What Are Multiple Lung Nodules?

Cancer is common, but other benign causes exist

Doctor reviewing x-ray
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If you've had a chest X-ray and have been advised that the radiologist spotted "multiple lung nodules," the first thing that may come to mind is cancer. And while, yes, cancer may certainly be the cause, there may be other explanations, as well.

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 nodules are seen on a scan, the first assumption is cancer. It 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 "most common" doesn't mean "only." There are 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 one centimeter (roughly 1/4 inch) or more in diameter. Nodules less than five 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.

Moreover, if your nodules are described as "calcified," it is more likely to be benign. By contrast, nodules described as having a "ground glass" appearance are more likely to be malignant.

Causes of Multiple Lung Nodules

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

  • Cancer is the primary cause of MPN, especially in persons with a family history of cancer. it is most associated with metastasis of breast cancer, colon cancer, prostate cancer, and bladder cancer.
  • 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 eosinophilia.
  • 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.
  • 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.
  • Scars from past infection can also show up on chest X-rays, often in persons who never realized they had an infection.

Diagnosis of Mulitple 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 to look for a breast tumor or a colonoscopy to look for colon tumor.

Additional imaging tests can also be used, including:

Studies have suggested that the combination of CT and PET scans may be more useful in determining the cause of MPNs 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.

Treatment of Multiple Lung Nodules

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

If metastatic cancer is diagnosed, the treatment would be prescribed based predominately on the location of the primary tumor. Newer generation techniques such as stereotactic body radiotherapy (SBRT) may be used to treat a single, and sometimes multiple, metastases. Newer, targeted approaches to therapy are offering longer survival times with few treatment effects than ever before.

Sources:

Baldwin, D.; Callister, M.; and Guideline Development Group. "The British Thoracic Society guidelines on the investigation and management of pulmonary nodules." Thorax. 2015; 70(8):794-8.

Callister, M. and Baldwin, D. "How Should Pulmonary Nodules be Optimally Investigated and Managed?" Lung Cancer. 2016; 91:48-55.

de Hoop, B.; van Ginneken, B.; Gietema, H.; and Prokop, M. "Pulmonary perifissural nodules on CT scans: rapid growth is not a predictor of malignancy." Radiology. 2012; 265(2):611-6.

Detterbeck, F.; Marom, E.; Arenberg, D.; et al. "Cancer Presenting as Multiple Nodules with Ground Glass or Lepidic Features or a Pneumonic Type of Involvement in the Forthcoming Eighth Edition of the TNM Classification." Journal of Thoracic Oncology. 2016; 11(5):666-80.

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 (Epub ahead of print).

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