Healthy Living

Causes of Lung Nodules


What are lung nodules?

Lung nodules are spots present on the lung. These spots are usually around 1.5 inches or three centimeters in diameter. Lung nodules seen on imaging tests are often called as coin lesions. If a lung X-ray shows spots that are more than three centimeters, it is regarded as a lung mass and not a nodule. These lung findings are more likely to be malignant. For lung nodules to be seen on a chest X-ray, they need have a size of at least one centimeter. When using a CT scan, lung nodules need to be around 1-2 millimeters for them to be seen.

Each year, around 150,000 lung nodules are detected in people living in the United States. Lung nodules are common and are usually found on one in every 500 chest X-rays. When a CT scan is used, lung nodules are found on one in every 100 chest scans. It is estimated that half of the people who smoke and are 50 years old and above are likely to have nodules on a chest CT scan. When chest X-rays detect potential lung nodules, a CT scan must be performed for confirmation. There are cases in which small cancers are unidentified on chest X-rays. 


Lung nodules can either be malignant (cancerous) or benign (noncancerous). Most lung nodules with a size smaller than two centimeters in diameter are benign. Benign lung nodules can have a number of causes, but many cases are a result of lung inflammation due to infection or inflammation that leads to illness in the body. Lung nodules may also indicate active scarring or the formation of scar tissue before inflammation.

1. Infections

Lung nodules may be caused by the following infections:

  • Bacterial Infections - Tuberculosis and other mycobacterial infections
  • Parasitic Infections - Ascariasis (roundworm infection), echinococcosis (hydatid disease)and paragonimiasis (lung fluke disease)

2. Inflammation

Conditions that can lead to granulomas (small areas of inflammation in the tissue) may include:

3. Benign Tumors

The following benign tumors may appear as lung nodules on a chest X-ray:

  • Hamartomas - The most common benign tumors in the lung, which consist of fat, cartilage, smooth muscle, and connective tissue.
  • Fibromas - Also called fibroids or fibroid tumors, are benign tumors that comprise connective, fibrous tissue.
  • Neurofibromas - These are benign nerve tumors that grow on the nerves all over the body.
  • Hemangiomas - Benign tumors that are formed by a group of excess blood vessels.

4. Malignant Tumors 

Lung nodules may also be cancerous:

  • Lung Cancer - A malignant lung tumor with uncontrolled growth of cells in lung tissues.
  • Carcinoid - A small cancerous tumor that gradually grows.
  • Lymphoma - A malignant growth that contains lymphoid tissue.
  • Metastatic Tumors - Tumors that spread to other areas of the body.
  • Sarcoma - A malignant tumor of the connective tissues.

5. Metastases 

Metastases from other types of cancer, such as breast cancer, bladder cancer, prostate cancer, and colon cancer may cause lung nodules.

6. Other Benign Nodules 

Other possible causes of lung nodules include:

  • Pulmonary Infarctions - Occurs when areas of the lung tissue are without blood supply.  
  • Atelectasis - The complete or partial collapse of a lung.  
  • Pulmonary fibrosis - A progressive and chronic disease of the lungs, wherein the air sacs become stiff and scarred. It causes breathing problems and difficulty getting sufficient oxygen into the blood.
  • Amyloidosis - A disease that occurs when amyloid (an abnormal protein) accumulates in the organs and tissues.


A nodule present in the lung may not cause any symptoms. They are often accidentally found when a person takes an X-ray examination. However, if the symptoms are present, they include difficulty breathing or shortness of breath, coughing up blood, wheezing, or lung infections. 


Lung nodules are often initially detected on a chest X-ray. Further testing may be required to confirm the nodules and to help identify if they are cancerous or not. The doctor usually takes your medical history along with asking questions related to smoking, secondhand smoke exposure, or exposure to certain environmental chemicals.

The size and shape of the lung nodule are then examined. There would be an increased risk of having malignant lung nodules if they are large and irregularly shaped. To obtain more information about the nodules, a CT scan may be performed. It produces clearer images of the nodule and more detailed information about its size, shape, and location. When nodules are smooth and small, the doctor usually monitors their growth to observe whether changes in shape and size take place. A repeat CT scan can be done at regular intervals. Nodules that remain small without any changes for two years are unlikely to be malignant.

Aside from a CT scan, a tuberculin skin test may be performed to screen for tuberculosis. Blood may also be drawn for further tests. More tests may be ordered if the doctor suspects a malignant nodule. The following diagnostic tests may be used to rule out cancer:

  • Positron Emission Tomography (PET Scan): This imaging scan uses a tracer (a radioactive substance) to identify lung diseases such as lung cancer.
  • Biopsy: If the PET scan results are inconclusive, the doctor may order a biopsy. In this procedure, a tissue sample is collected from the lung nodule. The collected sample is then examined under the microscope to look for cancer cells. A biopsy can be done by inserting a needle near the lung through the chest wall. Another procedure called bronchoscopy can also be done, wherein a scope is inserted through the mouth or nose and into the airways to collect a tissue sample. 


A benign lung nodule does not usually require treatment. If an infection or inflammation in the body is detected, treatment is often based on the identified condition and its symptoms. A malignant nodule may be surgically removed if the patient is fit and cancer has not spread. 


It is safe to say in most cases that lung nodules are not malignant if they remain small in size over a period of two years. Moreover, no further testing is required when you reach this point. However, if one nodule is found to be cancerous, it is more likely in its early stages. Treatment usually offers increased chances of cure. 

Treatment will depend on the original cancer if lung nodules are caused by metastasis. Other major causes of lung nodules may include inflammatory conditions, infections, and benign cysts or tumors. Treatment will also depend on these underlying conditions.