A Review of Inflammatory Processes of the Breast with a Focus on Diagnosis in Core Biopsy Samples

Abstract

Inflammatory and reactive lesions of the breast are relatively uncommon among benign breast lesions and can be the source of an abnormality on imaging. Such lesions can simulate a malignant process, based on both clinical and radiographic findings, and core biopsy is often performed to rule out malignancy. Furthermore, some inflammatory processes can mimic carcinoma or other malignancy microscopically, and vice versa. Diagnostic difficulty may arise due to the small and fragmented sample of a core biopsy. This review will focus on the pertinent clinical, radiographic, and histopathologic features of the more commonly encountered inflammatory lesions of the breast that can be characterized in a core biopsy sample. These include fat necrosis, mammary duct ectasia, granulomatous lobular mastitis, diabetic mastopathy, and abscess. The microscopic differential diagnoses for these lesions when seen in a core biopsy sample will be discussed.

Keywords: Breast; Core biopsy; Inflammatory; Mammogram.

Fig. 1.

Mammographic and microscopic features of fat necrosis in core biopsy samples. (A) Mammography shows a calcified lipid cyst, a characteristic feature of fat necrosis. (B) Core biopsy shows foamy histiocytes in adipose tissue. (C) Chronic inflammation is present and histiocyte-lined cysts are evident (right). (D) Necrotic adipocytes, chronic inflammation, and fibrosis are seen. (E, F) Fat necrosis is seen in stereotactic core biopsies obtained due to calcifications. (E) Calcifications formed within necrotic fat. (F) Calcified fibrous wall of a lipid cyst.

Fig. 2.

Mammary duct ectasia. (A) Core biopsy performed for an “intraductal mass” shows a portion of a fibrotic duct wall lined with foamy histiocytes. (B) Disrupted/ruptured duct wall with histiocytes in periductal stroma. (C) Flattened epithelium and fragments within the proteinacious luminal contents. The sample lacks prominent inflammatory features. (D) Brown histiocytes, or “ochrocytes,” are seen in the periductal stroma. Intraepithelial foamy histiocytes are also present. (E) An older lesion shows intraductal calcification. (F) Intraductal “cholesteroloma” formed within a duct with rupture into surrounding stroma.

Fig. 3.

Granulomatous lobular mastitis. (A, B) Non-necrotizing granulomas are centered within lobules. Granulomas contain Langhans giant cells, and are associated with lymphocytes and plasma cells. (C) Cystic neutrophilic granulomatous mastitis showing neutrophil-lined cysts within granulomas. (D) Gram-positive coryneform bacilli are present within the cysts.

Fig. 4.

Diabetic mastopathy. (A) Lymphoid infiltrates surround ducts, lobules, and small vessels. The stroma has a hyalinized appearance. (B, C) Plump epithelioid fibroblasts are present in the stroma (C inset, high power). Perilobular (B) and perivascular (C) chronic inflammation is seen. (D) Fibroblasts in diabetic mastopathy compared with granular cell tumor (E) and multinucleated stromal giant cells (F).