Axilla (ARM PIT)
The axilla is a pyramidal space situated between the upper part of the arm and the chest wall. It resembles a four sided pyramid, and has following: (i) an apex (ii) a base (iii) four walls (anterior, posterior, medial and lateral).
- Anterior (pectoral) wall: - Formed by (i) Pectoralis major, (ii) Pectoralis minor, and (iii) Subclavius. The latter two muscles enclosed by clavipectoral fascia.
- Posterior (subscapular) wall: - Formed by (i) Subscapularis, (ii) Teres major and (iii) Latissimus dorsi.
- Medial (thoracic) wall: - Formed by (i) Upper four ribs (with their intercostal muscles), and (ii) Upper part of serratus anterior.
- Lateral (humeral) wall :- Formed by (i) Upper part of humerus with bicipital groove lodging the tendon of longheadof biceps, and (ii) Corachobrachialis and short head of biceps -
- Base: - Formed by skin, superficial fascia and deep (axillary) fascia. It is directed downwards.
- Apex: - It is directed upwards and medially towards the root of neck. It communicates with supraclavicular triangle of neck, hence referred to as Cervicoaxillarycanal.lt is triangular in shape and is bounded anteriorly by clavicle, posteriorly by upper part of scapula and medially by outer border of first rib. The axillary artery and brachial plexus enter the axilla through this canal.
Contents of axilla
- Three cords of brachial plexus and their branches.
- Axillary artery and its branches.
- Axillary vein and its tributaries, including the terminal part of cephalic vein.
- Axillary group of lymph nodes.
- Axillary sheath, prolongation of prevertebrallayer of deep cervical fascia around axillary artery and cords of brachial plexus.
- In females, the axillary tail of Spence.
Axillary lymph nodes
The axillary lymph nodes are divided into 5 groups:-
- Anterior (pectoral) group: - Lie along lateral thoracic vessels, i.e. along the lateral border of Pectoralis minor. They receive lymph from upper half of the anterior wall of trunk and from major part of breast.
- Posterior (scapular) group: - Lie along the Subscapular vessels. They receive lymph from the upper half of the posterior wall of trunk and axillary tail.
- Lateral group :- Lie along the upper part ofthehumerus, medial to the axillary vein. They receive lymph from upper limb.
- Central group: - Lie in the fat of the upper axilla. The receive lymph from the preceding groups and drain into apical group. The intercostobrachial nerve is closely related to them.
- Apical (infraclavicular) group: - Lie deep to the clavipectoral fascia along the axillary vessels. They receive lymph from central group, upper part of breast and the thumb and its web. These are called terminal group of lymph nodes, as they receive lymphatics from other nodes of breast.
These axillary lymph nodes are divided into three levels for defying the dissection level in breast cancer metastasis.
Part of axilla
Lymph nodes lateral to the lateral border of pectoralis minor (central group, lateral group, anterior group, posterior group)
Lymph nodes between the lateral and medial borders of pectoralis minor.
Plus Potter (interpectoral) lymph nodes
Lymph nodes medial to medial margin of pectoralis minor (including subclavicular; infraclavicular or apical)
It is a strong sheet offascia, situated deep to pectoralis major muscle and extends from the pectoralis minor to the clavicle. It splits in upper part to enclose subclavius and splits in lower part to enclose pectoralis minor. Below this it is continuous as suspensory ligament.
Clavipectoral fascia is pierced by:-
- Thoraco-Acromial vessels.
- Lateral pectoral nerve.
- Lymphatics passing from breast and pectoral region to apical-axillary lymph nodes.
- Cephalic vein.
Breast (mammary gland) is a modified sweat gland present in the superficial fascia of pectoral region. Vertically it extends from 2nd to 6th ribs at midclavicular lineand horizontal extent is from sternal margin to midaxillary line at the level of 4th rib.
Arterial supply of breast
Arterial supply of breast includes -
- Perforating branches of internal mammary artery in 2nd to 4thintercostal spaces.
- Thoracoacromial, lateral thoracic and superior thoracic branches of axillary.
- Mammary branches, from 2nd, 3rd and 4th posterior intercostal arteries.
There is an anastomotic circle of veins around the base of nipple-the circulus venosus of Haller. Veins from this and from the glandular tissue radiate to the circumference of the gland and drain into axillary, internal mammary and posterior intercostal veins.
Sensory and sympathetic innervation is via anterior and lateral cutaneous branches of 4th, 5th and 6th intercostal nerves. Nipple is mainly innervated by the 4th intercostal nerve.
Lymph vessels of the breast are grouped into
- Superficial lymphatics draining skin
- Deep lymphatics drain the parenchyma of breast along with nipple and areola. Just beneath the areola is the sub areolar plexus of Sappey.
- 75% lymph from breast goes to the axillary group of nodes; 20% goes to internal mammary orparasternal nodes; 5% goes to posterior intercostal lymph nodes.
- Among the axillary nodes, the lymphatics end mostly in the anterior groups and partly the posterior and apical groups. Lymph from the anterior and posterior groups passes to the central and lateral groups and through them to the apical groups. Finally it reaches the supraclavicular nodes.
- Lymphatics from superior quadrants cross over the clavicle and drain directly into supraclavicular lymph nodes (lower deep cervical.
- Parasternal lymph nodes of both the sides are interconnected across the sternum. Moreover, lymphatics of one breast communicate with the lymphatics of contralateral breast across sternum.
- Majority oflymphatics from lateral quadrants accompany axillary tail and drain mainly into the pectoral group lymphatics pass to central and then to the apical group of axillary lymph nodes.
- Infraclavicular (cephalic) lymph node interrupts lymphatics from superolateral quadrant.
- Some lymphatics of parenchyma pass deeply piercing through pectoral fascia, pectoralis major, Pectoralis minor and clavipectoral fascia. This pathway may be interrupted by interpectoral nodes of Rotter lying between the two pectoral muscles. Sometimes, one of the apical axillary nodes (Helstedt's node) lies behind the clavicle.
- Some lymphatic vessels from inferomedial quadrant communicate with subperitoneallymphatic plexus. Via this pathway cancer of the breast can spread to peritoneum, liver (hepatic lymph nodes) and other abdominal viscera. From subperitoneal plexus, cancer cells can migratetranscoelomically and aided by gravity fall into the pelvic cavity. Krukenberg'stumor is a secondary tumor of ovary.
- Blockade of cutaneous lymphatics by cancer cells produce an orange peel-like appearance of the skin-peaud'orange.
- Dimpling of the skin occurs by retraction and shortening of suspensory ligament of Cooper when cancer invades it. Retraction of nipple can occur if carcinoma spreads along lactiferous ducts.