Breast Anatomy

Breast Structure and Function

• The breast rests on the pectoral fascia covering the pectoralis major (2/3) and the fascia covering the serratus anterior muscle (1/3)
• The retromammary space (bursa) separates the breast from the deep pectoral fascia, allowing for some degree of movement
• The breast is composed of 15-20 lobules of glandular tissue, each drained by a lactiferous duct that opens independently on the nipple
• Each duct has a dilated portion, the lactiferous sinus, just deep to the areola

Breast Quadrants

• The breast is divided into four quadrants for anatomical location and description of pathology (e.g., cysts and tumors)
• The axillary tail is an extension of the mammary gland of the superolateral quadrant

Vascularity

• The arterial supply of the breast is derived from:
  • Medial mammary branches of perforating branches and anterior intercostal branches of the internal thoracic artery
  • Lateral thoracic and thoraco-acromial arteries, branches of the axillary artery
  • Posterior intercostal arteries, branches of the thoracic aorta in the intercostal spaces
• Venous drainage is mainly to the axillary vein, with some drainage to the internal thoracic vein

Lymphatic Drainage

• Lymphatic drainage is important for the metastasis (spread) of cancer cells
• Lymph passes from the nipple, areola, and lobules of the gland to the subareolar lymphatic plexus, and from it:
  • Most lymph (>75%) drains to the axillary lymph nodes (pectoral, humeral, subscapular, central, and apical)
  • Some lymph may drain directly to other axillary nodes, or to interpectoral, deltopectoral, supraclavicular, or inferior deep cervical nodes
• Lymph from the medial breast quadrants drains to the parasternal lymph nodes or to the opposite breast
• Lymph from the inferior breast quadrants may pass deeply to abdominal lymph nodes (inferior phrenic nodes)
• Lymph from the axillary nodes drains to infraclavicular and supraclavicular nodes and from them to the subclavian lymphatic trunk

Carcinoma of Breast

• Carcinomas of the breast are malignant tumors, usually adenocarcinomas arising from the epithelial cells of the lactiferous ducts
• Breast cancer can spread via lymphatics (lymphogenic metastasis) and veins
• Clinical signs include:
  • Lymphedema (edema, excess fluid in the subcutaneous tissue), which may result in deviation of the nipple and a thickened, leatherlike appearance of the skin
  • Peau d'orange sign (orange-peel appearance)