Axillary region

Boundaries and External Landmarks

The axillary region itself (regio axillaris) is bounded by muscular contours that are clearly visible upon inspection. The boundaries of the region should not be confused with the walls of the axillary fossa.

• Anterior boundary: lower margin of the pectoralis major muscle (m. pectoralis major).
• Posterior boundary: lower margin of the latissimus dorsi muscle (m. latissimus dorsi).
• Medial boundary: a conventional line on the chest wall connecting the margins of the specified muscles.
• Lateral boundary: a similar line connecting the muscles on the medial surface of the arm.

Some landmarks are closely related to the scapular region. The superior angle of the scapula corresponds to the level of the 2nd rib, the spine of the scapula (spina scapulae) to the 3rd rib, and the inferior angle to the 8th rib. Palpatorily, the most reliable landmarks are the medial border, inferior angle, scapular spine, and acromion. The projection of the lateral border of the scapula is traced along a line from the lateral part of the acromion to the inferior angle.

Layer-by-layer Structure

1. Skin. Thin within the region itself, but thick and fixed closer to the scapula. Contains hair and numerous glands (sweat, sebaceous, apocrine). Their blockage leads to the formation of retention cysts (atheromas).
2. Subcutaneous adipose tissue (SAT). Weakly developed, single-layered. Pierced by connective tissue septa extending from the skin to the deep fascia. Contains cutaneous nerve branches and superficial lymph nodes.
3. Superficial fascia. Poorly developed, represented by thin layers.
4. Deep fascia (fascia axillaris). Thin in the center of the region, perforated by gaps for vessels. Thickens at the borders and transitions anteriorly into the pectoral fascia, posteriorly into the thoracolumbar fascia, medially into the deep thoracic fascia, and laterally into the arm fascia. The suspensory ligament of the axilla (lig. suspensorium axillae) pulls it upward, forming the vault of the fossa.

Walls of the Axillary Fossa

The axillary fossa (fossa axillaris) has the shape of a four-sided pyramid, the base of which is formed by the axillary fascia, while the apex is directed toward the middle of the clavicle.

• Anterior wall: formed by the pectoralis major muscle, as well as the clavipectoral fascia (f. clavipectoralis) with the pectoralis minor muscle.
• Medial wall: serratus anterior muscle (m. serratus anterior) and its covering fascia. The lateral thoracic artery and the long thoracic nerve of Bell (n. thoracicus longus) run along it from top to bottom.
• Lateral wall: coracobrachialis muscle (m. coracobrachialis) and the short head of the biceps brachii. The neurovascular bundle runs along the inner margin of the former—this site is used for digital compression of the axillary artery.
• Posterior wall: formed by fascia and muscles—the subscapularis and latissimus dorsi.

Openings of the Posterior Wall of the Fossa

A gap is formed between the muscles on the posterior wall, which is divided by the tendon of the long head of the triceps into two important anatomical openings:

1. Quadrangular space (foramen quadrilaterum). Located more laterally.

Boundaries: superiorly — subscapularis and teres minor muscles; inferiorly — teres major muscle; medially — long head of the triceps; laterally — surgical neck of the humerus. Contents: axillary nerve (n. axillaris) and posterior circumflex humeral artery.

1. Triangular space (foramen trilaterum). Located more medially.

Boundaries: superiorly and inferiorly — the same; laterally — long head of the triceps. Contents: circumflex scapular artery (a. circumflexa scapulae), passing into the scapular region.

Interfascial spaces communications

The adipose tissue of the axillary fossa contains 5 groups of lymph nodes (apical, central, lateral, anterior, posterior) and has multiple pathways of communication through which purulent-inflammatory processes can spread:

• Proximally along the course of the neurovascular bundle — into the fascial spaces of the neck and further into the anterior mediastinum.
• Distally — into the fascial space of the arm.
• Through the clavipectoral fascia (along a. thoracoacromialis) — into the subpectoral space.
• Through the quadrangular space — into the subdeltoid space.
• Through the triangular space — to the posterior surface of the scapular region.
• Between the deep surface of the scapula and the chest wall — into the subscapular space.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Formation and Branches of the Brachial Plexus in the Axillary Cavity
• Collateral Circulation of the Upper Extremity
• Topography of the Subscapular and Subdeltoid Spaces
• Proper Fascia and Osteofascial Compartments of the Deep Back Muscles
• Lymphatic Drainage from the Breast via Apical Lymph Nodes

Other topics in the "Upper Extremity" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.