Axilla Anatomy: Boundaries, Arteries, Veins and Lymph Nodes Explained

Short Summary

This Osmosis video provides a focused tour of the axilla (armpit), explaining its boundaries, the key neurovascular structures that traverse it, and the five groups of axillary lymph nodes. The presenter uses a train-station analogy to describe how signals, blood, and lymphatics pass through en route to their destinations, and covers the three parts of the axillary artery and their branches, the formation of the axillary vein, and the major lymph node groups.

• Boundaries and pyramid shape: apex (cervico-axillary canal), base (armpit skin and fascia), four walls with muscular and skeletal landmarks.
• Axillary artery in three parts with one, two, and three branches per part, plus a memory trick for branches.
• Axillary vein formation and drainage into the subclavian vein.
• Axillary lymph node groups: anterior, posterior, lateral, central, apical.

• Key insights include the boundaries forming the anatomical gateway, the arterial branching pattern, and the lymphatic drainage through central to apical nodes.

Introduction

The video offers a detailed anatomical tour of the axilla, emphasizing its boundaries, contents, and the neurovascular structures that traverse this pivotal space at the junction of the arm and thorax. The tone blends clinical anatomy with memorable metaphors to help learners visualize how signals, blood, and lymphatics reach their targets.

Boundaries of the Axilla

The axilla is located at the border between the arm and thorax and connects superiorly to the neck, anteriorly to the pectoral region, inferolaterally to the upper limb, and inferomedially to the thoracic wall. It is described as a pyramid with an apex, a base, and four walls. The apex, also called the cervico-axillary canal, serves as the doorway between the neck and the axilla and is bounded by the first rib, the clavicle, and the superior edge of the scapula. The base is formed by skin, subcutaneous tissue, and axillary fascia, creating the axillary fossa or armpit. The anterior wall comprises the pectoralis major and minor, with the anterior axillary fold formed by the pectoralis major. The posterior wall is mainly the scapula and subscapularis, with the inferior portion formed by the teres major and latissimus dorsi, constituting the posterior axillary fold. The medial wall is formed by serratus anterior along the first to fourth ribs, and the lateral wall is the intertubercular sulcus of the humerus.

"The apex of the axilla is also called the cervico axillary canal, which is the door between the neck and the axilla." - Osmosis

Contents of the Axilla

Deep to the skin, fat and connective tissue surround the axillary sheath, which envelops the axillary vein, the axillary artery, and the surrounding brachial plexus. The axilla contains lymphatic vessels and axillary lymph nodes, essential for drainage from the upper limb and chest wall.

The Axillary Artery: Three Parts and Branches

The axillary artery begins as a continuation of the subclavian artery at the lateral border of the first rib and ends at the inferior border of the teres major when it becomes the brachial artery. As it passes posterior to the pectoralis minor, it is divided into three parts. The first part lies between the lateral border of the first rib and the medial border of the pectoralis minor and contains one branch, the superior thoracic artery. The second part lies posterior to the pectoralis minor and typically has two branches, the thoracoacromial artery and the lateral thoracic artery. The thoracoacromial trunk divides into four branches: clavicular, pectoral, deltoid, and acromial, which supply nearby muscles and joints. The lateral thoracic artery travels along the lateral edge of the pectoralis minor toward the thoracic wall, supplying the pectoralis muscles, serratus anterior, intercostal muscles, axillary lymph nodes, and the lateral breast. The third part extends from the lateral border of the pectoralis minor to the teres major and has three branches: the subscapular artery, the anterior circumflex humeral artery, and the posterior circumflex humeral artery. The subscapular artery is the largest, giving two terminal branches, the circumflex scapular and the thoracodorsal arteries; the circumflex scapular passes posterior to reach the dorsal scapular region, forming an important anastomosis with the suprascapular artery, while the thoracodorsal travels with the thoracodorsal nerve to the latissimus dorsi. The anterior and posterior circumflex humeral arteries encircle the surgical neck of the humerus, supplying the shoulder joint and surrounding muscles, and form an arterial “hug” around the humerus. The posterior circumflex humeral artery travels posterior to the teres major and minor in concert with the axillary nerve to supply the glenohumeral joint and deltoid. Because the space between teres major and minor forms a quadrilateral, it is called the quadrangular space; its medial boundary is the long head of the triceps and its lateral boundary is the humerus.

"The part number also tells you how many branches it has." - Osmosis

The Axillary Vein and Lymph Nodes

The axillary vein is formed by the union of the brachial veins and basilic vein at the inferior border of the teres major and ends at the lateral border of the first rib, where it becomes the subclavian vein. The axilla houses five major groups of axillary lymph nodes arranged like a pyramid with a triangular base and a central apex. The anterior (pectoral) nodes lie along the medial wall and drain the anterior thoracic wall and most of the breast. The posterior (subscapular) nodes lie along the posterior axillary fold and receive drainage from the posterior thoracic wall and the scapular region. The lateral (humeral) nodes run along the lateral wall around the axillary vein and drain most of the upper limb. Central nodes lie deep to the pectoralis minor, and the apical nodes sit at the apex and also receive lymph from the cephalic vein. Lymph from the anterior, posterior, and lateral groups passes to the central nodes, which then drain to the apical nodes. This lymphatic network forms a critical drainage pathway from the breast and chest wall to the venous system and lymphatic circulation.

"The lymph from the anterior, posterior and lateral nodes passes through efferent lymphatic vessels towards the central nodes." - Osmosis

Recap and Quick Take

In summary, the axilla is a pyramid-shaped space bridging the thorax and upper limb. It contains a fatty matrix with the axillary artery in three parts and its branches, the axillary vein and its tributaries, and the five groups of axillary lymph nodes, all bound by well-defined anatomical walls and margins that guide neurovascular and lymphatic passage.

"Alright. As a quick recap, the axilla is a pyramid shaped space that lies between the thorax and the arm and serves as a connection point between the arm, neck, thorax and pectoral regions." - Osmosis