Evaluation of magnetic resonance imaging (MRI) findings of idiopathic granulomatous mastitis and inflammatory breast cancer

Objective: Idiopathic granulomatous mastitis (IGM) is a rare benign disease with an unknown etiology, which may mimic breast carcinoma. In this study, we aimed to distinguish idiopathic granulomatous mastitis (IGM) from inflammatory breast carcinoma (IBC) via magnetic resonance imaging (MRI). Materials and Methods: 1249 patients who underwent breast MRI between January 2014 and April 2020 were retrospectively reviewed from our institution's database. Based on pathology reports, patients who had breast lesions with accompanying inflammatory signs (skin thickening, edema, redness) were classified as benign or malignant. 20 patients diagnosed with pathologically proven IGM and 18 patients with pathologically proven IBC were included in this study. The lesions were evaluated according to MRI features such as morphology, multifocality, T2 signal intensity ratios, ADC values, kinetic contrast enhancement curves and presence of lymphadenopathy. Chi- square test or Fisher exact Chi-square test were used for statistical analysis. Results: The patients were younger in IGM group. No significant difference was observed in terms of lesion size, shape and margin between IGM and IBC groups. Axillary lymphadenopathy was more common in IBC group. ADC values of benign inflammatory lesions were not significantly different from those of malignant lesions (p=0,0163). While type 1 and 2 dynamic curves were mostly observed in benign lesions, type 3 dynamic curve was more common in malignant inflammatory lesions. The T2 SI ratio for IGM was significantly higher than IBC (p<0,01). The mean T2 SI ratios were 1.41 ± 0.38 and 0.61 ± 0.18 for IGM and IBC, respectively. The optimal cut-off point for the T2 SI ratio was determined as 0,9 according to Youden index with a sensitivity of %100 and specificity of %95 (AUC: 0,985). Conclusion: The distinction between benign and malignant inflammatory lesions can be challenging since they have similar clinical features. While the diffusion- weighted images do not aid in differential diagnosis of breast inflammatory disease alone, dynamic curves and T2 SI ratio can be useful. The value of the T2 SI greater than 1 and type 1-2 dynamic curves indicate that the lesion is benign. If IGM is suspected before biopsy, samples should be provided in order to eliminate tuberculosis. Keywords: Idiopathic Granulomatous Mastitis (IGM), Inflammatory Breast Cancer (IBC), Magnetic Resonance Imaging (MRI)