Lymph nodes serve as filters for our lymphatic system and are normally present throughout the body. The mere presence of a lymph node in the breast does not automatically signal the presence of breast cancer. In fact, lymph nodes within the breast tissue are common and are referred to as intramammary lymph nodes.
What to Know about Your Lymph Nodes
Lymph nodes can vary in size and shape, but all lymph nodes have an outer cellular component referred to as the cortex and an inner fatty component referred to as the fatty hilum. Normal intramammary lymph nodes are no exception and can vary in size, but they are generally smaller than lymph nodes encountered in the axilla (armpit). Lymph nodes also have a distinct shape often compared to a kidney bean. Although lymph nodes are normally seen in the breast, there are certain scenarios in which these lymph nodes prompt additional diagnostic breast imaging from a screening mammogram, which could possibly lead to an ultrasound-guided biopsy. Here are the most common scenarios encountered:
- Baseline (first time) screening mammograms or women who obtain a mammogram and we are not able to locate any prior mammograms for comparison poses a unique challenge for the breast radiologist. If a breast mass that cannot be definitively classified as a lymph node is seen, additional diagnostic imaging will be necessary to prove that the mass is in fact a lymph node and not a small cancer. In this scenario not having any prior mammograms is a hindrance. If prior mammograms were available and the mass is in fact a lymph node, we would be able to show that the mass has not changed over a period of time and can safely call the small mass benign (non-cancerous).
- A previously visible lymph node increases in size or shape as seen on the screening mammogram.
- Markedly enlarged lymph nodes may be felt as a lump. Generally, enlarged lymph nodes that are felt by the patient are found in the axilla. The lymph nodes in the breast are generally too small and malleable for patients to feel, even when abnormal.
To diagnose a normal lymph node on a mammogram and/or breast ultrasound, we are looking for the central fatty hilum and thin outer cortex. The kidney bean shape is also nice to see but not a requirement to make the diagnosis. When lymph nodes are small the central fatty hila may not be visible on the mammogram. 3D mammography has improved visualization of the central fatty hila for smaller lymph nodes, but not in all cases. If the lymph node appearance is not definitive by mammography, an ultrasound will then be performed. Fortunately, or unfortunately, depending on your perspective, small normal lymph nodes can be difficult to see by ultrasound.
The fatty hilum is the prominent component of the normal lymph node. This fatty hilum can easily blend into the normal fatty tissue of the breast. If the cortex is thin enough, it is nearly impossible to distinguish the normal lymph node from the surrounding fatty breast tissue. In this scenario, we are reassured that the original mammogram finding represents a lymph node if we cannot find ANY mass– be it a lymph node, cyst, small cancer, or fibroadenoma– on ultrasound in that region of the breast. Depending on the radiologist, a few additional mammograms may be performed at 6-month intervals to ensure that the presumed lymph node does not increase in size on the mammogram.
In the second and third scenarios, it must be determined why the lymph node has enlarged on the screening mammogram or has led to a new lump felt by the patient. Lymph nodes can enlarge for many reasons. Infection, inflammation, recent vaccination in the arm, metastasis (spreading cancer), and cancer of the lymphatic system (i.e. lymphoma) are a few of the more common reasons lymph nodes enlarge. As stated before, the lymph nodes serve as the filtration system of the lymphatic system. Anything that increases the flow of the lymphatic system can cause transient or permanent changes in the size and appearance of the lymph nodes. Not only can lymph nodes increase in size, but the cortex will also increase in thickness and the fatty hilum will be partially or completely displaced or replaced by the thickening cortex. The changes in cortex thickness are best visualized with breast ultrasound.
There are many ultrasound features we are looking for in the lymph node to try to decide if the changes are due to non-cancerous causes vs. cancerous causes. However, if there is no known history of trauma or infection, we usually recommend an ultrasound-guided breast biopsy for any lymph node that has enlarged by imaging or is newly felt by the patient, even if the imaging features are not overly suspicious. This is a conservative approach, and most of the biopsies reveal normal lymph node tissue, or “reactive” lymph node, meaning it is more active due to an infection or inflammation affecting the lymphatic system.
However, it is possible to have breast cancer that is not visible on the mammogram and has spread to local lymph nodes, causing them to enlarge. In this case, the pathology results show breast cancer cells in the lymph node, confirming that more imaging is necessary to find breast cancer. Lymphoma may also be identified at the time of biopsy of an enlarged lymph node in the breast or axilla. If there is a known history of trauma, infection, or recent vaccination in the same arm as the lymph node(s) in question, we will likely have the patient return for follow-up imaging at shorter intervals to ensure that the lymph node decreases in size or at least does not continue to enlarge.
Seeing a lymph node on a patient’s first mammogram may prompt additional imaging to ensure that the mass is in fact a normal lymph node. Additionally, any changes in previously seen normal lymph nodes will also prompt additional imaging evaluation. However, if there is no known personal history of cancer, the vast majority of lymph nodes encountered in the breast are benign. Once we establish a normal baseline appearance for intramammary and axillary lymph nodes through imaging or possibly biopsy, we can be confident on future mammograms that the mass represents a benign lymph node as long as no imaging changes have occurred.