Breast Anatomy Overview

Breast Structure

• The breast is primarily composed of fibrous and fatty tissue, with glandular tissue being sparse in the non-lactating state.
• The breast extends vertically from the second to sixth rib and horizontally from the lateral sternal border to the mid-axillary line.
• The majority of breast cancers develop in the upper outer quadrant.
• The axillary tail of Spence is a normal extension of breast tissue into the axilla.

Breast Position and Extent

• The breast is located in the superficial fascia of the pectoral region.
• Modified sweat glands (apocrine) are present in both sexes, but are rudimentary in males.
• Two-thirds of the breast overlies the pectoralis major muscle, and one-third overlies the serratus anterior muscle.
• A loose connective tissue plane, the retromammary space, is located between the breast and deep pectoral fascia, allowing for movement.

Breast Structure

• The parenchyma of the breast consists of 15-20 lobes of glandular tissue separated by connective tissue.
• Each lobe contains lobules, which in turn consist of acini (“bulbs”), responsible for milk production.
• Lactiferous ducts drain each lobe and converge to empty into the nipple.
• The lactiferous ducts widen into lactiferous sinuses before opening onto the surface.
• The skin surrounding the nipple is the areola, containing modified sebaceous glands (Montgomery’s tubercles) that lubricate the nipple during breastfeeding.
• The nipple and areola complex form the nipple-areola complex (NAC).
• The fibrous stroma of the breast, or suspensory ligaments of Cooper, divide the parenchyma into 15-20 segments, anchoring the skin to the deep fascia, and providing structural support.

Breast Development

• Breast development begins as early as the fourth week of gestation from a thickened mammary ridge (milk line).
• Milk line ectoderm forms a line from the axilla to the inguinal region, on which nipples or additional glands may appear.
• Lobule formation takes place after puberty, solely in the female breast.

Lactation

• The resting breast is mostly fibrous and fatty tissue.
• During pregnancy, alveoli bud from smaller ducts, leading to significant breast enlargement.
• Perforating arteries increase in size during pregnancy and lactation to provide sufficient blood supply to mammary glands.
• Secretory tissue involutes when lactation ceases.
• Atrophy of the lobes and ducts is progressive after menopause.

Male Breast

• Male breasts resemble rudimentary female breasts, with no lobules or alveoli.
• The nipple and areola overlie the fourth intercostal space.
• Breast cancer is rare in males.

Arterial Supply of the Breast

• Most breast arteries supply the anterior surface, while the posterior surface is relatively avascular.
• The major arteries supplying the breast include the internal thoracic artery, lateral thoracic artery, thoracoacromial artery, and posterior intercostal arteries.
• Medial aspect is supplied by internal thoracic artery, lateral aspect by lateral thoracic artery, and thoracoacromial artery, and the posterior aspect by posterior intercostal arteries

Venous Drainage of the Breast

• Most of the breast drains into the axillary vein, specifically via the lateral thoracic vein.
• Additional veins involved include the internal thoracic vein and posterior intercostal veins, which communicate with the vertebral venous plexus (allowing for potential cancer spread).

Lymphatics of the Breast

• The largest group of lymph nodes draining the breast is the axillary lymph nodes, which drain approximately 75% of the breast.
• Parasternal (internal mammary) nodes drain the inner quadrants.
• Infraclavicular or deltopectoral nodes drain the anterolateral aspect of the upper limb.
• Supraclavicular nodes serve as the final common pathway for lymphatic drainage to the central venous system.
• Other important lymphatic groups include the lateral, pectoral, and subscapular nodes.
• The drainage areas encompass the upper limb, breast, and trunk above the umbilicus.
• Individual axillary lymph nodes are categorized into five groups, including anterior/pectoral, posterior/subscapular, lateral/humeral, central, and apical/subclavicular.

Dermatomes

• A dermatome is a specific area of skin supplied by a single spinal nerve.
• The sensory innervation of the breast primarily originates from spinal nerves T3-T5 .

Learning Objectives

• Describe the structure of the breast.
• Describe the arterial supply and venous drainage of the breast.
• Describe the dermatomal innervation of the breast.
• Describe the lymphatic drainage of the breast.

Clinical Considerations

• Breast cancer is most prevalent in the upper outer quadrant.
• Lesions are described using a clock-face reference system on the breast.