Swollen Popliteal Lymph Nodes: Causes, Anatomy, and Diagnosis

The popliteal lymph nodes lie in the tissues behind a person’s knee. Many conditions can cause them to swell, such as infections and autoimmune conditions. It is rare for cancer to affect the popliteal lymph nodes.

This article takes a detailed look at swollen popliteal lymph nodes. It discusses what can cause swelling, diagnostic tests, and what happens after diagnosis. It also explains the anatomy and function of popliteal lymph nodes.

Lymphadenopathy is swelling of the lymph nodes. It occurs when too many lymphocytes build up in the lymph nodes. Lymphocytes are special types of white blood cells, a type of cell of the immune system.

According to a 2022 review, many health conditions can cause lymphocytes to build up. Some possible causes of swollen popliteal lymph nodes include:

  • infections: Several types of infections can cause lymphadenopathy. These include bacterial, viral, and fungal infections.
  • Autoimmune Diseases: Some autoimmune diseases can cause dysfunctions with immune cells. These conditions include sarcoidosis, amyloidosis, and rheumatoid arthritis.
  • Lymphoproliferative Disorders: Lymphoproliferative disorders are when the immune system produces too many lymphocytes. For example, hemophagocytic lymphohistiocytosis can cause lymphadenopathy.

Swollen popliteal lymph nodes can also be due to cancer.

Read more about lymph nodes here.

Could it be cancer?

Several cancers can cause lymphadenopathy. These include lymphomas, which are cancers that start in the lymph nodes. However, other cancers can spread to the lymph nodes, from leukemia to cervical cancer.

According to the American Cancer Society (ACS) most swollen lymph nodes are due to a condition that is not cancer. Moreover, an older study notes that this is so rare for cancer to spread to the popliteal lymph nodes.

Read more about cancer in the lymph nodes here.

Swollen popliteal lymph nodes caused by infection may show the following symptoms:

  • pain, redness, and tenderness behind the knee
  • a pea-sized lump that can swell to half an inch in diameter
  • a knob that moves freely when pressed

These symptoms indicate an infection and should disappear within 2 weeks once the infection subsides.

Swollen popliteal lymph nodes that show the following symptoms should be checked by a doctor:

  • painless swelling behind the knee
  • a swelling greater than half an inch in diameter
  • a hard lump that does not move freely when pressed
  • swelling lasts longer than 2 weeks

Scientists describe popliteal lymph nodes as located deep within the popliteal fossa.

The popliteal fossa is a diamond-shaped part of the leg. It lies behind the knee joint. There are 2-9 lymph nodes in each popliteal fossa.

The image below shows swollen popliteal lymph nodes in the popliteal fossa.

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Anatomy of the back of the knee showing the popliteal lymph nodes. Medical illustration by Bailey Mariner

Lymph nodes are part of the lymphatic system. The lymphatic system has many important functions. For example, it moves immune cells around the body and manages the accumulation of fluid between cells.

Within the lymphatic system, lymph nodes help filter body fluids. Lymph nodes are connected to lymphatic vessels, which carry these fluids into them. The filtering process involves removing harmful cells, molecules or pathogens. Lymph nodes can do this because they contain various immune cells.

Lymph nodes receive fluids from different parts of the body. The popliteal lymph nodes filter fluids from deep structures in the leg and foot.

Read more about the anatomy of the lower leg here.

Doctors can diagnose swollen lymph nodes based on a physical exam. A person with swollen popliteal lymph nodes may feel a lump in their popliteal fossa.

Swollen lymph nodes may show up in imaging tests, such as computed tomography (CT) scans.

Because so many different conditions cause lymphadopathy, doctors can find it challenging to pinpoint the cause. Doctors may recommend the following to test:

  • Detailed physical examination: Doctors can glean useful information from a physical exam. This information includes the size, firmness, and possible pain of a swollen lymph node.
  • Blood tests: Doctors may use a blood sample for testing in a laboratory. Tests include complete blood count, complete metabolic panel, and fungal serologies.
  • CT scans: Doctors can use a CT scan to check if a person has other swollen lymph nodes. These scans can also help schedule lymph node biopsies.
  • Lymph node biopsy: In this surgical procedure, doctors remove all or part of a swollen lymph node. They will then send this sample for lab testing. Although lymph node biopsies are not always necessary, doctors must perform them to diagnose conditions such as cancer.

A person may need to see several doctors before receiving a diagnosis. The process can take several weeks.

After diagnosis, doctors can recommend treatments. This varies greatly depending on the underlying cause of swollen popliteal lymph nodes. Possible treatments Involving:

  • For cancers: Surgery, radiation, or chemotherapy may help. Sometimes doctors recommend a combination of these.
  • For autoimmune diseases: Treatment may include immunotherapy and systemic glucocorticosteroids.
  • For infectious conditions: Treatment may include antibiotics, antifungals, or antiviral medications, depending on the type of infection.

Some medications can cause swollen lymph nodes. When this happens, doctors may recommend changing the medications or their dosages.

The popliteal fossa is an area of ​​tissue behind a person’s knee joints. Deep within this structure lie 2-9 popliteal lymph nodes. As part of the lymphatic system, these lymph nodes filter fluids from the leg and foot.

There are several causes of swollen popliteal lymph nodes, including infections, autoimmune disorders, and conditions that increase lymphocyte production. Cancers can also cause swollen popliteal lymph nodes, although this is rare.

Doctors can diagnose swollen popliteal lymph nodes with a physical exam. To determine the cause, they may use imaging tests, lab tests, or biopsies.

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