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M10.08.01 Clinical Anatomy of the Breasts and Axillae
The female breast lies against the anterior thoracic wall, extending from the clavicle and 2nd rib down to the 6th rib, and from the sternum across to the midaxillary line. The breast surface area is generally rectangular rather than round, overlying the pectoralis major and at its inferior margin, the serratus anterior.
Structure and Components
The breast is composed of several key structures:
- Pectoralis Major and Serratus Anterior: Muscles that the breast tissue overlays.
- Nipple and Areola: Central structures, rich in smooth muscle and sensory innervation.
- Glandular Tissue: Comprising secretory tubuloalveolar glands and ducts.
- Fibrous Connective Tissue: Provides structural support.
- Adipose Tissue: Surrounds the glandular structures, with proportions varying with age, nutrition, and hormonal changes.
Detailed Anatomy
- Quadrants and Localization
- The breast is divided into four quadrants for clinical description:
- Upper inner quadrant
- Lower inner quadrant
- Upper outer quadrant
- Lower outer quadrant
- An axillary tail extends toward the anterior axillary fold.
- Findings can also be localized using the clock face method (e.g., 3 o’clock) and distance from the nipple.
- The breast is divided into four quadrants for clinical description:
- Hormonal Sensitivity
- The breast is sensitive to hormonal changes related to menstrual cycles and aging.
- Glandular Tissue: Contains 15 to 20 lobes, each with smaller lobules draining into milk-producing ducts.
- Fibrous Connective Tissue: Contains suspensory ligaments connected to skin and underlying fascia.
- Adipose Tissue: Predominantly in superficial and peripheral areas.
- Nipple and Areola
- Small rounded elevations due to sebaceous glands, sweat glands, and accessory areolar glands.
- Rich in smooth muscle, aiding in milk expression during breastfeeding.
Visual Aids
- Figures: Diagrams showing the anatomical structure and quadrants of the breast, the arrangement of glandular tissues, ducts, and their relationship to surrounding muscles and lymph nodes.
Changes with Aging
- Adulthood
- Breasts may feel granular, nodular, or lumpy (physiologic nodularity).
- These changes are often bilateral and can be more pronounced premenstrually.
- Aging
- Glandular tissue atrophies, replaced by fat.
- Breasts become flaccid and pendulous.
- Ducts around the nipple may become more palpable.
Lymphatic System
- Lymphatic Drainage: Most breast lymphatics drain towards the axilla.
- Axillary Lymph Nodes: Central nodes are palpable most frequently.
- Pectoral Nodes: Drain the anterior chest wall and much of the breast.
- Subscapular Nodes: Drain the posterior chest wall and a portion of the arm.
- Lateral Nodes: Drain most of the arm.
Tables and Figures
| Quadrant | Description |
|---|---|
| Upper Inner Quadrant | Closest to the sternum, above the nipple |
| Lower Inner Quadrant | Closest to the sternum, below the nipple |
| Upper Outer Quadrant | Closest to the axilla, above the nipple |
| Lower Outer Quadrant | Closest to the axilla, below the nipple |
Lymph Node Groups
| Node Group | Location | Drainage Area |
|---|---|---|
| Pectoral Nodes | Anterior chest wall, much of the breast | Anterior chest wall, much of breast |
| Subscapular Nodes | The lateral border of the scapula | Posterior chest wall, portion of arm |
| Lateral Nodes | Upper humerus | Most of the arm |
Illustrations
- Figure 1: Anatomical layout of the breast, including quadrants and key structures.
- Figure 2: Cross-section of breast tissue, showing glandular and ductal systems.
Clinical Notes
- Extra or Supernumerary Nipples: Sometimes present along the “milk line”, usually harmless.
- Male Breast: Chiefly consists of a small nipple and areola with a thin disc of undeveloped breast tissue.