Idiopathic Granulomatous Mastitis: Diagnosis and Histopathologic Features, A Review

Background: Idiopathic granulomatous mastitis (IGM) is a rare benign inflammatory breast condition, mostly affecting women of reproductive age within a few years of pregnancy. Due to diverse clinical and radiologic features, IGM can mimic a vast spectrum of breast conditions. Therefore, histological findings are one of the most essential bases of diagnosis. Methods: A literature search was performed to review the characteristics of IGM with an emphasis on histopathological features in English sources from 2010 to 2022. The key words used for PubMed database search were “breast”, “granulomatous mastitis”, “histopathology”, and “pathology.” Results: In total, 192 articles were retrieved, from which 38 most relevant manuscripts were selected for this review article. Conclusion: The diagnosis of IGM depends on clinical, radiologic, and pathologic findings. Palpable mass is the most frequent complaint. An irregular hypoechoic mass with varying degrees of posterior phenomena is the most common sonographic finding. Histologically, IGM is characterized by a non-caseating lobulocentric granulomatous inflammation; composed of tight aggregates of epithelioid histiocytes with or without multinucleated giant cells. At times, the presence of cystic empty vacuoles lined by neutrophils is noted that is commonly associated with cystic neutrophilic granulomatous mastitis (CNGM), a variant of IGM. Atypical findings for IGM includes: The presence of atypia and/or malignancy, caseous necrosis, marked eosinophilic infiltration, absence of granulomatous inflammation, etc.