Gross anatomy of breast and axillary lymph nodes

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Here is a comprehensive overview of the gross anatomy of the breast and axillary lymph nodes, drawn from Sabiston's Textbook of Surgery, Fischer's Mastery of Surgery, Gray's Anatomy for Students, and the THIEME Atlas.

Gross Anatomy of the Breast and Axillary Lymph Nodes

1. Position and Surface Anatomy

The female breast sits on the anterior thoracic wall, between ribs II and VI in the midclavicular line. It overlies three muscles: pectoralis major (central and medial), serratus anterior (lateral), and external oblique (inferolateral). A superolateral tongue of glandular tissue, the axillary tail (axillary process), extends around the lower margin of the pectoralis major to enter the axilla - this is clinically relevant because it may be palpated in the axilla and may harbor tumors.

Gray's Anatomy for Students

2. Structural Layers (Deep to Superficial)

Cross-section of the mature breast showing Cooper ligaments, lactiferous sinuses, TDLUs, and the retromammary space

The breast is composed of three principal tissue types:

Glandular epithelium - the functional secretory tissue
Fibrous stroma - provides structural support
Adipose tissue - surrounds and cushions the gland

It lies between:

Anteriorly: skin and subcutaneous fat
Posteriorly: superficial pectoral fascia and pectoralis major; a potential retromammary space lies between the deep breast surface and the pectoral fascia, allowing the breast to move
Sabiston Textbook of Surgery

3. Suspensory Ligaments of Cooper

Multiple fibrous bands - Cooper's ligaments - run between the deep fascia of the chest wall and the dermis, anchoring the breast and giving it shape. When tumors infiltrate these ligaments or cause edema:

Traction produces skin dimpling
Dermal lymphatic blockage produces peau d'orange (orange-peel skin appearance)
Sabiston Textbook of Surgery

4. Ductal System and Lobular Unit

The glandular apparatus is arranged in a radial, tree-like pattern spreading from the nipple-areolar complex (NAC):

15-20 lobes per breast, each draining via a lactiferous duct opening at the nipple
Each duct has a dilated segment beneath the NAC: the lactiferous sinus
Ducts progressively branch, ending in terminal ductules (acini)
The terminal duct lobular unit (TDLU) = one lobule + its terminal duct - the basic secretory unit and the site where most malignant breast tumors originate

The ductal epithelium is surrounded by contractile myoepithelial cells, outside which lies a continuous basement membrane (laminin, type IV collagen). Invasion through this membrane defines the transition from DCIS to invasive carcinoma.

Sabiston Textbook of Surgery; THIEME Atlas

5. Blood Supply

Arterial and venous supply of the breast

The breast receives blood from three sources:

Source	Branches	Region supplied
Internal thoracic (mammary) artery	Perforating branches (2nd-4th intercostal spaces) - medial mammary branches	Medial breast (major contributor, ~60%)
Lateral thoracic artery	Lateral mammary branches	Lateral and superior breast
Intercostal arteries (2nd-5th)	Mammary branches	Direct branches to parenchyma

Venous drainage mirrors the arterial supply via internal thoracic veins and lateral thoracic veins, ultimately draining to the axillary and subclavian veins.

THIEME Atlas of Anatomy; Fischer's Mastery of Surgery

6. Nerve Supply

The breast has segmental sensory innervation from branches of the 2nd-6th intercostal nerves (medial and lateral mammary branches). The supraclavicular nerves (cervical plexus, C3-C4) supply the upper and anterior breast. The nipple is primarily supplied by the lateral cutaneous branch of T4.

THIEME Atlas of Anatomy

7. Lymphatic Drainage

The lymphatic system is a primary route of breast cancer metastasis. Lymphatic channels are abundant in both the breast parenchyma and the dermis.

Subareolar (Sappey's) Plexus

Specialized lymphatics collect under the nipple-areola to form Sappey's plexus (described 1885). Lymph flows from the skin into this plexus and then into the interlobular lymphatics of the parenchyma. This plexus is the basis for successful sentinel lymph node mapping.

Routes of Drainage

70-80% drains to the axillary lymph nodes (primary route)
~20% drains to internal mammary lymph nodes as a secondary route
Internal mammary nodes are the predominant drainage in 2-3% of patients
Minor drainage through the pectoralis muscle to medial lymph node groups
The lower inner quadrant drains via a plexus over the rectus sheath that can communicate with the subperitoneal plexus (explaining rare Krukenberg's tumor metastasis to the ovary)
Sabiston Textbook of Surgery; S. Das Manual on Clinical Surgery

8. Axillary Lymph Nodes - Levels and Groups

Axillary lymph node levels I, II, III relative to pectoralis minor, with key nerves labeled

The axillary nodes are classified into three surgical levels based on their relationship to the pectoralis minor muscle:

Level I - Lower Axillary Group (lateral to pectoralis minor)

Node Group	Location	Notes
Pectoral (anterior/external mammary)	Deep to lateral edge of pectoralis major; along lateral thoracic artery	First nodes to receive breast lymphatics; functionally the sentinel node is usually here
Subscapular (posterior)	Along subscapular vessels and thoracodorsal branches	Intercostobrachial and thoracodorsal nerves pass through
Lateral (humeral/axillary vein)	Along axillary vein, from tendon of latissimus dorsi to thoracoacromial vein	Receive most lymphatics from upper extremity
Paramammary	Along the lateral breast border

Level II - Middle Axillary Group (along/posterior to pectoralis minor)

Node Group	Location	Notes
Central	Fat in central axilla, ~midway between anterior and posterior folds	May lie subcutaneously; drain to apical nodes
Interpectoral (Rotter's nodes)	Areolar tissue between pectoralis major and clavipectoral fascia	Associated with pectoral branches of thoracoacromial artery

Level III - Upper Infraclavicular Group (medial to pectoralis minor)

Node Group	Location	Notes
Apical (infraclavicular)	Along axillary vein proximal to thoracoacromial vein; posterior to subclavius	Receive all other axillary node drainage; efferent drains to inferior deep cervical nodes or venous angle (junction of internal jugular and subclavian veins)

After level III, drainage continues to supraclavicular nodes (considered outside the anatomic boundaries of the axilla).

Axillary lymph node groups and levels with their named components

Sabiston Textbook of Surgery; Fischer's Mastery of Surgery; THIEME Atlas

9. Surgical Boundaries and Key Nerves of the Axilla

The surgical axilla is bounded by:

Medially: serratus anterior muscle and chest wall
Posteriorly: latissimus dorsi, teres major, subscapularis
Anteriorly: pectoralis major and minor
Superiorly: axillary vein (which becomes the subclavian vein at the costoclavicular/Halsted's ligament - the apex of the axilla)

Three Nerves Critical to Preserve During Axillary Dissection

Nerve	Origin	Innervation	Injury consequence
Long thoracic nerve (nerve of Bell)	C5-C7 roots	Serratus anterior	Winged scapula
Thoracodorsal nerve	Posterior cord, brachial plexus	Latissimus dorsi	Weak shoulder extension/adduction
Medial pectoral nerve	Medial cord, brachial plexus	Pectoralis major (and minor)	Atrophy of pectoralis major; also a landmark for the axillary vein (just cephalad and deep to the medial pectoral neurovascular bundle)

Additionally, 3-5 intercostobrachial nerves cross the axilla horizontally, supplying sensation to the upper inner arm and posterior axillary skin. Division causes numbness and occasionally chronic pain in that distribution.

Sabiston Textbook of Surgery; Fischer's Mastery of Surgery

10. Clinical Correlates

Finding	Anatomical Basis
Peau d'orange	Tumor emboli blocking dermal lymphatics
Skin dimpling	Cooper's ligament traction by scirrhous tumor
Winged scapula post-mastectomy	Long thoracic nerve injury
Lymphedema post-ALND	Disruption of upper limb lymphatics draining via axillary vein region
Axillary tail mistaken for lymph node	Extension of breast parenchyma into axilla
Sentinel lymph node usually in Level I	External mammary/pectoral group receives first breast lymphatics

Sources: Sabiston Textbook of Surgery (Fig. 68.1, 68.4, 68.5); Fischer's Mastery of Surgery (Ch. 57); THIEME Atlas of General Anatomy & Musculoskeletal System; Gray's Anatomy for Students; S. Das Manual on Clinical Surgery

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