E1483. What You See May Not Be What You Get: Imaging of Granulomatous Mastitis
  1. Brian Yep; UC Irvine Medical Center
  2. Nu Na; UC Irvine Medical Center
  3. Freddie Combs; UC Irvine Medical Center
Granulomatous mastitis is an unusual inflammatory disease of the breast with unknown etiology. Pathologically, this condition is characterized by chronic non-caseating, non-necrotizing granulomatous lobular inflammation. There has been a strong association with breastfeeding whether recent or remote, but the causative agent remains unknown and therefore no effective treatment is available. Granulomatous mastitis can present as a palpable, tender mass with overlying skin erythema and edema as well as occasional purulent drainage. Findings on conventional breast imaging with mammography and ultrasound can mimic other pathologies most significantly breast cancer, underscoring the necessity of biopsy and tissue diagnosis to guide further management. We present a review of the imaging findings seen in cases of granulomatous mastitis encountered at our institution’s breast imaging center.

Educational Goals / Teaching Points
The primary objectives of this educational exhibit are to describe the salient pathologic and clinical features of granulomatous mastitis, illustrate imaging findings from pathology confirmed cases, and review differential diagnostic considerations. The target audience are trainees in radiology as well as general radiologists.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
As a non-infectious inflammatory condition, granulomatous mastitis can have imaging appearances that overlap with both malignant and benign etiologies, often similar to abscess. On mammography, granulomatous mastitis can appear as an irregular or obscured mass, focal asymmetry, or global asymmetry. In heterogeneously dense or extremely dense breast tissue, granulomatous mastitis may have no mammographic findings. Calcifications are typically not identified. On ultrasound, it can appear as an irregular and hypoechoic mass that can mimic cancer. There may be associated hypoechoic tubular structures, skin thickening and edema and sinus tracts. Core biopsy with histopathologic correlation is essential for definitive diagnosis. As this process can take many months to resolve, consideration should be given to repeat ultrasound and possible repeat biopsy to ensure a cancer diagnosis is not being missed.

Granulomatous mastitis is a complex diagnostic consideration given overlapping imaging features with both benign and malignant conditions. Understanding and familiarity with this process is key to ensure appropriate clinical management. Collaboration with a breast surgeon with expertise in this condition will allow the patient to avoid unnecessary medical or surgical therapy.