What Are Solitary Pulmonary Nodules?

Could They Be Lung Cancer?

X-ray of lungs

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Every year in the U.S., more than 150,000 people will be told they have a solitary pulmonary nodule, and this is expected to increase as more people have screening tests for lung cancer. There are many possible causes of a solitary pulmonary nodule, only one of which is lung cancer. What are the chances that a lung nodule is due to lung cancer, and what tests might your doctor recommend to find out?

Solitary Pulmonary Nodule: Definition

A solitary pulmonary nodule is defined as a single nodule (abnormality) seen on an x-ray or CT scan, that is less than or equal to 3 cm (1 ½ inches) in diameter. If a "spot" on the lung is larger than 3 cm it is considered a lung mass, and there is a greater chance that it is cancer. To be classified as a "solitary pulmonary nodule" it means that the nodule is surrounded by normal tissue, and no other signs that might suggest cancer (such as enlarged lymph nodes or a pleural effusion) are present. Solitary pulmonary nodules are usually found incidentally when an x-ray is done for another reason. They are fairly common, being found on roughly 1 in every 500 chest x-rays done.

If more than one nodule is present, the possible causes and recommended tests may be different. Learn more about the causes and evaluation of multiple pulmonary nodules.

Possible Causes of a Solitary Pulmonary Nodule

There are many causes of solitary pulmonary nodules (SPN), some being more common depending on age and geographical location. Some of these include:

  • Lung cancer: Early lung cancer can present as an SPN. When lung cancer is discovered at this stage, the chances for cure are much higher than they are at later stages.
  • Other cancers: Metastatic cancer from cancers in other parts of the body (such as breast cancer), or lymphomas may show up as a solitary pulmonary nodule, though most often lung metastases include multiple pulmonary nodules.
  • Infections (new and old): Bacterial infections such as tuberculosis, fungal infections such as blastomycosis, histoplasmosis, coccidiomycosis, and cryptococcosis, and parasitic infections such as dirofilariasis and ascariasis may cause an SPN.
  • Rheumatoid conditions: Diseases such as rheumatoid arthritis, sarcoidosis, and granulomatosis with polyangiitis can cause an SPN.
  • Congenital conditions: Cysts and abnormal development of arteries and veins in the lungs (AV malformations) can cause solitary pulmonary nodules.

These are only a few of the conditions which may cause a solitary pulmonary nodule. Learn more about the possible causes of lung nodules.

What Are the Chances That a Solitary Pulmonary Nodule Is Cancer?

Overall, the chance that a solitary pulmonary nodule is cancer is around 40 percent, but this varies widely for individual people depending upon several factors. These include:

  • Age: In younger people, an SPN is more likely to be benign, whereas, in individuals over age 50, they are more likely to be malignant (cancerous).
  • Tobacco use: A history of smoking raises the likelihood that an SPN is malignant. It's important to note, however, that people who smoke may have a benign lung nodule. Similarly, people who have never smoked may have lung cancer. At the current time, lung cancer occurs more commonly in former smokers and people who never smoked than in those who currently smoke. When people quit smoking, the risk of lung cancer remains elevated, even for those who haven't smoked for decades.
  • A history of cancer: Having a history of almost any type of cancer makes it more likely that an SPN is cancer.
  • Geographical location/foreign travel: In regions of the world where the infections above are common, an SNP is more likely to be due to an infection. For example, in some parts of the world, tuberculosis is the most common cause of an SPN. Fungal diseases such as coccidiomycosis are common in the Southwest region of the United States. It's not uncommon for the disease to be asymptomatic and only discovered because of the presence of a nodule.
  • Size: The larger the size of an SPN, the more likely it is to be cancer.
  • The appearance of the SPN on x-ray: Pulmonary nodules that look round and smooth on x-ray are more likely to be benign, whereas those that appear irregular are more likely to be malignant. There are several other radiological findings that radiologists look for to predict the likelihood that an SPN is malignant or not. For example, the presence of calcifications means the nodule is more likely to be benign.

What Happens After My Doctor Finds a Solitary Pulmonary Nodule?

After finding an SPN, the first thing your doctor will want to do is check to see if you have any old chest x-rays or CT scans that he or she can compare with your current tests. SPN's that have not changed in size for two years are considered benign and do not usually require further follow-up. If you do not have any previous chest x-rays, or if the nodule appears to be growing, there are several options that may be considered. Some of these include:

  • Observation: If an SNP is most likely benign, following it with repeat x-rays/CT scans may be recommended.
  • Repeat scans: Whenever medical tests are done, there is the chance that the results are in error. Sometimes a shadow, or how you are positioned when an x-ray is done, makes it look like there is something there when there isn’t. Repeating the test to make sure a nodule is indeed present may be recommended.
  • Further tests: Combining the results of a chest x-ray or CT scan with another test, such as a PET scan, may help your physician understand whether a nodule is something of concern. It's important to note that chest x-rays can miss cancers, and if there is any chance the SPN is malignant, your doctor will order a CT scan (or you can ask for one if it has not been ordered.)
  • Biopsy: The only way to know conclusively if an SNP is benign or malignant is to get a sample of tissue that can be examined under a microscope. Depending upon the location of the SNP, options that may be recommended include bronchoscopy, fine-needle aspiration biopsy (FNA), video-assisted thoracoscopic surgery (VATS,) or an open lung biopsy via thoracotomy. Learn more about understanding your lung biopsy.

    Solitary Pulmonary Nodules on Lung Cancer Screening

    With the approval and increasing availability of CT lung cancer screening, it's likely that solitary pulmonary nodules will be increasingly diagnosed. This poses a diagnostic dilemma at times, and recent studies suggest that less invasive measures of diagnosis, such as fine needle biopsies, may be of more benefit that both PET scans (which cannot give a tissue diagnosis) and more invasive procedures.

    If your SPN was found on lung cancer screening, learn more about predicting whether a nodule found on screening is cancer or not.

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