Position. The armpit, and more particularly the axillary region, is the pyramidal space located at the junction of the arm with the thorax. It constitutes the part located below the scapulo-humeral joint and above the axillary fascia (1).

Structure. The armpit is bounded by (1):

• Its apex, bordered by the clavicle and the first rib, serves as a point of passage for the arteries, veins, nerves and lymphatics from the neck to the arm;
• Its base, extending from the arm to the chest wall, consists of the axillary fascia, subcutaneous tissue and skin;
• Its anterior wall is formed by the pectoralis major and pectoralis minor muscles as well as the associated fasciae;
• Its posterior wall is essentially formed by the scapula, or shoulder blade, as well as by the scapular muscle, the teres major muscle and the latissimus dorsi muscle;
• Its posterior wall is essentially formed by the scapula, or shoulder blade, as well as by the scapular muscle, the teres major muscle and the latissimus dorsi muscle;
• Its lateral wall is narrow and formed by the intertubercular groove of the humerus.

Composition. The axillary region contains (2):

• the axillary artery and its associated branches;

• the axillary vein and its associated tributaries;

• axillary lymph vessels and nodes;

• part of the brachial plexus;

• the coraco-brachialis muscle and the long and short heads of the biceps brachii. 

Passageway. The armpit and axillary region provide a passageway for nerves and vessels to the upper limb.

Different pathologies can develop in the armpit. They can in particular be of vascular, nervous, lymphatic or even tumor origin.

• Vascular pathologies. Thrombosis or blood clots can form in the axillary veins. The axillary artery can also dilate and lead to an aneurysm, which can lead to compression of the brachial plexus. This compression can be manifested by pain in the armpit and arm or by loss of feeling (1).
• Nerve pathologies. In the armpit, the brachial plexus can undergo nerve damage, which can go as far as rupture of the nerves. This can lead to partial or total paralysis of the upper limb (3). The cause of these paralyzes is most often accidental pulling or stretching.
• Lymphomas. They correspond to the development of malignant tumors within the lymphatic system. In the armpit, lymphomas can develop in the many lymph nodes present in this area. There are two main types of lymphoma: Hodgkin’s disease and non-Hodgkin’s lymphoma (4).

Orthopedic treatment. Depending on the pathology diagnosed, immobilization of the upper limb may be necessary, for example with the wearing of an orthopedic vest.

Surgical treatment. Depending on the type of lesions, surgery may be performed under brachial plexus anesthesia. An anesthetic solution is injected into the brachial plexus in order to stop the nerve impulses and to numb the upper limb.

Chemotherapy, radiotherapy or targeted therapy. Depending on the type and stage of the tumor, chemotherapy, radiation therapy or targeted therapy may be used to destroy cancer cells.

Physical examination. First, a clinical examination is performed to assess the symptoms perceived by the patient.

Medical imaging examination To establish or confirm the diagnosis, a CT scan, MRI, CT angiography, arteriography or x-ray may be performed.

Electromyogram. This test measures the activity of a nerve or muscle.

Biopsy. To confirm the presence of lymphoma, cells may be taken from a lymph node or bone marrow.

Aesthetic and hygienic aspects of the armpitss. Armpit hair removal is increasingly practiced for aesthetic and hygienic purposes. Temporary or permanent, many methods have been developed to facilitate this practice.