Mills Ch3 Breast

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CHAPTER 3:  Breast

A

B

FIGURE 3.17  Lactating breast tissue. A: There are numerous acini in this lobule, and these are enlarged and dilated. There is minimal intervening stroma. B: Higher-power view illustrates prominent epithelial cell enlargement, cytoplasmic vacuolization, and protrusion of cells into the acinar lumen. Some of the cells have a hobnail appearance. Myoepithelial cells are inconspicuous.

the end of the first trimester, there is grossly evident breast enlargement, superficial venous dilatation, and increased pigmentation of the areola. During the second and third trimesters, lobular growth continues, and the acinar units begin to appear monolayered. The myoepithelial cells in the acini are difficult to discern at this time due to the increase in size and volume of the epithe- lial cells, but they remain clearly evident in the extralobular ducts. The cytoplasm of the epithelial cells becomes vacu- olated, and secretion accumulates in the greatly expanded lobules. After parturition, the lactating breast is character- ized by distension of the lobular acini as a result of abundant accumulated secretory material and prominent epithelial cell cytoplasmic vacuolization. Many of the epithelial cells have a bulbous or hobnail appearance and protrude into the acinar lumina (Fig. 3.17). Myoepithelial cells remain attenuated and inconspicuous. The florid changes seen in pregnancy and lactation can be alarming to the inexperienced observer; areas of infarction, which occasionally occur in the pregnant breast, may compound the problem (63). When lactation ceases, the lobules involute and return to their normal resting appearance. Involution usually pro- ceeds unevenly and takes several months. Involuting lob- ules are irregular in contour and are frequently infiltrated by lymphocytes and plasma cells (64,65). Occasionally, an isolated lobule showing secretory changes may be seen in the breasts of women who are not pregnant; this phenom- enon may occur in the nulliparous woman as well.

and atrophy of the mammary TDLUs, with reduction in the size and complexity of the acini, and there is loss of the specialized intralobular stroma (66,67). Ducts may become variably ectatic. The postmenopausal breast is characterized by a marked reduction in glandular tissue and collagenous stroma, often with a concomi- tant increase in stromal adipose tissue. The end stage of menopausal involution is typified by remnants of the TDLUs, typically composed of ducts with atrophic acini, surrounded by hyalinized connective tissue or embedded within adipose tissue with little or no surrounding stroma (Fig. 3.18). BLOOD SUPPLY The principal arterial supply to the breast is provided by the internal mammary and lateral thoracic arteries. Perfo- rating branches of the internal mammary artery provide the blood supply to approximately 60% of the breast, mainly the medial and central portions. Approximately 30% of the breast, mainly the upper and outer portions, receives blood from the lateral thoracic artery. Branches of the thoracoacromial, intercostal, subscapular, and thoracodor- sal arteries make minor contributions to the mammary blood supply (7). Venous drainage of the breast, as in other locations, shows considerable individual variation but largely follows the arterial system. There is a superficial venous complex that runs transversely from lateral to medial in the subcuta- neous tissue. These vessels then drain into the internal tho- racic vein. Deep venous drainage of the breast is via three routes: the perforating branches of the internal thoracic vein, branches of the axillary vein, and tributaries of the

MENOPAUSE During the postmenopausal period, with the reduction of estrogen and progesterone levels, there is involution