Multiple Lung Nodules: Causes and Diagnosis

Multiple pulmonary nodules can be benign or malignant

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If you've had a chest X-ray and have been advised that the radiologist spotted "multiple lung nodules" or "multiple pulmonary nodules," the first thing that may come to mind is cancer. And while cancer may be the cause, there are other possible explanations. Let's look at the definition of a lung nodule, how it differs from a mass and some of the characteristics of a nodule that may suggest it is either cancerous or non-cancerous.

Causes of Multiple Lung Nodules
Illustration by Jessica Olah, Verywell

Understanding Multiple Lung Nodules

Lung nodules (also known as pulmonary nodules) are typically seen as "spots” or "lesions" on an X-ray and will measure three centimeters (around one and a half inches) or less in diameter. Multiple pulmonary nodules (MPN) simply mean that two or more lesions were spotted as opposed to a solitary pulmonary nodule (SPN).

Lung nodules are fairly common, occurring in one of every 500 chest X-rays. In one study, 51 percent of smokers age 50 and older had MPN on a lung scan.

Characteristics of Cancerous and Non-Cancerous Nodules

When multiple pulmonary nodules (MPN) are seen on a scan, the first assumption is cancer. Cancer is the most common cause of MPN and is usually the result of metastasis (when cancer spreads from a primary tumor to the other parts of the body).

But the "most common" doesn't mean "only." There are nearly as many benign (non-cancerous) causes of MPN as there are malignant (cancerous) ones. Moreover, the way the nodules look on a scan can suggest which type they are.

Multiple nodules are more likely to be cancerous if they are 1 centimeter (roughly 1/4 inch) or more in diameter. Nodules less than 5 millimeters (1/4 inch), especially when distributed in the fissures between the lobes of the lung or along the tissue that lines the lung, are more likely to be benign.

Also, nodules that are described as "calcified" are more likely to be benign. By contrast, nodules described as having a "ground glass" appearance are more likely to be malignant.

Causes

Multiple pulmonary nodules may be caused by malignant or benign diseases. Some of the more common causes include the following.

causes of multiple lung nodules
Illustration by Jessica Olah, Verywell
  • Metastatic cancer is the most common cause of MPN, especially in persons with a family history of cancer. It is most associated with metastases to the lung from breast cancer, colon cancer, prostate cancer, and bladder cancer. MPNs have also been seen with metastases from medullary carcinoma of the thyroid, melanoma, prostate cancer, squamous cell cancers of the head and neck, and others.
  • Primary cancer may also be the cause of MPNs, with lung cancer (particularly a type of lung adenocarcinoma formerly known as bronchioloalveolar carcinoma) and lymphomas most commonly present.
  • Lymph nodes are located along the lining of the lung (called the pleura) and, like all lymph nodes, can become enlarged during infection. This can sometimes be read as a spot on an X-ray.
  • Benign tumors can also develop in the lungs, the most common of which are tissue malformations called hamartomas. Other types of benign tumors include fibromas, bronchial adenomas, hemangiomas, and blastomas.
  • Autoimmune disorders are those in which the immune system inadvertently attacks the body's own cells. They can sometimes form granulations and growths that appear as spots on an X-ray. Causes include rheumatoid arthritis, sarcoidosis, and eosinophilic lung diseases.
  • Infections of the lung can sometimes appear as multiple or diffuse nodules on a scan. These include bacterial infections such as tuberculosis, fungal infections such as histoplasmosis and cryptococcosis, and parasitic infections such as echinococcosis.
  • Coal worker's pneumoconiosis, also known as black lung disease, still occurs in around 2 percent of coal miners and is associated with the formation of one- to two-millimeter nodules. There has been a recent increase in the incidence of severe black lung disease (progressive massive fibrosis) in young coal workers in Appalachia. Silicosis may also cause MPNs.
  • Scars from past infection can also show up on chest X-rays, often in persons who never realized they had an infection.

Diagnosis of Multiple Pulmonary Nodules

Since the most common cause of MPN is metastatic cancer, doctors will often begin their investigation by looking for the primary (original) tumor.

Depending on what the early diagnostics say, the doctor may order a mammogram and/or breast MRI to look for a breast tumor or a colonoscopy to look for a colon tumor.

Additional imaging tests can also be used, including:

Studies have attempted to evaluate the best strategy for diagnosing MPNs.

It's thought that the combination of CT and PET scans may be more useful in determining the cause of multiple lung nodules than the individual tests on their own.

If the cause of your nodules is still unclear after imaging, a lung biopsy may be performed to obtain a tissue sample.

The distribution of lung nodules can also be helpful in narrowing down potential causes. For example, silicosis and coal worker's pneumoconiosis most often cause nodules that are predominant in the upper lobes.

Treatment of Multiple Lung Nodules

The treatment of MPN will depend on the cause. Benign nodules often may be left alone. Nodules related to an infection can be treated with the appropriate antibiotic, antifungal, or antiparasitic.

If metastatic cancer is diagnosed, the mainstay of treatment would be prescribed based predominately on the location of the primary tumor. For example, for nodules related to metastatic breast cancer, treatment may include chemotherapy, endocrine therapy, and other approaches depending on the type of molecular makeup of the tumor. Newer, targeted approaches to therapy, when a targetable mutation or gene alteration is present, are sometimes offering longer survival times with fewer treatment effects than ever before.

Newer generation techniques such as stereotactic body radiotherapy (SBRT) may be used to treat a single, and sometimes several, metastases. In this setting of a limited number of metastases (oligometastases), treating the nodules (metastases) with a curative approach may sometimes improve survival.

A Word From Verywell

No matter your medical history, being told that you have multiple lung nodules is frightening. We won't give you false hope, and do admit that many of these nodules are cancerous. But keep in mind that there are many benign causes. From autoimmune conditions to fungal infections, many people fear they have cancer and then learn that their nodules have a very treatable cause.

Even if your nodules are cancerous, there are almost always treatment options available. Perhaps not treatments that are curative, but treatments that can reduce symptoms and often extend life.

The best thing you can do, other than gathering your support system together and learn to receive love and help, is to be your own advocate in your care. As we mentioned, even metastatic cancer to the lungs is often treatable, and those treatment options are changing rapidly. We've learned that being an active part of your health care team not only empowers you but taking your place in the driver's seat of your health care may affect your outcome as well.

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  1. Sato, Y.; Fujimoto, D.; Morimoto, T.; et al. Natural History and Clinical Characteristics of Multiple Pulmonary Nodules with Ground Glass Opacity. Respirology. 2017; DOI: 10.1111/resp.13089

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