Anatomy of The Axilla

The axilla also called the is a small pyramidal space between the upper part of the arm and the chest wall. It resembles a four-sided pyramid and has four sides, as well as an apex and a base. The four sides are :

1. The Anterior Wall
2. The Posterior wall
3. The Medial wall
4. The Lateral Wall



1. THE APEX or CERVICOAXILLARY SPACE

The apex of the axilla is pointed upwards and medially towards the root of the neck. It has the following boundaries.

• Posteriorly it is bounded by the superior surface of the scapula and the coracoid process of the scapula.
• Anteriorly it is bounded by the Posterior surface of clavicle
• Medially by the outer border of first rib.

The cervicoaxillary space or the axilla serves as a passage for the axillary vessels and the brachial plexus.

 THE FOUR SIDES:

• The anterior wall of the axilla is made of the Pectoralis major, the clavipectoral fascia, and the pectoral minor.
• The posterior wall of the axilla is made up of the Subscapularis, Teres major and the Latissimus dorsi.
• The medial wall of the axilla is composed of the upper four ribs and their intercostal muscles, then upper part of the serratus anterior muscle.
• The lateral wall of the axilla is made of the upper part of the shaft of the humerus near the bicipital groove, and short heads of biceps brachii and coracobrachialis.

CONTENTS OF THE AXILLA

The Axilla contains the following:

• Axillary Artery and its branches
• Axillary vein and its tributaries
• Infraclavicular part of the brachial plexus
• The five categories of the axillary lymph nodes and the associated lymphatics
• Axillary fat and areola tissues
• The long thoracic and intercostobrachial nerves

THE AXILLARY ARTERY

The axillary artery is a continuation of the subclavian artery. It extends from the outer border of first rib to the lower surface of the Teres Major. It is divided into 3 parts by the pectoralis minor muscle -

• The superior (proximal part)
• The middle (deep) part
• The Inferior ( Distal ) part

NOTE:  All the three parts have relations to them - Anteriorly, Posteriorly, Medially, and Laterally.

Axillary Artery has 6 Branches:

• 1 branch from the superior (Proximal) part - SUPERIOR THORACIC ARTERY
• 2 branches from the Middle (deep) part - THORACOACROMIAL ARTERY and LATERAL THORACIC ARTERY
• 3 Branches from the Inferior (distal) part - ANTERIOR CIRCUMFLEX HUMERAL ARTERY, POSTERIOR CIRCUMFLEX HUMERAL ARTERY and SUBSCAPULAR ARTERY.

NOTE: The subscapular artery has two other braches - THE SCAPULAR CIRCUMFLEX ARTERY and THORACODORSAL ARTERY.

HOW THE BRANCHES OF THE AXILLARY ARTERY SUPPLY BLOOD

1. The superior thoracic supplies the pectoral muscles.
2. The Thoracoacromial artery has four branches:

• The pectoral branch - supplies the pectoral region and breast
• The deltoid branch - runs into the deltopectoral groove.
• Acromial branch - supplies the acromion.
• Clavicular branch - supplies the sternoclavicular joint and the subclavius.

  3. Lateral thoracic artery supplies the breast
  4. Anterior circumflex humeral artery supplies the gives off an ascending branch and supplies the head of the humerus and the shoulder joint.
  5. Posterior circumflex humeral artery - supplies the deltoid, shoulder joint, muscles surrounding the quadrangular space, it gives off a descending branch which forms a circumflex with profunda brachii artery.
   6. Subscapular Artery the largest branch of axillary artery. It runs along the lower border of subscapularies and suplies the latissimus dorsi and serratus anterior. It gave two branches:

• Circumflex humeral artery
• Thoracodorsal artery (which is simply a coninuation of the subscapular artery.

ANASTOMOSES and COLLATERAL CIRCULATION

The branches from the axillary artery anastomose with the branches of the neighbouring arteries like internal thoracic artery, intercostal artery, profunda brachii artery and  form anastomoses with one another. So when the axillary artery is blocked, collateral circulation is established through the anastomoses around the scapula which the upper part of the subclavius artery with the third part of the axillary artery,

AXILLARY VEIN

The axillary vein is the continuation of the basilic vein. It lies on the medial side of the axillary artery.

At the outer border of the first rib, it becomes the subclavian vein. It also have tributaries that accompany the axillary artery, and at the upper part it received the cephalic vein.

AXILLARY LYMPH NODES

These are lymph nodes scattered in the fibrofatty tissues of the axilla. They are divided into five groups:

• The Anterior group - lie along the lateral thoracic vessels. Receive lymph from the upper part of the anterior wall of the trunk and major parts of the breast.
• The Posterior group - Lie along subscapular vessels and receive lymph from posterior wall of upper part of the trunk and the axillary tail of breast.
• The Lateral group - Lie in upper part of the Humerus.
• The Central Group - lie in fat of upper axilla. Receives lymph from the preceding group and drain into the apical group.
• The Apical group - Along clavipectoral fascia - Receive lymph from central group, upper part of breast, from the thumb and its web.

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