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AN9.1-3 | Pectoral region — Part 3
CLINICAL PEARL
Quadrant rule for lymphatic spread in breast cancer:
- Upper outer quadrant (~50% of breast cancers) — axillary nodes Level I first
- Upper inner quadrant — internal mammary nodes (clinically silent, harder to detect)
- Lower outer — axillary nodes Level I
- Lower inner — both internal mammary AND axillary nodes
This quadrant-to-lymph-node mapping is a guaranteed exam question in surgery. Learn it now; you will use it in 3rd year clinicals and surgical postings.
The axillary tail of Spence drains directly into Level I axillary nodes — a lump felt in the axilla may be breast tissue rather than lymphadenopathy.
SELF-CHECK — Self-Check: Breast Anatomy
A patient has skin dimpling over a breast mass. What structure is being invaded by the tumour to cause this sign?
A. Lactiferous sinuses
B. Cooper's ligaments (suspensory ligaments of the breast)
C. Retromammary space
D. Montgomery glands
Reveal Answer
Answer: B. Cooper's ligaments (suspensory ligaments of the breast)
During sentinel node biopsy for a tumour in the upper outer quadrant, the radiotracer first appears in a node lateral to pectoralis minor. What level is this node?
A. Level I
B. Level II
C. Level III
D. Internal mammary chain
Reveal Answer
Answer: A. Level I
Which artery provides the major blood supply to the upper outer quadrant of the breast?
A. Internal thoracic artery
B. Lateral thoracic artery
C. Thoracoacromial artery
D. Posterior intercostal arteries
Reveal Answer
Answer: B. Lateral thoracic artery
Development of the Breast, Age Changes, and Congenital Anomalies
Embryological development:
The breast develops from ectodermal thickening along the mammary ridge (milk line) — a pair of ridges running from the axilla to the groin, appearing in week 6 of embryonic development.
- In humans, only ONE pair of breasts develops at the 4th intercostal space level. The rest of the ridge normally regresses.
- The breast starts as an epithelial bud that sinks into the underlying mesenchyme and branches to form the 15–20 lactiferous ducts by birth.
Hormonal milestones and age changes:
• Puberty: oestrogen drives duct and fat growth; progesterone promotes lobular development; breast grows through 5 Tanner stages
• Pregnancy: massive alveolar and ductal proliferation under oestrogen, progesterone, prolactin, and human placental lactogen
• Lactation: prolactin drives milk synthesis; oxytocin triggers myoepithelial cell contraction (milk ejection reflex)
• Menopause: oestrogen withdrawal causes glandular atrophy; post-menopausal breast appears more radiolucent on mammogram
Congenital anomalies:
| Anomaly | Definition | Clinical significance |
|---|---|---|
| Polythelia | Extra nipples along the milk line | Common (1–5%), usually benign |
| Polymastia | Extra breast tissue along the milk line | Can develop cancer; may lactate in pregnancy |
| Amastia | Absent breast and nipple | May be part of Poland syndrome |
| Gynaecomastia | Breast enlargement in males | Oestrogen excess (liver disease, drugs, puberty) |
| Inverted nipple | Nipple fails to evert | Normal at birth; NEW inversion in adult = malignancy until proven otherwise |