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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.
Key Words: Breast; Core biopsy; Inflammatory; Mammogram
Inflammatory and reactive conditions of the breast are relatively uncommon among benign breast lesions, and may present with clinical and radiologic abnormalities akin to malignant processes. As such, core biopsy may be performed to exclude the possibility of malignancy. In most cases, the diagnosis based on microscopy is clear, but in fragmented core biopsy samples, some conditions may mimic malignancy. Conversely, some malignancies can also simulate benign inflammatory or reactive conditions.
The clinical, radiographic, and histologic features of commonly encountered inflammatory and reactive breast lesions, namely, fat necrosis, mammary duct ectasia, granulomatous lobular mastitis, diabetic mastopathy, and abscess will be reviewed (Table 1). In addition, we will discuss the histologic features on core biopsy that distinguish the items on this differential.
FAT NECROSIS
Fat necrosis is most often seen in traumatized breast tissue, particularly in areas of prior surgery or biopsy. Radiation therapy can also lead to fat necrosis in breast1-3 and has been seen in up to 50% of patients following balloon-based brachytherapy.4 Clinically, fat necrosis can present as a palpable mass with or without skin retraction, or it can be asymptomatic.5
On mammography, oil or lipid cysts, which are often calcified, are characteristic of fat necrosis (Fig. 1A). Calcifications in fat necrosis may be clustered, pleomorphic, and linear, simulating ductal carcinoma in situ (DCIS).6,7 Fat necrosis can also appear as a stellate mass with irregular margins...