Understanding lung nodules: Determining risks and diagnosing

The lungs are an impressive organ. They're one of the biggest in the body, with a surface area about the size of a tennis court and about 1,500 miles of airways. The lungs are efficiently adapted to deliver oxygen and remove carbon dioxide to keep the body running smoothly. They circulate air exchange in about 17,000 or more breaths every day.

Yet, like other organs, issues can develop in the lungs. Lung nodules are a common condition that should be evaluated by medical professionals. Nodules are areas that are denser than normal lung tissue and usually don't cause symptoms.

Lung nodules often are discovered incidentally during imaging for other health conditions, such as a chest X-ray or CT scan. For example, lower lobe lung nodules often are found during a CT scan of the abdomen or pelvis.

Most lung nodules aren't cancer, and no additional treatment is necessary. However, some nodules are cancerous. All lung nodules should be carefully evaluated because lung cancer is the No. 1 cause of cancer deaths in U.S. adults. Early detection of lung cancer is critical. Like other cancers, it's more difficult to treat as it advances.

Risk factors

Lung nodules can vary in size and location within the lung. They're caused by various factors but usually are caused by scar tissue due to previous infections or irritants, inflammation or cancer.

The most common risk factors for lung nodules are tobacco use and radon exposure. About 90% of men who died from lung cancer had been smokers. Nonsmokers have a 20% to 30% higher risk of developing lung nodules or cancer if they have been exposed to secondhand smoke.

Radon exposure often is an overlooked risk factor. This odorless, invisible radioactive gas is the leading cause of lung cancer in nonsmokers. It's more common in the homes of some areas of the U.S.

Finally, people with suppressed immune systems are at a greater risk of developing lung nodules.

Risk stratification

Most lung nodules aren't cancer, but a careful review of the patient's risks and a nodule's characteristics is important to identify those that could be. This is called risk stratification.

When a nodule is identified, the health care team will review the patient's medical history, including past and current tobacco use, exposure to radon, recent infections, inflammation and history of cancer. The risk stratification process also considers the nodule's location, size, speed of growth, calcification and whether the border margins are smooth, irregular or spiculated.

Nodule growth

The growth rate of a nodule is important to consider when determining the risk that the it's cancer. Nodules that are small and aren't growing are not likely to be cancerous.

A series of images can provide a snapshot of the nodule over time. If a nodule isn't growing, it's usually not cancer. However, if the nodule is enlarging, then the patient will be put into active surveillance with serial imaging, generally with CT scans. The interval and frequency of those scans will be determined by the health care team.

Additional tests

PET scans may be offered to identify high metabolic activity in nodules that are growing or larger than 1 centimeter. A PET scan cannot definitively diagnose cancer, but it can identify areas with high metabolic activity. A biopsy is the only true way to determine if the nodule is cancerous.

Biopsies can be performed using a robotic-assisted bronchoscopy. With this technology, the patient's CT scan is used to create a road map of the airways that will lead to the nodule. Using a catheter with fiber optic shape-sensing technology, the pulmonologist can navigate to nodules in the lung and confirm their position with real-time integrated imaging before biopsying them. This greatly increases safety and diagnostic precision.

The catheter takes tissues from the nodule, which then can be tested to determine if the nodule is cancerous. The bronchoscopy has a built-in ultrasound probe to also check the lymph nodes in the chest. This is called endobronchial ultrasound (EBUS) and ­— if the nodule is found to be cancer ­— helps the health care team stage the nodule, which helps determine the appropriate treatment plan.

Although not all lung nodules are cancerous, it's important to be aware of the risk factors for lung cancer and to talk with your health care team about any lung nodules you might have. Take steps to reduce your risk for lung cancer. If you smoke, quit. Regularly check your home for radon. Ask your health care team if you qualify for low-dose, CT scan lung cancer screening.

June Chae, M.D., is a pulmonologist and intensive care physician in La Crosse, Wisconsin.