Pulmonary, or lung, nodules are small, round masses of tissue that grow in the lung. Most are less than half an inch in diameter. They’re denser than ordinary lung tissue, so they show up as a white spot on an X-ray or CT scan.

The causes of lung nodules include:

• Scar tissue
• A current or past infection
• Air pollution or other lung irritants
• Inflammation from diseases like rheumatoid arthritis or sarcoidosis
• Cancer

Risk factors for lung nodules include:

• Smoking tobacco or second-hand smoke
• Exposure to radon gas or other air pollution
• Age
• Family history of lung cancer
• Scarring of the lungs

Lung nodules usually don’t cause symptoms. Doctors often find them when they order a chest X-ray or CT scan for some other reason. If you have a high risk of lung cancer, your doctor may order a lung cancer screening, which can also find pulmonary nodules.

Doctors group lung nodules into 2 categories: cancerous (malignant) and non-cancerous (benign).

Benign and malignant nodules look different. You may have more than one lung nodule, so doctors will want to look at all of them.

Non-cancerous nodules tend to be smaller, with a smooth, round shape. They’re solid and grow very slowly. Most lung nodules are benign, meaning they aren’t cancerous. But your doctor may want to run some tests to make sure.

Malignant nodules are larger and grow faster than benign ones. They tend to look rougher and spikier, not smooth. They aren’t as solid as benign nodules. Fewer than 5% of all nodules end up being cancerous.

When we find a lung nodule on an X-ray or CT scan, your doctor will order follow-up tests. These include:

• Repeat CT scan: Your doctor will have you do another CT scan in a few months to a year to see if the nodule has grown. The time frame depends on how likely it is that the nodule is cancerous, based on how it looks on the scan. 
• Lung cancer evaluation: If the nodule has grown, we may order a positron emission tomography scan. This test helps us know if the nodule is cancerous and checks the rest of the body for cancer.
• Lung biopsy: We take a sample of the nodule tissue to test for cancer. We use either a long, thin tube (bronchoscope) or a thin hollow needle. 
• Monitoring: We continue to check your lung nodules at regular intervals to see if they’ve grown or show any other signs of becoming cancerous. If there's no growth in a 2-year period, it's safe to stop watching the nodules.

If the nodule is cancerous, treatments include:

• Removal procedures: If there’s a high chance that it’s cancerous, we may remove the nodule and surrounding lung tissue. We typically remove cancerous lung nodules with minimally invasive surgery, especially if they’re small and haven’t spread elsewhere. 
• Cancer treatment: We use a mix of surgery, radiation, and cancer medicines, including chemotherapy, immunotherapy, and targeted therapy, to treat lung cancer. Your care plan depends on your lung cancer and how advanced it is.