The Axillary Region

Original Editor - Alyssa Brooks-Wells

Top Contributors - Alyssa Brooks-Wells and Kim Jackson  

Description

The axillary region (also known as the arm pit) is a pyramid-shaped area located between the shoulder girdle and thorax. It serves as a space for neurovascular and lymphatic structures to travel through to reach the upper extremity from the neck[1].

Structure/Borders

Superficial Axilla.png

The structure of the axilla is dependent upon the position of the upper extremity - an expansive region when the arm is elevated and minimized when adducted[2].

[4]

Contents

Axillary artery.png

The axillary artery is an extension of the subclavian artery, and is called so after passing the first rib. It is renamed and considered the brachial artery after passing the teres major and exiting the axilla. The artery is encompassed by the axillary sheath and the brachial plexus cords and branches. The axillary artery is divided into three parts with arterial branches associated with each section. The branches of the axillary artery include the superior thoracic, thoracoacromial, lateral thoracic, subscapular, anterior humeral circumflex and posterior humeral circumflex arteries. The scapular and humeral anastomoses created by these branches are important factors to compensate if there are any occlusions of the axillary artery[3].

The brachial plexus' cords and branches surround the axillary artery and are named in reference to their position relative to the artery. The nerves of the brachial plexus course past the first rib, inferior to the clavicle and through the axilla from its cervical and thoracic roots (C5-T1) towards its peripheral innervation destinations. Within the axillary region, the brachial plexus gives rise to peripheral nerves, including the medial and lateral pectoral, medial cutaneous of arm and forearm, upper and lower subscapular, and thoracodorsal nerves, supplying muscles of the shoulder girdle and chest as well as sensation to certain areas of the upper extremity[2].

Medial to the axillary artery lies the axillary vein, receiving deoxygenated blood from the cephalic vein, basilic vein, and other tributaries correlating with branches of the axillary artery, ultimately serving as the major vessel of drainage for the upper extremity[1][2]. The axillary vein becomes the subclavian vein after exiting the apex of the axilla. Like the axillary artery, the axillary vein features anastomoses to compensate for any blockages that may form[2].

Axillary lymph vessels and nodes process lymph from the upper extremity and chest. The superficial vessels drain the skin while the deep vessels drain the bones and muscles. There are five groups of axillary nodes present in the axilla including pectoral, lateral, posterior (subscapular), central, and apical[3].

In addition to the neurovascular bundle, the axillary region also contains the short head of the biceps brachii muscle, coracobrachialis muscle, fascia and adipose tissue. Mammary tissue is also possibly present[2].

Clinical Relevance

  • Thoracic Outlet Syndrome (TOS) results from the compression of nerves and/or vessels at or around the apex of the axilla. The clinical presentation and distribution of TOS is dependent upon the structures compressed. A patient with TOS may complain of ipsilateral upper extremity pain, parasthesia, paresis, discoloration, and/or cold sensitivity[3]. See the content page on TOS for more information.
  • The breast is mostly drained through the axillary lymph vessels and nodes. Breast cancer can spread to the surrounding lymphatic system as well as the pectoralis major muscle and it's fascia. Decreased filtration of the axillary lymph nodes from cancerous infiltration, damage, or surgical removal as a form of treatment can result in swollen axillary lymph nodes or upper extremity lymphedema[3]. An additional risk of surgical removal is the damage of the long thoracic nerve, which would clinically present as scapular winging due to the resulting denervation of the serratus anterior muscle[1].
  • If the neck or upper extremity is forcefully stretched or trauma is inflicted upon the axillary region a brachial plexus injury may result. The clinical presentation of a brachial plexus injury is dependent upon the specific nerves and nerve roots damaged. It results in loss or diminishment of sensation and motor control of the associated innervation of the nerve(s) damaged. Upper trunk injuries (C4-C6) are more common than lower trunk injuries (C7-T1). Brachial plexus injuries may also be a result of a cervical rib or apical lung cancer growth[3]. See the content page on brachial plexus injuries, Erb's palsy, and Klumpke's palsy for more information.
  • If not properly fit, positioned and trained, axillary crutches can cause unnecessary pressures and damage to the contents of the axilla[3]. A clinician should also consider which type of crutch (axillary, forearm, gutter) or assistive device is most appropriate for the patient. See the content page on crutches for more information of proper fitting.

Related Pages

  1. Shoulder
  2. Brachial Plexus
  3. Thoracic Outlet Syndrome
  4. Breast Cancer
  5. Lymphoedema
  6. Brachial Plexus Injury (Erb's Palsy and Klumpke's Paralysis)
  7. Crutches

References

  1. 1.0 1.1 1.2 1.3 TeachMeAnatomy. The Axilla Region. Available from: https://teachmeanatomy.info/upper-limb/areas/axilla/ (accessed 15 September 2020).
  2. 2.0 2.1 2.2 2.3 2.4 2.5 Macéa JR, Fregnani JHTG. Anatomy of the thoracic wall, axilla and breast. Int. J. Morphol. 2006;24(4):691-704.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Lumley JS, Craven JL, Abrahams PH, Tunstall RG, editors. Bailey & Love's Essential Clinical Anatomy. CRC Press; 2018 Nov 5.
  4. About Medicine. 3D Tour of the Axilla. Available from: http://www.youtube.com/watch?v=QQAqDhBVe-o [last accessed 9/16/2020]