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

Formation and relations of the brachial plexus, cutaneal supplies/dermatome of upper limb w.r.t. MS1 level. Netter's atlas diagram and suitable textbooks

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Netter's Atlas brachial plexus formation diagram plate number

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I now have all the material needed for a thorough MS1-level response. Here is the complete, well-structured answer:

Brachial Plexus: Formation, Relations, Branches, and Cutaneous Supply of the Upper Limb

Sources: Gray's Anatomy for Students (Moore & Dalley), THIEME Atlas of General Anatomy & Musculoskeletal System, Fischer's Mastery of Surgery

1. Formation - The Basics

The brachial plexus is a somatic nerve plexus formed by the anterior rami (ventral rami) of C5, C6, C7, C8, and T1. It is organized into five sequential parts from proximal to distal:

Mnemonic: "Real Teenagers Drink Cold Beer" - Roots → Trunks → Divisions → Cords → Branches

Brachial plexus components in the neck and axilla showing roots between scalene muscles, trunks over rib I, and cords around the axillary artery

(Gray's Anatomy for Students, Fig. 7.52A - Major components in the neck and axilla)

2. Parts of the Brachial Plexus

Roots (C5-T1)

The roots pass between the anterior scalene and middle scalene muscles in the posterior triangle of the neck.
They lie superior and posterior to the subclavian artery.
Each root receives gray rami communicantes from the sympathetic trunk, carrying postganglionic sympathetic fibers to the periphery.

Trunks (3)

The roots unite to form three trunks that cross over rib I to enter the axilla:

Trunk	Formed by	Position
Superior (upper)	C5 + C6	Most superior
Middle	C7 alone	Intermediate
Inferior (lower)	C8 + T1	Lies on rib I, posterior to subclavian artery

Divisions (6)

Each trunk divides into an anterior and a posterior division (6 total). No peripheral nerves arise directly from the divisions.

Anterior divisions → supply flexor (anterior) compartments
Posterior divisions → supply extensor (posterior) compartments

Cords (3) - Named by their position relative to the 2nd part of the axillary artery

Cord	Formed from	Roots	Position
Lateral	Anterior divisions of superior + middle trunks	C5-C7	Lateral to axillary artery
Medial	Anterior division of inferior trunk	C8-T1	Medial to axillary artery
Posterior	All three posterior divisions	C5-T1	Posterior to axillary artery

Schematic brachial plexus showing roots to terminal nerves via trunks, divisions, and cords, with cords arranged around the 2nd part of axillary artery

(Gray's Anatomy for Students, Fig. 7.52B - Schematic)

3. Relations

In the Neck (posterior triangle)

Roots/trunks pass between anterior and middle scalene muscles
The plexus lies posterior and superior to the subclavian artery
The inferior trunk lies directly on rib I, behind the subclavian artery (clinically: a cervical rib or Pancoast tumor at the lung apex may compress the inferior trunk → Klumpke's palsy pattern)

In the Axilla

Cords surround the axillary artery (named for their positions relative to its 2nd part)
The pectoralis minor muscle is the key landmark:
- Level I nodes (and lateral cord) = lateral to pectoralis minor
- Level II (posterior cord) = at the level of pectoralis minor
- Level III (medial cord/apical nodes) = medial to pectoralis minor
The musculocutaneous nerve, lateral root of median, median nerve, medial root of median, and ulnar nerve form an "M" shape over the 3rd part of the axillary artery - a useful intraoperative landmark

4. Branches - Complete Table

Full brachial plexus schematic (A) with all named branches and their origins, and (B) 3D relations to the axillary artery showing all terminal nerves

(Gray's Anatomy for Students, Fig. 7.53 - Brachial plexus branches and relationship to axillary artery)

From the Roots

Nerve	Root	Target
Dorsal scapular	C5	Rhomboid major, rhomboid minor
Long thoracic	C5, C6, C7	Serratus anterior (injury = winged scapula)
C5 contribution	C5	Phrenic nerve

From the Trunks (both from superior trunk only)

Nerve	Root	Target
Suprascapular	C5, C6	Supraspinatus, infraspinatus
Nerve to subclavius	C5, C6	Subclavius muscle

From the Lateral Cord (C5-C7)

Nerve	Target/Function
Lateral pectoral nerve	Pectoralis major (clavicular head)
Musculocutaneous nerve	Coracobrachialis, biceps, brachialis; terminates as lateral cutaneous nerve of forearm (sensory to lateral forearm)
Lateral root of median nerve	Joins medial root to form median nerve

From the Medial Cord (C8-T1)

Nerve	Target/Function
Medial pectoral nerve	Pectoralis minor + sternocostal head of pectoralis major
Medial cutaneous nerve of the arm	Skin - medial distal 1/3 of arm
Medial cutaneous nerve of the forearm	Skin - medial (ulnar) side of forearm to wrist
Medial root of median nerve	Joins lateral root to form median nerve
Ulnar nerve	FCU, medial half FDP; all intrinsic hand muscles except 3 thenar + 2 lateral lumbricals; skin - medial 1.5 digits (palmar + dorsal), medial palm

From the Posterior Cord (C5-T1)

Nerve	Target/Function
Superior subscapular	Subscapularis
Thoracodorsal	Latissimus dorsi
Inferior subscapular	Subscapularis + teres major
Axillary nerve	Deltoid + teres minor; superior lateral cutaneous nerve of arm (sensory to deltoid patch, "regimental badge area")
Radial nerve	All posterior compartment muscles of arm and forearm; sensory to posterior arm, posterior forearm, and dorsal lateral hand + dorsal aspect of lateral 3.5 digits

5. Terminal Nerves - Summary (Netter's Atlas Plate reference: Plate 401-410, 7th edition)

Note: Netter's Atlas of Human Anatomy covers the brachial plexus schema at Plates 401-402 (Brachial Plexus Schema), with cutaneous nerves of the upper limb at Plates 462-465 in the 7th edition. The key Netter plates for MS1 study are:

Plate 401: Brachial plexus schema (roots → terminal nerves)
Plate 462-463: Cutaneous innervation of upper limb (anterior/posterior)
Plate 464-465: Dermatomes of upper limb

6. Cutaneous (Peripheral) Nerve Supply of the Upper Limb

Anterior View

(THIEME Atlas, Fig. 5.1D - Anterior view peripheral cutaneous innervation)

Posterior View

(THIEME Atlas, Fig. 5.2F - Posterior view peripheral cutaneous innervation)

7. Dermatomes of the Upper Limb (Radicular/Segmental Innervation)

Key dermatome map (from THIEME Atlas):

Dermatome bands of upper limb posterior view showing C4-C8 and T1-T5 elongated segmental strips

(THIEME Atlas - Posterior dermatomes C4-T5; note how C5-C7 become separated from the thoracic body wall)

With limb outgrowth during development, the sensory segments become elongated into narrow longitudinal bands. Segments C5-C7 become separated from the body wall as the limb buds out:

Spinal Level	Dermatome Area
C4	Shoulder cap (over deltoid/trapezius)
C5	Lateral arm (deltoid patch, lateral upper arm)
C6	Lateral forearm, thumb, index finger
C7	Middle finger (autonomous zone); posterior forearm
C8	Ring and little fingers, medial forearm
T1	Medial arm (proximal part, near axilla)
T2	Axilla, upper medial arm (intercostobrachial nerve)

Important Distinctions for MS1:

Dermatome (radicular) vs. peripheral cutaneous territory - these are NOT the same. A single peripheral nerve may carry fibers from multiple roots. Injury to a nerve root (e.g., disc herniation at C6) produces a dermatome-shaped sensory loss. Injury to a peripheral nerve (e.g., median nerve at wrist) produces a peripheral territory loss.
Autonomous zones (minimal overlap, reliable for testing):
- C6 = tip of index finger
- C7 = tip of middle finger
- C8 = tip of little finger
- Axillary nerve = regimental badge area (lateral deltoid)
- Radial nerve = dorsal first web space
- Median nerve = tip of index finger (palmar)
- Ulnar nerve = tip of little finger

8. Full Body Peripheral Cutaneous Innervation (Including Upper Limb)

Full body peripheral cutaneous innervation showing all nerves - anterior and posterior views, with upper limb labeled including axillary, radial, musculocutaneous, medial brachial, medial antebrachial, ulnar, and median nerves

(THIEME Atlas - Whole body peripheral cutaneous innervation, anterior and posterior)

9. Clinical Correlates (MS1 High-Yield)

Injury	Mechanism	Deficit
Erb's palsy (C5-C6)	Upper plexus - shoulder dystocia, lateral neck stretching	"Waiter's tip" - arm adducted, internally rotated, forearm pronated; loss of shoulder abduction/flexion, elbow flexion
Klumpke's palsy (C8-T1)	Lower plexus - arm pulled superiorly, Pancoast tumor	Claw hand (intrinsics lost), Horner's syndrome if T1 sympathetics involved
Long thoracic nerve (C5-7)	Axillary dissection, carrying heavy loads on shoulder	Winged scapula
Axillary nerve	Surgical neck humerus fracture, shoulder dislocation	Deltoid paralysis (shoulder abduction lost after 15°), sensory loss over regimental badge area
Radial nerve	Midshaft humerus fracture in spiral groove	Wrist drop (posterior interosseous), sensory loss dorsal lateral hand
Median nerve at wrist	Carpal tunnel syndrome	Thenar wasting, sensory loss lateral 3.5 digits (palmar)
Ulnar nerve at elbow	Cubital tunnel	Claw hand (ring + little), sensory medial 1.5 digits

Sources used:

Gray's Anatomy for Students (Moore, Dalley, Agur) - Figs. 7.52-7.56, Table 7.7
THIEME Atlas of General Anatomy and Musculoskeletal System - pp. 106-108, 229, 396-398
Netter's Atlas of Human Anatomy (7th ed): Plates 401-402 (brachial plexus schema), 462-465 (cutaneous/dermatomes upper limb) - the standard MS1 reference for visual plate study

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