Axillary lymph nodes
The axillary lymph nodes are a collection of grouped lymph nodes found in the axillary region of the upper limb. The axillary region is commonly referred to as the ‘armpit’, although it is a three-dimensional space bound inferiorly by skin and anteriorly by the clavicle.
It is a quadrilateral space which changes shape based upon whether the arm is adducted or abducted.
The lymph nodes of the axillary region are responsible for the lymphatic drainage of a large section of human anatomy. Due to this arrangement and duty, they have a particular clinical relevance.
This is particularly evident with breast cancer, where axillary lymph node status, with regards to cancer, defines the treatment algorithm and approach. In this article we will discuss the anatomy and function of the axillary lymph nodes. In addition we will discuss function and clinical relevance.
The axillary lymph nodes lie within the axillary region of the upper limb. They are approximately 20 to 30 (up to 40 have been noted) separate nodes which function to drain the:
- vessels of the upper limb
- chest walls
- abdomen above the umbilicus
- lateral quadrant of the breast
Lymph flow is similar to venous blood flow. Lymph is conveyed towards the heart.
These are also known as the pectoral group. They can be located across the inferior border of the pectoralis minor muscle and the superior border of the pectoralis major muscle. There are usually 4-5 large nodes. The lymph flows from the anterolateral aspect of the abdominal wall superior to the level of the umbilicus and the lateral quadrants of the breast. It coveys the lymph to more central nodes.
This group is also known as the subscapular group. This group of 6-7 nodes can be found anterior to the subscapularis muscle and receives superficial lymph vessels located more commonly within the upper portion of the back and posterior neck. However, these can receive lymph from as far inferior as the superior border of the iliac crests.
This group of 4-6 nodes can be found against the axillary vein. The vast majority of the lymph vessels of the upper limb flow into this group. The superficial group of nodes however, drains the lateral aspect of the upper limb and flows into the infraclavicular nodes.
This group of 3-4 nodes is found at the base and centrally located in the axilla. These nodes are interspread amongst the adipose (fat) of the region. These are the most important group of nodes in terms of drainage because these receive lymph flow from the three groups of nodes mentioned above (anterior, posterior, and lateral).
This group of 4-5 nodes lies at the apex of the axilla and is located at the lateral border of the first rib. It is also referred to as the subclavicular group. This group receives efferent lymph vessels from the other axillary group of nodes. The apical group of nodes then drains into the subclavian lymph trunk. The drainage is different on the left and right sides. The left side axillary drainage flows into the thoracic duct, whereas on the right side the drainage is into the right lymphatic trunk.
This group is also known as the deltopectoral group. They cannot be referred to as axillary lymph nodes as they are located outside the axillary fossa and the axillary region. However, they do form a close association with the axillary group and lie in the deltopectoral groove (muscular superficial space between the deltoid and the pectoralis major). This space is also where the cephalic vein passes. In addition to this, this lymph node group of 2-3 nodes drains the major muscles of the forearm, hand, and arm, as well as the superficial lymph vessels of surrounding regions.
Thoracic DuctThe thoracic duct is main lymphatic duct of the body. It conveys the lymph from the lower limbs, abdomen, and the left side of trunk, upper limb, neck, and face. A portion of the thoracic duct in the abdomen is a dilated sac referred to as the ‘cisterna chyli’ or milk tank. This is because it contains the lymph fluid from the intestines, which is rich in chyle. This chyle is formed by fatty molecules (emulsified fats) and lymph from the lacteals. It is different from the lymph vessels that drain the limbs, where the drainage is purely lymph, and therefore clearer.
The thoracic duct is typically around 40 cm in length and has a diameter of 3-5 millimeters. The drainage of the thoracic duct is into the junction of the left jugulars and left subclavian vein. It is here that the lymphatic drainage of the bowels and body enters the systemic circulation. The drainage of the right upper limb, thorax, head, and neck drains into the right lymphatic duct.
Breast cancer is a disease that has many risk factors associated with it such as:
- advancing age
- oestrogen exposure
Risk factors for raised oestrogen exposure include early menarche, late menopause, combined oral contraceptive use, oestrogen containing hormone replacement therapy, no pregnancies, and lack of breastfeeding.
Every breast lump is assessed with triple assessment. This is a three phase process that has a very high rate of detection of cancerous masses. The history and clinical examination of the patient is the first part. The next step is imaging, where the preferred imaging modality is ultrasound (if the woman is younger and the breast tissue is dense - fibrous), or mammography (if the woman is older and the breast tissue is more fatty and less dense - less fibrous). The final step is to gain a histological sample through biopsy. This is usually performed as a fine needle aspiration, with a followup core biopsy if the initial fine needle aspiration shows potential cancer cells. The biopsy is reviewed by a pathologist.
All cancerous masses are removed surgically. This is either as a mastectomy (removal of the breast) or a lumpectomy (removal of affected tissue vs. whole breast), with or without a wide local excision of the axillary lymph nodes. Mastectomy procedures are used for central large masses and the lumpectomy is used in smaller more peripheral masses. A degree of clinical decision making and patient preference is important in determining the choice of operation.
A radical mastectomy is removal of breast, pectoralis major and pectoralis minor muscles, as well as the axillary lymph nodes. This is the most radical surgical option and is referred for highly invasive and dangerous cancers. The amount of axillary lymph node removal depends upon the investment and degree of metastasis of cancer. Partial mastectomies are employed for patients who wish to preserve as much of the breast tissue as possible and they have a smaller more focal disease. There is a higher degree of recurrence of cancer in these patients.
A lumpectomy is a more focused excision of the cancerous lump. The sentinel node (the first node that drains the breast) is identified and a histological section is checked for the presence of cancer. If there is cancer present, then all the lymph nodes surrounding with investment in the sentinel node are removed, as they could all theoretically have cancer cells within them. If these are found to be free of cancer then the process stops, if these are found to be positive for cancerous cells then the process continues until the lymph nodes are free and clear of cancer. This procedure may cause damage to the nerves, vessels, and tissue of the region. There is also a risk of postoperative lymphoedema, where the lymph drainage of the breast and upper limb may be compromised, resulting in a swelling over these regions.
All patients who have a lumpectomy and wide local excision have postoperative radiotherapy, as do mastectomy patients with more than a certain number of positive lymph nodes in the axilla. Medical treatment of breast cancer is dependent on the hormonal status of the cancer. Specifically it depends on the receptors the cancer cell has on it’s surface. If the cancer is oestrogen receptor positive, then tamoxifen is the treatment in premenopausal women. Aromatase inhibitors are used in postmenopausal women. Those with HER2 receptor positive cancers may have Herceptin, which is a monoclonal antibody.
In cases of gastric malignancy, there may be a visibly enlarged lymph node in the left supraclavicular fossa. This is a good clinical sign, but is not necessarily present in all patients who have abdominal or pelvic cancers that metastasize.
This is a cancer involving the lymph nodes and is divided into Hodgkin’s and non-Hodgkin’s types. Hodgkin’s lymphoma is defined by the presence of Reed-Sternberg cells. Signs and symptoms include:
- night sweats
- weight loss
- rubbery enlargement of the cervical lymph nodes
- systemic fever
Treatment of both types is chemotherapy and radiotherapy in some cases.