Causes of Lung Nodules Benign and Malignant

Common and Uncommon Causes of Lung Nodules

doctor speaking with patient
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 percent, 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.

    Continue Reading