Pectoral Region and Axilla

Pectoral Muscles & Fascia - Chest Power Players

Pectoral Muscles (OINA):

• Pectoral Fascia: Covers Pectoralis Major.
• Clavipectoral Fascia: Encloses Subclavius & P. Minor.
  • Pierced by (📌 LTC rule): Lateral Pectoral N., Thoracoacromial A.&V., Cephalic Vein.
• Suspensory Ligament of Axilla: Supports axillary floor.

⭐ The cephalic vein, found in the deltopectoral groove, pierces the clavipectoral fascia to drain into the axillary vein.

Mammary Gland - Glandular Grandeur

• Structure: Modified sweat gland; 15-20 lobules → lactiferous ducts → nipple. Cooper's ligaments.
• Blood Supply:
  • Arterial: Internal thoracic, lateral thoracic, thoracoacromial, posterior intercostal aa.
  • Venous: Axillary, internal thoracic vv.
• Nerve Supply: 4th-6th intercostal nn. (sensory/sympathetic).
• Lymphatic Drainage: (📌 Axillary Levels: I, II, III re: Pec Minor)

  Lymph Group	Drains	%
  Axillary	Most of breast (esp. outer quadrants)	~75%
  Parasternal	Medial quadrants	~20%
  Post. Intercostal	Deep posterior parts	~5%

⭐ Carcinoma of the breast most commonly occurs in the superolateral quadrant and primarily metastasizes via lymphatic routes to axillary lymph nodes.

Axilla Boundaries & Contents - Armpit's Inner Sanctum

The axilla is a pyramidal space:

• Apex (Cervico-axillary canal): Gateway neck & axilla.
  • Medial: 1st rib.
  • Anterior: Clavicle (posterior).
  • Posterior: Scapula (superior border).
• Base: Axillary fascia, skin; concave upwards.
• Anterior Wall: Pectoralis major & minor, clavipectoral fascia.
• Posterior Wall: Subscapularis, teres major, latissimus dorsi. 📌 (STL)
• Medial Wall: Serratus anterior, upper 4-5 ribs, intercostals.
• Lateral Wall: Intertubercular groove of humerus.

Major Contents:

• Axillary artery & branches
• Axillary vein & tributaries
• Brachial plexus (cords, branches)
• Axillary lymph nodes (5 groups)
• Long thoracic & Intercostobrachial nerves
• Fat & areolar tissue

⭐ The apex of the axilla, or cervico-axillary canal, is bounded by the 1st rib, clavicle, and superior border of the scapula, transmitting structures between the neck and axilla.

Axillary Neurovascular & Lymph - Axilla's Lifelines

Axillary Artery: 3 parts (by Pectoralis Minor). 📌 Mnemonic (Branches): "Screw The Lawyer, Save A Patient"

• Lateral Cord: Lat. Pectoral N, Musculocutaneous N, Lat. root Median N.
• Medial Cord: Med. Pectoral N, Med. Cut. N Arm/Forearm, Med. root Median N, Ulnar N.
• Posterior Cord: Upper/Lower Subscapular N, Thoracodorsal N, Axillary N, Radial N.

Axillary Lymph Nodes: 5 principal groups.

• Anterior (Pectoral): Drains most breast.
• Posterior (Subscapular): Drains back, shoulder.
• Lateral (Humeral): Drains upper limb.
• Central: Receives from Ant, Post, Lat.
• Apical: Final common pathway to supraclavicular nodes.

⭐ Injury to the long thoracic nerve (C5, C6, C7) results in paralysis of the serratus anterior, causing winging of the scapula.

High‑Yield Points - ⚡ Biggest Takeaways

• Cephalic vein pierces clavipectoral fascia in the deltopectoral groove.
• Pectoralis minor divides the axillary artery into three parts.
• Long thoracic nerve (C5-C7) injury: winged scapula (serratus anterior paralysis).
• Axillary nerve (C5,C6) injury: deltoid paralysis, regimental badge anesthesia.
• Quadrangular space transmits the axillary nerve and posterior circumflex humeral artery.
• The axillary sheath encloses the axillary artery, vein, and brachial plexus cords.
• Apical lymph nodes are the final drainage for axillary nodes, crucial in breast cancer.