Lymph nodes are small organs, located in various locations throughout the body. They are connected to the body and to each other by small channels called lymphatics which contain fluid.
Lymph nodes are part of the immune system and their primary function is to ‘sample’ the fluids that circulate around the body in order to detect changes such as infection, injury, or cancer. The average person has hundreds or even thousands of lymph nodes although most people will never see or feel one of them unless it becomes enlarged.
Doctors use the word lymphadenopathy to describe large or abnormal looking lymph nodes. Your doctor may find abnormal lymph nodes during a physical examination or with the help of radiologic imaging such as an x-ray, CT scan, or MRI.
Lymph nodes can become enlarged in response to an infection or if they become full of cancer cells. A lymph node that is enlarged as a result of an infection is often referred to as ‘reactive’. Cancer cells may travel to a lymph node from another area of the body in a process called lymph node metastasis or they can arise from the cells that are normally in the lymph node (this kind of cancer is called lymphoma).
Enlarged lymph nodes are often sent for pathological examination in order to determine the cause for the enlargement. This is particularly important when a doctor is unsure if an enlarged lymph node is caused by an infection or the presence of cancer cells.
In other cases, lymph nodes are removed with a tumour in order to see if any of the lymph nodes contain cancer cells (lymph node metastases). In these cases each lymph node will be described as ‘positive’ or ‘negative’ with positive meaning that cancer cells were found in the lymph node.