Background: Idiopathic granulomatous mastitis (IGM) is a benign, inflammatory breast disease of unknown etiology. Although it is rare, it frequently presents in a manner similar to that of breast carcinoma.
Case: A 41-year-old female developed unilateral idiopathic granulomatous mastitis, diagnosed by fine needle aspiration cytology. The clinical presentation and mammographic findings were suspicious for carcinoma. Fine needle aspiration cytology showed granulomatous inflammation. Histopathologic examination revealed a noncaseating, granulomatous lesion. Further clinical, radiologic and laboratory investigations disclosed no etiology. Therefore, we considered the case to be idiopathic granulomatous mastitis.
Conclusion: Cytologically it may be difficult to distinguish IGM from carcinoma of the breast. Typical cytologic findings of the lesion are helpful to rule out cancer. In the differential diagnosis, all known causes of granulomatous changes have to be excluded before a diagnosis of idiopathic granulomatous mastitis is made.