surgical anatomy of breast Surgery exam.

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Surgical Anatomy of the Breast

Sources: Mulholland & Greenfield's Surgery 7e (Ch. 74); Fischer's Mastery of Surgery 8e (Ch. 51); Current Surgical Therapy 14e

1. Surface Boundaries

The adult breast occupies the anterior thoracic wall within the superficial fascia. Its boundaries are:

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

Breast tissue also extends superolaterally into the axilla as the Axillary Tail of Spence, making the upper outer quadrant the largest quadrant and the most common site of both benign and malignant disease.

Adult female breast - surface and deep relations

Fig. 74.1 - The upper/medial breast rests on pectoralis major; the inferolateral portion on serratus anterior.

2. Layers and Deep Relations

Posteriorly, the breast lies on the deep investing fasciae of:

Pectoralis major (upper/medial)
Serratus anterior (inferolateral)
External abdominal oblique (inferior)
Upper rectus sheath (inferomedial)

Between the breast and the pectoral fascia lies the retromammary (submammary) space - a relatively avascular plane used in mastectomy and augmentation. The breast is entirely contained within the superficial fascia, which provides an easy dissection plane.

Sagittal section showing retromammary space and Cooper's ligaments

Fig. 51.1B (Fischer's) - Note retromammary space, pectoral fascia, suspensory ligaments of Cooper, lactiferous sinuses and ducts.

3. Internal Structure

Sagittal section: lobes, lobules, alveoli, ducts

Fig. 74.2 - 15-20 lobes with lobules composed of tubuloalveolar glands, each ending in a lactiferous duct.

The breast parenchyma consists of:

15-20 lobes of glandular tissue, separated by connective tissue and fat
Each lobe is composed of 20-40 lobules
Each lobule has 10-100 alveoli
Each lobe terminates in a lactiferous duct → dilates into a lactiferous sinus → opens at the nipple via a constricted orifice
Glandular tissue is located more centrally; fat is more peripheral

Suspensory Ligaments of Cooper: Fibrous bands running from the deep fascia to the dermis - they provide support and mobility. More pronounced superiorly than inferiorly. Their tethering to skin causes skin dimpling in breast carcinoma.

Average weight: 150-225 g (nonlactating); can exceed 500 g when lactating. Left breast is commonly slightly larger than the right.

4. Nipple-Areolar Complex

Skin is highly pigmented stratified squamous epithelium
Deep to the nipple and areola are bundles of smooth muscle arranged radially, circumferentially, and longitudinally (allow erection of the nipple)
Montgomery glands (modified sebaceous glands) on the areolar margin open as nodular elevations called Tubercles of Morgagni
Nipple contains free sensory nerve endings + Meissner corpuscles
Areola contains Ruffini-like endings + Krause end-bulbs

5. Blood Supply

Arterial Supply

Three main sources (principal supply enters superolaterally and superomedially):

Source	Branches
Internal mammary (thoracic) artery	2nd, 3rd, 4th perforating branches (2nd perforator is the largest)
Axillary artery	Superior thoracic artery; lateral thoracic artery; pectoral branches of thoracoacromial artery
Posterior intercostal arteries	2nd, 3rd, 4th lateral branches

The plane deep to the breast is typically avascular - key for dissection.

Venous Drainage

Parallels the arterial supply:

Internal mammary veins
Posterior intercostal veins
Axillary vein tributaries

(Batson's plexus - the valveless vertebral venous plexus - provides a route for haematogenous spread to spine in breast cancer)

6. Lymphatic Drainage

Lymphatic flow is unidirectional through thin-walled, valveless vessels. Three interconnected plexuses:

Interlobular plexus - primary, within the gland along lactiferous ducts
Subareolar plexus (of Sappey) - drains skin, nipple/areola, and central gland
Deep (posterior) plexus - on the deep surface of breast, communicates with fascia

Drainage Routes

Route	%
Axillary lymph nodes	>75%
Internal mammary (parasternal) nodes	~25%
Occasional: subclavicular, subperitoneal, inferior phrenic, rectus sheath	minority

Key point: The flow to axillary vs. parasternal nodes is independent of the quadrant of origin.

7. Axillary Lymph Nodes - Levels

The axilla is a pyramidal space with:

Anterior wall: Pectoralis major, pectoralis minor, pectoral fascia
Posterior wall: Subscapularis, teres major, latissimus dorsi
Medial wall: Serratus anterior + upper 4-5 ribs
Lateral wall: Humerus (bicipital groove)
Apex: Cervicoaxillary canal (bounded by clavicle anteriorly, scapula posteriorly, 1st rib medially)
Base: Axillary fascia + skin

Axillary lymph node levels relative to pectoralis minor

Fig. 74.3 - Level I nodes: lateral/inferior to pec minor. Level II: behind pec minor. Level III: medial to pec minor (subclavicular).

Level Classification (relative to pectoralis minor)

Level	Location	Node Groups
Level I	Inferior & lateral to pec. minor	External mammary (anterior/pectoral), axillary vein, subscapular (scapular) nodes
Level II	Behind pec. minor	Central nodes, some subclavicular nodes
Level III	Medial to pec. minor	Subclavicular (apical/infraclavicular) nodes

Rotter's (Interpectoral) Nodes: Located between pectoralis major and minor along the lateral pectoral nerve - surgically important in modified radical mastectomy.

Internal mammary nodes: Located in the 1st-6th intercostal spaces within 3 cm of the sternum.

Supraclavicular nodes: Contiguous with apex of axilla - their involvement indicates advanced disease (N3c in TNM staging).

8. Nerves - Surgically Important

During axillary surgery, the following nerves must be identified and preserved:

Nerve	Origin	Action	If Damaged
Long thoracic nerve (of Bell)	C5, C6, C7	Serratus anterior	Winged scapula
Thoracodorsal nerve	Posterior cord	Latissimus dorsi	Weakness of internal rotation/extension of arm
Medial pectoral nerve	Medial cord	Pectoralis major (lower) & minor	Chest wall deformity
Lateral pectoral nerve	Lateral cord	Pectoralis major (upper)	Atrophy of pec major upper head
Intercostobrachial nerve	Lateral cutaneous branch of T2	Sensation - medial upper arm	Numbness/dysesthesia of inner arm (most commonly sacrificed)

The boundaries of axillary lymph node dissection (ALND):

Superior: Axillary vein
Medial: Serratus anterior muscle + long thoracic nerve
Lateral: Latissimus dorsi muscle + thoracodorsal nerve/bundle

9. Sensory Innervation of the Breast

Main supply: lateral and anterior cutaneous branches of the 2nd through 6th intercostal nerves
Small region of upper breast skin: anterior/medial branches of the supraclavicular nerve (from cervical plexus)
The 4th intercostal nerve (lateral cutaneous branch) provides the most important innervation to the nipple-areolar complex - at risk in reconstructive and cosmetic procedures

10. Surgical Significance Summary

Structure	Clinical Relevance
Suspensory ligaments of Cooper	Skin dimpling in carcinoma; traction dimple sign
Axillary tail of Spence	Must be included in mastectomy; site of missed tumors
Retromammary space	Avascular plane for mastectomy and implant placement
Subareolar plexus	Basis of sentinel lymph node biopsy (SLNB)
Level I-III nodes	Staging; axillary dissection extent
Long thoracic nerve	Winged scapula if damaged during ALND
Thoracodorsal nerve + vessels	Pedicle for latissimus dorsi flap reconstruction
Internal mammary nodes	Important in medial quadrant tumors; target in radiation
Rotter's nodes	Must clear in complete ALND

Mulholland & Greenfield's Surgery, Scientific Principles and Practice - 7e, p. 3866-3870 (Ch. 74) | Fischer's Mastery of Surgery 8e, Ch. 51 (Mastery Keys: Surgical Anatomy of Breast)

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