Lymph nodes are small, bean-shaped structures that are part of the body’s lymphatic system. The lymphatic system is a network of tissues and organs, including lymph nodes, that help the body fight infections and other diseases. Each lymph node acts like a filter, trapping germs, cellular debris, foreign particles, and cancer cells.
Lymph nodes play an essential role in the body’s immune system. They filter lymph fluid containing waste products, bacteria, and other harmful substances. The lymph nodes also store white blood cells, which help the body identify and fight infections. When there is an infection, inflammation, or cancer, the lymph nodes may swell as they work to filter out harmful substances and produce more white blood cells.
Lymph nodes are found throughout the body, often in clusters. Some of the most well-known locations include the neck, armpits, chest, abdomen, and groin. There are hundreds of lymph nodes in the body, and they are usually located near major blood vessels and in areas where infections are most likely to enter the body.
A normal lymph node has a distinct structure with an outer layer called the capsule and an internal tissue network. The inside of the lymph node is divided into two main areas: the cortex and the medulla. The cortex contains groups of cells called follicles, which are mainly made up of B cells. B cells are a type of white blood cell that helps produce antibodies to fight infections. The medulla contains T cells, another type of white blood cell that directly attacks infected or abnormal cells. The lymph node also has spaces called sinuses that allow lymph fluid to flow through the node, carrying cells and waste products.
The size of a normal lymph node can vary depending on its location in the body. Generally, most normal lymph nodes are small, ranging from 1 to 2 centimeters (cm) in diameter. Lymph nodes in the neck or groin areas may be slightly larger, while those in the chest or abdomen are often smaller. A lymph node larger than 2 cm, especially if it continues to grow or is firm and fixed in place, may indicate an underlying condition that requires further examination. In imaging studies, such as MRI or CT scans, the term “lymphadenopathy” is often used to describe enlarged lymph nodes.
Lymph nodes can be affected by a variety of conditions, including:
A reactive lymph node means that it is responding to an infection, inflammation, or other stimulus. In this situation, the lymph node enlarges and may contain more white blood cells than usual to help fight the infection or inflammation. Reactive lymph nodes are not cancerous and usually return to their normal size once the underlying cause is resolved.
The most common type of cancer that starts in a lymph node is called lymphoma. Lymphoma is a cancer of the lymphatic system, which includes lymph nodes, the spleen, and other lymphoid tissues. Lymphomas are divided into two main types: Hodgkin lymphoma and non-Hodgkin lymphoma.
Lymphomas can affect lymph nodes in a localized area or spread to multiple lymph nodes throughout the body.
Carcinomas and melanoma are types of cancers that commonly spread to lymph nodes.
In contrast, sarcoma, a cancer that begins in tissues like muscles, bones, fat, and nerves, is much less likely to spread to lymph nodes. Instead, sarcomas are more likely to spread to other areas, such as the lungs.
Lymph node metastasis occurs when cancer cells spread from their original site to a nearby lymph node. This process is a common way for some cancers to spread, especially breast, lung, and colon cancers. When cancer cells are found in a lymph node, it indicates that the cancer has started to spread beyond its original location. The presence of metastasis in lymph nodes changes the cancer stage and guides treatment decisions.
Pathologists examine lymph nodes to help diagnose conditions and guide treatment. For example, examining lymph nodes in cancer can provide information about whether the cancer has spread and how advanced it may be. The pathologist looks at the lymph nodes under a microscope to check for the presence of cancer cells, infections, or other abnormalities. The findings can help doctors determine the best treatment plan and predict the likely outcome for the patient.