Breast Anatomy Complete information

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Breast Anatomy - Complete Reference

1. Position and Surface Boundaries

The breast (mammary gland) lies between the skin and the superficial pectoral fascia on the anterior thoracic wall. In the adult female, its boundaries are:

Superior: 2nd rib
Inferior: 6th rib
Medial: Lateral sternal edge
Lateral: Midaxillary line

Posteriorly, the breast overlies the pectoralis major (upper and medial portions), the serratus anterior (inferolateral), the external abdominal oblique, and the upper rectus sheath. A tongue-like projection of glandular tissue extends superlaterally around the lower margin of the pectoralis major into the axilla - this is the axillary tail (of Spence).

Adult female breast showing position on thoracic wall over pectoralis major and serratus anterior

Figure: The adult female breast. The upper and medial portions rest on the pectoralis major muscle; the inferolateral portion rests on serratus anterior. (Fischer's Mastery of Surgery)

2. Gross Internal Structure

Cutaway diagram of mature resting breast showing all layers and structures

Figure: Cutaway diagram of the mature resting breast showing lactiferous ducts, lactiferous sinus, Cooper ligaments, TDLU, deep fascia, and pectoralis major. (Sabiston Textbook of Surgery)

The breast is composed of three principal tissue types:

Glandular epithelium - the functional secretory component
Fibrous stroma - connective tissue scaffolding
Adipose tissue - fills the inter-lobar spaces; determines breast size

In adolescents, epithelium and stroma predominate. After menopause, glandular structures involute and are largely replaced by adipose tissue, reducing mammographic density.

Lobes and Ducts

The breast contains 15-20 lobes of glandular tissue, arranged radially around the nipple-areolar complex (NAC).
Each lobe is made up of 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 areola, then narrows again to open through a constricted orifice at the nipple.
There is no cross-communication between the independent duct systems.

Terminal Duct Lobular Unit (TDLU)

TDLU histology diagram showing intralobular terminal duct, lobular acini, intralobular and extralobular stroma

Figure: Mature resting terminal duct lobular unit (TDLU). (Sabiston Textbook of Surgery)

The TDLU is the fundamental secretory and pathological unit of the breast:

Consists of a terminal duct + its associated lobule (cluster of acini)
Intralobular stroma is a loose, specialized connective tissue containing capillaries and lymphocytes
Distinct from the denser interlobular stroma containing larger ducts, blood vessels, and fat
The entire ductal system is lined by epithelial cells surrounded by myoepithelial cells (contractile - propel milk toward nipple)
A continuous basement membrane (laminin, type IV collagen, proteoglycans) surrounds the ducts - breaching this membrane = invasion = metastatic potential
The TDLU is the origin of the majority of breast malignancies

Weight

Average non-lactating breast: 150-225 g
Lactating breast: may exceed 500 g
The left breast is commonly slightly larger than the right

3. Suspensory Ligaments of Cooper

Fibrous connective bands (Cooper's ligaments) run between the deep fascia and the dermis, providing both support and mobility to the breast. They:

Fuse with the overlying superficial fascia just under the dermis
Coalesce as interlobular fascia within the parenchyma
Connect to the deep fascia over the pectoralis muscle
Are anchored into the skin - infiltration by cancer or breast edema causes them to contract, producing skin dimpling and the "peau d'orange" (orange-skin) appearance

4. Nipple-Areolar Complex (NAC)

Skin is highly pigmented, composed of stratified squamous epithelium
Beneath the NAC are bundles of smooth muscle fibers arranged radially, circumferentially, and longitudinally - allow nipple erection from stimuli
Montgomery glands (accessory sebaceous/mammary glands) are present along the areolar margin, with their openings - the Tubercles of Morgagni - visible as nodular elevations on the areolar surface
Rich sensory innervation: the nipple contains numerous free nerve endings and Meissner corpuscles; the areola contains Ruffini-like endings and Krause end-bulbs

5. Blood Supply

Blood supply to the breast showing all arterial and venous vessels

Figure: Vasculature of the breast - medial mammary branches, perforating branches, lateral thoracic branches. (THIEME Atlas of Anatomy)

Arterial Supply (three main sources)

Artery	Branch	Supply
Internal thoracic (mammary) artery	Perforating branches (2nd-4th intercostal spaces) - medial mammary branches	Medial and central breast (~60%)
Lateral thoracic artery	Lateral mammary branches	Lateral breast
Axillary artery branches	Superior thoracic a., lateral thoracic a., pectoral branches of thoracoacromial a.	Upper and lateral breast
Posterior intercostal arteries	Lateral branches (2nd-5th spaces) - mammary branches	Posterior and lateral breast

Venous Drainage

Parallels the arterial supply:

Internal thoracic veins (drain medially)
Lateral thoracic veins (drain laterally into axillary vein)
Intercostal veins (drain posteriorly into azygos/hemiazygos)

The venous connection to the azygos and intercostal veins is a route for haematogenous metastasis - particularly to the vertebral column and lungs.

6. Lymphatic Drainage

Lymphatic channels are abundant in breast parenchyma and dermis. Specialized subareolar lymphatics form the Sappey's plexus under the nipple and areola.

Direction of flow: skin → subareolar (Sappey's) plexus → interlobular parenchymal lymphatics

Drainage Route	Proportion
Axillary lymph nodes	70-80% (primary)
Internal mammary nodes	Predominant in ~2-3%; secondary route in ~20%
Supraclavicular nodes	Via Level III nodes

Axillary Lymph Node Levels

Defined by relationship to the pectoralis minor muscle:

Level I - lateral to the lateral border of pectoralis minor (low axilla)
Level II - posterior to pectoralis minor + interpectoral (Rotter's) nodes between pectoralis major and minor
Level III - medial to pectoralis minor; includes infraclavicular nodes

The apex of the axilla is the costoclavicular (Halsted) ligament, where the axillary vein becomes the subclavian vein. Drainage continues to supraclavicular nodes (outside the axilla proper).

7. Nerve Supply (Sensory Innervation)

The sensory innervation has a segmental arrangement:

Lateral and anterior cutaneous branches of intercostal nerves T2-T6 - primary supply to the breast
Medial branches of supraclavicular nerves (from cervical plexus C3-C4) - supply upper breast skin
The 4th intercostal nerve (lateral cutaneous branch, T4) provides the dominant innervation to the nipple-areolar complex

8. Important Surgical Nerves in the Axilla

Nerve	Origin	Muscle Innervated	Injury Consequence
Long thoracic nerve (nerve of Bell)	C5, C6, C7	Serratus anterior	Winged scapula
Thoracodorsal nerve	Posterior cord of brachial plexus	Latissimus dorsi	Weakness in shoulder extension/adduction
Medial pectoral nerve	Medial cord of brachial plexus	Pectoralis major	Weakness in adduction/medial rotation
Intercostobrachial nerves	Lateral cutaneous branches T1-T3	Sensation (medial upper arm + chest wall)	Numbness/chronic pain syndrome

9. Fascial Relationships

The breast lies within the superficial fascia of the anterior thoracic wall
The retromammary space (between deep surface of breast and pectoralis fascia) contains loose areolar tissue and lymphatics - allows the breast to move freely over the chest wall
The clavipectoral fascia encloses the pectoralis minor and extends laterally to fuse with the axillary fascia

10. Breast Development and Age-Related Changes

Phase	Changes
Adolescence	Epithelium and stroma predominate; ductal growth under estrogen
Reproductive years	TDLU development; cyclic changes (breast volume increases by ~15-45 mL during the luteal phase)
Pregnancy (wk 5-6)	Ductal sprouting under estrogen; new terminal buds develop
Mid-pregnancy	Ducts canalize; alveoli differentiate under prolactin and progesterone
Lactation	Columnar glandular cells secrete milk (apocrine secretion); myoepithelial cells contract under oxytocin; prolactin maintained by nipple stimulation
Post-menopausal (involution begins 35-45 yrs)	Glandular tissue replaced by adipose; Cooper ligaments lose tension; mammographic density decreases

11. Quadrant Distribution

The breast is divided into four quadrants for clinical reference:

Upper outer quadrant (UOQ)
Upper inner quadrant (UIQ)
Lower outer quadrant (LOQ)
Lower inner quadrant (LIQ)
Retroareolar region (central)

The upper outer quadrant contains the greatest volume of breast parenchyma and is the most frequent site of both benign and malignant breast disease.

12. Breast Density and Clinical Significance

The ACR BI-RADS system defines four density patterns (1 = almost entirely fatty → 4 = extremely dense):

Younger women: denser background (more glandular)
Older women: less dense (replaced by fat)
Women with the densest background have 4-6 times the risk of breast cancer vs. almost entirely fatty breasts
Dense tissue also obscures lesions on mammography

Key Sources:

Sabiston Textbook of Surgery, Ch. 68 - Breast Anatomy, Development, and Physiology
Fischer's Mastery of Surgery (8th ed.), Ch. 74 - Anatomy of the Breast
Mulholland and Greenfield's Surgery (7th ed.), Ch. 74 - Surgical Anatomy of the Breast
THIEME Atlas of Anatomy - General Anatomy and Musculoskeletal System, Ch. C/D - Gross, Microscopic Anatomy, Blood and Nerve Supply
Color Atlas of Human Anatomy Vol. 2 - Internal Organs - Microscopic Structure and Function of the Female Breast
Grainger & Allison's Diagnostic Radiology - Normal Breast Anatomy (Radiological perspective)
Gray's Anatomy for Students - Surface Anatomy of the Breast

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