Mammary Gland — Complete Anatomy (10 Marks)

1. Location

• Vertically: Extends from the 2nd rib superiorly to the 6th rib inferiorly
• Horizontally: From the lateral sternal edge medially to the midaxillary line laterally
• The upper and medial portions overlie the pectoralis major; the inferolateral portion rests on the serratus anterior
• The retromammary space (a loose areolar tissue layer) separates the deep surface of the breast from the pectoral fascia, allowing the breast a degree of mobility

— Mulholland and Greenfield's Surgery, 7e; Sabiston Textbook of Surgery

2. Extent

• Superolaterally, the glandular tissue extends around the inferior border of the pectoralis major muscle into the axilla — this projection is called the axillary tail (axillary process/tail of Spence)
• The axillary process may penetrate the deep fascia (clavipectoral fascia) and occasionally reaches the apex of the axilla
• The upper outer quadrant contains the most parenchymal tissue and is therefore the most common site of both benign and malignant breast disease

— Gray's Anatomy for Students; Mulholland and Greenfield's Surgery

3. Gross Anatomy

Structure

1. Glandular epithelium (15–20 lobes)
2. Fibrous stroma (supporting framework)
3. Adipose tissue (fills spaces between lobes)

Lobar Organization

• The breast contains 15–20 lobes of glandular tissue arranged radially around the nipple
• Each lobe is divided into 20–40 lobules, each lobule containing 10–100 alveoli (acini)
• Each lobe ends in a lactiferous duct, which dilates into a lactiferous sinus just beneath the nipple-areolar complex (NAC), then opens at the nipple through a constricted orifice
• The acini and their ductules form the Terminal Duct Lobular Units (TDLUs) — the functional milk-secreting units

Suspensory Ligaments of Cooper

• Fibrous connective tissue bands extending from the deep fascia to the dermis, providing shape and structural support
• Infiltration by cancer causes dimpling of the skin → the "peau d'orange" (orange peel) appearance, also contributing to retraction of the nipple

Nipple and Areola

• The skin is highly pigmented and covered with stratified squamous epithelium
• Deep to the nipple are radial, circumferential, and longitudinal smooth muscle bundles allowing nipple erection
• The areola contains sebaceous glands, sweat glands, and Montgomery glands (accessory areolar glands with tubercles of Morgagni)
• The nipple contains Meissner corpuscles; the areola contains Ruffini-like endings and Krause end-bulbs

Weight

• Non-lactating breast: 150–225 g; Lactating breast: may exceed 500 g
• The left breast is commonly slightly larger than the right

— Sabiston Textbook of Surgery; Mulholland and Greenfield's Surgery

4. Blood Supply

Arterial Supply

Venous Drainage

1. Perforating branches of the internal thoracic (mammary) vein
2. Perforating branches of the posterior intercostal veins
3. Tributaries of the axillary vein

Clinical note: Batson's vertebral venous plexus provides a route for breast cancer metastases to the vertebrae, skull, pelvic bones, and CNS without passing through the pulmonary circulation.

— Schwartz's Principles of Surgery, 11e; Mulholland and Greenfield's Surgery

5. Nerve Supply

Sensory Innervation

• Lateral cutaneous branches of the 3rd–6th intercostal nerves → lateral mammary branches (exit between slips of serratus anterior)
• Anterior cutaneous branches of the 2nd–6th intercostal nerves → medial mammary branches
• Anterior (medial) branches of the supraclavicular nerve (from cervical plexus, C3–C4) → small area of skin over the upper breast

Nipple and Areola

• The 4th intercostal nerve provides the primary sensory innervation of the nipple (clinically important — damage during mastectomy causes sensory loss)
• The areola and nipple also have autonomic innervation (sympathetic) producing smooth muscle contraction (erection)

Additional Note

• The intercostobrachial nerve = lateral cutaneous branch of the 2nd intercostal nerve — passes through the axilla; its resection during axillary dissection causes loss of sensation over the medial aspect of the upper arm

— Schwartz's Principles of Surgery; Mulholland and Greenfield's Surgery; Gray's Anatomy for Students

6. Lymphatic Drainage

Main Routes

Axillary Lymph Node Levels (defined by relationship to pectoralis minor)

• Level I (lateral to pectoralis minor): axillary vein group, external mammary (anterior/pectoral) group, scapular (posterior/subscapular) group
• Level II (posterior to pectoralis minor): central group + interpectoral group (Rotter's nodes)
• Level III (medial to pectoralis minor): subclavicular (apical/infraclavicular) group

Clinical significance: Axillary lymph node dissection or irradiation for breast cancer can obstruct lymphatic drainage → lymphedema of the upper limb.

— Sabiston Textbook of Surgery; Schwartz's Principles of Surgery; Gray's Anatomy for Students

7. Clinical Conditions

A. Breast Cancer (Carcinoma of the Breast)

• Most common malignancy in women; arises from cells of the acini, lactiferous ducts, and lobules (TDLUs)
• Ductal carcinoma in situ (DCIS): confined within the basement membrane
• Invasive/infiltrating ductal carcinoma: breaches basement membrane → access to lymphatics and blood vessels → metastatic potential
• Signs: palpable lump (usually painless), nipple retraction, peau d'orange (Cooper ligament invasion), skin dimpling, bloody nipple discharge
• Primary metastatic route: axillary lymph nodes (upper outer quadrant tumors); also internal mammary nodes; hematogenous spread via Batson's plexus to spine, skull, pelvis

B. Peau d'Orange (Orange Skin Appearance)

• Caused by cutaneous lymphedema + tethering of Cooper's ligaments by tumor infiltration
• Classic sign of inflammatory breast cancer or advanced carcinoma

C. Mastitis

• Inflammation of the breast — most commonly lactational/puerperal mastitis (postpartum, usually due to Staphylococcus aureus)
• Non-lactational mastitis also occurs (periductal mastitis)
• Can progress to breast abscess requiring surgical drainage

D. Fibroadenoma

• Most common benign breast tumor; occurs in young women
• Well-defined, mobile, firm, rubbery, non-tender mass ("breast mouse")
• Composed of both epithelial and fibrous stromal elements

E. Fibrocystic Change

• Most common benign breast condition; cyclical breast pain (mastalgia), nodularity, and cyst formation
• Linked to hormonal fluctuation (estrogen/progesterone imbalance)

F. Gynecomastia

• Enlargement of the male breast due to proliferation of ductal and stromal tissue
• Causes: puberty, hepatic disease, drugs (spironolactone, digoxin, cimetidine), hormone-secreting tumors (testicular, adrenal)
• Must be distinguished from male breast cancer (rare, ~1% of all breast cancers)

G. Nipple Discharge

• Milky (galactorrhea): hyperprolactinemia, drugs
• Bloody/serosanguinous: intraductal papilloma (most common), DCIS, carcinoma
• Green/brown: fibrocystic change

H. Lymphedema Post-Mastectomy

• Following axillary lymph node dissection (ALND) or radiotherapy, lymphatic obstruction → chronic arm lymphedema
• Managed with compression, physiotherapy, or surgical lymphovenous bypass

• Sabiston Textbook of Surgery, 21e (Chapter 68)
• Schwartz's Principles of Surgery, 11e (Chapter 17)
• Mulholland and Greenfield's Surgery, 7e (Chapter 74)
• Gray's Anatomy for Students, 4e