Idiopathic Granulomatous Mastitis: Diagnosis and Histopathologic Features, A Review

Abstract

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.

Pathological manifestations of granulomatous lobular mastitis

“…In granulomatous lesions, neutrophil aggregation bands have more peripheral CD3+ lymphocytes than CD20+ lymphocytes (49). Anousha et al suggest that granulomas, lobular central inflammation, and neutrophil infiltration are the pathological triad of GLM (50). This may be related to the different clinical staging of the obtained GLM tissue, with Yu et al noting that the microscopic neutrophil count varies from the mass stage to the abscess stage to the post-ulcerative stage, and can vary from rare to numerous neutrophil infiltrates (28).…”

“…There may be mild fibrosis of the interlobular stroma surrounding the lesion. Fat necrosis may be seen (42,50). Squamous epithelial metaplasia may occur in both lobules and ducts (23).…”

“…This feature has not been described by others and its significance is unknown. Other uncommon features are caseous necrosis, marked eosinophil infiltration, non-granulomatous inflammation, and foamy histiocyte infiltration, granulation tissue formation (48,50).…”

“…Özşen M reported 2 cases of ductal carcinoma in situ associated with lesions detected in patients with recurrent GLM (52). Sometimes breast cancer can also cause inflammation and look like GLM (50,54). This tells us to be careful in identifying GLM even when pathological tissue is obtained, and that as much breast tissue as possible will be better for a clear diagnosis, which is why we do not recommend fine needle aspiration.…”

“…Gram-positive bacilli in lipid vacuoles are currently dominated by Corynebacterium, with the most common isolate being C. kroppenstedtii, followed by C. amycolatum and C. tuberculostearicum (50,58). Other pathogens such as P. oleovorans, human gammaherpesvirus 4, A. baumannii, T. thermophilus are likely to be closely related to GLM (48).…”