I. BREAST (Figure 3-1) A. Components
1. The breast lies in the superficial fascia of the anterior chest wall that overlies the pectoralis major and serratus anterior muscles and extends into the superior lateral quadrant of the axilla as the axillary tail. A high percentage of tumors occur in the axillary tail.
2. In a fully developed woman, the breast extends vertically from rib 2 to rib 6 and laterally from the sternum to the midaxillary line.
3. The retromammary space lies between the breast and the pectoral (deep) fascia. This space allows free movement of the breast. If breast carcinoma invades the retromammary space and pectoral fascia, contraction of the pectoralis major may-cause the whole breast to move superiorly.
4. Suspensory (Cooper) ligaments extend from the dermis of the skin to the pectoral fascia and provide support for the breast. If breast carcinoma invades the suspensory ligaments, the ligaments may shorten and cause dimpling of the skin or inversion of the nipple.
5. Adipose tissue within the breast contributes largely to the contour and size of the breast.
6. Glandular tissue (mammary gland) within the breast is a modified sweat gland consisting of acini. The acini are drained by 15—20 lactiferous ducts that open onto the nipple. Just below the surface of the nipple, each lactiferous duct expands into a lactiferous sinus, which serves as a reservoir for milk during lactation.
7. The arterial supply is from the internal thoracic, lateral thoracic, and intercostal arteries.
8. The chief venous drainage is to the axillary vein. The internal thoracic, lateral thoracic, and intercostal veins also participate. Breast carcinoma may metastasize to the brain by the following route: cancer cells enter an intercostal vein > external vertebral venous plexus —► internal vertebral venous plexus ► cranial dural sinuses.
9. The chief lymphatic drainage is to the axillary nodes. Breast carcinoma may metastasize through the lymphatic vessels, or it may block lymph flow, causing thick, leathery skin.
10. Sensory innervation is via intercostal nerves 2—6.
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