Characterization of Novel MRI Findings in Idiopathic Granulomatous Mastitis: Diagnostic Significance and Clinical Perspectives.

objectivesIdiopathic granulomatous mastitis (IGM) is an uncommon, benign, chronic inflammatory breast disease that frequently mimics carcinoma both clinically and radiologically, posing diagnostic challenges. While classical imaging manifestations have been described, the full spectrum of MRI features remains incompletely characterized. This study aimed to identify and characterize novel MRI descriptors of histopathologically confirmed IGM and assess their reproducibility and potential clinical implications.

methodsIn this retrospective single-center study, 45 consecutive women with biopsy-proven IGM were evaluated using 1.5 T breast MRI. Imaging protocols included T2-weighted fat-suppressed, T1-weighted, diffusion-weighted, and dynamic contrast-enhanced sequences. Two experienced radiologists, blinded to clinical and pathological data, independently reviewed all cases for classical and novel MRI features. Interobserver agreement was assessed using raw agreement and Cohen's κ statistics. Associations between imaging descriptors and clinical-demographic variables were tested with nonparametric methods.

resultsThe most common MRI pattern was a heterogeneously enhancing mass with concomitant nonmass enhancement (NME) (75.6%), followed by rim-enhancing microabscesses (62.2%) and isolated NME (48.9%). Four novel MRI features were identified: spherical transformation of mammary fat lobules (62.2%), disruption of fibroglandular tissue architecture (73.3%), ring-like enhancement with asymmetric wall morphology (46.6%), and nipple-areolar complex retraction (11.1%). Interobserver reproducibility was high (κ = 0.786-1.000; raw agreement > 90%). Novel descriptors, particularly spherical lobule transformation, fibroglandular disruption, and ring-like enhancement, were strongly associated with NME (all p < 0.001), but not with age or lesion laterality.

conclusionThese imaging descriptors may contribute to a better radiologic understanding of the morphological manifestations of IGM and may assist radiologists in recognizing imaging patterns associated with granulomatous inflammation. However, given the retrospective design and absence of a comparative cohort, these findings should be considered exploratory and hypothesis-generating.