An Overview of Lymph Nodes

Lymph nodes, sometimes referred to as lymph glands, are an important part of the immune system. Lymph nodes are clustered throughout the body and function as filters, removing foreign particles from fluids that run through the lymphatic vessels.

Within lymph nodes are a dense population of white blood cells called lymphocytes that help neutralize foreign agents like bacteria.

This article describes the structure and function of lymph nodes as well as the types and locations of lymph nodes throughout the body. It also lists the different conditions, including cancer, that can affect lymph nodes.

Structure

Lymph nodes are small, bean-shaped organs that are part of the lymphatic system. The lymphatic system is a network of vessels and organs that isolate and neutralize foreign agents and particles that can do the body harm.

In addition to lymph nodes, lymphatic fluid, and lymphatic vessels, the system is comprised of the thymus gland, tonsils, spleen, and bone marrow.

Lymph nodes vary in size from a few millimeters to up to 2 centimeters in diameter. There are hundreds located throughout the body, but they are mainly clustered in certain parts of the body.

Function

The many functions of lymph nodes are to filter and identify foreign agents that cause infections. To do this, lymph nodes contain two different types of white blood cells:

• B lymphocytes (B cells) that produce called antibodies that help fight bacteria, viruses, fungi, and other infectious agents
• T lymphocytes (T cells) that instigate the adaptive immune response (meaning the immune response specific to the infectious agent)

When a foreign agent has been trapped and the immune defenses are activated, the body will respond with inflammation. This causes the lymph nodes to swell.

Swollen lymph nodes, referred to as lymphadenopathy, are a sign that the body is fighting an infection. Swollen lymph nodes can often be felt and seen, but not always. Some may be painful; others are not.

Not every particle that is filtered by the lymph nodes can be neutralized. One example is cancer cells that are shed from a nearby tumor. Even though lymph nodes cannot kill the cancer cells, they may be able to isolate and contain them during the early stages of the disease.

Types and Locations

Lymph nodes are clustered throughout the body in key locations. These include the armpits, neck, groin, upper abdomen, and mediastinum (the area between the lungs that contains all the principal organs of the chest).

Swollen lymph nodes in the armpits, neck, and groin can often be felt. Those in the mediastinum and upper abdomen may only be revealed with imaging tests such as a computed tomography (CT) scan or ultrasound.

The types and locations of lymph nodes vary as follows:

Cervical Lymph Nodes

Cervical lymph nodes are those in the neck. They are further broken down by their location:

• Anterior cervical lymph nodes are those nearest the front of the neck. These typically swell when you have a cold or strep.
• Posterior cervical lymph nodes are located behind the band of muscles on the side of the neck. These often swell when you have infectious mononucleosis.
• Occipital lymph nodes are located at the back of the neck at the base of the skull. These often swell with infections like HIV.

Axillary Lymph Nodes

Axillary lymph nodes are the lymph nodes located in the armpit (axilla). There are usually between 10 and 40 lymph nodes in the axilla.

The axillary lymph nodes are important in the diagnosis of breast cancer. When cancer cells are shed from a breast tumor, they first travel to the axillary nodes. Because cancer cells tend to spread through lymph nodes in a specific pattern, doctors can often tell how advanced the cancer is.

Supraclavicular Lymph Nodes

Supraclavicular lymph nodes are located just above the collarbone (clavicle). Most of the time, t enlargement of supraclavicular lymph nodes is a sign of a serious disease such as lung cancer or lymphoma (a type of blood cancer).

Mediastinal Lymph Nodes

Mediastinal lymph nodes reside in the center of the chest cavity between the lungs. People cannot feel mediastinal lymph nodes, but they can be seen in imaging studies such as a CT scan or positron emission tomography (PET) scan.

Checking mediastinal lymph nodes is essential to the staging of lung cancer and some lymphomas.

Inguinal Lymph Nodes

Inguinal lymph nodes are located in the groin. Because they are responsible for filtering lymphatic fluids from the feet to the groin, they can become swollen for many reasons. These include injuries, sexually transmitted diseases, skin infections, yeast infections, and cancer.

Retroperitoneal Lymph Nodes

Retroperitoneal lymph nodes are situated at the back of the abdomen behind the tissues that cover the abdominal wall. These are the nodes to which testicular cancer first spreads. They can only be seen in imaging studies.

Mesenteric Lymph Nodes

Mesenteric lymph nodes lie deep within the abdomen in the membranes that surround the intestine. These nodes often become swollen due to gastroenteritis (stomach flu) but are also sometimes affected by inflammatory bowel disease (IBD) and lymphoma.

Pelvic Lymph Nodes

Pelvic lymph nodes are situated in the lower abdomen in the area that contains the hip bones, bladder, rectum, and reproductive organs. Pelvic lymph nodes can only be seen in imaging studies. Swollen pelvic lymph nodes may be a sign of bladder, prostate, cervical, ovarian, or anal cancer.

Associated Conditions

There are many conditions that can directly or indirectly affect the lymph nodes. Some are relatively mild and treatable, while others are more serious.

Lymphadenopathy

Lymphadenopathy, or the swelling of lymph nodes, is not a disease but a symptom of a disease. Based on its location and features, lymphadenopathy can reveal a lot about what is going on inside the body.

The features of lymphadenopathy may be described as:

• Mobile vs. fixed: Mobile lymph nodes are those that can be easily moved, while fixed lymph nodes are stuck to an internal structure. Mobile nodes are generally benign (non-cancerous), while fixed nodes are commonly seen with cancer.
• Painful vs. non-painful: Tender lymph nodes generally occur with infections, while cancerous nodes are typically non-tender.
• Localized vs. generalized: Localized lymphadenopathy, which affects one part of the body, is often due to a local infection such as strep throat. Generalized lymphadenopathy, affecting many parts of the body, can occur with autoimmune diseases, cancer, or drug reactions.

Lymphadenitis/Lymphangitis

Lymph nodes can "catch" viruses and bacteria but are also susceptible to infections themselves.

• Lymphadenitis is the enlargement in one or more lymph nodes, usually due to an infection.
• Lymphangitis is inflammation of lymphatic vessels, mainly due to an infection, that can involve lymph nodes as well

One such example is a bacterial infection from cats called cat scratch fever. The disease can cause swollen lymph nodes that last for months as well as fever, muscle aches, and nausea.

Cancer

Lymph nodes are commonly involved with cancer, but their role differs based on whether a solid tumor or lymphoma is involved.

With solid tumors such as breast cancer, cancer cells usually travel to nearby lymph nodes before metastasizing (spreading to other parts of the body).

Solid tumor cancers are typically staged based on the TNM system. The TNM system describes the severity of the disease based on the size of the tumor (T), the number and location of lymph nodes with cancer (N), and the presence or absence of metastasis (M).

With lymphoma, cancer starts in the lymph nodes. When lymphomas spread to other parts of the body, it is not referred to as metastasis but rather as "extranodal involvement."

Lymphoma is staged based on the number and location of affected lymph nodes, whether one or both sides of the body are involved, and if there is extranodal involvement.

Summary

Lymph nodes are small, bean-shaped organs that support the immune system by trapping foreign agents and killing them. The main function of lymph nodes is to fight infection. They do so by filtering bacteria, viruses, and other disease-causing agents circulating in the lymphatic system. White blood cells, called lymphocytes, are then recruited to control the infection.

Lymph nodes are clustered throughout the body, including the neck (cervical lymph nodes), groin (inguinal lymph nodes), armpits (axillary lymph nodes). There are also internal lymph nodes in the abdomen (mesenteric and retroperitoneal), chest cavity (mediastinal), and lower abdomen (pelvic).

Swollen lymph nodes (lymphadenopathy) can occur in response to an infection or disease in any part of the body. When a lymph node is infected and becomes swollen, it is referred to as lymphadenitis. Cancer can also affect lymph nodes either as it spreads from a tumor or starts in the lymph nodes themselves (lymphoma).