Enlarged lymph nodes in the axilla or arm pit on one side are more concerning then on both sides. These are often seen on CT scans as enlarged, often 1 cm or more when measured on the shortest side. They may also look abnormal or be clustered in increased numbers.
Lymph nodes contain immune cells and are glands that filter a fluid called lymph that circulates throughout channels in your body. Lymph nodes help protect your body from infection, abnormal diseased cells or substances. Lymph nodes enlarge when they accumulate the invaders or diseased cells.
Swollen or enlarged lymph nodes mean the gland is active in doing it’s job. Often the swollen glands will be near the process causing them, but in some cases it may be a problem throughout your body. Some common causes of enlarged lymph nodes are infections such as a cold, ear infection, strep throat or a more systemic condition like lupus or HIV. Any cancers that spread can cause lymph nodes to swell. A primary cancer of the lymphatic system is called lymphoma.
In the arm pit, the most concerning condition would be cancer. This can be spread from other parts of your body like the breast or a primary cancer like lymphoma. Infections of the breast or arm can also cause the lymph nodes to enlarge. Certain systemic conditions will cause enlarged lymph nodes but these will be more widespread.
Your doctor will best determine the cause of the enlargement by taking a careful history and examining the area. It will be more concerning for cancer if no infection or inflammatory condition is found or if the lymph nodes have been growing over time. If you have a history of a cancer elsewhere in the body, then cancer becomes more concerning.
Further testing may include non invasive imaging like a pet scan. Abnormal cancerous lymph nodes will light up more on this test then inflamed nodes but there is unfortunately overlap between the two. Your doctor may order a CT scan of your body to make sure there are no other suspicious areas. A biopsy will allow for the most accurate diagnosis since this will allow to see the actual cells involved.