What Causes Multiple Nodules in the Lungs?

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Having multiple lung nodules means you have two or more lesions in your lungs. Multiple lung nodules are also called pulmonary nodules. These lesions can be seen on an imaging scan like an X-ray. You may not have any symptoms of multiple lung nodules.

If you've had a chest X-ray and learned that you have multiple, lung nodules, you might worry it means you have cancer. If you only have one lung nodule (solitary pulmonary nodule), it probably is not cancer. However, if you have several or many lung nodules, the risk of cancer increases.

This article will go over what causes multiple lung nodules and how they can be diagnosed. You will also learn how multiple lung nodules are treated.

What Are Multiple Lung Nodules?

Having multiple lung nodules simply means you have more than one nodule in your lungs. Although multiple lung nodules can be cancerous, they are more likely to be benign than malignant.

Non-cancerous lung nodules can form after there has been inflammation of some kind in the lung. These nodules start as a small clump of cells called a granuloma. Over time, the granuloma can harden or "calcify," forming a lung nodule. 

A cancerous lung nodule forms when cells develop changes or mutations. These changes sometimes happen for unknown reasons and are sometimes related to previous damage caused by something you inhaled, such as cigarette smoke. The changes cause the cells to begin multiplying abnormally, forming a tumor. Cancerous nodules in the lung can also form when cancer cells spread to the lungs from a primary tumor in another part of the body (metastasis).

Causes

Multiple lung nodules can be caused by benign or malignant diseases. Here are some of the most common causes of lung nodules.

causes of multiple lung nodules
Illustration by Jessica Olah, Verywell

Benign Lung Nodules

There are more noncancerous (benign) causes of multiple lung nodules than cancerous (malignant) ones.

  • Mediastinal lymph nodes are located along the lining of the lung. Like all lymph nodes, they can become enlarged during infection. This can sometimes be seen as a spot on an X-ray.
  • Benign tumors can also develop in the lungs. The most common are tissue malformations called hamartomas. Other types of benign tumors include fibromas, bronchial adenomas, hemangiomas, and blastomas.
  • Autoimmune disorders occur when 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.
  • Lung infections can sometimes appear as solitary or multiple spread-out (diffuse) nodules on a scan. Common lung infections include bacterial infections such as tuberculosis, fungal infections such as cryptococcosis, and parasitic infections such as echinococcosis.
  • Coal workers' pneumoconiosis, also known as black lung disease, occurs in around 2% of coal miners. People with the disease often have 1-millimeter to 2-millimeter lung nodules. There has been an increase in the incidence of severe black lung disease (progressive massive fibrosis) in young coal workers in Appalachia.
  • Scars from past infections can also show up on chest X-rays as nodules. Often, people never knew they were sick.

Cancerous Lung Nodules

Diagnosis

Most lung nodules do not cause any symptoms. Although some people do experience coughing and wheezing or shortness of breath, many only find out they have lung nodules when they're seen on a scan.

Multiple lung nodules look like spots or lesions on an X-ray. They usually measure 3 centimeters (roughly 1.2 inches) or less in diameter. Multiple lung nodules are a common finding, occurring in between 3.9 and 6.6 of every 1,000 chest X-rays in the United States.

Cancer is a concern whenever there are multiple lung nodules seen on a scan. Although lung nodules are more likely to have one of many different benign causes, cancer is still the single most common cause of multiple lung nodules.

The way that the nodules look on a scan can give providers hints about which type they are.

More Likely to Be Cancerous
  • Multiple nodules that are 8 millimeters (mm), roughly 1/4 inch, or more in diameter

  • Nodules described as "non-calcified" (with evenly distributed "ground-glass" appearance)

More Likely to Be Benign
  • Nodules that are less than 5 mm (1/5 inch) are more likely to be benign, especially when distributed in the fissures between the lobes of the lung or along the tissue that lines the lung

  • Nodules described as "calcified" (seen on X-ray with random spots and flecks)

The way the lung nodules are arranged and spread out (distributed) can also be helpful in narrowing down possible causes. For example, coal workers' pneumoconiosis most often causes nodules that are predominant in the upper lobes. In lymphoma, the nodules are usually around the airways.

Cancerous lung nodules are more likely to be metastatic, meaning they spread to the lungs from somewhere else in the body. Providers will usually start by looking for the primary (original) tumor. Depending on what they find, a provider may order other tests—for example, mammogram or breast magnetic resonance imaging (MRI) to look for a breast tumor, or a colonoscopy to look for a colon tumor.

Other tests that might be used after finding multiple lung nodules include the following:

Radiologists usually prefer a combination of CT and PET scans for figuring out the cause of multiple lung nodules rather than doing each test individually.

If the cause of multiple lung nodules is still unclear when the imaging tests are done, a sample of tissue from your lung (lung biopsy) can be taken.

Treatment

The treatment for multiple lung nodules depends on the cause. Benign nodules can often be left alone. Nodules related to an infection can be treated with the appropriate antibiotic, antifungal, or antiparasitic drugs.

If metastatic cancer is diagnosed, treatment is based on where the tumor is. Cancer's spread is also a factor when deciding on treatment. For example:

Summary

Being told that you have multiple lung nodules can be frightening, especially if you don't have any symptoms and are worried you could have cancer. Keep in mind that multiple lung nodules are not always cancer and may not even require treatment.

If your lung nodules are cancerous, there are usually treatments. They may not be curative, but they can reduce symptoms and help you live longer.

Frequently Asked Questions

  • What percentage of multiple lung nodules are cancerous?

    About 40% of lung nodules turn out to be cancer.

  • Can COVID-19 cause multiple lung nodules?

    Researchers studying people with COVID-19 have seen cases where people with the infection have lung nodules. Some people just have nodule while others may have several.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Lynne Eldridge, MD
 Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."