1. Breast Anatomy
- Location and Structure:
- The breast lies between the subdermal layer of adipose tissue and the superficial pectoral fascia.
- It is composed of lobes that contain multiple lobules, which are the basic structural units of the mammary gland.
- The breast parenchyma is supported by fibrous bands called the suspensory ligaments of Cooper, which run from the chest wall to the dermis.
- The retromammary fat pad is a relatively avascular space located between the breast and the pectoralis major muscle.
- The pectoralis minor muscle, located deep to the pectoralis major, is enclosed in the clavipectoral fascia, which extends laterally to fuse with the axillary fascia.
- Boundaries and Attachments:
- The breast is bounded superiorly by the clavicle, inferiorly by the inframammary fold, medially by the lateral edge of the sternum, and laterally by the anterior border of the latissimus dorsi.
- A thin layer of mammary tissue extends from the clavicle above to the seventh or eighth ribs below and from the midline to the edge of the latissimus dorsi posteriorly.
- The breast is traditionally divided into four quadrants: upper inner, upper outer, lower inner, and lower outer.
- Axillary Tail:
- The axillary tail of the breast is a protrusion of mammary tissue that extends toward the axilla. It is sometimes palpable and can be mistaken for enlarged lymph nodes or a lipoma.
- Ligaments of Cooper:
- These are hollow conical projections of fibrous tissue filled with breast tissue. They attach firmly to the superficial fascia and skin, causing dimpling of the skin when associated with carcinoma.
- Areola and Nipple:
- The areola contains involuntary muscle arranged concentrically and radially, along with sweat and sebaceous glands (Montgomery’s tubercles) that enlarge during pregnancy.
- The nipple is covered by thick, corrugated skin and contains smooth muscle fibers arranged concentrically and longitudinally, making it an erectile structure.
2. Neurovascular Anatomy
- Arterial Supply:
- The upper outer quadrant of the breast is supplied by the lateral thoracic artery (from the axillary artery), while the central and medial portions are supplied by perforating branches of the internal thoracic artery (internal mammary artery).
- Venous Drainage:
- Venous drainage occurs through the axillary vein, internal mammary vein, and intercostal veins.
- Sensory Innervation:
- Sensory innervation to the breast is provided by lateral and anterior cutaneous branches of the second to sixth intercostal nerves.
3. Lymphatic Anatomy
- Lymphatic Drainage:
- Lymphatic channels are abundant in the breast parenchyma and dermis. Lymph flows from the skin to the subareolar plexus (Sappey plexus) and then into the interlobular lymphatics of the breast parenchyma.
- Approximately 75% of lymphatic flow from the breast drains into the axillary lymph nodes, while a minor amount drains through the pectoralis muscle into medial lymph node groups.
- The internal mammary lymph nodes serve as the predominant drainage route in 5% of patients and as a secondary route in approximately 20% of patients.
- Axillary Lymph Nodes:
- Axillary lymph nodes are grouped by location and divided into three levels based on their relationship to the pectoralis minor muscle:
| Level of Nodes | Anatomic Location |
| Level I | Lateral to the lateral border of the pectoralis minor muscle. |
| Level II | Posterior to the pectoralis minor muscle and anterior to the pectoralis major (Rotter or interpectoral nodes). |
| Level III | Medial to the pectoralis minor muscle, including the subclavicular nodes. |
- The apical nodes, located above the pectoralis minor tendon, receive efferents from all other groups and drain into the subclavian lymph trunk.
- Sentinel Lymph Node:
- The sentinel node is the first lymph node draining the tumor-bearing area of the breast and is crucial for lymph node staging in breast cancer.
4. Axillary Anatomy
- Borders of the Axilla:
- Superiorly: Axillary vein, outer border of the first rib, and posterior border of the clavicle.
- Laterally: Latissimus dorsi muscle.
- Medially: Serratus anterior muscle.
- Posteriorly: Subscapularis and teres major muscles.
- Anteriorly: Pectoralis major and minor muscles.
- Contents of the Axilla:
- The axilla contains the axillary artery and vein, which are the major vasculature for the upper limb.
- It also contains important lymphatic structures and nerves, including the long thoracic nerve, thoracodorsal nerve, medial pectoral nerve, and intercostal brachial nerves.
- Nerves in the Axilla:
| Nerve | Anatomic Location | Function | Deficit Associated with Injury |
| Long Thoracic Nerve | Courses along the chest wall and medially within the axilla over the serratus anterior muscle. | Innervates the serratus anterior muscle. | Injury causes a “winged scapula”. |
| Thoracodorsal Nerve | Courses along the posterior border of the axilla to the latissimus dorsi muscle. | Innervates the latissimus dorsi muscle. | Injury causes weakness in shoulder adduction and medial rotation. |
| Medial Pectoral Nerve | Courses from the posterior aspect of the pectoralis minor muscle around its lateral border. | Innervates the lateral third of the pectoralis major muscle. | Injury results in atrophy of the pectoralis major muscle. |
| Intercostal Brachial Nerves | Course laterally in the axilla from the second intercostal space to the medial upper arm. | Provide sensory innervation to the upper arm. | Transection causes numbness in the posterior and medial surfaces of the upper arm. |
5. Clinical Significance
- Lymph Node Staging:
- Understanding lymphatic flow and axillary lymph node anatomy is essential for sentinel lymph node surgery and preventing lymphedema during lymphadenectomy.
- Surgical Considerations:
- Preservation of the long thoracic nerve, thoracodorsal nerve, and medial pectoral nerve is crucial during axillary dissection to avoid functional deficits.
- Division of intercostal brachial nerves may result in cutaneous anesthesia and chronic pain syndromes, so their preservation is preferred when possible.