Axilla and Brachial Plexus - EASY

• The axilla also known as the axillary fossa or armpit.
• It is the fossa between the lateral part of the thorax, upper part of the humerus, and lower part of the shoulder.
• This area serves as a passageway for vessels and nerves from the trunk to the upper limb.
• The axilla is roughly pyramidal in shape with an apex, a floor, and four walls.

Walls of the Axilla:

Anterior Wall

• Pectoralis major and minor muscles.
• Pectoral and clavipectoral fasciae.

Posterior Wall

• Subscapularis muscle.
• Teres major and latissimus dorsi muscles.

Medial Wall

• First to fourth ribs
• Associated intercostal muscles.
• Serratus anterior muscle.

Lateral Wall

• Intertubercular groove of the humerus.

Apex

• Anteriorly by the clavicle.
• Posteriorly by the superior margin of the scapula.
• Medially by the first rib.

Base

• The base is directed inferiorly and is formed by the fascia and skin.

Contents of the Axilla:

• Axillary artery and its branches.
• Axillary vein and its branches.
• Axillary lymph nodes.
• Brachial plexus.
• The axillary artery, axillary vein, and the infraclavicular part of the brachial plexus are enclosed within a fascia called the axillary sheath.
• The axillary sheath is the continuation of the prevertebral layer of the deep cervical fascia.

Axillary Artery:

• The axillary artery begins at the lateral border of the first rib as a continuation of the subclavian artery.
• It terminates at the inferior border of the teres major muscle and continues as the brachial artery.
• The axillary artery is divided into three parts according to its relation with the pectoralis minor muscle.

Parts and Branches of the Axillary Artery:

1st Part

• Superior thoracic artery.

2nd Part

• Thoracoacromial artery.
• Lateral thoracic artery.

3rd Part

• Subscapular artery.
• Anterior circumflex humeral artery.
• Posterior circumflex humeral artery.
• In profuse bleeding of the Upper limb, it may be necessary to compress the axillary artery against humerus

Axillary Vein:

• The axillary vein lies along the medial side of the axillary artery.
• It is a continuation of the basilic vein.
• The axillary vein begins at the inferior border of the teres major muscle and ends at the lateral border of the first rib, where it becomes the subclavian vein.

Axillary Lymph Nodes:

• Lymph from the upper limb, shoulder, scapular region, pectoral region (including the mammary gland), and the upper part of the anterior abdominal wall drain into the axillary lymph nodes.
• There are about 15 to 20 lymph nodes arranged into five groups:
• Pectoral (anterior)
• Lateral.
• Posterior (or subscapular).
• Central.
• Apical.
• The apical group of axillary lymph nodes receives lymph from all other groups.
• The efferent vessels of the apical group unite together to form the subclavian lymphatic trunk.
• On the right side, the subclavian lymphatic trunk unites with either the jugular trunk or the bronchomediastinal trunk to form the short right lymphatic duct, which opens into the right venous angle.
• On the left side, the subclavian lymphatic trunk joins the thoracic duct, which opens into the left venous angle.
• Enlargement of any lymph node is called lymphadenopathy.
• This may be due to inflammation (as a result of infection) and/or the spread of cancer (metastasis) to the nodes.
• Infections of the upper limb and spread of breast cancers are common causes of lymphadenopathy

Dissection:

• Excision of the axillary lymph node may be necessary during the surgical treatment of breast cancer.
• Pathologic examination of the lymph nodes determines the staging of the cancer and further treatment of the patient.

Brachial Plexus:

• It's a network of nerves providing motor (GSE), sensory (GSA) and autonomic (GVE and GVA) innervation to the upper limb.
• There is one exception that all of the muscles of the upper limb are supplied by branches of the brachial plexus: The trapezius muscle is supplied by the accessory nerve (CN XI).
• The brachial plexus starts in the neck, extends to the axilla, and passes through the apex of the axilla.
• It is formed by the ventral rami of the spinal nerves C5-T1
• There are 31 pairs of spinal nerves arising from each side of the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.
• A spinal nerve is formed by the union of the sensory (dorsal) and motor (ventral) roots arising from a segment of the spinal cord.
• Autonomic fibers also contribute to the formation of the spinal nerves.
• A spinal nerve carries axons of the types GSA, GSE, GVA and GVE
• Once a spinal nerve is formed, it gives off a ventral rams and dorsal ramus
• Dorsal rami extend posteriorly to innervate the skin and muscles of the back.
• Ventral rami form plexuses except in the thoracic region (thoracic spinal nerves continue as the intercostal nerves).

Plexuses formed:

• Cervical plexus
• Brachial plexus
• Lumbar plexus
• Sacral plexus
• The parts of the plexus is formed of tree parts: starting from the roots, trunks, divisions, cords and terminal branches
• It is formed of ventral rami of following spinal nerves (there is also a small contribution from C4 and T2):C5, C6, C7, C8, T1
• Roots of C5 and C6 unite to form the superior trunk.
• Root of C7 forms the middle trunk.
• Roots of C8 and T1 unite to form the inferior trunk.
• Each of the three trunks divides into an anterior division and a posterior division.
• Posterior divisions of all trunks unite to form the posterior cord.
• Anterior divisions of the superior and middle trunks form the lateral cord.
• Anterior division of the inferior trunk forms the medial cord.
• Each cord gives of two terminal branches:
• Posterior cord divides into axillary nerve and radial nerve.
• Lateral cord divides into musculocutaneous nerve and the lateral branch of the median nerve.
• Medial cord divides into ulnar nerve and the medial branch of the median nerve.

Divisions:

• Supraclavicular part
• Lies in the neck
• Supraclavicular branches arise from the roots and trunks
• Infraclavicular part
• Lies in the axilla
• Infraclavicular branches arise from the cords