Breast anatomy

Overview of Breast Anatomy

Location:

• Subcutaneous tissue (superficial fascia) of anterior thoracic wall

Base of Breast Landmarks

• From sternal edge to near the midaxillary line
• From the 2nd to 6th ribs
• Overlies Pectoralis Major overlapping onto Serratus Anterior and onto small part of rectus sheath and external oblique muscle

Axillary Tail

• Extension of upper outer quadrant towards axilla
• Usually lies in subcutaneous fat
• Rarely penetrates deep fascia of axillary floor and lie adjacent to axillary lymph nodes

Behind Breast

• Superficial fascia (upward continuation of membranous layer of Scarpa’s fascia of abdo wall) condensed to form posterior capsule
• Retromammary space – loose connective tissue between posterior capsule and fascia over pectoralis major

Overlying Skin

• Suspensory ligaments of Cooper – fibrous tissue connecting dermis of overlying skin to ducts of the breast and to posterior capsule
  • Atrophy with age – breast becomes more pendulous
• Contracts via fibrosis associated with certain breast ca. causing dimpling of overlying skin
• Cause pitting of oedematous skin resulting from malignant involvement of dermal lymphatics (peau d’orange)

Male Breast

• No lobules or alveoli
• Small nipple and areola lie over 4th intercostal space

Ducts

• Lactiferous ducts
  • 15-20 in number
  • Each drains a lobe of breast
  • Converge in radial direction to open individually on tip of nipple
  • Each duct has a dilated sinus at its terminal portion

Nipple

• Projection below centre of breast surrounded by area of pigmented skin, the areola
• Smooth muscle cells present – contraction ⇒ erection of nipple
• Sebaceous glands, sweat glands, and other areolar glands present in areola skin
• Areolar glands form small elevations (tubercles of Montgomery), esp. when they enlarge during pregnancy

Blood Supply

Arteries

• Lateral thoracic artery

  • Origin: Medial surface of 2nd part of the Axillary artery (second part)

• Branches curl around border of pectoralis major and other branches that pierce the muscle

• At the level of the fifth rib, along the inferior bundle of the serratus anterior muscles, the long thoracic nerve runs beside the main branch of the lateral thoracic artery

• Internal Thoracic Artery

  • Origin: First part of Subclavian Artery
  • Branches through the intercostal spaces behind sternum
  • Largest branches: through the 2nd and 3rd intercostal spaces

• Posterior Intercostal Arteries

  • Origin: 1st and 2nd from Supreme Intercostal Artery (a branch of the Costocervical Trunk of the Subclavian Artery), lower 9 from back of the thoracic aorta
    • Similar perforating branches to internal thoracic artery but smaller

• Pectoral branch of Thoracoacromial Artery

  • Origin: 2nd part of the Axillary Artery
  • Supplies upper part of the breast

Veins

• Circumareolar venous plexus + from glandular tissue ⇒ via deep veins running with main arteries to internal thoracic and axillary veins
• Posterior drainage via posterior intercostal veins
• Important link to the internal vertebral venous plexus veins and, thus, pathway for metastatic spread to bone

Lymph Drainage

• Subareolar plexus of lymphatics communicates with lymphatics within breast
• Axillary lymph nodes – 75% of lymphatic drainage
  • Mainly anterior nodes
  • Some to posterior nodes
  • Direct drainage to central or apical nodes possible
• Parasternal nodes along internal thoracic artery – esp. medial part of breast
• Posterior intercostal nodes – a few lymphatics following intercostal arteries
• Infraclavicular nodes in deltopectoral groove – occasional
• Interpectoral nodes between pectoralis major and minor – occasional
• Lymph nodes of opposite breast – superficial lymphatics have connections with those of opposite breast and anterior abdominal wall
• Posterior mediastinal lymph nodes – via extraperitoneal tissues and drainage through the diaphragm
• Supraclavicular nodes (Inferior deep cervical nodes) – possible
• Minor pathways convey lymph when major channels obstructed by malignant disease

Development and Structure

• Development starts at 4th week gestation
• Downgrowth from a thickened mammary ridge of ectoderm along a line from the axilla to the inguinal region
• Supranumerary nipples or glands proper can form at lower levels on this line
• During puberty:
• Lobules form
• Each lactiferous duct is connected to a tree-like system of ducts and lobules intermingled and enclosed by connective tissue to form a lobe of the gland
• During pregnancy:
  • Alveoli bud off from smaller ducts
• After menopause:
  • Atrophy of lobes and ducts