Lung nodules (also called pulmonary nodules) are spots or shadows that may show up in the lung during a chest imaging study, usually a CT scan. A lung nodule typically appears as a white spot and are under three centimeters in size. Nodules larger than three centimeters are considered lung masses.

It’s not uncommon to find a lung nodule. In fact, roughly 50 percent of CT scans in adults will reveal at least one lung nodule in their lifetime, according to the American Thoracic Society (ATS).

Possible causes

Although a lung nodule could be an early cancer, less than 5 percent of small nodules turn out to be early lung cancer (malignant nodule), according to the ATS.

Other, more likely causes of lung nodules include:

• Noncancerous (benign) tumors or cysts
• Inflammatory diseases
• Scar tissue from an old infection
• Congenital lung abnormalities

Lung nodules are often too small to cause symptoms like pain or breathing problems, and most are found when an imaging study is done to evaluate chest symptoms or as part of a screening exam.

What happens after a pulmonary nodule or nodules is discovered depends on three factors:  

• How the nodule looks on the imaging study
• Personal risk factors for lung cancer 
• If the nodule grows over time

Because a biopsy can cause complications like bleeding, infection or a collapsed lung, it’s only done if the risk of cancer is high enough to justify the risk of biopsy.

Nodule size is the most important factor in assessing risk. Based on a review in Annals of Thoracic Medicine, nodules that are smaller than 6 millimeters have a less than 1 percent risk of being cancerous. 

One of the most important things that doctors do to evaluate a nodule is look at any available old lung imaging studies. If a nodule was present in a past study and it hasn’t grown over time, it’s unlikely to be cancerous. 

Nodules located in an upper lung lobe are more likely to be cancerous and those that show strands extending out from the surface—called spiculations—are more dangerous.

Personal risk factors for lung cancer are also important to consider. These risk factors may increase the risk of a nodule being cancerous:

• History of smoking
• Older age
• A history of previous cancer, including lung, head and neck, pancreatic or bladder cancer
• A family history of lung cancer
• A history of treatment with radiation therapy or chemotherapy for lymphoma
• Occupational exposure to dusts, metals or fumes that have been linked to lung cancer
• Lung disease, like COPD or pulmonary fibrosis
  

Once your doctor has evaluated the risks, options may include no additional tests, scheduling a follow-up CT scan, scheduling a more sensitive imaging scan (PET scan), or performing a biopsy to diagnose the nodule. Some of the options are:

• If you’re young and the nodule is small, or a past imaging study shows no change in the nodule over two years, you may not need any further evaluation.
• If your doctor thinks a nodule is at all suspicious, you may have another CT scan scheduled in a few months to see if the nodule is growing.
• If your nodule is larger, your doctor may order a PET scan, because this type of study gives better detail for large nodules.
• If your nodule is high risk or if it grows on a follow-up imaging study, your doctor may schedule a biopsy.

A biopsy involves taking a sample of cells from a nodule, so cells can be checked under a microscope for signs of cancer (pathology exam). The biopsy may be taken through a tube placed down into the lung, called a bronchoscopy. If the nodule is in an outer area of the lung, a needle may be placed through the chest into the lung to remove tissue. If a nodule is very suspicious or difficult to reach, open surgery may be done to remove the nodule.

Even in the rare case where a biopsy does show cancer, nodules are often early cancers that respond better with treatment. To reduce your risk, quit smoking and let your doctor know if you develop any of these symptoms:

• A change or increase in cough
• Coughing up blood
• Shortness of breath
• Chest pain
• Unintended weight loss of 10 pounds or more