Axilla: Boundary & Contents

Boundary of Axilla

Notes from an M2: 
I missed several points throughout anatomy because I did not nail down the walls of the axilla. Know which organs go in which spaces, and be familiar with the barriers. You'll get about 3 points from knowing the brachial plexus diagram. Lymphatics are lower yield, just know the basics. You will be tested repeatedly on the cubital fossa. Remember 

Walls of the Axilla

  • Anterior Wall:
    • Formed by the lateral part of the pectoralis major, pectoralis minor muscles, and clavipectoral fascia.
    • The inferior most part of the anterior wall is the anterior axillary fold.
  • Posterior Wall:
    • Comprised of the subscapularis muscle, the distal part of the latissimus dorsi, and the distal part of teres major muscle.
    • The inferior most part of the posterior wall is the posterior axillary fold.
  • Medial Wall:
    • Formed by the upper thoracic wall and serratus anterior muscle.
  • Lateral Wall:
    • Narrow and formed by the intertubercular sulcus of the humerus.


Other Boundaries

  • Apex (Inlet):
    • Continuous superiorly with the neck.
    • Margins formed by the lateral border of the 1st rib (medially), the posterior surface of the clavicle (anteriorly), and the superior border of the scapula (posteriorly).
  • Base (Floor):
    • Formed by the skin of the armpit.
    • Opens laterally into the arm.


Contents of the Axilla

Neurovascular Structures

  • Axillary Artery:
    • Branches include the superior thoracic artery, thoraco-acromial artery, lateral thoracic artery, subscapular artery, anterior circumflex humeral artery, and posterior circumflex humeral artery.
  • Axillary Vein:
    • Tributaries include the cephalic vein, basilic vein, and paired brachial veins, with branches corresponding to the axillary artery.

  • Brachial Plexus:
    • Includes roots (C5-T1), trunks, divisions, cords, and terminal branches such as the musculocutaneous nerve, median nerve, ulnar nerve, radial nerve, and axillary nerve.



Lymphatic Structures

  • Lymph Nodes:
    • Arranged in 5 groups (apical, central, subscapular, humeral, and pectoral), named according to their location in the axilla.
    • Responsible for receiving 75% of the drainage from the breast.
  • Axillary Process of the Breast:
    • Extends into the axilla for additional lymphatic drainage.


Other Notable Structures

  • Superficial Veins:
    • Include the cephalic, median cubital (frequently used for venipuncture), and basilic veins.
    • Muscle contractions help push venous blood toward the heart, while one-way valves prevent backflow.


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