Lymph nodes and lymphatic circulation
In addition to the bloodstream, in the human body there is another important network of vessels, which branches off to reach every part of the body: we are talking about the so-called lymphatic system.
The liquid that flows inside the lymphatic system is called lymph and has a composition very similar to that of plasma (water, electrolytes and proteins), plus a certain percentage of white blood cells, cell waste products, foreign particles and fats. food absorbed in the intestine.
The lymphatic circulation originates at the level of thin capillaries, with a blind bottom, which are distributed in the various tissues to collect the interstitial fluids. The convergent system of lymphatic capillaries gives rise to gradually increasing caliber vessels, which transport the lymph to the level of the large veins at the base of the neck, where it enters the bloodstream.
Filters called lymph nodes or lymph nodes are found along the complex system of lymphatic vessels. These filters are located at the confluence points of several lymphatic vessels and filter the lymph by retaining and eliminating foreign particles (such as viruses, bacteria and aged or abnormal cells, including cancer).
To perform their function in the best possible way, the individual lymph nodes are particularly rich in macrophages (capable of incorporating and digesting pathogens and altered cells) and other white blood cells (lymphocytes).
We can therefore compare the lymph nodes to a sort of customs office, capable of intercepting and neutralizing the "anomalous loads" to prevent them from spreading to the rest of the body.
The lymph nodes are organized in aggregate packages, or in chains arranged along the path of the main veins like pearls strung on a necklace.
Sentinel lymph node
The sentinel lymph node is the first lymph node to receive lymphatic drainage from the primary tumor. Depending on the case, the sentinel lymph node may still be intact or may already be infiltrated with neoplastic cells.
Malignant tumors are so defined because - unlike benign ones - they have cells capable of invading and destroying surrounding tissues; moreover, the same cells can spread through the blood or lymphatic capillaries and take root in other organs, giving rise to the so-called metastases (secondary tumors in locations far from the original one).
Some tumors metastasize preferentially through the lymphatic system, and in all these cases the evaluation of the sentinel lymph node is of great importance.
If spread through the lymphatic circulation, the cancer cells enter the local lymphatic capillaries, which in turn carry them along with the lymph into the sentinel lymph node. At the level of this filter, the local white blood cells try to fight the malignant cells to counteract their spread to the other sites of the organism; if this defensive line is exceeded, the malignant cells spread to the next lymph node and so on, spreading in the organism and drastically reducing the chances of cure.
According to the sentinel lymph node theory, if there are no cancer cells inside the sentinel lymph node, the involvement of the other nearby lymph nodes can also be ruled out.
Clinical significance
When and why it is important to evaluate the sentinel lymph node
The evaluation of the sentinel lymph node is of great clinical importance in the so-called tumor staging process, which in turn allows us to understand how large and widespread the tumor is. In this way, the medical staff can plan an adequate treatment and establish a reliable prognosis. For example, in breast cancer the evaluation of the sentinel lymph node allows - in case of negative results - to save unnecessary and harmful operations (axillary dissections) (because they would lead to swelling problems of the ipsilateral arm); see the dedicated article for further information.
For tumor staging, the so-called TNM system is mainly used, which is based on the evaluation of three elements:
- T: extension of the primary tumor;
- N: absence or presence of metastases to regional lymph nodes;
- M: absence or presence of distant metastases.
The addition of numbers to these 3 components indicates the extension of the tumor, which is all the more serious the greater the number; specifically we have:
- T0 (very small tumor), T1, T2, T3, T4 (very large tumor)
- N0 (no lymph nodes involved), N1, N2, N3 (many regional lymph nodes involved)
- M0 (no distant metastases), M1 (presence of metastases)
Regarding the evaluation of the sentinel lymph node, we have:
- N0 (sn): metastasis-free sentinel lymph node
- N1 (sn): metastasis in the sentinel lymph node
- NX (sn): sentinel lymph node not evaluable
The sentinel lymph node must first be identified by the doctor; for this purpose, a marker substance is injected into the area surrounding the tumor, then, through imaging techniques, the path of this tracer is observed up to the first lymph node it encounters. Subsequently, a biopsy and pathological evaluation of the lymph node is performed to ascertain the presence of malignant cells.
In case of involvement of the sentinel lymph node, the doctor can opt for its surgical removal (lymphadenectomy).
Currently (May 2015) the use of the sentinel lymph node as a diagnostic technique has been widely validated in breast cancer and melanoma. Several studies are underway to understand if it can also be applied to other cancers, such as colon cancer, to prostate, testicles, penis and renal cell carcinoma.
Enlarged lymph nodes: when to worry
The enlargement of a lymph node is generally caused by the increase in the number of immune cells inside it. In most cases this phenomenon is due to completely benign causes (eg. A sore throat, other infectious diseases or local inflammatory diseases); only in rare cases it can be the indicator of a neoplastic disease. It argues in favor of the possible presence of a tumor the fact that the swollen lymph nodes:
- remain so for many days;
- they tend to increase in volume over time;
- are located on one side of the body only;
- are located above the collarbone;
- are associated with fever;
- are associated with significant weight loss;
- are associated with other signs or symptoms that indicate the possible presence of a tumor.
