Causes of Lung Nodules Benign and Malignant

Common and Uncommon Causes of Lung Nodules

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What are some causes of lung nodules?. Hero Images/Digital Vision/Getty Images

What causes lung nodules? With 150,000 people being diagnosed with a lung nodule on a chest x-ray every year in the U.S., this is a common question. What are some of the benign (non-cancerous) and malignant (cancerous) causes?

First, it is important to define what a lung nodule is. A lung nodule is a “spot” on the lung that is less than 3 cm (or 1½ inches) in diameter. If a spot is larger than 3 cm, it is considered a lung mass, rather than a lung nodule.

The overall chance that a lung nodule is cancer is 40 percent, but that risk varies a lot depending on factors such as your age, if you have smoked, and what the nodule looks like on ​an x-ray.

The chance that a nodule on lung cancer screening is cancer is significantly less, perhaps less than 6 percent, but may be due to many of the same causes as those found otherwise.

Benign (Non-Cancerous) Lung Nodules

Benign lung nodules are responsible for 60 percent of “spots” seen on a lung x-ray. A nodule is more likely to be benign if:

  • You are young (in people less than 35 years of age, 99 percent of lung nodules are benign)
  • You are a non-smoker
  • You haven’t worked in occupations that raise the risk of lung cancer
  • The nodule is slow-growing (or grows very rapidly)
  • The nodule has calcifications
  • The nodule is smooth and regular in appearance
  • You don’t have a history of cancer in the past
  • You have traveled outside of the United States

    Causes of benign lung nodules include

    Inflammatory lung nodules (granulomas):

    Bacterial infections:

    Fungal infections:

    Parasitic infections:

    • Ascariasis (roundworm)
    • Echinococcus (hydatid cyst)
    • Paragonimus (oriental lung fluke)

    Benign lung tumors:

    • Bronchial adenomas
    • Hamartomas - Hamartomas are the most common cause of benign lung nodules.
    • Fibromas
    • Blastomas
    • Neurofibromas
    • Hemangiomas

    Other benign lung nodules:

    • Pulmonary infarcts (areas of lung tissue that have lost their blood supply)
    • Blood vessel abnormalities
    • Bronchogenic cysts
    • Atelectasis (collapse of part of a lung) - This is a common cause in people who have had lung conditions or lung surgery.
    • Anthracosilicosis
    • Pulmonary fibrosis (fibrosing alveolitis) – scar tissue in the lungs
    • Amyloidosis

    Malignant (Cancerous) Lung Nodules

    A lung nodule is more likely to be malignant if:

    • You are older – half of lung nodules in people over age 50 are malignant
    • You have a history of cancer in the past
    • You smoke or have smoked in the past
    • You work in an occupation where you are exposed to substances that cause lung cancer
    • The nodule is irregular or “spiculated”
    • The nodule is not calcified
    • The nodule is growing on repeat x-rays

    Causes of malignant lung nodules include

    As noted above, there are many possible causes of lung nodules. While the likelihood of cancer is less than 50%, it is very important to discuss a lung nodule carefully with your doctor. When lung cancer is found at an early stage, the chances of a cure is much higher than at later stages of the disease.


    MacMahon, H. et al. Guidelines for Management of Small Pulmonary Nodules Detected on CT Scans: A Statement from the Fleischner Society. Radiology. 2005. 237:395-400.

    National Library of Medicine. MedlinePlus. Solitary Pulmonary Nodule. Updated 08/01/15.

    Weinberger, S. Diagnostic evaluation and management of the solitary pulmonary nodule. UpToDate. Updated 05/25/16.

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