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CASE 16-1

A 32-year-old G4P4 woman presents with complaints of a new lump in her left breast. Her past medical history is negative for a family history of breast carcinoma. Physical examination reveals a 3 cm firm, ill-defined mass that is tender to palpation. Ultrasound studies demonstrate a 4 cm solid-appearing mass with ill-defined borders. Due to the solid-appearing nature of the lesion and ill-defined borders, the lesion is categorized as suspicious and biopsy is recommended. Ultrasound-guided core biopsy is performed yielding the histology demonstrated in Figure 16-1.

Pathologic diagnosis: Granulomatous mastitis.


Granulomatous mastitis. The breast stroma is involved by a dense inflammatory process consisting of dense aggregates of histiocytes (arrow) and a background of lymphocytes.

Normal Anatomy and Histology

The breast lies anterior to the chest wall over the pectoralis major muscle and typically extends from the second to the sixth rib in the vertical axis and from the sternal edge to the midaxillary line in the horizontal axis. Bundles of dense fibrous connective tissue, the suspensory ligaments of Cooper, extend from the skin to the pectoral fascia and provide support for the breast. At puberty, estradiol and progesterone levels increase to initiate breast development. The adult female breast consists of a series of branching ducts that terminate in lobules. The arrangement of these structures resembles a branching tree with 5–10 primary milk ducts in the nipple, 20–40 segmental ducts, and 10–100 subsegmental ducts that end in glandular units called terminal-duct lobular units (TDLU) (Figure 16-2). The TDLU represents the functional unit of the breast (Figure 16-3). During lactation, there is a dramatic increase in the number of lobules, and the epithelial cells in the TDLU undergo secretory changes consisting of cytoplasmic vacuoles (Figure 16-4). The accumulated secretions are then transported via the ductal system to the nipple. When lactation ceases, the lobules involute and return to their normal resting appearance. The mammary ducts and lobules are embedded within a stroma composed of varying amounts of fibrous and adipose tissue. The stromal component comprises the major portion of the nonlactating adult breast, consisting of lobular stroma and interlobular stroma. The proportions of fibrous and adipose tissue vary with age and among individuals and may affect the sensitivity and specificity of mammographic studies. During menopause, as a result of reduction in estrogen and progesterone, there is involution and atrophy of the TDLUs associated with loss of the specialized intralobular stroma. The postmenopausal breast is characterized by marked reduction in the glandular and fibrous stroma components, typically with concomitant increase in stromal adipose tissue.


Anatomy of the breast (diagrammatic sagittal section). The ductal system extends from the nipple to multiple lobes of terminal-duct lobular units (TDLUs) branching in a treelike fashion. The TDLU is the site of origin ...

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