A lung nodule is a common finding, often described as a “spot on the lung.” These small growths are frequently discovered incidentally during imaging tests performed for other reasons. Most lung nodules are not cancerous and do not pose a serious health risk.
What a Lung Nodule Is
A lung nodule is a small, distinct growth of tissue within the lung. On imaging scans like a chest X-ray or CT scan, it appears as a white, rounded, or oval-shaped area. To be classified as a nodule, its diameter is generally less than 3 centimeters (about 1.2 inches); anything larger is usually termed a lung mass.
These nodules are common, with nearly half of all adults undergoing a chest CT scan having at least one. They are often discovered incidentally during scans for unrelated conditions, such as evaluating pneumonia, after an injury, or during routine health screenings. Most lung nodules do not cause symptoms themselves due to their small size.
Why Lung Nodules Form
Lung nodules form for various reasons, with the majority being benign, or non-cancerous. One common cause is scar tissue from past infections, such as bacterial infections like tuberculosis, or fungal infections, which can leave behind small clumps of immune cells called granulomas.
Inflammation from certain autoimmune diseases, such as rheumatoid arthritis or sarcoidosis, can also lead to lung nodules. Additionally, benign tumors, like hamartomas (malformations of normal lung tissue), can present as nodules. These benign causes represent the most frequent reasons for a nodule’s presence.
While less common, a lung nodule can sometimes indicate cancer. This could be primary lung cancer or a metastatic cancer that has spread to the lung from another part of the body. The goal of further medical assessment is to distinguish between these possibilities.
Evaluating a Lung Nodule
Upon discovering a lung nodule, healthcare providers consider several factors to assess its potential seriousness. Imaging characteristics of the nodule are important. Larger nodules, especially those greater than 8 millimeters, carry a higher risk of being cancerous. The nodule’s shape also provides clues; irregular or spiky (spiculated) margins are more suspicious than smooth, round borders.
The nodule’s density on a CT scan is also evaluated. Solid nodules appear dense, while subsolid nodules, including pure ground-glass or part-solid types, have a hazier appearance. Growth over time is a significant indicator; a nodule that increases in size or changes appearance raises greater concern. Providers often compare current scans with prior imaging to check for stability.
Patient risk factors are also important. A history of smoking, older age, a personal history of other cancers, or a family history of lung cancer can increase the likelihood of a nodule being malignant. These factors, combined with imaging characteristics, guide the decision-making process.
Managing a Lung Nodule
Management of a lung nodule depends on its assessed risk. For many small, low-risk nodules, the initial strategy is watchful waiting, also known as active surveillance. This involves regular follow-up CT scans over several months or even years to monitor for changes in size or appearance. If a nodule remains stable for two years, it is usually considered benign.
For higher-risk nodules, further diagnostic tests may be recommended. A positron emission tomography (PET) scan can assess the nodule’s metabolic activity, as cancerous cells often show higher activity. However, PET scans are generally not useful for very small nodules.
If a nodule remains suspicious, a biopsy may be performed to obtain a tissue sample for definitive diagnosis. This tissue is then examined under a microscope to determine if cancer cells are present. Biopsy methods vary depending on the nodule’s location and may include needle biopsy or bronchoscopy.