An Overview of Lymph Nodes

Lymph nodes or lymph glands are an important part of the immune system, acting as "nodes" between the lymphatic vessels that span the body. Immune cells that are "parked" in these nodes stand ready to attack any bacteria, viruses, or other foreign substances that enter the body. Like other parts of the body, lymph nodes are also susceptible to diseases, such as infections, cancer, and trauma. Let's look at the role these nodes play in the day to day function of your body, as well as their role in disease.

Lymph nodes are small, bean-shaped glands that are located along the lymphatic system (a system of vessels similar to arteries and veins through which lymph fluid travels). Lymph nodes are classified as "secondary" lymphoid organs, with the primary lymph organs being the thymus gland, tonsils, spleen, and bone marrow.

If you visualize the primary lymph organs as the courthouse, the lymphatic vessels are the highways the immune police cells travel to survey the body, and the lymph nodes are like police stations along the way.

There are hundreds of lymph nodes throughout the body, but they are clustered in certain regions.

The structure of a lymph node is actually quite complex. Lymph nodes are divided into lobules, each of which contains an outer cortex, followed by a paracortex, with the medulla (core) on the inside. Simplistically, B lymphocytes (B cells) are found in the cortex, with T lymphocytes (T cells) and dendritic cells in the paracortex. Plasma cells and macrophages are present in the medulla. The entire lymph node is enclosed by a tough fibrous capsule.

Lymph nodes can vary in size from only a few millimeters to up to 2 centimeters in diameter.

Lymph nodes work like filters, or in our analogy security guards to filter bacteria, viruses, parasites, other foreign material (even cancer cells) that are brought to the nodes via lymphatic vessels.

This is the reason that lymph nodes are evaluated in people with cancer, as this is the first place where cancer cells may be "caught" on their journey to explore and set up home elsewhere in the body.

Lymph nodes play an important role in fighting infections in a few ways. Not only do they "trap" viruses and bacteria so that T cells can attack, but one type of T cells presents the invader (or an antigen from the invader) to B cells so the B cells can make antibodies against the invader. In this way, lymph nodes are a place where immune cells can communicate and work together.

Lymph nodes are well-known as the "swollen glands" people may note in their neck when they are fighting a cold or sore throat, but these nodes are actually located in many regions of the body.

Lymph nodes are more easily felt in people who are thin, and sometimes finding nodes that are seldom felt in general can be alarming. Some important lymph nodes include:

Cervical lymph nodes are the nodes you have likely felt in your neck when fighting an upper respiratory tract infection, and filter lymphatic fluid coming from the head, scalp, and neck. Cervical lymph nodes (lymph nodes in the neck) in turn, can be broken down into three primary regions, and which region is involved can give doctors important information when diagnosing an illness.

• Anterior cervical lymph nodes: Lymph nodes nearest the front of your neck are referred to as anterior cervical lymph nodes. It is these nodes that most people have felt at some time when battling the common cold or strep throat.
• Posterior cervical lymph nodes: Lying behind the band of muscle that runs on the lateral side of the neck (sternocleidomastoid) lie the posterior nodes. These nodes are frequently enlarged when people contract mono (infectious mononucleosis).
• Occipital lymph nodes: These nodes lie on the back of the neck at the base of the skull, and are also frequently enlarged in people who have mono.

Lymph nodes may also be felt in front of and behind the ear and along the jawline.

Axillary lymph nodes are the lymph nodes located in your armpit. In the movie Terms of Endearment, it was these nodes that heralded breast cancer, but causes other than breast cancer are a more common cause of enlargement. There are usually between 20 and 40 lymph nodes in the axilla, many of which are removed when a person has an axillary lymph node dissection for breast cancer.

The axillary lymph nodes can be used to describe an important finding with cancer. When cancer cells are picked up in lymphatic fluid, they first travel to lymph nodes. It's been found that these lymph nodes are affected in order, and now a sentinel lymph node biopsy may be done with breast cancer (and melanoma) that can often spare a person from having all nodes removed. A tracer is injected into the cancer, and only the first few nodes to which the cancer would travel may be to be biopsied.

Supraclavicular lymph nodes, when enlarged, can be felt just above the collarbone (clavicle). Most of the time, enlargement of these nodes signifies a serious underlying problem (such as lung cancer or a lymphoma).

Mediastinal lymph nodes reside in the mediastinum, the area in the center of the chest between the lungs. People cannot feel these nodes, but they can be visualized on imaging studies such as a CT scan or PET scan. Determining whether cancer is present in these nodes is important in staging lung cancer and some lymphomas.

Inguinal lymph nodes are present in the groin region. Since they drain tissues from the feet to the groin, there are many reasons why these nodes can become inflamed. Most often they become swollen after an injury or infection in the legs, but may also be a sign of anything from a sexually transmitted disease to cancer. Keep in mind that most people experience swollen inguinal nodes at some time, and the vast majority of the time they are not a problem; they are only doing their job of catching viruses or bacteria that enter your body from a sore on your feet or legs.

Retroperitoneal lymph nodes lie deep in the abdomen and can only be seen on imaging studies. They are the nodes to which testicular cancer first spreads.

Mesenteric lymph nodes are similar to retroperitoneal nodes, lying deep in the abdomen in the membranes that surround the intestine. In adolescents, these nodes may become inflamed (mesenteric lymphadenitis) with symptoms that can sometimes mimic appendicitis. They may be enlarged with some cancers, but this is much less common.

Pelvic lymph nodes lie deep in the pelvis and can only be seen on imaging studies. They may be involved with cancers such as those of the bladder, prostate, and more.

There are clusters of lymph nodes near the elbow, behind the knee, along the large airways (tracheobronchial), along the aorta (paraaortic), and many other regions of the body.

There are many conditions in which lymph nodes become involved. Doctors use the term "lymphadenopathy" to describe inflammation or swelling in these glands. When doctors evaluate lymph nodes there are a number of terms they may use:

• Mobile vs. fixed: Mobile lymph nodes are those that can easily be moved around when touched, whereas fixed appear to be attached to a structure deeper in the body. In general, mobile lymph nodes are benign whereas fixed nodes suggest the possibility of cancer.
• Painful vs. non-painful: In general, infections can cause tender lymph nodes and cancerous nodes are often not tender. But there are many exceptions.
• Localized vs. generalized: The term localized refers to enlarged lymph nodes in only one location. When generalized lymphadenopathy (enlarged nodes) is present, it is more likely to be infections such as mononucleosis (but can also be due to other conditions).
• Matted: Sometimes lymph nodes appear to be attached together in a clump and the term matted is used.

Since lymph nodes store the white blood cells that are our first line of defense against infection, they are often enlarged due to infections. Enlargement of lymph nodes with an infection can be good or bad. It is good in the sense that they are the powerhouses storing immune cells. In other words, enlargement of the lymph nodes may mean your body is doing its job to resolve ​an infection.

This concept was not always well understood, however, and for a long time it was thought that removing the tonsils would help prevent infections. When tonsils are severely damaged, removing them can be a good idea. But if they are healthy and only doing their job, removing them gets rid of the functional "first place" where bacteria traveling in the lymphatic vessels could be "arrested."

Lymph nodes can catch viruses and bacteria but are also susceptible to infections themselves. For those who have been told to watch for a "red streak" after an injury have learned that infections (usually staph or strep) may begin in an infected wound and spread rapidly along lymph channels. Infections involving the lymph nodes often cause a significant fever and chills.

Cat scratch fever is an infection caused by the bacterium Bartonella henselae and is transmitted by exposure (usually via a break in the skin) from an infected cat. Enlarged lymph nodes related to catch scratch fever are usually non-tender but can be very large.

Lymph nodes are commonly involved with cancer, but their role often differs between solid tumors and lymphomas.

Solid Tumors: With solid tumors such as breast cancer, the cancer cells usually travels to lymph nodes before traveling (metastasizing) to other regions of the body. Cancers that have spread to lymph nodes are usually a higher stage than those that have not, meaning they have a greater risk of recurring or spreading. In a sense, the spread of cancer cells to lymph nodes has declared its intent to travel elsewhere.

Lymphomas: With lymphomas, in contrast, the cancer begins in the lymph nodes. When lymphomas spread to regions other than lymph nodes, it is not referred to as metastasis as with solid tumors, but rather as "extranodal involvement."

There are many other conditions that can cause enlarged lymph nodes, ranging from autoimmune diseases (such as rheumatoid arthritis), to genetic syndromes, to sarcoidosis, and more.

Since the lymph nodes are the rest stops for the "workers" or the white blood cells which clean up a site of trauma, they are often enlarged with any injury. You can think of the lymph nodes as being a truck stop near a natural disaster where the firemen and paramedics are hanging out ready to do their job.

We often think of lymph nodes as heralding disease, but most of the time they are performing their job in fighting off foreign invaders. Even with solid tumors, the lymph nodes are catching the first cancer cells to travel before they can move farther in the body.