Human Anatomy
Pectoral Region and Breast
Pectoral region and breast anatomy for MBBS: pectoral muscles, clavipectoral fascia, breast structure, blood supply and lymphatics, mapped to NMC codes AN9.1 to AN9.3.
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Pectoral Region and Breast
Pectoral region and breast anatomy for MBBS: pectoral muscles, clavipectoral fascia, breast structure, blood supply and lymphatics, mapped to NMC codes AN9.1 to AN9.3.
This chapter covers the pectoral muscles and the female breast, one of the most heavily examined regions in first-year anatomy. It links the muscle attachments and clavipectoral fascia to the structure, blood supply and lymphatic drainage of the breast, and to the clinical signs of breast carcinoma.
High-yield: Pectoral Region and Breast
- Pectoralis major arises from the clavicle, sternum and upper costal cartilages and inserts into the lateral lip of the bicipital groove.
- Pectoralis major is a powerful adductor and medial rotator of the arm and is supplied by the medial and lateral pectoral nerves.
- Pectoralis minor arises from the third to fifth ribs and inserts into the coracoid process, and it divides the axillary artery into three parts.
- The clavipectoral fascia is pierced by the cephalic vein, the thoraco-acromial artery, the lateral pectoral nerve and lymphatics.
- The breast lies over the second to sixth ribs and extends from the sternum to the mid-axillary line.
- The axillary tail of Spence extends into the axilla through an opening in the deep fascia.
- The breast is separated from the pectoral fascia by the retromammary space, allowing it to move on the chest wall.
- Suspensory ligaments of Cooper anchor the breast to the skin; their invasion causes skin dimpling in carcinoma.
- About three-quarters of breast lymph drains to the axillary nodes and the rest mainly to the parasternal nodes.
- Lymphatic spread of breast carcinoma follows these routes, which is why axillary nodes are sampled at surgery.
- The nipple lies at the fourth intercostal space in the male and is surrounded by the pigmented areola.
- Peau d'orange skin is caused by lymphatic obstruction and oedema in advanced breast cancer.
- The breast is supplied by branches of the internal thoracic, lateral thoracic and posterior intercostal arteries.
- The retromammary space is a plane used surgically to mobilise the breast.
Breast lymphatic drainage
- **Axillary nodes:** Receive about 75% of breast lymph, mainly from the lateral quadrants; central to cancer staging.
- **Parasternal nodes:** Receive most of the remainder, mainly from the medial quadrants, alongside the internal thoracic vessels.
- **Cooper's ligaments:** Suspensory ligaments to the skin; their invasion causes tethering and skin dimpling.
- **Peau d'orange:** Skin dimpling from lymphatic oedema in advanced carcinoma, resembling orange peel.
NMC competencies in this chapter
- **AN9.1:** Pectoral muscles and clavipectoral fascia
- **AN9.2:** Structure and blood supply of the breast
- **AN9.3:** Lymphatic drainage and applied anatomy of the breast
Frequently Asked Questions
Where does most breast lymph drain?
About three-quarters of breast lymph drains to the axillary lymph nodes, mainly from the lateral quadrants, and most of the remainder drains to the parasternal nodes along the internal thoracic vessels.
What causes skin dimpling in breast cancer?
A carcinoma can invade and shorten the suspensory ligaments of Cooper, which tether the skin to the deeper tissue, pulling the overlying skin inward and producing a dimple.
What structures pierce the clavipectoral fascia?
The cephalic vein, the thoraco-acromial artery, the lateral pectoral nerve and lymphatics from the breast all pierce the clavipectoral fascia between the clavicle and pectoralis minor.
What is peau d'orange?
Peau d'orange is skin that looks like orange peel, caused by obstruction of subcutaneous lymphatics in advanced breast cancer. The oedematous skin is tethered at hair follicles, giving a dimpled appearance.
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