What Are Solitary Pulmonary Nodules?

Could a Solitary Pulmonary Nodule Be Lung Cancer?

Chest x-ray showing a nodule with an arrow pointing at it
What are solitary pulmonary nodules and when could they be cancer?. A.D.A.M. Medical Encyclopedia

What exactly is a solitary pulmonary nodule, and what are the chances it iscancer?

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. What does it mean if you are diagnosed with a solitary pulmonary nodule?

What Is a 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. 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:

What Are Possible Causes?

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 cancersMetastatic cancer from cancers in other parts of the body, or lymphomas.
  • Infections (new and old) – Bacterial infections such as tuberculosis, Fungal infections such as blastomycosis, histoplasmosis, coccidiomycosis, and cryptococcosis, Parasitic infections including dirofilariasis, ascariasis.
  • Rheumatoid conditions – Diseases such as rheumatoid arthritis, sarcoidosis, Wegener granulomatosis.
  • Congenital conditions – Cysts, and abnormal development of arteries and veins in the lungs (AV malformation).

Learn more about the possible causes of lung nodules here.

What Are the Chances it Means Cancer?

Overall, the chance that a solitary pulmonary nodule is cancer is around 40 percent, but this varies depending upon several factors:

  • 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.
  • A history of cancer – Having a history of 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.
  • Size – The larger an SPN is, the more likely it is to be cancer.
  • 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.

More about the differences between benign and malignant nodules and masses:

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 2 years are considered benign and do not 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.
  • 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). Learn more in this article on understanding your lung biopsy.


National Institute of Health. Medline Plus. Solitary Pulmonary Nodule. Updated 02/02/16. https://medlineplus.gov/ency/article/000071.htm

Soubani, A. The evaluation and management of the solitary pulmonary nodule. Postgraduate Medical Journal. 2008. 84(995):459-66.

van Westeinde, S. et al. How to deal with incidentally detected pulmonary nodules less than 10mm in size on CT in a healthy person. Lung Cancer. 2008. 60(2):151-9.

Wahidi, M. et al. Evidence for the treatment of patients with pulmonary nodules: when is it cancer?: ACCP evidence-based clinical practice guidelines (2nd edition). Chest. 2007. 132(3 Suppl):94S-107S.

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