Clinical anatomy for axillary artery

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Axillary Artery - Clinical Anatomy

Overview

The axillary artery is the main arterial trunk supplying the upper limb and axillary walls. It is the direct continuation of the subclavian artery, beginning at the lateral margin of the first rib and ending at the lower border of teres major, where it becomes the brachial artery.

Three-part division of the axillary artery showing its relationship to pectoralis minor, subclavius, and the brachial artery

Fig. 7.49 - Three-part division of the axillary artery - Gray's Anatomy for Students

Three Parts (Divided by Pectoralis Minor)

The pectoralis minor crosses anteriorly over the vessel and divides it into three parts. A useful mnemonic: 1 branch, 2 branches, 3 branches (the number of branches matches the part number).

Part	Position relative to pectoralis minor	Number of branches
1st part	Proximal to (medial to) pectoralis minor	1 branch
2nd part	Posterior to (deep to) pectoralis minor	2 branches
3rd part	Distal to (lateral to) pectoralis minor	3 branches

The artery lies within the axillary sheath proximally, in close relation to the cords and branches of the brachial plexus throughout its course.

CTA rendering showing 3-part division with segments 1 (green), 2 (yellow), and 3 (blue) in relation to pectoralis minor and subscapularis

Fig. 4.16 - Axillary artery segments on CTA - Imaging Anatomy Atlas Vol. 3

Six Branches

Complete branch diagram showing all 6 branches of the axillary artery with spatial relationships

Fig. 7.50 - Branches of the Axillary Artery - Gray's Anatomy for Students

1st Part (1 branch)

Superior thoracic artery

Small vessel from the anterior surface of the 1st part
Supplies the upper medial and anterior axillary walls

2nd Part (2 branches)

Thoraco-acromial artery

Short trunk from the anterior surface of the 2nd part, just proximal to the medial margin of pectoralis minor
Curves around the superior border of the muscle, pierces the clavipectoral fascia
Divides into four branches: pectoral, deltoid, clavicular, and acromial
Pectoral branch contributes to breast supply; deltoid branch accompanies the cephalic vein in the deltopectoral triangle

Lateral thoracic artery

Arises posterior to the lateral (inferior) margin of pectoralis minor
Follows the muscle margin to the thoracic wall
Supplies medial and anterior axillary walls; in women, branches emerge around the inferior border of pectoralis major to supply the breast

3rd Part (3 branches)

Subscapular artery (largest branch)

Originates from the posterior surface of the 3rd part
Follows the inferior margin of subscapularis briefly, then divides into two terminal branches:
- Circumflex scapular artery - passes through the triangular space (bounded by subscapularis above, teres major below, long head of triceps medially); enters the infraspinous fossa and anastomoses with suprascapular and dorsal scapular arteries
- Thoracodorsal artery - follows the lateral border of the scapula toward the inferior angle; supplies posterior and medial axillary walls

Anterior circumflex humeral artery (ACHA)

Small; arises from the lateral side of the 3rd part
Passes anterior to the surgical neck of the humerus
Supplies the glenohumeral joint and head of humerus
Anastomoses with posterior circumflex humeral artery

Posterior circumflex humeral artery (PCHA)

Originates immediately posterior to the ACHA origin
Exits the axilla with the axillary nerve through the quadrangular space (bounded by teres minor above, teres major below, long head of triceps medially, surgical neck of humerus laterally)
Winds around the surgical neck of humerus
Supplies surrounding muscles, glenohumeral joint
Anastomoses with ACHA, profunda brachii, suprascapular, and thoraco-acromial arteries

Angiographic Appearance

DSA angiogram of the axillary artery showing subscapular, circumflex scapular, thoracodorsal, and posterior circumflex humeral branches

Fig. 4.17b - DSA angiogram showing axillary artery branches - Imaging Anatomy Atlas Vol. 3

Relations in the Axilla

The axillary artery is surrounded by the contents of the axilla:

The axillary vein lies medial and anterior to the artery throughout
The brachial plexus cords wrap around the 2nd part: lateral cord lies lateral, medial cord lies medial, posterior cord lies posteriorly
The axillary lymph nodes and fat surround the neurovascular bundle
Anterior wall: pectoralis major + pectoral fascia (superficial layer); pectoralis minor + clavipectoral fascia (deep layer)
Posterior wall: subscapularis (anteriorly), teres major + latissimus dorsi (inferiorly)
Medial wall: thoracic wall with serratus anterior
Lateral wall: intertubercular sulcus of the humerus

Peri-scapular Anastomotic Network (Clinical Importance)

A rich anastomotic network around the scapula provides collateral circulation when the axillary artery is occluded. The key vessels involved include:

Transverse cervical artery (dorsal scapular branch) -- 1st part of subclavian
Suprascapular artery -- thyrocervical trunk
Subscapular artery (circumflex scapular branch) -- 3rd part of axillary

This network connects the 1st part of the subclavian to the 3rd part of the axillary artery, so occlusion proximal to the subscapular origin can still be compensated.

Branching Variations (Surgically Important)

Branching patterns are highly variable, particularly involving the subscapular and posterior circumflex humeral arteries (~66% of people show a variant):

High origin of subscapular artery from the 2nd part: 29-36%
Common trunk of subscapular + PCHA (from 2nd or 3rd part): 12-42%
Axillary origin of the thoracodorsal artery (without arising from subscapular): 3-10%
Superficial brachial artery: early bifurcation of the axillary into a superficial and deep brachial artery

These variations are important in axillary dissection (breast surgery), free flap planning (latissimus dorsi, serratus anterior), and interpreting vascular imaging.

Clinical Correlations

Situation	Relevance
Anterior shoulder dislocation	3rd part of axillary artery is vulnerable (least protected, no overlying muscle); can be torn especially in elderly patients
Axillary node dissection (breast cancer)	Surgical borders: axillary vein superiorly, latissimus dorsi laterally, chest wall medially - artery lies just deep to vein
Quadrangular space syndrome	PCHA + axillary nerve compression - causes shoulder pain and deltoid wasting
PCHA embolization	Avascular necrosis of the humeral head (PCHA supplies a significant portion of humeral head via anterolateral ascending branch)
Axillary artery aneurysm	Can cause thromboembolism to distal upper limb or compress brachial plexus
Chronic lung disease (TB, bronchiectasis)	Hypertrophy of thoracoacromial, lateral thoracic, subscapular, and thoracodorsal arteries due to transpleural collateralization

Sources: Gray's Anatomy for Students, p. 853-855 | Imaging Anatomy Text and Atlas Vol. 3 (Bones, Joints, Vessels and Nerves), p. 154-156 | Fischer's Mastery of Surgery 8th ed., p. 1552-1553 | THIEME Atlas of General Anatomy and Musculoskeletal System

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