWI-based ILSS values were significantly higher in necrotic tumors compared to abscesses (mean ILSS: 2.28 vs. 0.85; 95% CI: 1.0–2.0; p < 0.001). Smooth hypointense rims were predominantly observed in abscesses (Sensitivity: 63.1%, 95% CI: 0.38–0.83; Specificity: 88.9%, 95% CI: 0.65–0.98; p = 0.001). Incomplete rim morphology was more frequent in tumors (Sensitivity: 78.9%, 95% CI: 0.54–0.93; Specificity: 77.8%, 95% CI: 0.52–0.93; p < 0.001). The double rim sign was highly specific for abscesses (Specificity: 95.2%, 95% CI: 0.76–0.99 p = 0.002). Conclusions: SWI provides valuable morphological information in differentiating abscesses from necrotic tumors on breast MRI. When used in combination with ADC values, it can enhance diagnostic accuracy.