The diagnostic dilemma of idiopathic granulomatous mastitis with an emphasis on histopathologic findings

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BACKGROUND: Idiopathic granulomatous mastitis (IGM) is a rare benign inflammatory breast condition with diverse clinical and radiologic features, often misdiagnosed as malignancy prior to sampling. Therefore, histological findings are one of the most essential bases of diagnosis. METHODS: We retrospectively searched the histopathologic database of the Cancer Institute of Imam Hospital for IGM cases and collected clinical and radiological data. After ruling out other causes of granulomatous mastitis, the histopathologic features of each case were evaluated. The pattern of inflammation was classed as lobulocentric, lobular spared, or confluent. The presence of granulomas was evaluated based on descriptive features, including well-formed or poorly defined granulomas, as well as the presence or absence of multinucleated giant cells. Granulation tissue, empty space, fat necrosis, and necrosis were also assessed. RESULTS: Overall, 40 cases of IGM were reviewed. All patients were female, within the age range of 22 to 64, with the majority falling into the 30-39 category. The most common clinical manifestation was a palpable mass. 30% of patients had a history of breastfeeding over the past 5 years, and one patient had a history of prolactinoma. BI-RADS 4a was the most reported radiologic score. In histopathologic assessment, lobulocentric inflammation was reported as a predominant finding (45% of cases). Granuloma was present in 39 cases (97.5%), but was only well-defined in 33 cases (82.5%). Neutrophilic aggregates were present in 37 cases (92.5%). CONCLUSION: The diagnosis of IGM depends on assessing the clinical and radiologic findings along with pathologic features. IGM is microscopically defined by a non-caseating lobulocentric granulomatous inflammation, composed of tight aggregates of epithelioid histiocytes. One of the variants, cystic neutrophilic granulomatous mastitis (CNGM), is characterized by the presence of cystic empty vacuoles lined by neutrophils.

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