This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The skin of the axilla is thin, loose, and abundantly supplied with sebaceous glands connected with the hair-follicles and sweat-glands. These glands are in the deeper layer of the skin and are superficial to the axillary fascia, hence abscesses originating from them tend to break externally; usually they do not become large nor extend deep into the axilla.
Abscesses originating from the lymphatics, on the contrary, may be either deep in the axilla along the axillary, pectoral, or subscapular vessels, or they may be in the axillary fat and tend to point toward the skin. If the lymphatics along the axillary vessels are the point of origin, the abscess may follow them down under the deep fascia to the elbow. If the nodes high up are involved, the abscess may work up under the clavicle into the neck. If, however, the nodes near the apex of the axilla form the starting-point then the abscess bulges through the cribriform portion of the axillary fascia (between the " Armbogen " and " Achselbogen") into the axilla and tends to discharge through the skin. Abscesses originating in the pectoral group of lymphatics point at the lower margin of the anterior axillary fold. The attachment of the serratus anterior to the side of the chest prevents them from working towards the back.
Fig. 276. - Subpectoral abscess.
Abscesses involving the subclavian nodes may cause a subpectoral abscess (Fig. 276). The pus collects superficial to the costocoracoid membrane and clavipectoral fascia and pushes the pectoralis major muscle outward, forming a large rounded prominence below the inner half of the clavicle. The pus cannot extend upward or toward the median line on account of the attachment of the pectoralis major muscle. It can burrow through the intercostal spaces and involve the pleural cavity, or break through the fibres of the pectoralis major anteriorly or between the pectoralis major and deltoid, or, as is most commonly the case, work its way under the pectoralis major muscle, over the pectoralis minor, until it reaches the border of the pectoralis major at the anterior fold of the axilla.
In emptying these abscesses an incision is to be made along the anterior axillary fold and a tube introduced beneath the pectoralis major.
In opening an axillary abscess one should bear in mind that the important veins and nerves accompany the arteries and that the arteries lie in three places, viz., externally along the humerus, anteriorly along the edge of the pectoral muscles, and posteriorly along the edge of the scapula; therefore these three localities are to be avoided and an incision made in the middle of the axilla and short enough not to endanger the brachial vessels on the outside or the long thoracic or subscapular on the inside near the chest-wall.
The incision may divide the skin and if desired the deeper structures can be parted by introducing a closed haemostatic forceps and separating its jaws.
Axillary abscesses, if of slow formation and unopened, tend to burrow and follow the vessels upward beneath the clavicle and appear in the supraclavicular space beneath the deep cervical fascia, and they may even enter the superior mediastinum. They may also descend the arm under the fascia covering the coracobrachialis muscle.