Multiple Lung Nodules

What Does it Mean if I Have Multiple Lung Nodules?

female doctor looking at a chest x-ray
What are the causes of multiple lung nodules and what are the chances it's cancer?.

If you’ve been told that you have multiple lung nodules after a test like an x-ray or a CT scan, it can be very frightening. What exactly are lung nodules (also called pulmonary nodules) what are some of the possible causes, and what might you expect as you work with your doctor to determine the cause?

Definition of Multiple Lung Nodules

Multiple lung nodules, in contrast to a solitary pulmonary nodule, include the finding of two or more nodules within the lungs.

Lung nodules are defined as “spots” on the lung that are 3 cm (about 1 ½ inches) or less in diameter. If an abnormality seen in the lungs is larger than this, it is called a lung mass

Causes of Multiple Lung Nodules (Differential Diagnosis)

Unfortunately, the most common cause of multiple lung nodules is cancer that has spread (metastasized) to the lungs from other regions of the body. That said, there are many benign (non-cancerous) causes of multiple nodules as well. 

Multiple nodules are more likely to be cancerous if they are greater than or equal to 1 cm in diameter (about half an inch.)  Smaller nodules less than 5 mm, especially if they are found along the fissures between the lobes of the lung or along the tissue that lines the lung (the pleura) are more likely to be benign (non-cancerous.)

Some possible causes of multiple nodules include:

  • Malignant (Cancerous) Tumors - As noted above, metastatic cancer to the lungs from other regions of the body is the most common cause of multiple lung nodules, especially if you have a history of cancer. Nearly any cancer can spread (metastasize) to the lungs. The most common of these include breast cancer, colon cancer, prostate cancer, and bladder cancer. In addition to lung cancer, cancers such as lymphomas, and Kaposi's sarcoma, may also lead to multiple nodules.
  • Lymph nodes - Lymph nodes may be enlarged and show up for many reasons. They are usually located, however, not scattered within the lung tissue, but along the lining of the lungs and the fissures that separate the lungs.
  • Benign Tumors - Such as hamartomas. Hamartomas are benign tumors that are made up of fat, cartilage, and connective tissue -- tissues that normally occur in the lungs, but grow in a disorderly way. These are the most common type of benign tumor found in the lungs.
  • Autoimmune - Conditions such as Wegeners granulomatosis, sarcoidosis, eosinophilic granules, and rheumatoid arthritis can appear as multiple nodules.
  • Infections - Several types of infections can result in the appearance of multiple nodules on a scan of the lungs. These include bacterial infections such as septic nodules (spread of infection via the bloodstream from another area of the body, tuberculosis, and nocardiosis, fungal infections such as aspergillosis, histoplasmosis, coccidiomycosis, and cryptococcosis, and parasitic infections such as echinococcosis (hydatid cysts), and paragonimus (liver flukes).
  • Inflammatory (pneumoconiosis) – better known as black lung disease (coal miner’s lung), silicosis.
  • Scars - For example, scars may form after previous severe episodes of pneumonia or after tuberculosis.

For a more comprehensive list of possible causes of lung nodules - both solitary and multiple, check out this article on the differential diagnosis of lung nodules.

How Common Are Lung Nodules?

Lung nodules are fairly common, being found on 1 in 500 chest x-rays and 1 in 100 CT scans.

In one study, 51 percent of smokers aged 50 and older had lung nodules on CT scans.

What Tests Might My Doctor Recommend?

Since the most common cause of multiple lung nodules is cancer that has spread from other parts of the body, tests may be recommended to look for a primary cancer – that is, a cancer in another part of the body that could have spread to the lungs. Examples of these may include a mammogram to look for a breast tumor or a colonoscopy to look for a colon tumor.

Your doctor may also recommend tests to further understand the nodules that are in your lungs. These may include CT scans, MRI studies, or a PET scan. A recent small study found that a combination of CT and PET scans helped in determining the cause of multiple nodules more accurately than either of these tests alone. If the cause of your lung nodules is not obvious based on other studies, a lung biopsy may be done to get a sample of one of the lung nodules in order to determine the cause.

Other tests will depend upon the possible causes of your nodules, for example, blood tests may be ordered to evaluate for infectious and inflammatory causes.

What Are the Chances That My Lung Nodules Are Cancer?

As noted above, if you have a history of cancer, the chance that your lung nodules are cancerous is higher. Larger lung nodules -- those greater than 1 cm (or ½ inch) in diameter -- are more likely to be malignant, whereas smaller nodules are more likely to be benign. If you are in good overall health and nodules are discovered incidentally (that is, accidentally) on a study done for some other reason, your nodules are more likely to be benign. Certain descriptions on x-ray studies may also suggest whether or not your nodules are likely to be cancerous. If your nodules are described as “calcified” it is more likely that they have a benign cause. In contrast, nodules described as having a “ground glass” appearance are more likely to be malignant.

(It's important to note that non-smokers can get lung cancer too, and lung cancer in never smokers is actually the 6th leading cause of cancer deaths in the United States.)

Benign vs Malignant Tumors

If you are working with your doctor to determine if a nodule you have is cancer, you're probably very frightened and confused. It probably feels like everyone is speaking in a foreign language as well.   There are several characteristics doctors look at to try to decide if a nodule is cancerous, such as whether or not it has calcifications, whether there is "cavitation" and more.  

This article discusses some of the differences between benign and malignant tumors, and may help answer some of your questions as well.

Treatment of Multiple Pulmonary Nodules

The treatment of your nodules will, of course, depend on what they are - the cause. Benign nodules may be left alone, or treated with antiparasitic drugs if due to an infection, or with drugs to treat rheumatoid arthritis in the case of rheumatoid nodules.

If your nodules are due to the spread of cancer, the treatment of the underlying cancer will be the goal of therapy. For some nodules related to spread of cancer, physicians are evaluating whether or not metastasectomy - removing the nodules - is helpful. In some cases, it's been found that this treatment can prolong survival, and in rare cases has even resulted in a cure.


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