E4611. Idiopathic Granulomatous Mastitis (IGM): Everything About This Rare Disease That the Radiologist Needs to Know
  1. Thomas Clifford; Keck School of Medicine
  2. Lucien Rizzo; Keck School of Medicine
  3. Linda Larsen; Keck School of Medicine
  4. Jennifer Choi; Keck School of Medicine
  5. Mary Yamashita; Keck School of Medicine
  6. Sandy Lee; Keck School of Medicine
Idiopathic granulomatous mastitis (IGM) is a rare chronic inflammatory disease of the breast that typically affects young, parous, premenopausal women and is more common in the Hispanic population. Although it is a rare disease entity, we see this diagnosis commonly at our large urban public hospital, which has a predominantly underserved Hispanic patient population. While the etiology remains uncertain, associations between IGM and pregnancy, lactation, and hyperprolactinemia have been demonstrated. IGM poses a diagnostic challenge as its clinical symptoms and imaging manifestations can mimic breast cancer and infectious mastitis/abscess, often resulting in misdiagnosis and delayed care because many radiologists are not familiar with this disease process. Although data are limited, its incidence has been estimated to be 2.4 per 100,000. There is no consensus on the most effective treatment for IGM, with the first line being supportive treatment, and the effectiveness of corticosteroids is controversial.

Educational Goals / Teaching Points
Present an update on granulomatous mastitis, building upon our initial research from 2009. Review epidemiology, imaging features, diagnosis, histopathology, course, and treatment of IGM, with review of current literature. Present multimodality imaging examples (digital mammogram, tomosynthesis, ultrasound, MRI) of biopsy-proven cases from our institution including bilateral IGM, multifocal IGM, recurrent IGM, cystic neutrophilic granulomatous mastitis, and biopsy-proven IGM with corynebacterium.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The pathophysiology of IGM is thought to be broadly related to milk stasis and abnormal breast duct permeability, which allows for translocation of luminal contents into the lobular breast stroma, resulting in granuloma formation. Clinical manifestations are variable, but the most described presentation is a tender, palpable breast mass. Synchronous bilateral breast involvement has been reported in 1–18% of cases and presents additional challenges in management. Multicentric, multifocal, and recurrent cases of IGM have been described, but the incidence has not been defined. Evaluation of IGM relies on mammography and ultrasound, but findings are varied and nonspecific. The most frequently reported mammographic appearance is focal asymmetry or irregular mass. Calcifications are rare. On ultrasound IGM is most frequently hypoechoic, irregular, parallel, and hypervascular. Skin thickening and axillary lymphadenopathy may be seen with both modalities. Diagnosis is made through biopsy or by exclusion, and prompt diagnosis facilitates appropriate management.

Familiarity with IGM including its varied clinical and imaging presentations is critical given its tendency to mimic breast cancer and infection. Thorough knowledge of the entity is important for any radiology trainee and breast radiologist to ensure appropriate clinical management.