Chapter 20: Diagnostic investigations
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Anatomy and physiology
The breast is a glandular and secretory organ which has the primary purpose of lactation. It is also a prominent secondary sexual feature. Prior to puberty there is no difference between the male and female breast bud. Commencement of female sex hormones at puberty causes significant development of the female breast tissue (Tortora and Derrikson [162]).
Breast tissue comprises 10–15% epithelial parenchyma, or functional tissue. The remaining tissue is the stroma, or framework tissue, to give it and maintain its form. Breast cancer arises within the functional parenchyma or epithelial cells. Differences in breast size and shape are generally due to the difference in stroma rather than parenchyma.
Breast parenchyma is composed of 15–20 lobes which can each sub‐divide into smaller lobules. The lobules are made up of branched tubuloalveolar glands. Each lobe drains into a lactiferous duct which runs toward the nipple (Figure 20.15). The lactiferous ducts dilate and coalesce into a lactiferous sinus beneath the areola and then open through a constricted orifice onto the nipple. Breast milk is secreted by the lobular tissue and transported toward the nipple by the breast ducts (Pandya and Moore [119]).
Figure 20.15 (a) Female breast (sagittal section). (b) Female breast (anterior view, partially sectioned). Source: Adapted from Tortora and Derrickson (2011). Reproduced with permission of John Wiley & Sons.
Oestrogen and progesterone both stimulate breast parenchyma during a normal menstrual cycle. Rising oestrogen levels in weeks 1–2 cause proliferation of the ductal system and, following ovulation, the rise in progesterone, synergistically with oestrogen, stimulates the lobular units. These changes give rise to the common breast changes which many women equate with their pre‐period state. If no pregnancy ensues, decreasing hormone levels cause regression of this stimulated tissue (Ellis and Mahadevan [44]).
With the onset of menopause, as ovarian tissue ceases to produce high cyclical levels of oestrogen and progesterone, the majority of breast glandular tissue involutes or ceases to be active. Usually more adipose tissue is deposited and the postmenopausal breast is less dense on imaging. Due to this, mammography is more sensitive and specific in the postmenopausal breast.
