The Axilla is a pyramidal region which lies between the medial aspect of the upper arm and the lateral thoracic wall. It has the shape of a four sided pyramid with a blunt apex and a concave base. Its four walls included:
· Anterior wall
· Posterior wall
· Lateral wall
· Medial wall.
The Axilla is directed superomedially with its apex directed into the root of the neck while the base is facing downwards and outwards.
It is a blunt truncated space directed superomedially into the root of the neck. It has a triangular bony boundary which is formed anteriorly by the posterior surface of the clavicle, medially by the external surface of the 1st rib and posteriorly by the superior border of the scapular. Through this space the axillary vessels and the cords of the brachial plexus pass from the root of the neck into the axilla. This passage is referred to as the cervicoaxillary canal.
It is directed downward and it is convex inconformity with the concavity of the armpit. It is broader toward the chest wall and narrow towards the arm. It is formed by the skin, superficial fascia and a thick layer of the axillary fascia.
It is formed by pectoralis major, pectoralis minor, the subclavius muscle and clavipectoral fascia. The pectoralis major forms the anterior axillary fold.
It is formed above by the subscapularies muscle which overlies the scapular, below by the teres major and latissmus dorsi muscles. The teres major and the Latissimus dorsi form the posterior axillary fold.
It is formed by the upper 4 ribs, upper four digitation of serratus anteror muscle and the intercostal muscles within the upper four intercostals space. The medial wall is convex.
The anterior wall and posterior wall converge at the lateral wall thereby limiting the space of the lateral wall which now is formed by the humeral intertubercular sulcus which lodges the tendon of the long head of biceps.
CONTENT OF THE AXILLA
1. Axillary vessels which include the axillary artery and vein.
2. The infraclavicular part of the brachial plexus.
3. The axillary group of lymph nodes and vessels.
4. Intercostobrachial nerve and some lateral branches of some intercostal nerves.
5. The axillary Adipose tissues & areolar tissue.
6. Axillary tail of Spence.
The arrangement of the fascia in the axilla determines the spread of pus during axillary abscess. The clavipectoral fascia which attaches to the clavicle enclosing the subclavius and pectoralis minor and then attaches to the axillary fascia provide 2 routes of spread of suppuration during axillary abscess, therefore pus suppuration can spread above the pectoralis minor accumulating between it and pectoralis major, accumulation is felt at the margin of anterior axillary fold. Pus could also accumulate below the pectoralis minor before surrounding the axillary vessels. It can also spread upward into the root of the neck, this is an area of least resistance. Suppuration can also spread into the arm by tracking along the axillary vessels.
In surgical procedure involving axillary abscess, incisions are made mid way between the anterior and posterior axillary folds close to the medial wall this is to avoid the laceration of lateral pectoral nerve, the suprascapular N and the axillary vessels which lie on the anterior, posterior, and the lateral wall respectively.